The test program and subsequent data analysis represent a collaborative effort of a technical 

working group consisting of representatives from the government and industry organizations 

listed on the front cover of this report. The work group prepared this report using methods 

believed to be consistent with accepted practice. All results and observations are based on 

information available using technologies that were state-of-the-art at the time of this effort. To 

the extent that additional information becomes available, or factors on which analyses are based 

change, the findings could subsequently be affected. 

ii 
Executive Summary

The Advanced Petroleum-Based Fuels—Diesel Emission Control (APBF-DEC) Program was a 

government/industry collaboration seeking the optimal combinations of low-sulfur diesel fuels, 

lubricants, diesel engines, and emission control systems (ECSs) to meet projected emission 

standards for the 2004 to 2010 time period. APBF-DEC consisted of five projects that used a 

systems approach to enhance the collective knowledge base on engines, diesel fuels, lubricants, 

and emission control technologies. The five test projects evaluated include: 

• Selective catalytic reduction/diesel particle filter (DPF) technologies 

• Nitrogen oxides adsorber catalyst (NAC)/DPF technologies for passenger cars, light-duty 

trucks/sport-utility vehicles (SUVs), and heavy-duty applications (three projects on 

different engine/vehicle platforms) 

• Lubricant formulations that may affect the performance and durability of advanced diesel 

ECSs. 

The National Renewable Energy Laboratory provided technical leadership for the APBF-DEC 

program, which was sponsored and conducted by a broad collaboration of government and 

industry organizations including: the U.S. Department of Energy, the American Chemistry 

Council, the American Petroleum Institute, the Engine Manufacturers Association, the 

Manufacturers of Emission Controls Association, the California Air Resources Board, and the 

South Coast Air Quality Management District. 

This report presents the results of a 2,000-hour test of an ECS consisting of a NAC in 

combination with a DPF, advanced fuels, and advanced engine controls in an SUV/pick-up truck 

vehicle platform. The 2,000-hour aging of this system represents approximately 100,000 miles of 

on-road use, which approaches the 120,000-mile useful life emission standard. 

Introduction 

The previously completed Diesel Emission Control – Sulfur Effects (DECSE) project (National 

Renewable Energy Laboratory 2002) quantified the impact of diesel fuel sulfur on the 

performance and short-term durability of individual diesel emission control devices, including 

diesel oxidation catalysts, lean-nitrogen oxides (NOx) catalysts, NACs, and DPFs. This project 

evaluated the performance of an entire system consisting of NAC technology in combination 

with DPFs, advanced fuels, and advanced engine controls. 

Project Overview 

The goal of this project was to demonstrate the ability of a NAC and DPF ECS to meet Tier 2– 

Bin 5 standards with Federal Test Procedure (FTP) transient test limits of 0.07 g/mi NOx and 

0.01 g/mi particulate matter (PM) in an SUV/pick-up truck vehicle platform without producing 

unreasonably high emissions during other modes of operation. Additionally, hydrocarbon and 

carbon monoxide (CO) emissions standards had to be met while minimizing impacts on fuel 

economy. 

iii 
The testing was performed for 2,000 hours with evaluations performed before and after 

desulfurizations that were performed every 100 hours. The majority of the testing was 

performed with 15-ppm sulfur fuel developed for the DECSE program. Additionally, an 8-ppm 

sulfur fuel was evaluated. Unregulated emissions tests were performed; however, these results 

will be presented in a separate report that incorporates findings from other APBF-DEC projects. 

Objectives 

The objectives of this project: 

1. Demonstrate the emissions potential of advanced fuels, engines, and ECSs for meeting 

federal Tier 2–Bin 5 emissions standards 

2. Evaluate the effect of fuel sulfur level on emissions and fuel economy, ECS performance, 

and catalyst degradation. 

The 2004-2009 federal standards are as follows: PM of 0.01 g/mi, NOx of 0.07 g/mi, and nonmethane hydrocarbons (NMHC) of 0.09 g/mi. These standards are to be met when testing over 

the FTP-75 test cycle at a full, useful life of 120,000 miles. 

Research Questions 

To achieve the project objectives, a series of study questions were developed to guide the 

experimental design and data analysis. They are organized into five categories: initial 

performance; aging and desulfurization; sulfur mass balance; fuel effects on regulated emissions; 

and unregulated emissions. 

Initial Performance 

These questions addressed the performance of the ECS during the initial 300-hours of aging, 

focusing on the initial impact of the ECS on regulated emissions and fuel economy, and the 

impact of sulfur on a fresh ECS. 

Q1.1 Can the system meet the 2004-2009 regulated emissions levels for NOx, NMHC, and 

PM? 

Q1.2 What is the impact on other regulated emissions [total hydrocarbons (THC) and CO] and 

fuel economy? 

Q1.3 How does system performance change during the early life (under 300-hours) of the 

system? 

Q1.4 Are there similar patterns for various transient, duty cycles [Cold- and Hot-Start Urban 

Dynamometer Driving Schedule, US06 (part of the Supplemental FTP), Highway Fuel 

Economy Test]? 

iv 
Aging and Desulfurization 

This area addressed the impact of 2,000-hours of aging and sulfur accumulation on ECS 

performance, and the effectiveness of periodic desulfurizations for restoring NOx reduction 

performance. The long-term impact on regulated emissions and fuel economy was also 

investigated. 

Q2.1 How do NOx emissions change as the system ages? Specifically, how do the maximum 

(pre-desulfurization), minimum (post-desulfurization), and average NOx levels change? 

Q2.2 Is the increase in NOx emissions between consecutive desulfurizations constant over 

time? 

Q2.3 How effective is desulfurization at restoring the initial NOx reduction performance of the 

system (initially and over time)? 

Q2.4 Does the performance of the system stabilize within the first 2,000 hours? If so, at what 

point does this occur? 

Q2.5 Are there temporal trends with respect to other regulated emissions or fuel economy? 

Sulfur Mass Balance 

Understanding the mechanisms by which sulfur from the fuel and lubricants interact with the 

ECS is important for designing an effective and durable system. A mass balance approach is 

used to gain insight on this issue. 

Q3.1 How much sulfur is emitted during the desulfurization process? 

Q3.2 How does the amount of sulfur emitted during the aging cycle compare to the amount 

emitted during the desulfurization process? Do these rates change over time? 

Q3.3 What happens to the differences between these amounts? 

Fuel Effects on Regulated Emissions 

Two different varieties of low-sulfur diesel fuels (15 ppm) were tested. This area considered 

whether the fuels have direct impacts on regulated emissions or fuel economy. 

Q4.1 Are there differences in emissions from DECSE and British Petroleum (BP) fuels? 

Q4.2 If such differences exist, are they consistent over time? 

Unregulated Emissions 

Periodic tests were performed to determine whether a fresh or aging ECS impacts emissions of 

unregulated gases and PM. The emissions of interest included selected hydrocarbon species, 

soluble organic fraction/sulfate, metals, nitroxy-alkanes, and polycyclic-aromatic 

hydrocarbons/nitro-polycyclic-aromatic hydrocarbon. 

v 
Q5.1 Which unregulated toxic (or potentially toxic) compounds are present in tailpipe 

emissions? 

Q5.2 How do the levels compare to engine-out emissions? 

Q5.3 How do unregulated emissions change with time? 

Methods 

The project was divided into two tasks: Task A and Task B. Task A involved the setup of the 

test cell with an engine and emissions measurement systems; measurement of baseline (engineout) emissions and fuel consumption; configuration and installation of the ECSs; and 

development of regeneration and desulfurization strategies as needed. The test vehicle was a 

2002 Chevrolet Silverado 2500 Series pick-up truck equipped with a Duramax 6.6L engine and 

ZF six-speed manual transmission. The engine/vehicle combination met the California mediumduty emission requirements for 2002. Two different ECS configurations were designed in Task 

A. In Task B, one of the two systems was aged for 2,000 hours, and periodically evaluated for 

regulated and unregulated emissions using selected low-sulfur fuels (15 ppm). The ECS tested 

in Task B consisted of NACs, oxidation catalysts, and a catalyzed DPF configured as shown in 

Figure ES-1. The system included a diesel fuel burner used for thermal management and 

supplemental fuel injectors for control of the regeneration reductant. 

vi 
EGR 

VALVE 

6600 Duramax 

INTAKE 

THROTTLE 

AIR 

FILTER 

Air Charge Cooler 

SFI 

SFI 

Diesel Fuel 

Burner 

DPF 

DPF 

#1 OC NAC

F

#1C

DPF 

#1 OC NAC

F 

#1C

OC

Figure ES-1. Schematic of tested ECS 

Findings and Conclusions 

The following is a summary of the significant conclusions from the study. Further details are 

provided in Section 4 of the report. 

Initial Performance 

• During the first 200 hours of testing, tailpipe emissions of NOx averaged 0.095 g/mi (+/­

0.026 g/mi with 95% confidence) using the FTP composite test cycle. Although higher than 

the regulated emissions limit of 0.07 g/mi, the estimated NOx emissions were 97.8% lower 

than engine-out emissions without EGR and 95.5% lower than engine-out emissions with 

EGR. Figure ES-2 presents the NOx emissions and reduction efficiency results during the 

first 300 hours of testing. 

• The ECS reductions in NOx (97.8%), CO (87.2%), and PM (91.6%) emissions were 

statistically significant, as was the reduction in fuel economy (18.7%). The 16.7% decrease 

in NMHC emissions (from 0.198 to 0.165 g/mi) was also statistically significant. Initial 

tailpipe emissions of CO and PM were below the regulated limits; however, the engine-out 

vii 
and tailpipe emissions of NMHC were above the Tier 2–Bin 5 limit of 0.09 g/mi. These test 

results are shown in Figure ES-3. 

NOx Reduction Efficiency 

90% 

92% 

94% 

96% 

98% 

100% 

0 50 100 150 200 250 300 350 

Age (hours) 

NOx Reduction 

FTP Composite (D15) FTP Composite (BP15) Standard-D 15 

Desulfurization 

NOx Emissions 

0.0 

0.1 

0.2 

0.3 

0.4 

0.5 

0 50 100 150 200 250 300 350 

Age (hours) 

Catalyst Out

NOx (g/mi) 

FTP Composite (D15) FTP Composite (BP15) 

Desulf urization 

Figure ES-2. NOx composite FTP emissions and reduction efficiency during the first 300 

hours of aging (Error bars indicate the range of individual test results.) 

viii 
NMHC Emissions 

0.0 

0.1 

0.2 

0.3 

0.4 

0.5 

0 50 100 150 200 250 300 350 

Age (hours) 

Catalyst Out

NMHC (g/mi) 

FTP Composite (D15) FTP Composite (BP15) 

PM Emissions 

0.000 

0.003 

0.006 

0.009 

0.012 

0.015 

0 50 100 150 200 250 300 350 

Age (hours) 

Catalyst Out

PM (g/mi) 

FTP Composite (D15) FTP Composite (BP15) 

Fuel Economy 

14.0 

14.5 

15.0 

15.5 

16.0 

16.5 

0 50 100 150 200 250 300 350 

Age (hours) 

Catalyst Out

FE (mi/gal) 

FTP Composite (D15) FTP Composite (BP15) 

CO Emissions 

0.0 

0.1 

0.2 

0.3 

0.4 

0.5 

0 50 100 150 200 250 300 350 

Age (hours) 

Catalyst Out

CO (g/mi) 

FTP Composite (D15) FTP Composite (BP15) 

Figure ES-3. Composite FTP emissions of NMHC, CO, and PM, and fuel economy during 

the first 300 hours of aging 

Aging and Desulfurization 

• The loss in NOx reduction efficiency of the catalysts between consecutive desulfurization 

events increased slightly from 4% to 6% throughout the 2,000-hour test. However, the 

desulfurization process was effective at restoring catalyst performance. The desulfurization 

process produced an improvement in NOx reduction efficiency that changed from 3% at the 

beginning of the test to 6% at end of the 2,000-hour test. 

• Although there was a decrease in NOx reduction efficiency during the early aging periods, 

Figure ES-4 illustrates that the increase in NOx emissions—or decrease in NOx reduction 

efficiency—was not statistically significant after approximately 850 hours of testing. 

ix 
0.0 

0.2 

0.4 

0.6 

0.8 

1.0 

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

NOx (g/mi) 

Pre Desulfurization Average Post Desulfurization 

Pre Trend Average Trend Post Trend 

80% 

84% 

88% 

92% 

96% 

100% 

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

NOx Reduction Efficiency 

Pre Desulfurization Average Post Desulfurization 

Pre Trend Average Trend Post Trend 

•

Figure ES-4. Statistical trends in FTP composite NOx emissions and NOx conversion at 

pre-desulfurization, post-desulfurization, and midpoint between desulfurizations are not 

statistically significant after 800, 900, and 850 hours, respectively 

• There were statistically significant increases in NMHC and CO emissions, and fuel 

consumption during the 2,000-hour test; but there was no significant change in PM 

emissions. Table ES-1 compares the initial estimated engine-out regulated emissions and 

fuel economy (with and without EGR) with the estimated tailpipe emissions at 1,950 hours— 

midway between the last two desulfurization events. The system achieved emissions 

reduction efficiencies of 85.9% for NOx, 69.3% for CO, and 91.8% for PM. Fuel economy 

decreased by 16%; and NMHC emissions increased by 87.6%, this was partially due to the 

use of the diesel fuel burner and use of the diesel fuel as a reductant for catalyst regeneration. 

x 
Table ES-1. Average Engine-Out and Estimated 1,950-Hour Average Tailpipe Composite 

FTP Regulated Emissions and Fuel Economy—with 95% Confidence Intervals 

Engine Out Tailpipe Average (1,950 Hours) w/ EGR 

Emission 

Parameter Unit EGR Average1 

95% 

Confidence 

Interval Average2 

95% 

Confidence 

Interval 

Percent 

Reduction 

Regulated 

Emission 

Standard3 

Without 4.38 (4.34, 4.42) 85.9% NOX g/mi 

With 2.12 -

4 0.616 (0.558, 0.675) 

70.9% 

0.07 

Without 0.20 (0.19, 0.207) -87.6% NMHC g/mi 

With no data -

0.372 (0.349, 0.395) 

-

0.09 

Without 0.20 (0.194, 0.213) -257.8% THC g/mi 

With 0.26 -

0.730 (0.695, 0.764) 

-176.2% 

N/A 

Without 2.02 (1.85, 2.18) 69.3% CO g/mi 

With 4.43 -

0.620 (0.571, 0.669) 

86.0% 

4.2 

Without 0.07 (0.056, 0.074) 91.8% PM g/mi 

With 0.15 -

0.005 (0.005, 0.006) 

96.3% 

0.01 

Fuel Without 18.40 (18.2, 18.6) 16.0% 

Economy mi/gal With 17.95 -

15.453 (15.312, 15.594) 

13.9% 

N/A 

1

 Engine-out average without EGR is based on 6 tests; engine-out average with EGR is based on 1 test. 2

 Estimates based on the regression model derived from measurements taken between 350 and 1,950 hours. 3

 Tier 2-Bin 5 full useful life 4

 Confidence intervals cannot be determined based on a single test; however, the values are generally consistent with the average 

engine-out results obtained during testing with the ECS.

N/A = Not applicable 

• A comparison of measured sulfur emissions, with the amount of sulfur contained in the fuel 

and lubricant, demonstrated that nearly all of the sulfur accumulated on the catalysts was 

effectively removed during the desulfurization process. 

Fuel Effects on Regulated Emissions 

• There were no consistent significant differences in the emissions from tests conducted with 

the DECSE and BP fuels. 

Unregulated Emissions 

• Unregulated emissions results are presented in a separate report. 

Future Work 

The results of this work have identified a number of areas worthy of additional study. These 

include further evaluation of the NAC desulfurization process analyzing both deterioration 

mechanisms and the composition of the liberated sulfur compounds, and the evaluation of other 

fuel formulations on the performance of emission control devices (e.g., the impact of biodiesel 

blends on NACs and DPFs). One specific area of research is related to the impact of biodiesel 

blends on DPF regeneration temperature. 

xi 
Table of Contents

Executive Summary.....................................................................................................................iii

Introduction................................................................................................................................iii 

Project Overview .......................................................................................................................iii 

Objectives .................................................................................................................................. iv 

Research Questions.................................................................................................................... iv 

Initial Performance..................................................................................................................... iv 

Aging and Desulfurization.......................................................................................................... v 

Sulfur Mass Balance ................................................................................................................... v 

Fuel Effects on Regulated Emissions ......................................................................................... v 

Unregulated Emissions ............................................................................................................... v 

Methods...................................................................................................................................... vi 

Findings and Conclusions......................................................................................................... vii 

Initial Performance.................................................................................................................... vii 

Aging and Desulfurization......................................................................................................... ix

Fuel Effects on Regulated Emissions ........................................................................................ xi

Unregulated Emissions .............................................................................................................. xi

Future Work............................................................................................................................... xi

Table of Contents ........................................................................................................................ xii

List of Tables .............................................................................................................................. xiv

List of Figures.............................................................................................................................. xv

Acronyms and Abbreviations .................................................................................................xviii

Section 1: Introduction................................................................................................................. 1

1.1 Advanced Petroleum-Based Fuels—Diesel Emission Control Program .............................. 1 

1.2 Background........................................................................................................................... 2 

1.3 NOx Adsorber Catalyst/Diesel Particle Filter Technologies................................................. 2 

1.3.1 Principle of Operation of NOx Adsorber Catalysts ..................................................... 2 

1.3.2 Principle of Operation of Diesel Particle Filters ......................................................... 4 

1.4 Project Scope, Goals, and Objectives ................................................................................... 4 

1.4.1 Initial Performance ...................................................................................................... 5 

1.4.2 Durability and Desulfurization.................................................................................... 5 

1.4.3 Sulfur Mass Balance.................................................................................................... 6 

1.4.4 Fuel Effects on Regulated Emissions.......................................................................... 6 

1.4.5 Unregulated Emissions................................................................................................ 6 

Section 2: Technical Approach.................................................................................................... 7

2.1 Experimental Design............................................................................................................. 7 

2.1.1 Engine Selection.......................................................................................................... 7

2.1.2 Emission Control Systems (A and B)........................................................................ 11 

2.1.3 Fuel/Lubricant Selection ........................................................................................... 13 

2.1.4 Emissions Measurements .......................................................................................... 16 

2.1.5 Test Matrix ................................................................................................................ 19 

2.2 Experimental Procedures .................................................................................................... 20 

2.2.1 Laboratory Setup ....................................................................................................... 20

2.2.2 Test Procedures ......................................................................................................... 27 

2.2.3 Sampling and Analysis Procedures ........................................................................... 43 

xii 
2.2.4 Data Handling............................................................................................................ 52 

2.2.5 Statistical Analysis and Modeling............................................................................. 53 

Section 3: System Development ................................................................................................. 55

3.1 Baseline Emissions and Exhaust Gas Recirculation Calibration........................................ 55 

3.1.1 Baseline Emissions.................................................................................................... 55 

3.1.2 Exhaust Gas Recirculation Calibration ..................................................................... 66 

3.2 Emissions System Calibration and Control (EGR+DPF+NAC) ........................................ 75 

3.2.1 Diesel-Fueled Burner ................................................................................................ 75 

3.2.2 Emission Control System Regeneration Control/Strategy ........................................ 80 

3.2.3 Fuel Economy Penalty Associated with Emission Control System Operation ......... 89 

3.3 Development of Desulfurization Process............................................................................ 96 

Section 4: Results ........................................................................................................................ 99

4.1 Initial Performance.............................................................................................................. 99 

4.2 Aging and Desulfurization (300 to 2,000-hours).............................................................. 103 

4.2.1 Average NOx Emissions and Reduction Efficiency over 2,000-hours.................... 104 

4.2.2 Performance Degradation and Desulfurization Effectiveness................................. 105 

4.2.3 Determination of System Stabilization.................................................................... 106 

4.2.4 Trends in Other Regulated Emissions and Fuel Economy...................................... 107 

4.2.5 Soluble Organic Fraction and Sulfate Emissions.................................................... 110 

4.3 Sulfur Mass Balance ......................................................................................................... 112 

4.4 Fuel Effects on Regulated Emissions (D15 vs. BP15) ..................................................... 113 

4.5 Discussion of Technical Problems and Remedial Actions ............................................... 116 

4.5.1 Second-Generation Emission Control System Components................................... 116 

4.5.2 Diesel-Fueled Burner .............................................................................................. 120 

4.5.3 In-Exhaust Injectors ................................................................................................ 121 

4.5.4 Exhaust System and Flow Maldistribution ............................................................. 121 

4.5.5 Particle Sampling .................................................................................................... 121 

4.5.6 Engine-Related Components................................................................................... 122 

4.5.7 Test Cell Equipment................................................................................................ 122 

4.5.8 Emission Control System Components/Regeneration Control System Performance.. 122 

4.5.9 Possible Improvements to Emission Control System/Exhaust Configuration ........ 125 

Section 5: Conclusions .............................................................................................................. 127

Objectives ............................................................................................................................... 127 

Initial Performance.................................................................................................................. 127 

Aging and Desulfurization...................................................................................................... 128 

Fuel Effects on Regulated Emissions ..................................................................................... 128 

Unregulated Emissions ........................................................................................................... 128 

Future Work............................................................................................................................ 128 

References.................................................................................................................................. 129

xiii 
List of Tables 

Table ES-1. Average Engine-Out and Estimated 1,950-Hour Average Tailpipe Composite FTP 

Regulated Emissions and Fuel Economy—with 95% Confidence Intervals........................ xi

Table 1. APBF-DEC Project Summary........................................................................................ 1 

Table 2. Engine Specifications for MY 2002 Duramax ............................................................... 9 

Table 3. Test Fuel Properties...................................................................................................... 14 

Table 4. Properties of Sulfur Doping Compounds ..................................................................... 14 

Table 5. Lubricating Oil Specifications...................................................................................... 15 

Table 6. Summary of Emission Measurements Performed during Emission Evaluations......... 18 

Table 7. Test Matrix ................................................................................................................... 19 

Table 8. Operational Characteristics of Select Light-Duty Chassis Dynamometer Test Cycles 30 

Table 9. RPM and APP Analysis of the CARB Unified Driving Cycle .................................... 37 

Table 10. Frequency of RPM and APP Combinations over the CARB Unified Driving Cycle.. 37 

Table 11. Steady-State Evaluation Point Information.................................................................. 39 

Table 12. Summary of Modified CARB Unified Cycle Based on Aging Cycle Operating

Conditions and Mode Order................................................................................................. 42 

Table 13. Select Engine Oil Properties after Various Aging Hours............................................. 43 

Table 14. Low- and High-Span Gas Concentrations.................................................................... 46 

Table 15. Composition of IS Spiking Solutions for PUF Traps and TIGF Filters....................... 50 

Table 16. Light-Duty FTP As-Received, Engine-Out Emissions with EGR ............................... 61 

Table 17. Light-Duty FTP As-Received, Engine-Out Emissions without EGR .......................... 61 

Table 18. Test Cycle Work for Drive-Cycle Emulation on Motoring Dynamometer.................. 66 

Table 19. EGR Mapping Points.................................................................................................... 70 

Table 19. EGR Mapping Points (continued) ................................................................................ 71 

Table 20. NOx and PM Mass Emissions for Different EGR Calibrations.................................... 74 

Table 21. Sulfur Mass Summary for 1,300- and 1,400-Hour Desulfurizations ........................... 98 

Table 22. H2S Mass Measured during 1,600-Hour Desulfurization ............................................ 98 

Table 23. Average Engine-Out and Initial Tailpipe Composite FTP Regulated Emissions and 

Fuel Economy—with 95% Confidence Intervals .............................................................. 100 

Table 24. Average Engine-Out and Estimated 1,950-Hour Average Tailpipe Composite FTP 

Regulated Emissions and Fuel Economy—with 95% Confidence Intervals..................... 110 

Table 25. Sulfur Mass Balance between Engine-Out and Desulfurization Emissions............... 113 

xiv 
List of Figures 

Figure ES-1. Schematic of tested ECS ......................................................................................... vii 

Figure ES-2. Ox composite FTP emissions and reduction efficiency during the first 300 hours 

of aging (Error bars indicate the range of individual test results.).........................................viii 

Figure ES-3. Composite FTP emissions of NMHC, CO, and PM, and fuel economy during the 

first 300 hours of aging............................................................................................................ ix

Figure ES-4. Statistical trends in FTP composite NOx emissions and NOx conversion at 

pre-desulfurization, post-desulfurization, and midpoint between desulfurizations are not 

statistically significant after 800, 900, and 850 hours, respectively ......................................... x 

Figure 1. Development fleet vehicle supplied by GM equipped with Duramax 6.6L engine...... 8 

Figure 2. Isuzu Duramax 6.6L engine........................................................................................ 10 

Figure 3. Vehicle underbody showing stock exhaust system..................................................... 11 

Figure 4. Initial road-load curve utilized for 2002 Chevrolet Silverado test vehicle................. 21 

Figure 5. Accumulated NOx mass over the FTP ........................................................................ 22 

Figure 6. Accumulated NOx mass over the US06...................................................................... 22 

Figure 7. Exhaust gas temperatures over the FTP...................................................................... 23 

Figure 8. Exhaust gas temperatures over the US06.................................................................... 23 

Figure 9. Proposed System A ECS configuration (single, in-line system) ................................ 25 

Figure 10a. Proposed System B1 ECS configuration (dual-leg system) ...................................... 25 

Figure 10b. Proposed System B2 ECS configuration (dual-leg system)...................................... 26 

Figure 10c. Proposed System B3 ECS configuration (dual-leg system) ...................................... 26 

Figure 11. System B, final ECS configuration utilized................................................................ 27 

Figure 12. Indicated vehicle speed versus time for Cold-Start UDDS and Hot-Start UDDS 

driving schedules .................................................................................................................... 28 

Figure 13. Indicated vehicle speed versus time for HFET prep and test driving schedule.......... 29 

Figure 14. Indicated vehicle speed versus time for US06 prep and test driving schedule........... 30 

Figure 15. Test command cycle (engine speed and torque) for Cold-Start UDDS cycle ............ 31 

Figure 16. Test cell command cycle (engine speed and torque) for Hot-Start UDDS................. 32 

Figure 17. Test cell command cycle (engine speed and torque) for HFET cycle ........................ 32 

Figure 18. Test cell command cycle (engine speed and torque) for US06 cycle ......................... 33 

Figure 19. Comparison of accumulated engine-out NOx mass over the Cold-Start UDDS for a 

vehicle test and test cell run.................................................................................................... 33 

Figure 20. Comparison of accumulated engine-out CO2 mass over the Cold-Start UDDS for a 

vehicle test and test cell run.................................................................................................... 34 

Figure 21. Comparison of exhaust gas temperature over the Cold-Start UDDS for a vehicle test 

and test cell run ....................................................................................................................... 34 

Figure 22. Vehicle speed versus time for CARB Unified Driving Schedule............................... 36 

Figure 23. Ten most frequent operating points over CARB Unified Driving cycle .................... 38 

Figure 24. Aging cycle operating points with steady-state evaluation point (based on CARB

Unified Driving cycle) ............................................................................................................ 39 

Figure 25. Comparison of engine speed and load for the original and modified aging cycles .... 40 

Figure 26. Comparison of oxidation and NAC bed temperatures over the original and modified 

aging cycles............................................................................................................................. 41 

Figure 27. Test cell emissions sampling system .......................................................................... 44 

xv 
Figure 28. Power curves for 2002 Chevrolet Silverado test vehicle ............................................ 56 

Figure 29. Estimated and actual chassis dynamometer power curves ......................................... 57 

Figure 30. Exhaust gas temperature after oxidation catalyst over the FTP and US06 test 

cycles ..................................................................................................................................... 58 

Figure 31. Engine-out NOx concentration and instantaneous mass map over light-duty FTP and 

US06 test cycles...................................................................................................................... 59 

Figure 32. Engine-out CO2 concentration and instantaneous mass map over light-duty FTP and 

US06 test cycles...................................................................................................................... 60 

Figure 33. Range of APP (volts) and engine speed (RPM) across the light-duty FTP and US06 

test cycles ................................................................................................................................ 60 

Figure 33. Comparison of regulated engine-out emissions to program goals (EPA Tier 2 Bin 5) 

for the light-duty FTP ............................................................................................................. 62 

Figure 34. Accumulated engine-out NOx mass over the Cold-Start UDDS cycle ....................... 63 

Figure 35. Exhaust gas temperature (downpipe location) over the Cold-Start UDDS cycle....... 63 

Figure 37. Exhaust gas temperature (downpipe location) over the US06 cycle .......................... 64 

Figure 38. Continuous engine-out NOx mass and program goal over the Cold-Start UDDS 

Test cycle ................................................................................................................................ 65 

Figure 39. Measured NOx concentration as a function of engine speed (no EGR)...................... 67 

Figure 40. NOx concentration—stock engine calibration—no EGR ........................................... 68 

Figure 41. Maximum and minimum EGR rates as a function of engine speed and load............. 72 

Figure 42. Engine-out smoke opacity over Hot-Start UDDS cycle for no EGR and high-EGR 

calibration ............................................................................................................................... 74 

Figure 43. NOx/PM trade-off for different EGR strategies over the Hot-Start UDDS Test cycle75 

Figure 44. Heat loss paths in an engine-based regeneration and thermal management 

configuration........................................................................................................................... 76 

Figure 45. Heat loss paths in an In-exhaust burner-based regeneration and thermal management 

configuration........................................................................................................................... 77 

Figure 46. Emissions system configuration utilizing a fuel burner, in-exhaust supplemental fuel 

injection, and pre-catalyst upstream of NAC-DPF system..................................................... 78 

Figure 47. Photographs of the diesel fuel-burner head ................................................................ 79 

Figure 48. Photographs of the burner installed in the engine exhaust with an oxidation catalyst 

and one NAC........................................................................................................................... 80 

Figure 49. Schematic of an ECS .................................................................................................. 81 

Figure 50. Schematic overview of software controller designed for ECS management.............. 83 

Figure 51. NOx mass model concept............................................................................................ 85 

Figure 52. Exhaust gas temperature at catalyst inlet location for burner + oxidation catalyst and 

stock, no-EGR configuration .................................................................................................. 86 

Figure 53. NAC1 bed temperature for S1 .................................................................................... 87 

Figure 54. Effect of cold-start strategy on NAC1 bed temperatures............................................ 88 

Figure 55. Impact of accelerated NAC S4 on DPF warm up....................................................... 89 

Figure 56. Exhaust gas temperature over the Cold-Start UDDS and desired operating window 

for ECS.................................................................................................................................... 91 

Figure 57. Exhaust mass flow rate over the Cold-Start UDDS with and without EGR............... 92 

Figure 58. NOx reduction for various NOx inlet concentrations at constant inlet temperature.... 93 

Figure 59. NOx reduction for various NOx inlet concentrations at constant inlet temperature.... 94 

Figure 60. Fuel economy penalty and source over Hot-Start UDDS, HFET, and US06............. 95 

xvi 
Figure 61. Regeneration penalty and associated NOx reduction for the Hot-Start UDDS, HFET, 

and US06................................................................................................................................. 95 

Figure 62. Example of engine-out lambda and NAC system temperatures during

Figure 63. NOx Composite FTP emissions and reduction efficiency during the first 300 hours of 

Figure 64. NOx emissions and NOx reduction efficiency during the Cold-Start UDDS, Hot-Start 

Figure 65. Composite FTP emissions of NMHC, CO, and PM and fuel economy during the first 

Figure 66. NOx emissions (FTP composite) and NOx reduction efficiency versus ECS age 

desulfurization......................................................................................................................... 97 

aging ................................................................................................................................... 101 

UDDS, US06, and HFET test cycles over the first 300 hours of aging................................ 102 

300 hours of aging ................................................................................................................ 103 

(vertical lines identify desulfurization events)...................................................................... 104 

Figure 67. Effectiveness at desulfurization and deterioration of the catalyst between 

desulfurizations for FTP composite NOx emissions compared to aging hours (Trends for 

these were not statistically significant.)................................................................................ 105 

Figure 68. NOx emissions (FTP composite) and NOx reduction efficiency (FTP composite) 

versus ECS age with statistical trend lines: pre-desulfurization, post-desulfurization, and 

average results....................................................................................................................... 106 

Figure 69. Statistical trends in FTP composite NOx emissions and NOx conversion at predesulfurization, post-desulfurization, and midpoint between desulfurizations are not 

statistically significant after 800, 900, and 850 hours, respectively ..................................... 107 

Figure 70. FTP composite NMHC emissions compared to aging hours: pre-Desulfurization, 

post-desulfurization, and average results (Trend is statistically significant through 1,400 

Hours.) .................................................................................................................................. 108 

Figure 71. FTP composite percent NMHC emissions compared to aging hours: predesulfurization, post-desulfurization, and average results (Trend is not statistically significant 

after 1,100 hours.)................................................................................................................. 108 

Figure 72. FTP composite CO emissions compared to aging hours: pre-desulfurization, postdesulfurization, and average results (Trend is statistically significant through 1400 hours) 108 

Figure 73. FTP composite PM emissions compared to aging hours: pre-desulfurization, postFigure 74. FTP composite FE compared to aging hours: pre-desulfurization, postFigure 75. Sulfate emissions (Cold-Start UDDS, Hot-Start UDDS, US06, HFET, and FTP 

Figure 76. Percent SOF emissions (Cold-Start UDDS, Hot-Start UDDS, US06, HFET, and FTP 

desulfurization, and average results (Trend is not statistically significant.)......................... 109 

desulfurization, and average results (Trend is statistically significant through 1100 hours) 109 

composite) versus ECS age (vertical lines identify desulfurization events)......................... 111 

composite) versus ECS age (Vertical lines identify desulfurization events.)....................... 112 

Figure 77. Average NOx emissions with 95% confidence intervals by fuel type and ECS age. 115 

Figure 78. First-generation System B......................................................................................... 117 

Figure 79. Second-generation System B .................................................................................... 118 

Figure 80. Face plugging of pre-NAC oxidation catalyst .......................................................... 119 

Figure 81. NOx mass model accumulation for Leg 1 over Hot-Start UDDS ............................. 124 

Figure 82. Accumulated tailpipe NOx mass for three repeat runs after 1,500 hours of aging (postdesulfurization) for Hot-Start UDDS.................................................................................... 125 

Figure 83. Possible improved system design configuration....................................................... 126 

xvii 
Acronyms and Abbreviations 

APBF-DEC Advanced Petroleum-Based Fuels - Diesel Emission(s) Control 

API American Petroleum Institute 

APP accelerator pedal position 

ASTM American Society for Testing and Materials 

BP British Petroleum 

C degrees centigrade (Celsius) 

CARB California Air Resources Board 

CC continuing calibration 

CDPF coated [catalyzed] diesel particle filter 

CO carbon monoxide 

CO2 carbon dioxide 

CR-DPF continuously regenerating diesel particle filter 

CRC Coordinating Research Council 

CVS constant volume sampling [system] 

DCM dichloromethane 

DECSE Diesel Emission Control–Sulfur Effects 

DFI direct filter injection 

DOC diesel oxidation catalyst 

DPF diesel particle filter 

ECS emission control system 

EGR exhaust gas recirculation 

EMS engine management system 

EPA U.S. Environmental Protection Agency 

ERIC Emissions Reduction Integration Controller 

FID flame ionization detector 

FTIR Fourier transform infrared 

FTP Federal Test Procedure (engine cycle) 

GC Gas chromatography or chromatograph 

GM General Motors 

g/mi gram/mile 

H2S hydrogen sulfide 

HFET Highway Fuel Economy Test 

hp horsepower 

ICAL initial calibration 

IS internal standard 

Lambda (λ) calculated ratio of amount of air available for combustion to the amount of 

air required for combustion to be stoichiometric. 

LCS laboratory control sample 

LCSD laboratory control sample duplicate 

MAF mass airflow 

MECA Manufacturers of Emission Controls Association 

MS mass spectrometry 

xviii 
MY model year 

N2 nitrogen 

NAC nitrogen oxides adsorber catalyst 

ng nanogram 

NMHC nonmethane hydrocarbons 

NO nitrogen oxide 

NO2 nitrogen dioxide 

NOx oxides of nitrogen 

NPAH nitro-polycyclic-aromatic hydrocarbon 

O2 oxygen 

ORNL Oak Ridge National Laboratory 

PAH polycyclic-aromatic hydrocarbons 

PM particulate matter 

ppm parts per million 

PUF polyurethane foam 

QC quality control 

RRF relative response factor 

RPM/rpm revolutions per minute 

RSD relative standard deviation 

S1 cold-start strategy 1 

S2 cold-start strategy 2 

S3 cold-start strategy 3 

SFI supplemental [exhaust] fuel injection 

SO2 sulfur dioxide 

SO4 sulfate 

SOF soluble organic fraction 

SUV sport-utility vehicle 

SwRI Southwest Research Institute (San Antonio, Texas) 

THC total hydrocarbon 

TIGF Teflon-impregnated glass fiber [filter] 

TWC three-way conversion [catalyst] 

UDDS Urban Dynamometer Driving Schedule 

US06 part of the Supplemental Federal Test Procedure 

VOF volatile organic fraction 

xix 
 1

Section 1: Introduction 

1.1 Advanced Petroleum-Based Fuels—Diesel Emission Control Program 

Advanced Petroleum-Based Fuels—Diesel Emission Control (APBF-DEC) is a 

government/industry project to identify and evaluate: 

• The optimal combinations of low-sulfur diesel fuels, lubricants, diesel engines, and 

emission control systems (ECS) to meet projected emission standards for the 2004 to 

2010 time period 

• Properties of fuels and vehicle systems that could lead to even lower emissions beyond 

2010. 

The National Renewable Energy Laboratory provided technical leadership to this project, which 

was funded and directed by federal and state government agencies, trade associations, and private 

industry. The primary sponsors are the U.S. Department of Energy, the American Chemistry 

Council, the American Petroleum Institute (API), the Engine Manufacturers Association, the 

Manufacturers of Emission Controls Association (MECA), the California Air Resources Board 

(CARB), and the South Coast Air Quality Management District. The U.S. Environmental 

Protection Agency (EPA) is providing technical assistance. Additional technical support is being 

provided by the National Petrochemical and Refiners Association. Representatives from these 

and other agencies, associations, national laboratories, and private sector companies serve on the 

20-member APBF-DEC Steering Committee and its working groups. 

A systems approach is being used to simultaneously investigate how fuels, lubricants, engines, 

and ECSs can enable clean and efficient transportation systems. APBF-DEC Program consists of 

five individual projects to evaluate how sulfur and other compounds impact the performance and 

durability of advanced diesel ECSs. The projects are summarized in Table 1. 

Table 1. APBF-DEC Project Summary 

Technology Platform 

Test 

Vehicle/Engine Subcontractor 

Light-duty 1.9L TDI 

Audi A4 

FEV Engine Technology, 

Inc.

SUV/light truck Chevrolet Silverado 

Isuzu/GM Duramax 

Southwest Research 

Institute 

NOx Adsorber 

Catalysts and Diesel 

Particle Filters 

Heavy-duty Cummins ISX 

(engine only) 

Ricardo, Inc. 

Urea Selective 

Catalytic Reduction 

and Diesel Particle 

Filters 

Heavy-duty Caterpillar C12 Southwest Research 

Institute 

International T444E 

(Phase 1) 

Automotive Testing 

Laboratories (Phase 1) 

Lubricants Medium-duty 

Cummins ISB 

(Phase 2) 

Analytical Engineering, 

Inc. (Phase 2) 
This report summarizes the results from the APBF-DEC project that studied nitrogen oxides 

adsorber catalysts (NACs) and diesel particle filters (DPFs) for sport-utility vehicles (SUV)/light 

trucks. 

1.2 Background 

The previously completed Diesel Emission Control – Sulfur Effects (DECSE) Project (National 

Renewable Energy Laboratory 2002) quantified the impact of diesel fuel sulfur on the 

performance and short-term durability of diesel emission control devices [diesel oxidation 

catalysts (DOCs)], lean-nitrogen oxides (NOx) catalysts, NACs, and DPFs. Because some of 

these new technologies have demonstrated sensitivity to fuel-borne sulfur, considerable research 

was conducted, and regulations limiting the permissible levels of sulfur in diesel fuel were 

promulgated. Beginning in October 2006, on-highway diesel fuel will be subject to a maximum 

sulfur content of 15 ppm. 

This project aimed to demonstrate the potential of NAC technology in combination with DPFs, 

advanced fuels, and advanced engine controls to achieve stringent emission levels while 

maintaining high fuel economy. To meet stringent Tier 2 light-duty emissions standards, tailpipe 

emissions for NOx must be below 0.2 g/mi while particulate matter (PM) emissions levels must 

be below 0.02 g/mi. Goals of this project were to meet Tier 2 – Bin 5 with limits of 0.07 g/mi 

NOx and 0.01 g/mi PM. The goal was to achieve these emissions levels on the Federal Test 

Procedure (FTP) transient test cycle without producing high emissions during other modes of 

operation. 

Additionally, hydrocarbon and carbon monoxide (CO) emissions standards had to be met. 

Minimizing fuel economy impacts while meeting emissions requirements was also an important 

aspect of the project. The base fuel for the project was the 0.6-ppm sulfur DECSE base fuel. 

Additionally, the 8- and 15-ppm sulfur fuels were evaluated, with the majority of testing 

performed using the 15-ppm sulfur fuel. 

It is anticipated that, in order for light-duty vehicles to meet these low emission levels, active 

ECSs will be required. NACs in conjunction with DPFs and other engine and combustion 

strategies (e.g., exhaust gas recirculation or EGR, and high-pressure fuel injection) are seen as 

possible approaches to meet these goals. One of the key issues with these systems is their longterm tolerance to fuel-borne sulfur. For these reasons, this project was planned within APBFDEC to look specifically at fuel sulfur effects on catalyst durability and emissions in an 

SUV/pick-up truck vehicle platform. 

1.3 NOx Adsorber Catalyst/Diesel Particle Filter Technologies 

The following sections present brief discussions of the factors that are known to affect the 

performance of NACs and DPFs, respectively. 

1.3.1 Principle of Operation of NOx Adsorber Catalysts 

A NAC is a flow-through exhaust emissions control device, which has the potential to 

significantly lower NOx, hydrocarbon, and CO emissions present in diesel engine exhaust. 

Because it contains high levels of precious metals, it is also effective in oxidizing the soluble 

organic fraction (SOF) of diesel PM and other unregulated diesel emissions. 

2
A NOx adsorber is a storage device for NOx. During typical diesel engine operation, NOx in the 

lean exhaust gas is stored as a base metal nitrate. Before the NOx adsorbent becomes fully 

saturated, it must be regenerated. Regeneration is accomplished periodically by producing a 

fuel-rich exhaust. Under rich conditions, the stored NOx is released from the adsorbent and 

simultaneously reduced to nitrogen—and/or nitrous oxide or ammonia—over precious metal 

sites. Numerous approaches to achieving the fuel-rich exhaust conditions for NAC regeneration 

are being researched, including in-cylinder fuel injection and in-pipe fuel injection, among 

others. 

A NAC consists of two principal components: a NOx adsorbent and a three-way conversion 

(TWC) catalyst. The NOx adsorbent is typically an alkali or alkaline earth carbonate. These 

carbonates are capable of chemically interacting with NO2 and O2 present in typical diesel engine 

exhaust, resulting in the formation of an alkali or alkaline earth nitrate. Platinum in the TWC 

catalyst is responsible for the oxidation of nitrogen oxide (NO) to nitrogen dioxide (NO2) 

facilitating the adsorption process. Periodically, NOx stored by the adsorbent is released and 

reduced to nitrogen. This process requires a fuel-rich exhaust gas composition and a TWC 

catalyst. These catalysts are typically based on combinations of platinum, palladium, and 

rhodium and are capable of using reductants (CO, hydrogen, and hydrocarbon) present in rich 

engine exhaust to selectively reduce NOx to nitrogen. TWC catalysts have been utilized for more 

than 20 years to perform these same reactions in the exhaust of stoichiometric gasoline engines. 

An engine management system (EMS) is critically involved in the operation of a NOx adsorber 

system. The EMS must determine when the NOx adsorbent is approaching saturation and then 

trigger the change in engine operation resulting in the rich condition required for release and 

reduction of the stored NOx. The timing, duration, and stoichiometry of the rich pulse are also 

critical. If it is too long and/or too rich, hydrocarbon and CO can break through the adsorber 

resulting in poor control of these pollutants, as well as introducing an unnecessary increase in 

fuel economy penalty. 

It is well known that sulfur compounds in diesel fuel are combusted in the engine, resulting in 

the release of sulfur dioxide (SO2). In a NOx adsorber, this SO2 undergoes reactions, which are 

completely analogous to those of NOx, resulting in the formation of alkali and alkaline earth 

sulfates. Unlike their corresponding nitrates, these sulfates are extremely stable. It has been 

shown repeatedly in the literature that the decomposition of these sulfates requires a combination 

of rich condition and temperatures in excess of 600oC. As a result, SO2 in the exhaust effectively 

poisons the NOx adsorption sites, and special procedures to desulfurize the adsorber must be 

applied. Although the chemical processes for removal of NOx and sulfur are similar, the removal 

of sulfur requires higher temperatures and longer duration. As such, desulfurization is the term 

commonly used to describe sulfur removal, while regeneration refers to removal and reduction 

of NOx. 

3
1.3.2 Principle of Operation of Diesel Particle Filters 

The DPF system consists of a filter positioned in the exhaust stream designed to collect much of 

the particle emissions while allowing the exhaust gases to pass through the system. Because the 

volume of PM generated by a diesel engine is sufficient to fill up and plug a reasonably sized 

DPF over time, some means of disposing of this trapped PM must be provided. The most 

promising means of disposal is to burn or oxidize the PM in the filter, thus regenerating or 

cleansing the filter. Under some conditions, precious metals in the DPF can oxidize sulfur 

compounds—such as SO2 and sulfite to sulfuric acid—increasing the PM emissions. 

The two types of DPFs evaluated in the DECSE program were the catalyzed diesel particle filter 

(CDPF) and the continuously regenerating diesel particle filter (CR-DPF). The CR-DPF 

accomplishes filter regeneration by continuously generating NO2 from emitted NO over an 

oxidation catalyst placed upstream of the filter. It has been established that NO2 is an effective 

low-temperature oxidizing agent for diesel PM. The CDPF affects the filter regeneration by 

using a catalyst coating on the filter element to promote the oxidation/combustion of the 

collected PM using available oxygen in the diesel exhaust. A third DPF technology utilizes a 

fuel-borne catalyst to promote oxidation of the PM. 

A complete DPF system consists of the filter and the means to facilitate the regeneration. The 

EMS can play a key role in facilitating regeneration at appropriate intervals. 

1.4 Project Scope, Goals, and Objectives 

The objectives of this project were to: 

1. Demonstrate the emissions potential of advanced fuels, engines, and ECSs for meeting 

federal Tier 2-Bin 5 emissions standards 

2. Evaluate the effect of fuel sulfur level on emissions and fuel economy, ECS performance, 

and catalyst degradation. 

The 2004-2009 federal standards are as follows: 

• PM of 0.01 g/mi 

• NOx of 0.07 g/mi 

• Non-methane hydrocarbons (NMHC) of 0.09 g/mi. 

These standards are to be met when testing over the FTP-75 test cycle at a full useful life of 

120,000 miles. 

The project was divided into two tasks: Task A and Task B. Task A involved the setup of the 

test cell with an engine and emissions measurement systems, measurement of baseline (engineout) emissions and fuel consumption, configuration and installation of the ECSs, and 

development of regeneration and desulfurization strategies as needed. Two different 

4
configurations were designed in Task A. In Task B, one of the two systems was aged for 2,000 

hours and periodically evaluated for regulated and unregulated emissions using selected lowsulfur fuels (15 ppm). The 2,000-hour aging of this system represent approximately 100,000 

miles of on-road use, which approaches the 120,000-mile useful life emission standard. 

The experimental design and analysis of test data from Task B was guided by a series of study 

questions organized into five topic areas: initial performance; durability and desulfurization; 

sulfur mass balance; fuel effects on regulated emissions; and unregulated emissions. 

1.4.1 Initial Performance 

These questions address the performance of the ECS during the initial 300 hours of aging, 

focusing on the initial impact of the ECS on regulated emissions and fuel economy, and the 

impact of sulfur on a fresh ECS. 

Q1.1 Can the system meet the 2007-2010 regulated emissions levels for NOx, NMHC, and 

PM? 

Q1.2 What is the impact on other regulated emissions [total hydrocarbon (THC), CO, PM, and 

NMHC] and fuel economy? 

Q1.3 How does system performance change during the early life (under 300 hours) of the 

system? 

Q1.4 Are there similar patterns for various transient duty cycles [Cold- and Hot-Start Urban 

Dynamometer Driving Schedule (UDDS), US06 (part of the Supplemental Federal Test 

Procedure), Highway Fuel Economy Test (HFET)]? 

1.4.2 Durability and Desulfurization 

This area addresses the impact of 2,000 hours of aging and sulfur accumulation on ECS 

performance and the effectiveness of periodic desulfurizations for restoring NOx reduction 

performance. Long-term impact on regulated emissions and fuel economy are also investigated. 

Q2.1 How do NOx emissions change as the system ages? Specifically, how do the maximum 

(pre-desulfurization), minimum (post-desulfurization), and average NOx levels change? 

Q2.2 Is the increase in NOx emissions between consecutive desulfurizations constant over 

time? 

Q2.3 How effective is desulfurization at restoring the initial NOx reduction performance of the 

system (initially and over time)? 

Q2.4 Does the performance of the system stabilize within the first 2,000 hours? If so, at what 

point does this occur? 

Q2.5 Are there temporal trends with respect to other regulated emissions or fuel economy? 

5
1.4.3 Sulfur Mass Balance 

Understanding the mechanisms by which sulfur from the fuel and lubricants interacts with the 

ECS is important for designing an effective and durable system. A mass balance approach is 

used to gain insight on this issue. 

Q3.1 How much sulfur is emitted during the desulfurization process? 

Q3.2 How does the amount of sulfur emitted during the aging cycle compare to the amount 

emitted during desulfurization process? Do these rates change over time? 

Q3.3 What happens to the differences between these amounts? 

1.4.4 Fuel Effects on Regulated Emissions 

Two different ultra-low-sulfur diesel fuels (15 ppm) were tested. This area considers whether 

the fuels have direct impacts on regulated emissions or fuel economy. 

Q4.1 Are there differences in emissions from DECSE and BP fuels? 

Q4.2 If such differences exist, are they consistent over time? 

1.4.5 Unregulated Emissions 

Periodic tests were performed to determine whether a fresh or aged ECS impacts emissions of 

unregulated gases and PM. The emissions of interest include selected hydrocarbon species, 

SOF/sulfate metals, nitroxy-alkanes, and polycyclic-aromatic hydrocarbons 

(PAH)/nitropolycyclic-aromatic hydrocarbon (NPAH). 

Q5.1 Which unregulated toxic (or potentially toxic) compounds are present in tailpipe 

emissions? 

Q5.2 How do the levels compare to engine-out emissions? 

Q5.3 How do unregulated emissions change with time? 

The answers to these questions and associated discussions are included in a separate report 

focusing on unregulated emissions across all of the ABPF-DEC platforms. 

6
Section 2: Technical Approach 

The following section details the technical approach for this project. This includes a discussion 

of the experimental design, which includes the platform engine selection, emissions control 

system selection, and fuel and lubricant selection. In addition the section also covers 

experimental procedure, including laboratory testing setup, ECS configuration, test procedures, 

aging cycle development, oil analysis, emissions sampling and analysis, data handling, and 

statistical analysis. 

2.1 Experimental Design 

The original plan for this project was to develop two different ECSs, conduct limited testing on 

both systems for up to 300 hours, and then, select one system for durability testing up to 2,000 

hours. Selections of the engine and ECSs are discussed in Sections 2.1.1 and 2.1.2, respectively. 

Section 2.1.3 describes the fuels and lubricants used in this study. 

Emissions measurements on regulated gases and PM were made every 100 hours while operating 

over four different transient test cycles using DECSE 15-ppm sulfur fuel. Unregulated emissions 

in the form of metals, PAH, NPAH, and selected gases were measured at four different time 

points using the BP15 fuel. Section 2.1.4 contains a complete list of emissions parameters 

measured during this study. Finally, Section 2.1.5 presents a test matrix showing the 

combinations of test conditions encountered and measurements performed. 

2.1.1 Engine Selection 

At project inception (August 2001), no common-rail diesel engines sized appropriately for a 

typical SUV (3 to 5L) were commercially available nor offered by any of the program 

participants. Therefore a reasonable surrogate engine selected by the APBF-DEC program 

steering committee for use in this program was a model year (MY) 2002 Isuzu Duramax. This 

6.6 liter, V8 engine came equipped with a common-rail fuel injection system; a high-pressure 

EGR system incorporating a vacuum-actuated EGR valve and intake throttle; four-valve-percylinder heads; pilot injection; and met the 2002 California medium-duty emission regulations 

when equipped with an oxidation catalyst. A development fleet vehicle (2500 series Chevrolet 

Silverado, shown in Figure 1) equipped with this engine was supplied by General Motors (GM). 

This vehicle came equipped with a ZF six-speed manual transmission. Two additional loose 

engines were supplied by Isuzu Motors America. The engine specifications are shown in Table 

2, while the engine itself is shown in Figure 2. A photograph of the underbody of the vehicle, 

identifying the turbocharger exhaust downpipe and oxidation catalyst locations, is shown in 

Figure 3. 

7
Figure 1. Development fleet vehicle supplied by GM equipped with Duramax 6.6L engine 

8
Table 2. Engine Specifications for MY 2002 Duramax 

Rated Speed (rpm) 3000 

Rated Power (hp) 300 ± 12 

Engine Displacement (liters) 6.6 

Fuel Rate at Rated Speed and Power (lb/hr) 120

Fuel Temp. at Rated Speed and Power (°F) Min: 100 Max: 106 

Rated Torque Speed (rpm) 1800 

Rated Torque (lb-ft) 520 ± 20 

Fuel Rate at Rated Torque Speed and Torque 

(lb/hr) 

62 

Governed Speed (rpm) 3250 governed, 3400 ± 25 no load 

Low Idle (rpm) 680 ± 25 

Cranking Speed (rpm) 135-180 

Water Outlet Temperature (°F) 187-192 

Pressure Drop across Intercooler (in. H2O) 53 ± 1 

Air Temperature after Intercooler (°F) min. 116 max. 124 

Engine Oil Rating 15W40 

Engine Coolant Type 50% water + 50% DEX-COOL glycol 

Intake Restriction - Max (in. H2O) 2 

Exhaust Restriction - Max (w/converter) (in. Hg) 12 

Intake Restriction Location @Vehicle Adaptor (in. 

H2O) 

4.5 ± 0.5 

Exhaust Restriction Location @Center of Turbo 10.5 ± 0.5 

(in. Hg) 

Exhaust Pipe Diameter (inches) 3 

Exhaust Flow at Rated Power (kg/min) 22.8 

Exhaust Temperature Maximum at Rated Power 

(°C) 

575 

9
Figure 2. Isuzu Duramax 6.6L engine 

10
Turbocharger 

Downpipe 

Oxidation 

Catalyst 

Transmission 

Front of 

Vehicle 

Rear of

Vehicle 

Figure 3. Vehicle underbody showing stock exhaust system 

2.1.2 Emission Control Systems (A and B) 

Two different ECS configurations were initially planned to provide two different approaches to 

meet the program goals. System A was a single, in-line NAC/DPF combination, which was 

expected to have the lowest overall system cost and physical size. However, the ability of this 

configuration to meet the ambitious program emission goals was in question. System B was a 

more complex, physically larger, dual-leg NAC system that was expected to increase the overall 

NOx reduction efficiency of the system and reduce the fuel economy penalty. Schematics of the 

two different proposed systems are shown in Section 2.2.1. 

11
Baseline vehicle emission and exhaust temperature data for the selected driving cycles were 

generated using the selected engine/vehicle, and provided to the MECA supplier in order to 

appropriately size the NAC and DPF for meeting the program emission goals. In addition to the 

NACs and DPF, the Southwest Research Institute (SwRI) also requested some highly loaded 

oxidation catalysts (pre-NAC and pre-DPF) to assist in breaking down the selected reductant 

(diesel fuel) and help minimize hydrocarbon breakthrough during regeneration. A selective 

catalytic reduction system using an ammonia-based reductant was evaluated under a different 

project with the APBF-DEC activity. 

Diesel fuel was selected as the reductant to allow commonality between the engine fuel and ECS 

system reductant. In addition, it was felt that use of diesel fuel as the reductant was more 

realistic than laboratory-provided reductants, such as pure CO, hydrogen, or individual 

hydrocarbons. 

Over the course of the program two different generations of components were supplied. Both 

generations of components consisted of oxidation catalysts, NACs, and DPFs. 

The first-generation System B consisted of two pre-NAC oxidation catalysts, each 14.4-cm in 

diameter and 7.6-cm length (2.5L total volume). These catalysts were each followed by a NAC 

24.1-cm in diameter and 15.2cm in length (14L total volume). The two legs of the exhaust were 

then combined into a single pipe—which was followed by a single oxidation catalyst 14.4-cm in 

diameter and 7.6-cm long (2.5L); and a DPF 26.7-cm in diameter and 30.5-cm long (17L)—for a 

total ECS system volume of 36 liters. 

Second-generation components were provided in order to more appropriately size the oxidation 

catalysts and DPF for the system, and to provide more thermally durable NACs. The secondgeneration System B consisted of two pre-NAC oxidation catalysts 24.1-cm in diameter and 7.6­

cm length (7L total volume) installed immediately upstream of the new, more thermally durable 

NACs with the same dimensions as the first-generation system (24.1-cm diameter x 51.2-cm 

length, 14L total volume). The two exhaust legs were combined after the NACs—followed by 

an oxidation catalyst 24.3-cm in diameter and 7.6-cm in length (3.5L volume); and a DPF 22.9­

cm in diameter and 30.5-cm in length (12.5L volume)—for a total ECS system volume of 

approximately 37 liters. 

The final System B configuration included in-exhaust fuel injection upstream of each NAC to 

provide reductant for regeneration of the NACs and also a single in-exhaust injector upstream of 

the rear oxidation catalyst/DPF combination to provide fuel to ensure regeneration of the DPF. 

The two injectors upstream of the NACs were of a type using a frequency valve/poppet 

valve/air-assist combination, while the third injector was an air-assisted, pintle-type fuel injector. 

To provide the necessary heat to the system and assist in achieving overall reducing conditions 

required for efficient NAC regeneration, a diesel fuel burner was developed and included as part 

of the overall ECS system. This was required due to the relatively low engine loads for this 

engine in this application. 

12
2.1.3 Fuel/Lubricant Selection 

Four fuels were utilized in this project: three fuels designed for use in the DECSE program [1] 

and one 2006-type refinery fuel. The DECSE fuels were used for strategy and control 

development, aging operation, and regulated emissions testing. The DECSE fuel is a blended 

fuel that was designed to have similar properties to the national average diesel fuel. While this 

fuel is composed of a narrower range of hydrocarbon compounds, its density, viscosity, cetane 

number, aromatic content, and other properties meet the specifications for a 2006 No. 2 diesel 

fuel. The refinery fuel, referred to as BP15, was only used during full unregulated emissions 

evaluations. The DECSE fuels in this project used the base DECSE fuel doped to varying sulfur 

levels (3, 8, and 15 ppm). The dopant mixture contains a variety of classes of sulfur containing 

molecules that are in the same boiling range as diesel fuel, with an emphasis on thiophenes. The 

refinery fuel used had a nominal 15-ppm sulfur level. A complete summary of the fuel properties 

for the DECSE fuel, the refinery fuel, and dopants are presented in Tables 3 and 4. 

13
Table 3. Test Fuel Properties 

Fuel Property ASTM 

Method 

Base Fuel BP15 

Density (kg/m3) D4052 826.2 837.1 

Viscosity @40oC (mm

2

/s) D445 2.3 2.5 

Distillation 

IBP (oC) D86 180 164 

10% recovery (oC) D86 203 201 

20% recovery (oC) D86 219 218 

30% recovery (oC) D86 233 233 

40% recovery (oC) D86 244 246 

50% recovery (oC) D86 251 259 

60% recovery (oC) D86 257 272 

70% recovery (oC) D86 265 286 

80% recovery (oC) D86 279 302 

90% recovery (oC) D86 312 322 

FBP (oC) D86 352 346 

Cloud point (oC) D2500 -26 -12 

Pour point (oC) D97 -23 -18 

Flash point, PMCC (oC) D93 69 64 

Sulfur (ppm) D5453 0.6 13.3 

Aromatics (vol. %) D1319 23.9 29 

Olefins (vol. %) D1319 4.6 

Saturates (vol. %) D1319 71.4 

Aromatics (vol. %) D5186 26.9 25 

Polyaromatics (vol. %) D5186 8.4 4.2 

Non-aromatics (vol. %) D5186 64.7 70.8 

Cetane number D613 42.5 51.1 

Cetane index D976 51.5 48.8 

Table 4. Properties of Sulfur Doping Compounds 

Concentration 

(mass %) 

Compound Chemical Formula Boiling Point 

(

o

C) 

50 Dibenzo[b,d]thiophene C12H8S 333 

30 Benzo[b]thiophene C8H6S 222 

10 Di-t-butyl disulfide C8H18S2 200 

10 Ethyl phenyl sulfide CH10S 206 

BP15 is a 15-ppm sulfur fuel prepared by processing straight-run distillate stocks through a 

commercial single-stage hydrotreater employing a high-activity catalyst at maximum severity. 

This fuel was prepared in a commercial refinery unit (not a pilot plant), but cracked stocks were 

14 
excluded from the feed because the specification sulfur level could not have been achieved with 

their inclusion. In 2007, actual production will likely employ more advanced processing to allow 

the inclusion of cracked stocks. 

All tests were conducted with Shell Rotella T 15W-40 engine lubricant. This oil meets the 

requirements of the API CI-4 specification for EGR-equipped engines and has a sulfur content of 

approximately 0.6%, which is typical of engine oils meeting this specification. This oil was used 

in the DECSE program and in all other APBF-DEC activities. Table 5 lists the lubricant 

specifications. 

Table 5. Lubricating Oil Specifications 

Property Specification 

Viscosity grade 15W40 

Performance category API CI-4 

Sulfated ash 1.5% 

Sulfur 0.65% (6500-ppm) 

Calcium 0.36% (3600-ppm) 

Phosphorus 0.14% (1400-ppm) 

Density at 15oC 868.0 kg/m3 

Viscosity at 40oC 101 cSt 

Viscosity at 100oC 14.0 cSt 

15
2.1.4 Emissions Measurements 

Throughout the test program, both raw and dilute tailpipe exhaust samples were acquired to 

evaluate the engine-out emissions and the ECS effectiveness. These samples were analyzed for 

various compounds, both gaseous and solid particles. 

Dilute bag samples were acquired at the tailpipe location and analyses conducted for 

concentrations of THC, methane, CO, carbon dioxide (CO2), and NOx. These dilute samples 

were acquired over a test cycle and represent the average concentration over that test cycle. In 

addition, a dilute particle sample was collected on a 90-mm Pallflex® filter and subsequently 

analyzed for total mass, and in certain cases for sulfate, SOF, and volatile organic fraction 

(VOF). 

For the unregulated emission tests (conducted after 100, 300, 900, 1,500, and 2,000 hours of 

aging), dilute bag samples were also analyzed using methods discussed in Section 2.2.3 for the 

following individual hydrocarbons: 

Ethane 1,3-butadiene 

Ethylene 2-methylpropane (isobutane) 

Propane 1-butyne 

Propylene Cis-2-butene 

Acetylene 3-methyl-1-nutene 

Propadiene 2-methylbutane (isopentane) 

Butane 1-methylcyclopentene 

Trans-2-butene Benzene 

1-butene Cyclohexane 

2-methylpropene (isobutylene) 2,3,3-trimethylpentane 

2,2-dimethylpropane (neopentane) Toluene 

Propyne 2,3-dimethylhexane 

In addition, dilute exhaust samples were collected on a 47-mm Teflo filter for metals analysis 

and two Oak Ridge National Laboratory (ORNL)-supplied sampling cartridges connected in 

series for nitroxy-alkane analysis. 

An additional dilution tunnel incorporating a 50-cm x 50-cm Pallflex filter (for capturing 

particle-bound and solid phase components) and two cartridges of polyurethane foam (PUF) 

media (connected in parallel, for gaseous phase components) were utilized to collect exhaust 

samples for subsequent PAH/NPAH analysis. These samples were analyzed for the following 

individual PAH: 

16
Naphthalene Chrysene 

2-methylnaphthalene Benzo(b)fluoranthene 

Acenaphthylene Benzo(k)fluoranthene 

Acenaphthene Benzo(e)pyrene 

Fluorine Benzo(a)pyrene 

Phenanthrene Perylene 

Anthracene Indeno(1,2,3-cd)pyrene 

Fluoranthene Dibenzo(a,h)anthracene 

Pyrene Benzo(g,h,i)perylene 

Benzo(a)anthracene 

In addition, the samples were analyzed for the following individual NPAH: 

1-nitronaphthalene 4-nitropyrene 

2-me-1-nitronaphthalene 1-nitropyrene 

2-nitronaphthalene 7-nitrobenzo(a)anthracene 

2-nitrobiphenyl 6-nitrochrysene 

4-nitrobiphenyl 1,3-dinitropyrene 

5-nitroacenaphthene 1,6-dinitropyrene 

2-nitrofluorene 1,8-dinitropyrene 

9-nitroanthracene 6- nitrobenzo(a)pyrene 

3-nitrofluoranthene 

Raw tailpipe emissions were continuously sampled at 10Hz for THC, CO, CO2, and NOx 

concentration. In addition, during the unregulated emission sampling events, raw exhaust 

samples were acquired utilizing a bubbler technique for later determination of SO2 and hydrogen 

sulfide (H2S) concentration over the test cycle; impingers were used with a Fourier Transform 

Infrared (FTIR) analyzer to sample and analyses the raw exhaust for determining the 

concentration of the following compounds on a second-by-second basis: 

17
NO Formaldehyde 

NO2 Acetaldehyde 

NOx Benzene 

N2O Ammonia 

1,3-butadiene 

Raw, continuous exhaust samples were also taken at the engine-out location and after each NAC 

for determination of THC, CO, and NOx concentration. These samples were recorded at 10Hz 

and were instrumental in providing feedback during the development of the ECS strategy. 

Oxygen and NOx sensors also were recorded at 10Hz, and utilized at the engine-out location after 

each NAC and at the tailpipe location. 

Table 6 provides a summary of the different types of emission samples and the sample locations 

for the emission evaluations. 

Table 6. Summary of Emission Measurements Performed during Emission Evaluations 

Raw 

Engine-Out 

Raw 

after 

NAC1 

Raw 

after 

NAC2 

Raw 

Tailpipe 

Dilute 

Tailpipe 

Average THC, 

Methane, NOx, 

CO, CO2 

X 

Continuous THC, 

NOx, CO, CO2 

X X X 

Continuous THC, 

NOx, CO 

X X 

Average SO2 

and H2S Mass 

X 

Total PM Mass 

and Avg. Sulfate, 

SOF, and VOF 

X 

Hydrocarbon 

Speciation 

X 

FTIR X 

Metals Analysis X 

Nitroxy-alkanes X 

PAH/NPAH X 

Oxygen and NOx 

Sensors 

X X X X 

18
2.1.5 Test Matrix 

Table 7 summarizes the emissions evaluations that were performed during the study using 15­

ppm DECSE fuel. Each evaluation was a duplicate or triplicate test consisting of a Cold-Start 

UDDS followed by Hot-Start UDDS, US06, and HFET test cycles. PM samples were collected 

and weighed between each test cycle; however, when testing with the ECS, the SOF and sulfate 

measurements were made only when triplicate tests were performed. For those tests separate 

composite samples were made from the triplicate runs of the Cold-Start UDDS, Hot-Start 

UDDS, US06, and HFET cycles. Duplicate and triplicate tests alternated every 100 hours. 

Duplicate measurements were taken using 8-ppm DECSE and 15-ppm BP fuel at engine-out. 

Triplicate measurements were taken using 15-ppm BP fuel at 100, 300 (pre- and postdesulfurization), 900 (post-desulfurization), 1,500 (post-desulfurization), and 2,000 (postdesulfurization). Triplicate unregulated emissions samples were collected at specified aging 

points (100, 300, 900, 1,500, and 2,000-hours); however, each sample consisted of composite 

materials collected across the four test cycles. Section 2.1.4 contains a complete list of emissions 

parameters that were measured. 

Table 7. Test Matrix 

Number of Samples or Analyses1 

System 

Age from-to 

[by] hrs) Fuel 

Regulated 

Gases and 

Total PM 

SOF & 

Sulfate 

Unregulated 

Gases or 

Filters 

Engine-Out D8, 2 2 

n/a D15 2 2 

BP15 2 2 2 

NAC + DPF 0-300 [50] D15 2 or 3 each 0 or 1 each 

400-2,000 [100] 

pre- D15 2 or 3 each 0 or 1 each 

desulfurization 

200-2,000 [100] 

post- D15 3 or 2 each 1 or 0 each 

desulfurization 

100 BP15 3 1 each 3 

300, 900, 1,500, 

2,000 BP15 3 each 1 each 3 each 

postdesulfurization 

1

See Section 2.1.4 for a complete list of emissions parameters measured. 

19
2.2 Experimental Procedures 

This section describes the experimental (laboratory setup, testing, sampling, and analysis) and 

data (handling and analysis) procedures that were followed. 

2.2.1 Laboratory Setup 

The laboratory setup involved both initial vehicle tests and an ECS configuration, as described 

below. 

Initial Vehicle Tests. Initial testing was conducted on-vehicle utilizing a 48” single-roll, Horiba 

Chassis Dynamometer (Model LDV-48-86-125HP). This chassis dynamometer utilizes a feedforward control system for inertia and road-load simulation. The dynamometer electrically 

simulates vehicle tire/road interface forces, including parasitic and aerodynamic drag. The 

vehicle experiences the same speed, acceleration/deceleration, and distance traveled as it would 

on the road. A preprogrammed road-load curve is the basis for the required force during each 

second of the driving schedule. For light-duty passenger cars, observed road load and simulated 

inertia errors on this chassis dynamometer are typically less than ± 0.15%. 

In order to provide necessary engine related data (i.e., exhaust flow rates, temperatures, engineout emissions, etc.) to the designated MECA member supplying all the ECS components, an 

estimated road-load was utilized for chassis dynamometer testing prior to conducting the on-road 

coast-downs for the test vehicle supplied. As the emission targets for this program related to the 

light-duty FTP test, and the US06 cycle was the most aggressive driving schedule, the results 

from these two test cycles defined the exhaust environment. 

As this program was intended to address the fast-growing SUV market, an appropriate inertia 

weight at which to test the supplied pick-up truck was determined by calculating the average of 

the lightest and heaviest SUVs in which this engine could be theoretically offered. The lightest 

vehicle used in this determination was a 2002 Chevrolet Suburban 2500, two-wheel drive, LT, 

four door, 6.0L V8, 4A with a curb weight of 5,447 lb. The heaviest vehicle used in this 

determination was a 2002 Ford Excursion Limited Ultimate, four-wheel drive, four-door, 7.3L 

TDI V8, 4A with a curb weight of 7,688 lb. The average of these two values resulted in a curb 

weight of 6,568 lb. Adding an additional 300 lb for a driver and passenger, and rounding to the 

nearest 125 lb increment, resulted in a dynamometer inertia weight of 6,875 lb. 

Three vehicle tests were conducted over the light-duty FTP-75 and US06 cycles at the selected 

inertia weight of 6,875 lb using dynamometer road-load curve shown in Figure 4. This estimated 

road-load curve was determined by averaging the road-load curves of four vehicles of similar 

size and weight. The purpose of these initial tests was only to provide the initial engine-out data 

needed by the ECS supplier to properly size the individual components of the proposed ECS 

system. In addition, an appropriate transmission shift schedule was developed for the different 

test cycles. During the vehicle tests, raw NOx and CO2 concentrations were measured (after the 

oxidation catalyst) along with three exhaust temperatures (downpipe, after oxidation catalyst, 

and muffler inlet), engine back pressure, voltage output from the stock mass airflow (MAF) 

sensor, intake manifold vacuum/pressure, and EGR valve vacuum signal. Based on a calculated 

estimate of intake flow (using engine rpm, and intake pressure and temperature) and NOx 

concentration, a rough estimation of instantaneous and accumulated engine-out/tailpipe NOx 

mass was made. Figures 4 and 5 show the estimated accumulated engine-out NOx mass over the 

20
FTP and US06, respectively. The exhaust temperatures (measured in the downpipe and after the 

stock oxidation catalyst) are shown in Figures 6 and 7 for the FTP and US06, respectively. 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

100 

Road-Load (hp) 

Estimated Road Load 

Dyno Coefficients 

A=21.95 lbf 

B=-0.06365 lbf/mph 

C=0.043655 lbf/mph^2 

0 10 20 30 40 50 60 70 80 90 100

Vehicle Speed (mph) 

Figure 4. Initial road-load curve utilized for 2002 Chevrolet Silverado test vehicle 

21
20 

Accumulated N

OX Mass, grams 

Bag 1 Bag 2 Bag 3 

18 

16 Engine-Out (with EGR) 

14 

12 

10 

8 

6 

4 

2 

Composite NOx = 4.7 g/mi. 

0 

0 200 400 600 800 1000 1200 1400 1600 1800 2000 

Time, seconds 

Figure 5. Accumulated NOx mass over the FTP 

35 

30 

Accumulated NOX Mass, grams 25 

20 

15 

10 

5 

0 

Engine-Out (with EGR) 

Composite NOx = 3.8 g/mi. 

0 100 200 300 400 500 

Time, seconds 

Figure 6. Accumulated NOx mass over the US06 

22 

600 
450 

450 

Temperature, °C 

400 Downpipe Temperature (°C) 

350 After Oxidation Catalyst Temperature (°C) 

300 

250 

200 

150 

100 

50 

10-minute soak 

period 

0 

0 200 400 600 800 1000 1200 1400 1600 1800 2000 

Time, seconds 

Figure 7. Exhaust gas temperatures over the FTP Temperature, °C 

400 

350 

300 

250 

200 

150 Downpipe Temperature (°C) 

100 After Oxidation Catalyst Temperature (°C) 

50 

0 

0 100 200 300 400 500 600 

Time, seconds 

Figure 8. Exhaust gas temperatures over the US06 

23
ECS Configuration. Based upon the initial, “quick-look” vehicle test results, it was obvious 

that an extremely high level of NOx reduction would be required to meet the program goal 

(>98% over the FTP for the given level of engine-out NOx with the stock EGR calibration). 

Also, additional heat beyond that supplied by the engine would be required in order for any NOx 

adsorber system to function well (NACs typically require operating temperatures >275°C for 

greater than 90% NOx reduction efficiency). 

The original program plan was to examine two significantly different ECSs in order to gain a 

better understanding of the impact and trade-offs between the two systems. However, due to the 

extremely high level of NOx reduction required, availability of system components, and the 

desire to investigate the performance of the system after 2,000 hours of aging, only one system 

(System B described below) was ultimately utilized in this program. 

The first system to be studied (System A, shown in Figure 9) was a single, in-line DPF and NOx 

adsorber system utilizing known and available components. Configuration A represented the 

smallest physical package with the least complexity. In addition, as regeneration and 

desulfurization would occur under full-flow conditions, it would require the least amount of 

additional equipment to control the system. However, full-flow regeneration and desulfurization 

had the potential of incurring a large fuel economy penalty and provided no additional means for 

NOx adsorption when the efficiency of the NOx adsorber was low or regenerating. 

The second system to be studied (System B, variations shown in Figures 10a, 10b, 10c) was to be 

a dual-leg NOx adsorber-DPF system potentially utilizing more research-oriented components 

(i.e., sulfur traps, CO-generating catalysts). Configuration B would be physically larger than A, 

and would require exhaust valves to direct flow during regeneration and desulfurization. 

Additionally, supplemental exhaust fuel injection (SFI) would be required to provide reducing 

conditions to the regenerating leg. However, as regeneration would occur under partial flow 

conditions, and adsorption would continue during regeneration (in the opposite leg), System B 

had the potential for a lower fuel economy penalty and higher efficiency. The use of sulfur traps 

was intended to extend the time between regenerations, reducing the fuel economy penalty 

associated with desulfurization. A patent application was filed for System B3 and received on 

June 1, 2004 (US Patent No. 6,742,328). However, due to the desire to utilize known 

components (for durability purposes), the final version of System B, shown in Figure 11, was 

more similar to the version shown in Figure 10 b. 

24
EGR 

VALVE

6600 Duramax 

INTAKE 

THROTTLE 

AIR 

FILTER 

NAC DPF

SFI 

Air Charge Cooler Oxidation 

Catalyst 

(OC) 

NOX 

Adsorber 

Catalyst 

Diesel 

Particle 

Filter 

In-Exhaust 

Fuel 

Injection 

Figure 9. Proposed System A ECS configuration (single, in-line system) 

EGR 

VALVE 

6600 Duramax 

INTAKE 

THROTTLE 

AIR 

FILTER 

Air Charge Cooler 

NAC 

#2 

NAC 

#1 

DPF 

#2 

DPF 

#1 

SFI 

SFI 

OC 

EGR

VALVE

6600 Duramax

INTAKE

THROTTLE

AIR

FILTER

Air Charge Cooler

NAC

#2

NAC

#1

DPF

#2

DPF

#1

SFI

SFI

OC

NAC

#2

NAC

#1

DPF

#2

DPF

#1

SFI

SFI

OC

Figure 10a. Proposed System B1 ECS configuration (dual-leg system) 

25
EGR

VALVE

INTAKE

THROTTLE 

NAC 

#2 

NAC 

#1 

SFI 

COG 

SFI 

DPF

COG 

6600 Duramax

AIR 

FILTER 

Air Charge Cooler 

Figure 10b. Proposed System B2 ECS configuration (dual-leg system) 

EGR 

VALVE 

6600 Duramax 

INTAKE 

THROTTLE 

AIR 

FILTER 

Air Charge Cooler 

OC 

SFI 

COG 

SFI 

DPF 

COG

S-trap S-trap

NAC 

#1 

NAC 

#2 

Figure 10c. Proposed System B3 ECS configuration (dual-leg system) 

26
EGR 

VALVE 

6600 Duramax 

INTAKE 

THROTTLE 

AIR 

FILTER 

Air Charge Cooler 

SFI 

SFI 

Diesel Fuel 

Burner 

SFI 

OC DPF 

DPF OC N#1AC 

DPF OC N#1AC 

Figure 11. System B, final ECS configuration utilized 

2.2.2 Test Procedures 

Test procedures included chassis dynamometer test cycles; the development of equivalent test 

cell cycles to duplicate engine operation in the vehicle; an aging cycle; and tests of oil changes, 

additions, and sampling. 

Chassis Dynamometer Test Cycles. Four different vehicle-based transient test cycles were 

utilized in this project for evaluating the ECS effectiveness. The four cycles were the cold and 

hot portions (Cold-Start UDDS and Hot-Start UDDS) of the light-duty FTP-75 referred to as the 

Urban Dynamometer Driving Schedule (UDDS), the Highway Fuel Economy Test (HFET), and 

the US06 portion of the Supplemental FTP. The Cold-Start UDDS cycle is conducted after a 

vehicle ambient soak period of 12-36 hours, while the Hot-Start UDDS cycle is conducted after a 

10-minute soak period immediately following the Cold-Start UDDS (repeat of driving cycle). 

The HFET is conducted after operating over an HFET prep cycle, regardless of vehicle soaktime, while the US06 is conducted after completing one of a number of allowable different prep 

cycles. For this program, the US06 test cycle was preceded by a US06 prep cycle. The 

corresponding indicated vehicle speed versus time schedules for the different driving cycles 

(including the prep sequence) are shown in Figure 12 for the Cold -Start UDDS and Hot-Start 

UDDS cycle, Figure 13 for the HFET, and Figure 14 for the US06. 

27
70 

FTP-75 

60 

Cold Start UDDS 10-Minute Hot Start UDDS 

Soak Period 

50 

CLA-4 

HLA-4 

40 

30

Vehicle Speed, mph

20 

10 

0 

0 500 1000 1500 2000 2500 3000 3500 

Time, seconds 

Figure 12. Indicated vehicle speed versus time for Cold-Start UDDS and Hot-Start UDDS 

driving schedules 

28
0 

10 

20 

30 

40 

50 

60 

70 

Indicated Vehicle Speed, mph 

HFET Prep and Test Sequence 

Prep Sequence Test Sequence 

0 200 400 600 800 1000 1200 1400 1600 

Time, seconds 

Figure 13. Indicated vehicle speed versus time for HFET prep and test driving schedule 

29
Test Cycle UDDS HFET US06 

Average Speed, mph 19.5 48.2 48.0 

Maximum Speed, mph 56.7 59.9 80.3 

Maximum Accel, mph/s 3.6 3.2 8.4 

Duration, sec 1372 765 600 

Distance, mi. 7.5 10.26 8.01 

Idle Time, % 19.0 0.8 7.3 

90 

Prep Sequence Test Sequence 

80 

70 

60

Indicated Vehicle Speed, mph 

50 

40 

30 

10 

20 US06 Prep and 

Test Sequence 

0 

0 200 400 600 

Time, seconds 

800 1000 1200 

Figure 14. Indicated vehicle speed versus time for US06 prep and test driving schedule 

A comparison of the maximum speed, average speed, maximum acceleration, distance traveled 

and time for the different cycles is shown in Table 8. As can be seen in this table, the UDDS is a 

lightly loaded cycle where the engine spends significant time at idle conditions. 

Table 8. Operational Characteristics of Select Light-Duty Chassis Dynamometer Test 

Cycles 

Development of Equivalent Test Cell Cycles to Duplicate Engine Operation in the Vehicle. 

In order to speed the development of the NAC system control strategy, provide more repeatable 

test conditions, and allow multiple cold-start tests to be conducted in a single day, it was 

determined to be more efficient to forgo testing on the vehicle and move into a test cell 

environment. Different test cell control cycles for the Cold-Start UDDS, Hot-Start UDDS, 

30
HFET, and US06 were developed in order to duplicate engine operation in the vehicle. The 

vehicle was operated on the chassis dynamometer over the test cycles of interest while recording

important operational information such as engine speed, accelerator pedal position (APP), 

manifold absolute pressure, intake MAF, exhaust temperatures, etc. (with EGR disabled). 

Graphical representations of the resultant engine speed and torque output versus time for the

Cold-Start UDDS (with increased cold-idle speed), Hot-Start UDDS, HFET, and US06 are 

shown in Figures 15, 16, 17, and 18, respectively. These control cycles resulted in engine-out 

emissions, fuel consumption, and exhaust gas temperatures similar to those observed on-vehicle. 

A comparison of the engine-out accumulated NOx mass, CO2 mass, and exhaust gas temperature 

for a Cold-Start UDDS on the vehicle and in the test cell is shown in Figures 19, 20, and 21, 

respectively. A more complete description of the test cell control cycles developed and 

comparisons of various engine parameters can be found in Section 3.1 of this report. 

5000 400 

4500 300 

4000 200 

Engine Speed, rpm 3500 100 

3000 0 

Command Cycle Engine Speed 

2500 -100 Command Cycle Engine Torque Output

2000 -200 

1500 -300 

1000 -400 

500 -500 

0 200 400 600 800 1000 1200 1400 

Time, seconds 

Torque, lbf-ft 

Figure 15. Test command cycle (engine speed and torque) for Cold-Start UDDS cycle 

31
5000 500 

Command Cycle Engine Speed 

4500 400 Command Cycle Engine Torque Output

4000 300 

Engine Speed, rpm 3500 200 

3000 100 

2500 0 

2000 -100 

1500 -200 

1000 -300 

500 -400 

0 200 400 600 800 1000 1200 1400 

Time, seconds 

Figure 16. Test cell command cycle (engine speed and torque) for Hot-Start UDDS 

4500 400 

4000 300 

3500 200 

Engine Speed (rpm) 3000 100 

2500 0 

2000 -100 

1500 -200 

1000 -300 Command Cycle Engine Speed 

Command Cycle Engine Torque Output

500 -400

0 100 200 300 400 500 600 700 800

Time (seconds)

Torque, lbf-ft 

Torque (ft-lbs) 

Figure 17. Test cell command cycle (engine speed and torque) for HFET cycle 

32
6500 700 

Command Cycle Engine Speed 

Command Cycle Engine Torque Output

5500 500 

Engine Speed, rpm 4500 300 

3500 100 

2500 -100 

1500 -300 

500 -500

0 100 200 300 400 500 600

Time, seconds

Torque, lbf-ft 

Figure 18. Test cell command cycle (engine speed and torque) for US06 cycle 

45

40 Vehicle Test - No EGR

Raw

Accu

mulated 

N

Ox Mass (grams 

Test Cell - No EGR (Cold_Rev_8) 

35 

30 

25 

20 

15 

Test Cell Cycle (Cold_Rev_8) Results in

7% Lower NOx Compared to Vehicle Test

10 

5 

0

0 200 400 600 800 1000 1200 1400

Time (seconds)

Figure 19. Comparison of accumulated engine-out NOx mass over the Cold-Start UDDS 

for a vehicle test and test cell run

33
4500 

Vehicle Test - No EGR 4000 

Test Cell - No EGR (Cold_Rev_8) 

Raw Accumulated CO2 Mass (grams 

3500 

3000 

2500 

2000 

1500 

Test Cell Cycle (Cold_Rev_8) Results in 

2% Lower CO2 Compared to Vehicle Test

1000 

500 

0 

0 200 400 600 800 1000 1200 1400 

Time (seconds) 

Figure 20. Comparison of accumulated engine-out CO2 mass over the Cold-Start UDDS 

for a vehicle test and test cell run

300 

Vehicle Test - No EGR

250

Test Cell - No EGR (Cold_Rev_8)

200 

Te

mperature (°C) 150 

100 

50 

0 

0 200 400 600 800 1000 1200 1400

Time (seconds)

Figure 21. Comparison of exhaust gas temperature over the Cold-Start UDDS for a

vehicle test and test cell run 

34
Aging Cycle. In order to evaluate the impact of long-term operation on the ability of the NAC 

system to achieve high levels of NOx reduction, it was necessary to develop an aging cycle as 

there are no industry standards for aging NOx adsorber systems. As this program was a lightduty-based program, an aging cycle was developed that reflected more on light-duty-type 

operation (i.e., no extended high-load operation). Also, since the primary functions of the NAC 

are to adsorb, desorb, and reduce NOx, it was not known exactly how the aging of this device 

could be accelerated while still exercising these functions. Aging at elevated temperature is 

known to deactivate the NAC, but a correlation of elevated temperature exposure to miles was 

not known. Also it was not clear that thermal acceleration of aging alone would adequately 

simulate the aging process of the NAC. In addition, sulfur exposure of the NAC is a critical 

issue, and the frequency of desulfurization events was unknown at the start of testing. Therefore, 

the aging cycle was not intended to be an accelerated-type aging cycle; instead the cycle was to 

focus on exercising the emissions control system in a manner similar to what would be expected 

in-use. In the interest of repeatability and unmanned operation, a stepped, steady-state mode 

type of cycle was deemed appropriate (as opposed to a transient-type cycle). 

The aging cycle developed in this program was obtained by examining the most frequent 10 

modes of operation (engine speed and APP) during a vehicle test operating over the CARB 

Unified Driving cycle, also referred to as the LA92 cycle (speed versus time trace shown in 

Figure 22). This cycle was expected to expose the engine/vehicle to more “real-world” type 

driving conditions than seen on the FTP. The test vehicle was operated over the CARB Unified 

cycle on a chassis dynamometer to obtain engine operating information (i.e., speed, APP, 

exhaust temperatures, etc.). A summary of the frequency of operation for various engine speed 

and APP “bins” is shown in Table 9 where the 11 most frequent bins of operation are 

highlighted. The 1,350 rpm / 5% APP point was determined to be a motoring phase and was not 

included in the aging cycle. An engine dynamometer-based aging cycle was developed utilizing 

the remaining 10 bins of most frequent operation. The cycle was developed by fixing the desired 

total cycle length at 10 minutes, and basing each mode length on its corresponding percentage of 

total operation over the CARB Unified Driving cycle. Table 10 shows the various operating 

modes and their corresponding time duration. A ramp time of 5 seconds was incorporated 

between each mode where a change in engine speed was required. 

35
80 

Target Vehicle Speed

70 Duration = 1435 seconds 

Total Distance = 9.82 miles 

Average Speed = 24.6 mi/hr 60

50

40

30

20

10

0

0 300 600 900 1200 1500

Time, seconds

Figure 22. Vehicle speed versus time for CARB Unified Driving Schedule 

V

ehicle Spe

e

d, m

ph 

36
Table 9. RPM and APP Analysis of the CARB Unified Driving Cycle 

Engine Accelerator Pedal Position (APP) 

Speed 

RPM 5 15 25 35 45 55 65 75 85 95 

450 0.2% 0.1% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

750 9.2% 1.7% 0.8% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

1,050 2.7% 3.6% 4.0% 2.7% 0.8% 0.3% 0.0% 0.0% 0.0% 0.0% 

1,350 4.0% 6.0% 8.0% 8.2% 6.8% 3.7% 0.3% 0.0% 0.0% 0.0% 

1,650 1.6% 1.5% 1.5% 2.4% 3.1% 4.3% 1.1% 0.1% 0.0% 0.0% 

1,950 0.6% 0.3% 1.7% 5.5% 5.7% 3.1% 1.1% 0.4% 0.0% 0.0% 

2,250 0.1% 0.1% 0.1% 0.4% 0.4% 0.2% 0.3% 0.3% 0.1% 0.0% 

2,550 0.0% 0.0% 0.0% 0.0% 0.0% 0.1% 0.0% 0.2% 0.1% 0.0% 

2,850 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.1% 0.0% 

3,150 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

Table 10. Frequency of RPM and APP Combinations over the CARB Unified Driving Cycle 

Speed, 

rpm APP 

Percent of 

CARB 

Unified 

Cycle 

Percent of 

Aging Cycle 

Mode 

Time, sec 

Mode 1 680 0% 9.2% 14.2% 86 

Mode 2 1050 15% 3.6% 5.7% 34 

Mode 3 1050 25% 4.0% 6.3% 38 

Mode 4 1350 15% 6.0% 9.4% 56 

Mode 5 1350 25% 8.0% 12.5% 75 

Mode 6 1350 35% 8.2% 12.8% 77 

Mode 7 1350 45% 6.8% 10.6% 54 

Mode 8 1650 55% 4.3% 6.7% 40 

Mode 9 1950 35% 5.5% 8.7% 52 

Mode 10 1950 45% 5.7% 8.9% 53 

Ramps --- --- --- 4.2% 25 

Totals --- --- 61.3% 100.0% 600 

In an effort to harmonize the aging cycle developed for the medium-duty SUV and light-duty 

passenger car APBF-DEC programs, the aging cycle was modified to include a 20-minute, 

steady-state evaluation mode. The final aging cycle maintained the original 10 steady-state 

points (shown in Figure 23) and their relative weighting, but was expanded to include a steadystate evaluation point. The selected steady-state evaluation point was the highest speed and load 

point of the 10 cycle modes (1,950 rpm and 45% APP or 180 lb-ft torque). The steady-state 

evaluation point chosen had the highest space velocity and was expected to magnify any loss in 

performance of the NAC due to sulfur accumulation. In addition, this point had one of the 

highest fuel consumption rates and increased the sulfur mass exposure of the system. The 

evaluation point was also used to verify continuous DPF regeneration throughout the aging 

37
cycle. This point was run for 20 minutes, once every 4 hours (22, 10-minute cycles followed by 

the 20-minute, steady-state point). Table 11 provides the operating characteristics of the steadystate evaluation point. Figure 24 shows the percentage of time spent at each operating point for 

the aging cycle as a 4-hour set (22, 10-minute cycles plus one 20-minute evaluation). 

T

orque (lb-ft) 

300 

250 

200 

150 

100 

50 

0 

Top Ten Operating Points as a Percentage of LA92 Cycle 

(Compound Classification Analysis) 

4.3% 

5.7% 

6.8% 

5.5% 

8.2% 

4.0% 8.0% 

6.0% 

3.6% 

9.2% 

0 500 1000 1500 2000 2500 

Engine Speed (rpm) 

Figure 23. Ten most frequent operating points over CARB Unified Driving cycle 

38
Table 11. Steady-State Evaluation Point Information 

Engine Speed (rpm) 1950 

APP (Percent) 45 

Torque (lb-ft) 180 

Power (hp) 67 

Intake MAF Rate (g/s) 73 

EGR Rate (Percent) 24 

Fuel Consumption (lbs/hr) 27.8 

Engine Back Pressure (inHg) 2.4 

DPF DeltaP (inH2O) 17.2 

Exhaust Temp @ Manifold (oC) 446 

Oxi1 – 1” (oC) 370 

Oxi2 – 1” (oC) 355 

NAC1 – 1” (oC) 389 

NAC1 –5” (oC) 394 

NAC2 – 1” (oC) 405 

NAC2 – 5” (oC) 416 

Oxi3 - 1” (oC) 362 

DPF – 1” (oC) 364 

DPF – 11” (oC) 361 

Engine-Out NOx Concentration (ppm) 200 

Engine Speed (rpm) 

Figure 24. Aging cycle operating points with steady-state evaluation point (based on 

CARB Unified Driving cycle) 

The order of the modes was changed after 400 hours of aging due to undesirably high NAC bed 

temperatures and recurring oxidation catalyst face plugging. As a result, the time of operation at 

each mode was slightly modified to account for the additional time required to ramp between the 

modes. The new order of modes alternated the engine operation between high and low 

speeds/loads. A comparison of engine speed and load for the original aging cycle and the 

modified cycle is shown in Figure 25, while a comparison of oxidation and NAC bed 

temperature for the two different cycles is shown in Figure 26. A summary of the modified 

0 

50 

100 

150 

200 

250 

300 

0 500 1000 1500 2000 2500 

Torque (lb-ft) 

13.1% 

5.2% 

5.8% 

8.6% 

11.5% 

11.7% 

9.7% 

6.1% 

8.0% 

8.2% 

Top Ten Operating Points as a Percentage of Durability Cycle (including evaluation point) 

8.3% 

20 Minute Evaluation Point 

39
aging cycle (including the weighting of the steady-state evaluation point, Mode 10, and ramps 

between modes) is shown in Table 12. 

0 

500 

1000 

1500 

2000 

2500 

Engine Speed, rpm 

0 

120 

240 

360 

480 

600 

Torque, lb-ft 

Original Durability Cycle - Engine Speed 

Modified Durability Cycle - Engine Speed 

Original Durability Cycle - Torque 

Modified Durability Cycle - Torque 

1200 1300 1400 1500 1600 1700 1800

Time, seconds

Figure 25. Comparison of engine speed and load for the original and modified aging 

cycles 

40
700 1050 

NAC Bed Temperature, °C 

600

500

400

300

200

100

0 

-100 

-200 

1200

Original Durability Cycle - NAC1-1" 

Modified Durability Cycle - NAC1-1" 

Original Durability Cycle - Oxi1-1" 

Modified Durability Cycle - Oxi1-1" 

1400 1600 1800 2000 2200

Time, seconds

950

850

750

650

550

450

350

250

150

2400

Oxidation Catalyst Bed 

Temperature, °C 

Figure 26. Comparison of oxidation and NAC bed temperatures over the original and 

modified aging cycles 

41
Table 12. Summary of Modified CARB Unified Cycle Based on Aging Cycle Operating 

Conditions and Mode Order 

Step 

Original 

Mode 

Number 

Engine 

Speed, 

rpm APP 

Percent 

of CARB 

Unified 

Cycle 

Percent 

of Aging 

Cycle 

Mode 

Time, 

sec 

1 1 680 0% 9.2% 12.8% 84 

2 Ramp 680-1,950 0-35% - - - 0.8% 5 

3 9 1,950 35% 5.5% 7.8% 51 

4 Ramp 1,950­ 35-15% - - - 0.8% 5 

1,050 

5 2 1,050 15% 3.6% 4.9% 32 

6 Ramp 1,050­ 15-55% - - - 0.8% 5 

1,650 

7 8 1,650 55% 4.3% 6.0% 39 

8 Ramp 1,650­ 55-25% - - - 0.8% 5 

1,050 

9 3 1,050 25% 4.0% 5.5% 36 

10 Ramp 1,050­ 25-45% - - - 0.8% 5 

1,350 

11 7 1,350 45% 6.8% 9.6% 63 

12 Ramp 1,350­ 45-15% - - - 0.2% 1 

1,350 

13 4 1,350 15% 6.0% 8.4% 55 

14 Ramp 1,350 15-35% - - - 0.2% 1 

15 6 1,350 35% 8.2% 11.6% 76 

16 Ramp 1,350 35-25% - - - 0.2% 1 

17 5 1,350 25% 8.0% 11.3% 74 

18 Ramp 1,350 25-45% - - - 0.2% 5 

19 10 (SS) 1,950 45% 5.7% 16.3% 52 

20 Ramp 1,950-680 45-0% - - - 0.8% 5 

Totals - - - - - - 61.3% 100% 600 

Oil Changes/Additions/Sampling. As the program fuel sulfur level was very low (15 ppm), 

there was concern that engine oil consumption could have a significant impact on sulfur 

deposition on the NACs, and as such, it would be necessary to accurately monitor oil 

consumption throughout the test sequence. However, there was also a desire to accelerate the 

time frame of the program, and a decision was made to allow force-cooling between sets of tests 

to allow multiple cold starts in a single day, reducing the time required to conduct the emission 

evaluations by 50%. The force-cooling approach necessitated pumping the engine oil from the 

sump, through a cooler and back into the sump. This approach resulted in eliminating the 

possibility of accurately tracking oil consumption during the emission evaluation sequences. 

However, oil consumption and addition were monitored during the 100-hour aging sequences. 

The engine exhibited extremely low oil consumption throughout the aging, consuming 

approximately 7 liters of oil over the course of 2,000 hours of operation at a relatively constant 

rate. 

42
Oil samples were acquired after every 100-hour emission evaluation sequence. A portion of 

these samples were utilized for the VOF analysis detailed in Section 2.2.3. The engine oil was 

changed every 300 to 400 hours of aging (after the emission evaluations had been conducted, 

approximately 350 or 450 hours of total run time). This oil change interval was determined 

earlier in the project by conducting oil analyses at various intervals during aging and observing 

no significant change in oil properties after 300 hours of operation. Table 13 provides a 

summary of select engine oil properties after various aging hours. 

Table 13. Select Engine Oil Properties after Various Aging Hours 

Property 

0 

Hours 

148 

Hours 

221 

Hours 

277 

Hours 

Fuel Dilution (D322FD), wt.% 

Viscosity (D445, 100C), cSt 

Viscosity (D445, 40C), cSt 

Base Number (D4739 TBN), 

Inflect, mg KOH/g 

Base Number (D4739 TBN), 

Buffer, mg KOH/g 

Residue (D86), wt.% 

Volatile (D5480-93), wt.% 

Soot (Soot TGA), wt.% 

P (X-Ray SemiQ), wt.% 

S (X-Ray SemiQ), wt.% 

Ca (X-Ray SemiQ), wt.% 

Zn (X-Ray SemiQ), wt.% 

0 

14.55 

108.46 

10.4 

10.25 

1.2 

98.5 

0.286 

0.15 

0.64 

0.35 

0.14 

0 

14.23 

106.47 

10.32 

9.49 

1.3 

98.1 

0.557 

0.15 

0.62 

0.36 

0.16 

0 

14.42 

106.87 

9.98 

8.75 

1.3 

98.2 

0.539 

0.16 

0.52 

0.36 

0.16 

0 

14.72 

106.92 

10.05 

8.37 

1.39 

97.9 

0.855 

0.15 

0.59 

0.35 

0.15 

2.2.3 Sampling and Analysis Procedures 

The sampling system utilized in the test cell for obtaining exhaust samples is shown in Figure 27. 

The system was a constant volume sampling (CVS) system using positive displacement pumps. 

Engine exhaust traveled through a 102-mm diameter transfer pipe to a 58.4-cm diameter by 5.5­

m long, stainless-steel dilution tunnel (Figure 27), which was used to ensure proper mixing of 

gaseous and particle emissions prior to being sampled. The CVS system was operated at a 

nominal volumetric flow rate of 33.4 m3

/min, ensuring that the sample zone temperature 

remained below 51°C during the FTP-75, HFET, and US06 evaluations. Total dilute exhaust 

volume was determined for each test cycle given ambient and tunnel conditions (temperature, 

pressure, humidity) and blower counts. The calculated dilute exhaust volume from each test 

cycle was used to convert concentration values to mass values for the dilute exhaust samples. 

Sampling and analysis procedures included regulated gases such as THC, CO, and NOx in dilute 

bags; particle mass determination; tailpipe raw samples analyzed by an FTIR analyzer; 

speciation of volatile hydrocarbon compounds in dilute bags; H2S; SO2; PAH and NPAH; metals 

such as aluminum, silicon, and phosphorus; and total nitrogen compounds from nitroxy-alkane 

samples. 

43
To Pump

50-cm X 50-cm 

IN-LINE FILTER PARTICULATE 

SAMPLE 

ZONE 

ORIFICE MIXING 

PLATE 

EXHAUST FROM 

ENGINE 

FILTERED 

AIR 

MSA ULTRA 

FILTER 

CHARCOAL 

FILTER 

MSA 

DUSTFOE 

FILTER 

EXHAUST 

OUT 

CVS 

CONSTANT 

VOLUME 

SAMPLER 

2 x 10-cmPUF/XAD TRAP 

90-mm Filter 

-Total PM Mass 

-SOF, SO4 + 

VOF Content 

FTIR Sample 

Raw Tailpipe Emission Sample 

Impinger Sample 

47-mm Filter 

-Metals Analysis 

47-mm Filter 

Nitroxy-Alkane 

Cartridges 

-PAH/N-PAH 

-PAH/N-PAH 

Tedlar Sample Bags 

-THC, CH4, CO, CO2, NOX 

-HC Speciation 

Flow Control 

Orifice 

50-cm X 50-cm

IN-LINE FILTER PARTICULATE

SAMPLE

ZONE

ORIFICE MIXING

PLATE

EXHAUST FROM

ENGINE

FILTERED

AIR

MSA ULTRA

FILTER

CHARCOAL

FILTER

MSA 

DUSTFOE

FILTER

EXHAUST

OUT

CVS

CONSTANT

VOLUME

SAMPLER

2 x 10-cmPUF/XAD TRAP

50-cm X 50-cm

IN-LINE FILTER PARTICULATE

SAMPLE

ZONE

ORIFICE MIXING

PLATE

EXHAU

90-mm Filter

-Total PM Mass

-SOF, SO4 +

VOF Content

FTIR Sample

Raw Tailpipe Emission Sample

Impinger Sample

47-mm Filter

-Metals Analysis

47-mm Filter

Nitroxy-Alkane

Cartridges

-PAH/N-PAH

-PAH/N-PAH

Tedlar Sample Bags

-THC, CH4, CO, CO2, NOX

-HC Speciation

Flow Control 

Orifice

ST FROM

ENGINE

FILTERED

AIR

MSA ULTRA

FILTER

CHARCOAL

FILTER

MSA 

DUSTFOE

FILTER

EXHAUST

OUT

CVS

CONSTANT

VOLUME

SAMPLER

2 x 10-cmPUF/XAD TRAP

90-mm Filter

-Total PM Mass

-SOF, SO4 +

VOF Content

FTIR Sample

Raw Tailpipe Emission Sample

Impinger Sample

47-mm Filter

-Metals Analysis

47-mm Filter

Nitroxy-Alkane

Cartridges

-PAH/N-PAH

-PAH/N-PAH

Tedlar Sample Bags

-THC, CH4, CO, CO2, NOX

-HC Speciation

Flow Control 

Orifice

To Pump

DILUTION

AIR

TedlarBackground Bags

-THC, CH4, CO, CO2, NOX -THC, CH4, CO, CO2, NOX

-HC Speciation

-SO2+ H2S 

To Pump

Figure 27. Test cell emissions sampling system 

Regulated Gases (THC, methane, CO, CO2, NOx) – Dilute Bags. Proportional dilute exhaust 

samples, as well as ambient samples for the determination of THC, methane, NOx, CO, and CO2 

concentration, were collected in Tedlar® bags for analysis. THC concentration was measured 

using a flame ionization detector (FID). CO and carbon dioxide (CO2) were determined using 

nondispersive infrared instruments. NOx was measured using a chemiluminescent instrument. 

Methane was quantified using a gas chromatograph (GC) equipped with a FID. The dilute bag 

samples were taken over a given test cycle (i.e., Cold-Start UDDS, Hot-Start UDDS, HFET, or 

US06) at the location shown in Figure 27. 

Particle Mass Determination. A 12.7-mm diameter probe was used to collect a proportional 

sample of dilute exhaust from the dilution tunnel for gravimetric determination of total part PM 

exhaust emissions at the location shown in Figure 27. PM samples were collected on both a 

primary and backup 90-mm Pallflex® filter (glass fiber filter coated with fluorocarbon). The 

filters were weighed before and after use on a microbalance of 1-microgram sensitivity. Before 

weighing, the filters were properly conditioned in a temperature- and humidity-controlled 

chamber which also housed the microbalance. The controlled airflow, temperature, and 

humidity provided an absolute humidity of 10.7 ± 0.66 grams water per kilogram of dry air in the 

chamber. 

The volumetric flow rate of the 90-mm sampling system was approximately 177 l/min. For the 

engine-out tests, a new 90-mm filter pair was used for each test cycle. For the tests with the 

NAC/DPF system installed, a 90-mm filter pair was used for duplicate or triplicate tests for a 

given test cycle (i.e., three Cold-Start UDDS cycles collected on a single 90-mm filter). This 

approach was used in an attempt to collect a sufficient mass of sample to obtain a meaningful 

weight gain after installing the highly efficient DPF in the exhaust stream. 

44
Methods included direct filter injection (DFI)/GC for VOF determination; sulfate analysis; and 

SOF analysis. 

• DFI/GC for VOF Determination. Diesel exhaust PM is composed of elemental carbon and 

organic compounds derived from the combustion of diesel fuel and lubricating oil. A 

DFI/GC method was used to quantitatively measure and characterize the VOF of diesel 

exhaust PM collected on a 90-mm diameter Pallflex® filter media. This method employed a 

novel injection port into which 10% of the 90-mm filter media (pie-shaped portion) was 

placed, and thermally desorbed onto a non-polar column to separate the volatile 

hydrocarbons according to their boiling point. Chromatograms of the VOF from the actual 

lubricating oil and the VOF of PM samples were compared to determine the percent VOF 

and percent unburned oil. The difference was the remaining VOF, which may be attributed 

to fuel and partially burned fuel and lubricating oil. 

• Sulfate Analysis. Sulfuric acid was collected on the 90-mm Pallflex® filter media and 

converted to ammonium sulfate by exposure to ammonia vapor. The soluble sulfates were 

leached from the filter media (40%, pie-shaped portion of total filter) with a measured 

volume of 60% isopropanol/40% water solution. An aliquot of this extract was injected via 

an autosampler into an ion chromatograph. Anions were separated by an analytical column, 

and passed through a conductivity detector. The retention time on the analytical column 

provided identification of the anion, and the intensity of the signal corresponded to the 

concentration detected. This method was capable of detecting sulfate at levels lower than 

0.02 μg/mL. 

• SOF Analysis. The remaining 50% of the 90-mm Pallflex® filter was extracted with a 

toluene/ethanol binary solvent (32/68% wt/wt and boiling point of 76.6°C) in a 

Soxhlet extraction apparatus for 8.5 hours with a solvent cycle about every 15 minutes. 

After drying the filters for approximately 6 hours at room temperature, the filters 

were reweighed at a constant temperature and humidity. The loss of weight after this 

extraction was the mass of the SOF. A Coordinating Research Council (CRC) round-robin 

interlaboratory program has established a relative standard deviation of ±15% for a minimum 

sample of 1 mg for SOF. For samples of 10 mg and larger, precision within the laboratory 

should be ±10% or less. 

FTIR Analyzer—Tailpipe Raw Sample. A raw exhaust sample was taken at the tailpipe 

location (as shown in Figure 27) utilizing a Nicolet REGA 7000 RT Exhaust Gas Analyzer 

which incorporates a high-performance FTIR spectrometer (NEXUS 670). These data were 

recorded on a second-by-second basis and were acquired during the unregulated emission 

sampling tests (zero-hour engine-out tests; and 100-hr, 300-hr, 900-hr, 1,500-hr, and 2,000-hr 

aging points) as detailed in Section 2.1.5. The lowest and highest calibration points (multiple 

calibration points between) for the various compounds analyzed are shown in Table 14. Due to 

the known limitations of the analyzer, and the availability of alternate sampling procedures, 

separate analyses (based on average concentration over a given test cycle – dilute bag) were 

conducted for benzene, 1,3-butadiene, and SO2. 

45
Table 14. Low- and High-Span Gas Concentrations 

Compound Low- / High-Span Points (ppm) 

Acetaldehyde 1 / 8 

Ammonia 1 / 104 

Benzene 2 /100 

1,3-Butadiene 10 / 100 

Formaldehyde 8 / 79 

NO2 9 / 1,000 

Nitric Oxide 1 / 10,000 

Nitrous Oxide 5 / 50 

SO2 1 / 7 

Speciation of Volatile Hydrocarbon Compounds—Dilute Bag. Volatile hydrocarbon 

compounds were determined by hydrocarbon speciation. Analytical procedures for conducting 

the hydrocarbon speciation (C1 to C4 hydrocarbons, plus select C6 hydrocarbons) were similar 

to the CRC Auto/Oil Phase II methods.1 Three GC procedures and one high-performance liquid 

chromatograph procedure were used to identify and quantify specific compounds. One GC was 

used for the measurement of methane, a second for C2-C4 species; and a third GC was used to 

measure 1-methylcyclopentane, benzene, toluene, and 2,3,3-trimethylpentane, which co-elute 

and cannot be accurately quantified by other methods. The dilute tailpipe samples collected in 

Tedlar® bags for regulated emissions were also utilized for hydrocarbon speciation 

determination. In general, all emission “sample” bags were analyzed before the “background” 

bags, so that reactive exhaust compounds could be analyzed as quickly as possible. 

A brief description of these procedures is given below. These included methane speciation; C2– 

C4 species; and benzene and toluene. 

• Methane Speciation. A GC equipped with a FID was used for the analyses and in 

accordance with Society of Automotive Engineers’ J1151 procedures. The GC system was 

equipped with a packed column to resolve methane from other hydrocarbons in the sample. 

Samples were introduced into a 5-mL sample loop via a diaphragm pump. For analysis, the 

valve was switched to the inject position, and the helium carrier gas swept the sample from 

the loop toward the detector through a 61 cm × 0.3 cm Porapak N column in series with a 

122 cm × 0.3 cm molecular sieve 13X column. As soon as the methane peak passed into the 

molecular sieve column, the helium flow was reversed through the Porapak N column to 

vent. For quantification, sample peak areas were compared to those of external calibration 

standards. 

• C2-C4 Species. With the aid of a DB-WAX pre-column and a 10-port switching valve, the 

second GC procedure allows the separation and determination of exhaust concentrations of 

C2-C4 individual hydrocarbon species, including: ethane; ethylene; acetylene; propane; 

dimethylpropane; propyne; 1,3-butadiene; 2-methylpropane; 1-butyne; and cis-2-butene. 

Bag samples were analyzed with a GC system, which utilizes a Hewlett-Packard Model 5890 

Series II GC with an FID; two pneumatically operated and electrically controlled valves; and 

two analytical columns. The carrier gas was helium. One column is utilized to separate the 

C2-C4 hydrocarbons from the higher molecular weight hydrocarbons and the polar 

compounds. These higher molecular weight hydrocarbons (and water and alcohols) are 

retained on the pre-column while the C2-C4 hydrocarbons are passed through to the analytical 

46
column. While the C2-C4 hydrocarbons are separated on the analytical column, the precolumn is back-flushed with helium to prepare for the next run. The column flow was set by 

fine-tuning the column head pressure to give butane a retention time of 5.25 ± 0.05 minutes. 

The GC was calibrated daily using a CRC Auto/Oil 23-component calibration mixture. 

Detection limits for the procedure were on the order of 5 ppbC in dilute exhaust for all 

compounds. 

• Benzene and Toluene. Dilute bag samples were analyzed using a GC equipped with a FID. 

The GC system utilized a Hewlett-Packard Model 5890 Series II GC with a FID; a 

pneumatically operated and electrically controlled valve; and a DB-5 fused silica, open 

tubular column. The carrier gas was helium. Gaseous samples were pumped from the bag 

through a sample loop and then introduced into a liquid nitrogen-cooled column. The 

column oven was then programmed to a maximum temperature of 200°C. The analog signal 

from the FID was sent to a networked computer system via a buffered analog to digital 

converter. Column flow was set by fine-tuning the column head pressure to give propane a 

retention time of 5.40 ± 0.10 minutes using a temperature program. Detection limits for the 

procedure were on the order of 10 ppbC in dilute exhaust for all compounds. Separation of 

benzene and toluene from co-eluting peaks was carried out by fine-tuning the column head 

pressure to give benzene a retention time of 22 to 23 minutes. The GC was calibrated daily 

using a CRC 7-component calibration mixture consisting of propane; 1-methyl cyclopentene; 

cyclohexane; benzene; 2,3,3-trimethylpentane; 2,3-dimethylhexane; and toluene. 

Hydrogen Sulfide. The collection of H2S was accomplished by bubbling raw exhaust sampled 

at the tailpipe location through glass impingers containing a buffered zinc acetate solution at a 

nominal flow rate of 4 lpm (sample transported through a heated sample line). This solution 

traps the sulfide ion as zinc sulfide. The absorbing solution was then treated with N,N-dimethylpara-phenylene diamine sulfate and ferric ammonium sulfate. Cyclization occurs, forming the 

highly colored, heterocyclic compound methylene blue (3,9-bisdimethylaminophenazothionium 

sulfate). The resulting solution was analyzed with a spectrophotometer at 667nm in a 1-cm cell. 

Sample responses were then compared to a Beer's Law curve, which was standardized 

from known concentrations of a standard sulfide ion solution. The minimum detectable 

concentration was 0.01 ppm. 

•

Sulfur Dioxide. The collection of SO2 was accomplished by bubbling raw exhaust sampled at 

the tailpipe location through glass impingers containing a 3% solution of hydrogen peroxide at a 

nominal flow rate of 4 lpm (sample transported through a heated sample line).The temperature of 

the absorbing solution was kept at 0°C by means of an ice water bath. This solution trapped the 

SO2 as sulfate ion, and the samples were analyzed directly in an ion chromatograph and 

compared to external standards of known sulfate concentration. 

PAH/NPAH Sampling and Analytical Procedures. Dilute exhaust samples were acquired for 

the determination of PAH and NPAH. An additional sampling system was utilized for acquiring 

the samples as shown in Figure 27. Particle-bound PAH/NPAH were trapped on the 50-cm x 50­

cm Pallflex filter, and gaseous PAH/NPAH were trapped in the PUF cartridges. The 50-cm x 

50-cm filter sampling system had a nominal volumetric flow rate of 6371 L/min, while the PUF 

system flow rate was 708 l/min. For the engine-out only tests, a new 50cm x 50cm filter was 

installed before each individual test cycle to minimize the potential of the filter tearing due to the 

pressure drop across a loaded filter. The four filters for a set of tests (Cold-Start UDDS, HotStart UDDS, HFET, and US06) were extracted, combined, and analyzed as a single sample. 

47
With the NAC/DPF system in place, a single 50cm x 50cm filter was utilized across the four test 

cycles in an attempt to collect sufficient mass on the filter to provide for a meaningful analysis. 

These procedures included sampling media preparation; sample storage and extraction; sample 

extracts cleanup for PAH and NPAH analyses; GC/mass spectrometry (MS) analyses of PAHs 

and NPAHs; and quality control sample analysis. 

• Sampling Media Preparation. The PUF circles (10.8cm OD, 3.2cm thickness) were 

cleaned by extraction using a 15-liter Soxhlet extractor with acetone for 72 hours. At the 

end of the extraction, the acetone in the 22-liter round-bottom flask was replaced with 

new acetone, and the PUF circles were extracted for another 72 hours. One PUF circle 

was then extracted for a quality control (QC) check. The QC check was considered to 

have failed if total nanograms of naphthalene exceeded 400 ng or all other PAHs 

combined exceeded 200 ng, or if there were sizable interfering peaks in the PAH 

chromatogram. The PUF circles were then re-cleaned with new acetone for another 72 

hours before the next QC check took place. This process was repeated until the PUF QC 

check sample had passed the above-mentioned criteria. A lot number was assigned to the 

batch of PUFs that had passed the QC check. The cleaned PUF circles were used once 

only and then discarded. 

• The XAD-2 synthetic resin was cleaned using a 5-liter Soxhlet extractor with deionized 

water (4 siphons), methanol (72 hours), and acetone (72 hours). The XAD-2 was then 

purged dry with nitrogen, removed from the 5-liter Soxhlet extractor, and put into 

multiple one-liter Soxhlet extractors. The XAD-2 was further cleaned with 

dichloromethane (DCM) for 72 hours. Twenty grams of XAD-2 was removed, put into a 

250 mL Soxhlet extractor system, spiked with PAH international standard (IS) mixture, 

and extracted for 6 hours. The resulting extract was cleaned up and subject to GC/MS 

analysis for PAHs. If total nanograms of naphthalene exceed 200 ng, all other PAHs 

combined exceed 100 ng, or if there were sizable interfering peaks in the PAH 

chromatogram, the XAD-2 QC check was considered to have failed. The XAD-2 resin 

was re-cleaned for another 72 hours before another QC check took place. This process 

was repeated until the XAD-2 QC check sample passed the above-mentioned criteria. A 

lot number was assigned to the new XAD-2 resin that had passed the QC check. 

• The used XAD-2 was cleaned using one-liter Soxhlet extractors with DCM for 72 hours. 

At the end of cleaning, a 20-gram aliquot of XAD-2 was taken for a QC check. It had to 

pass the above-mentioned QC check for the XAD-2 before it was re-used for field 

sampling; otherwise, a repeated cleaning and QC check was performed. A lot number 

was assigned to the clean, used XAD-2 resin that had passed the QC check. 

• Each 10.2-cm, stainless-steel PUF/XAD-2 trap was packed in the following order: one 

piece of 10.8-cm PUF, 40 grams of clean XAD-2, and one piece of 10.8-cm PUF. Each 

trap was labeled with PUF and XAD-2 lot numbers; date of preparation; and the name of 

the person who prepared it. The prepared traps were then wrapped in aluminum foil, 

sealed in Ziplok bags, and kept in a freezer until the time of their use. 

• Sample Storage and Extraction. After sampling, all PUF traps and filters (after 

weighing) were stored in a freezer at -15°C in the dark until the time of extraction. At the 

time of extraction, the PUF and XAD-2 of each PUF trap were removed and loaded into a 

one-liter Soxhlet extractor with the XAD-2 resin sandwiched between the two PUF 

48
circles. The PUF on the top was then spiked with 20 uL each of PAH and NPAH internal 

standard (IS) mixtures with their compositions listed in Table 15. With a one-liter flask 

attached to the Soxhlet extractor, solvent (750 mL of DCM) was poured into the Soxhlet 

to initiate the extraction. The extraction process continued for 8 hours by using a heating 

mantle and a condenser. At the end of extraction, the 1-liter flask containing sample 

extract was allowed to cool down. The sample extract was carefully concentrated down to 

about 23 mL by distillation using a heating mantle, a six-bulb Snyder column, a 

condenser, and a solvent receiver. The sample extract was transferred into a labeled vial 

and stored in a freezer. 

• The filter samples were extracted using a microwave extractor (Milestone, ETHOS E 

Microwave Extraction Labstation) as follows: one quarter of each 50-cm x 50-cm FIFG 

filter was put into a 100-mL extraction rotor with interior tube made of Teflon. The filter 

sample was spiked with PAH and NPAH IS mixtures as listed in Table 15 and extracted 

with 30 mL of DCM. The temperature and energy program of the microwave extractor 

was as follows: at room temperature (~20oC) to 75oC at 5.5oC/minute with 800 watts 

energy, held at 75oC for 7.5 minutes using 500 watts, and naturally cooled down to room 

temperature (~30 minutes). The filter extract was piped out of the rotor and transferred 

into a labeled vial. The extraction process was repeated once more with 25 mL of fresh 

DCM. The two extracts were combined and blown down to about 20 mL, transferred into 

a labeled vial, and stored in a freezer. 

49
Table 15. Composition of IS Spiking Solutions for PUF Traps and TIGF Filters 

Compound IS mixture for PUF trap 

spiking (20 μL/trap) 

IS mixture for TIGF filter 

spiking (20 μL/sample) 

Deuterated PAH ng/μL ng/μL 

Naphthalene-d8 1000 60 

2-Methylnaphthalene-d10 1000 60 

Acenaphthylene-d8 300 30 

Phenanthrene-d10 100 10 

Fluoranthene-d10 100 10 

Benzo[a]anthracene-d12 5 5 

Chrysene-d12 5 5 

Benzo[b]fluoranthene-d12 5 5 

Benzo[k]fluoranthene-d12 5 5 

Benzo[a]pyrene-d12 5 5 

Perylene-d12 5 5 

Indeno(1,2,3-cd)pyrened12 

5 5 

Dibenz(a,h)anthracene-d14 5 5 

Benzo[g,h,i]perylene-d12 5 5 

Deuterated NPAH ng/μL ng/μL 

1-Nitronaphthalene-d7 5 5 

5-Nitroacenaphthene-d9 5 5 

2-Nitrofluorene-d9 5 5 

9-Nitroanthracene-d9 5 5 

3-Nitrofluoranthene-d9 5 5 

6-Nitrochrysene-d11 5 5 

1-Nitropyrene-d9 5 5 

6-Nitrobenzo(a)pyrene-d11 5 5 

• Sample Extracts Clean Up for PAH and NPAH Analyses. One-third of each of the PUF 

trap extracts and one-half of each of the filter extracts were taken for PAH analysis. A 25 

uL aliquot of alternate standard, Anthracene-d10 at 2.0 ng/uL was spiked to the sample 

extract just prior to the solvent exchange from DCM to mostly hexane. The solvent 

exchange was carried out by blowing down the sample extract to 0.5 mL and then 

brought back up to 3.0 mL with hexane in a 3-dram vial. Two mL of diluted sulfuric acid 

(25%) was added to the vial, and the two liquids were thoroughly mixed for 20 seconds 

using a vortex mixer (Fisher). A glass column (10-mm OD x 350-mm L) was packed 

with 5.0" silica gel (Fisher, Davisil Silica Gel 32 Sorbent, Grade 923, 100-200 mesh). 

The column was pre-cleaned with 15 mL of DCM and then 5 mL of hexane. The hexane 

layer of the acid washed sample extract was then transferred onto the column. Ten mL of 

hexane was used to elute the column, and the hexane eluate was discarded. The PAH 

fraction was collected by eluting the column with 23 mL of DCM/pentane (60/40, v/v). 

This fraction was carefully blown down, in three steps, to a final volume of 100 uL 

(toluene) in a labeled sample injection vial. 

50
• The same amount of PUF and filter extracts from each sample was solvent exchanged for 

NPAH cleanup as described above. A glass column (10 mm OD x 350mm L) was packed 

with 2.54cm silica gel (Fisher, Davisil Silica Gel 32 Sorbent, Grade 923, 100-200 mesh). 

The column was pre-cleaned with 6 mL of DCM and then 2 mL of hexane. The sample 

extract was then loaded onto the column. Ten mL of hexane was used to elute the 

column, and the eluate was discarded. The NPAH fraction was collected by eluting the 

column with 23 mL of DCM. This fraction was carefully blown down, in three steps, to a 

final volume of 100 uL (toluene) in a labeled sample injection vial. 

• GC/MS Analyses of PAHs and NPAHs. The PAH sample extracts were analyzed using 

an Agilent 6890N GC in conjunction with an Agilent 5973N mass selective detector 

(MSD) in the positive ion electron ionization mode. Two characteristic ions of each PAH 

were monitored. Prior to any sample analysis, an initial calibration (ICAL) consisting of 

five calibration standards were analyzed to establish the relative response factor (RRF) of 

the PAH target compounds relative to their corresponding deuterated PAHs. All RRFs 

must have had their percentage relative standard deviations (RSDs) at or below 25% 

before the ICAL was considered successful. For every subsequent 12-hour GC/MS 

sample analysis period, a continuing calibration (CC)—midpoint calibration standard, 

300 pg/uL—was analyzed, and the RRFs of the PAHs were calculated and compared 

with the mean RRFs of the ICAL. The %Ds (% difference) of the RRFs of the PAHs 

must be at or below 25%. The same RRF criteria for the deuterated PAHs (i.e., IS, 

relative to their corresponding deuterated PAH recovery standards) must also be met. 

These criteria must be met before a CC was considered acceptable and used for PAH 

sample extract analysis. 

• Just prior to PAH analysis by GC/MS/selected ion monitoring, each PAH sample extract 

was spiked with 10 uL of PAH recovery standard mixture containing three deuterated 

PAHs [Acenaphthene-d10, Pyrene-d10, and Benzo(e)pyrene-d12], each at 10 ng/uL. The 

PAH concentrations in the sample extracts were quantified using the RRFs of the CC as 

picograms (10-12 grams)/μL, which was later converted to total nanograms (10-9 grams) 

per sample. For all samples, the PAH extracts were solvent-diluted 20 times and analyzed 

to bring the lighter PAHs (naphthalene through pyrene) within calibration range. All PUF 

sample extracts were further analyzed by a high-resolution GC/MS for accurate 

quantification of the heavier PAH [benzo(a)anthracene through benzo(g,h,i)perylene]. 

• The NPAH sample extracts were analyzed using the same GC/MS except in the negative 

ion-chemical ionization mode using methane as chemical ionization reagent gas. All 

ICAL and CC criteria used on PAH analysis applied to the NPAH analysis. 

• QC Sample Analysis. For each set of field sample extraction, a solvent blank, a matrix 

blank (PUF/XAD-2, or filter), a lab control sample (LCS), and LCS duplicate (LCSD) 

were extracted. The LCS and LCSD were QC samples made up of clean sampling media 

(PUF/XAD-2 or filter) and spiked with known amounts of PAH and NPAH target 

compounds. All QC samples were spiked with PAH and NPAH IS mixtures, like the field 

samples, and were extracted, cleaned up, and analyzed using GC/MS alongside the field 

samples. The advisory recovery range for each PAH and NPAH in LCS/LCSD was set at 

50% to 150%. Any outliers on the LCS/LCSD report were evaluated and corrective 

actions taken, when deemed necessary, to improve their percentage recoveries. The IS 

recoveries for the PAHs and the NPAHs were also tabulated and evaluated. Most IS 

51
recoveries fell within 30% to 150%. Corrective actions were taken when low IS 

recoveries were encountered to improve IS recoveries in future analyses. 

Metals Analysis. A proportional exhaust sample was pulled through a 47-mm TefloTM filter at a 

volumetric flow rate of 50 lpm across four consecutive test cycles (i.e., Cold-Start UDDS, HotStart UDDS, HFET, and US06) at the location shown in Figure 27. The filter was weighed to 

determine the mass gain over the test duration and subsequently subjected to metals analysis by 

X–ray fluorescence. Aluminum, silicon, phosphorus, sulfur, chlorine, potassium, and calcium 

values determined by XRF were adjusted for large particle, self-absorption using the theoretical 

formulation developed by Dzubay and Nelson (1975). This adjustment is a function of particlesize distribution and composition. Because the actual particle size distribution and composition 

is unknown, the uncertainty of these adjustments is up to ± 25%, and is reflected in the reported 

uncertainty. Particle-size effects for sodium and magnesium are so large and variable that 

accurate corrections cannot be made for these two elements. Their raw, uncorrected 

concentrations are included in the data files, but they should not be considered quantitative. 

Toxic Nitrogen Compounds (Nitroxy-Alkane Samples). A proportional exhaust sample was 

pulled through another 47-mm TefloTM filter, which was followed by two ORNL-supplied, 

nitroxy-alkane sampling cartridges in series (primary and secondary). The 47-mm filter was 

used only to avoid contaminating/plugging the sampling cartridge. This sample was also 

obtained across four consecutive test cycles (i.e., Cold-Start UDDS, Hot-Start UDDS, HFET, 

and US06) at the location shown in Figure 27 with a volumetric flow rate of 1.25 lpm. 

2.2.4 Data Handling 

Data provided by the test laboratory included measurements of NOx, THC, NMHC, CO, and PM 

using D15 fuel taken at engine out with and without EGR. Tailpipe measurements using D15 

fuel were taken every 50 hours between 0 and 300 hours, with measurements made before and 

after desulfurizations at 200 and 300 hours. Between 300 and 2,000 hours, desulfurizations 

occurred every 100 hours; measurements using D15 fuel taken before and after each 

desulfurization. Measurements using BP15 fuel were taken at engine out, 300 hours pre- and 

post-desulfurization, 900 hours post-desulfurization, 1,500 hours post-desulfurization, and at 

2,000-hours post-desulfurization. The laboratory also measured nonregulated emissions using a 

continuous FTIR instrument, the analysis of speciation dilute bag samples, and by bubbling raw 

exhaust through a heated sample line. Metal emissions were measured using a TefloTM filter, 

and PAH and NPAH emissions were measured using a GC in conjunction with a MSD. 

Prior to conducting the statistical analysis, a data review was conducted to ensure data 

completeness and accuracy. After comparing the data received with the data collection plan, the 

data were stored in a controlled database. Changes, updates, and corrections were carefully 

monitored and controlled. To identify gross outliers (unusual and unexplained emissions results) 

and unexplained variations or trends associated with laboratory procedures, plots of emission 

data versus time were prepared and shared with the laboratories and the technical committee. 

Lists of outliers identified from the outlier analysis were sent to the laboratory with instructions 

to check for clerical errors, equipment failures, or other external factors that could explain the 

deviation in results. Clerical errors were corrected, and outliers due to known problems were 

corrected whenever possible. If the data could not be corrected, or the outliers were found to be 

52
associated with documented testing or measurement issues, they were eliminated from the 

analysis. 

2.2.5 Statistical Analysis and Modeling 

The statistical analysis approaches to address the study questions posed in Section 1.3 are as 

follows: initial performance; durability and desulfurization; sulfur mass balance; fuel effects on 

regulated emissions; and unregulated emissions. 

Initial Performance 

Q1.1 Can the system meet the 2007-2010 regulated emissions levels for NOx, NMHC, and 

PM? 

Q1.2 What is the impact on other regulated emissions (THC, CO, PM, and NMHC) and fuel 

economy? 

Q1.3 How does system performance change during the early life (under 300 hours) of the 

system? 

Q1.4 Are there similar patterns for various transient duty cycles (Cold- and Hot-Start UUDS, 

US06, HFET) 

In order to address study questions Q1.1 and Q1.2, the average composite FTP emissions from 

the seven engine-out tests (six without EGR and one with EGR) and from 18 tailpipe tests— 

conducted prior to the first desulfurization at 200 hours—and their corresponding 95% 

confidence intervals were produced. A standard t-test was used to determine if there were 

statistically significant differences between the average tailpipe emissions and the regulated 

emissions standards. Emission reductions were also calculated relative to engine-out emissions 

obtained both with and without EGR. The performance of the system before 300 hours was 

characterized by a series of plots for these emissions by mode. 

Durability and Desulfurization 

Q2.1 How do NOx emissions change as the system ages? Specifically, how do the maximum 

(pre-desulfurization), minimum (post-desulfurization), and average NOx levels change? 

Q2.2 Is the increase in NOx emissions between consecutive desulfurizations constant over 

time? 

Q2.3 How effective is desulfurization at restoring the initial NOx reduction performance of the 

system (initially and over time)? 

Q2.4 Does the performance of the system stabilize within the first 2,000 hours? If so, at what 

point does this occur? 

Q2.5 Are there temporal trends with respect to other regulated emissions or fuel economy? 

53
These questions were addressed through a series of plots of the observed FTP Composite NOx 

data. Trend lines using log-linear regression models were produced and analyzed to assess the 

behavior of NOx emissions over time. To account for the effects of desulfurization process, 

separate log-linear models were fit to three sets of NOx emissions data: (1) measurements made 

before a desulfurization event, (2) measurements made after a desulfurization event, and (3) the 

average of measurements made at the beginning (post-desulfurization) and end (predesulfurization) of each 100-hour aging period. To address the question of whether the 

performance of the system stabilizes over time, the left-most data from each of the three data sets 

were iteratively truncated; then the regression model was refitted, and the significance of the 

regression slope parameter was evaluated. This same process was applied to the other regulated 

emissions and fuel economy. 

Sulfur Mass Balance 

Q3.1 How much sulfur is emitted during the desulfurization process? 

Q3.2 How does the amount of sulfur emitted during the aging cycle compare to the amount 

emitted during desulfurization process? Do these rates change over time? 

Q3.3 What happens to the differences between these amounts? 

A table of summary calculations was used to answer these study questions. A series of special 

tests were performed periodically to measure the mass of SO2 and H2S emitted during 

desulfurization. These results were used to estimate total sulfur accumulation on the catalysts for 

comparison with the estimated engine-out emissions based on measured fuel and oil 

consumption. 

Fuel Effects on Regulated Emissions 

Q4.1 Are there differences in emissions from DECSE and BP fuels? 

Q4.2 If such differences exist, are they consistent over time? 

Analysis of variance models was used to determine if there were statistically significant 

differences between the two test fuels in terms of the average emissions of NOx, hydrocarbon, 

and PM and fuel economy. The models, which accounted for the effects of aging and test mode 

(Cold-Start UDDS, Hot-Start UDDS, US06, and HFET), were also used to produce 95% 

confidence intervals for the average emissions and fuel economy. 

Unregulated Emissions 

Q5.1 Which unregulated toxic (or potentially toxic) compounds are present in tailpipe 

emissions? 

Q5.2 How do the levels compare to engine-out emissions? 

Q5.3 How do unregulated emissions change with time? 

Unregulated emissions results are being presented in a separate report. 

54
Section 3: System Development 

The following section details the system development for this project. This includes a discussion 

of the baseline engine and EGR calibration, and emission systems calibration and control, 

including a discussion of the diesel fuel burner, NOx management, and cold-start strategies. In 

addition the section also covers the development of the NAC desulfurization strategy. 

3.1 Baseline Emissions and Exhaust Gas Recirculation Calibration 

To set an appropriate baseline for assessing the ECS performance, the emissions from the 

Duramax engine were measured as received and after EGR calibration changes. Since this engine 

was retrofitted with an EGR systems for this project, two baselines were established. That is, for 

the purpose of comparison, it was necessary to have two baselines for this project: one with an 

optimized EGR strategy and one with out EGR (i.e., original equipment manufacturer 

calibration). The following section details the baseline emissions and the EGR calibration 

process. 

3.1.1 Baseline Emissions 

After the initial “quick-look” vehicle tests were completed on the chassis dynamometer, the 

vehicle was ballasted to the previously determined test weight of 6,568 lbs and taken on the road 

for vehicle coast-downs to generate a vehicle road-load curve. After determining the actual onroad power requirements, the vehicle was placed on the chassis dynamometer, and the parasitic 

losses of the drive axle were determined. The dynamometer road-load curve was generated by 

subtracting the drive axle losses from the actual on-road power curve. The three individual 

curves are shown graphically in Figure 28. Figure 29 shows a comparison of the dynamometer 

load curve used for the quick-look emission tests and the actual dynamometer load curve 

determined. Due to the close similarity between the two curves, it was decided that the data 

previously provided to the ECS supplier were still a valid representation of the actual engine 

operating conditions. 

55
Power, hp 

120 

100 

80 

60 

40 

20 

0 

0 10 20 30 40 50 60 70 80 90 

Vehicle Speed, mph 

Actual Road-Load (Total) 

Drive Axle Frictional Load (hp) 

Dyno Power Curve 

A = 70.18 lbf 

B = -0.5772 lbf/mph 

C = 0.0452 lbf/mph^2 

Figure 28. Power curves for 2002 Chevrolet Silverado test vehicle 

56
0 

20 

40 

60 

80 

100 

120 

Power, hp

Actual Dyno Power Curve 

Estimated Dyno Power Curve 

0 10 20 30 40 50 60 70 80 90 

Vehicle Speed, mph 

Figure 29. Estimated and actual chassis dynamometer power curves 

Using the newly established road-load curve, the vehicle was operated on the chassis 

dynamometer over the FTP and US06 test cycles. Data collected during these cycles (triplicate 

runs) were used to develop vehicle-based maps. The maps were generated from the fully 

warmed-up data (i.e., the first 200 seconds of the cold-start FTP were dropped from the 

analysis). Maps of exhaust gas temperature; NOx; CO2 concentration and instantaneous mass; 

and EGR rate as a function of engine speed (rpm) and load (assumed to be a function of APP in 

volts) were developed. It was agreed that the EGR maps (and all other engine calibration related 

maps) would remain confidential to the manufacturer and not for public release. Figures 30, 31, 

and 32 show the resultant exhaust gas temperature, NOx, and CO2 concentration and 

instantaneous mass maps, respectively. The zeroes on the edge of the tables result from a lack of 

data in the region (i.e., the engine does not operate in this region in the vehicle over the drive 

cycles tested). Figure 33 shows a scatter plot of engine speed and APP over the FTP and US06. 

This figure provides information on the operating region for the Duramax across the light-duty 

drive cycles. As observed in this figure, the engine operates the vast majority of the time at low 

speeds and low loads over these test cycles. 

57
NOx, ppm -- STOCK MAP, FTP+US06 

HOLES FILLED, SMOOTHED 

NOx INSTANTANEOUS MASS 

1000.00 2000.00 3000.00 2.00 

4.00 

6.00 

0.00 

0.01 

0.02 

0.03 

1000.00 

6.00 

0.00 

500.00 

RPM 

APP, V 

NOX, 

g/sec 

APP 

NOX, 

ppm 

4.00 

2000.00 2.00 3000.00 

RPM 

APP1 

ENGINE

SPEED,

RPM 0.53 0.70 0.87 1.03 1.20 1.37 1.53 1.70 1.87 2.03 2.20 2.37 2.53 

500 147 140 516 779 419 450 497 973 0 0 0 0 0 

750 54 151 282 456 475 480 497 973 0 0 0 0 0 

1000 54 168 230 421 648 700 974 842 858 0 0 0 0 

1250 71 186 236 408 659 776 695 859 820 0 0 0 0 

1500 96 193 229 337 543 720 744 781 803 785 772 766 0 

1750 97 185 220 263 493 707 683 786 811 778 767 673 0 

2000 97 175 217 255 378 595 641 617 646 636 704 620 601 

2250 146 173 225 275 379 479 517 530 576 555 519 518 542 

2500 184 193 204 313 315 348 375 411 438 451 404 435 473 

2750 211 201 205 229 285 286 275 309 300 270 285 328 0 

3000 0 192 195 191 220 212 239 228 302 290 208 214 0 

3250 0 193 193 212 218 234 227 234 228 208 211 211 0 

Figure 30. Exhaust gas temperature after oxidation catalyst over the FTP and US06 test 

cycles 

58
 59

Figure 31. Engine-out NOx concentration and instantaneous mass map over light-duty 

FTP and US06 test cycles 

CO2, ppm -- STOCK MAP, FTP+US06 

HOLES FILLED, SMOOTHED

APP1

ENGINE 

SPEED, 

RPM 0.53 0.70 0.87 1.03 1.20 1.37 1.53 1.70 1.87 2.03 2.20 2.37 2.53

500 2.0 2.4 2.4 2.9 4.5 5.2 5.8 4.1 0.0 0.0 0.0 0.0 0.0

750 1.8 2.6 2.5 3.0 3.9 7.2 5.8 4.1 0.0 0.0 0.0 0.0 0.0

1000 2.8 3.3 3.8 4.0 4.5 6.2 4.1 5.0 5.8 0.0 0.0 0.0 0.0

1250 3.3 3.9 4.5 4.6 4.4 5.5 5.1 5.8 6.3 0.0 0.0 0.0 0.0

1500 3.6 3.7 4.6 5.5 5.1 5.8 6.3 6.7 8.5 10.0 10.0 10.1 0.0

1750 4.2 4.6 5.3 6.3 6.2 7.5 7.8 9.6 10.1 9.9 10.1 9.1 0.0

2000 5.1 4.7 5.5 6.4 7.0 7.5 9.5 8.7 9.3 9.1 9.5 8.4 8.7

2250 6.7 5.7 6.5 7.2 7.9 8.1 9.2 9.7 10.3 9.4 8.6 8.7 8.8

2500 7.2 8.3 8.7 7.7 8.1 9.0 9.6 10.6 10.4 8.8 8.7 8.4 8.6

2750 6.7 8.0 8.6 8.5 8.5 8.9 9.4 10.9 8.8 8.1 8.3 8.3 0.0

3000 0.0 7.2 8.0 8.2 8.5 9.4 7.1 7.8 8.9 8.1 7.3 7.9 0.0

3250 0.0 7.6 7.8 8.3 8.7 8.3 8.1 7.4 7.8 7.3 7.6 7.6 0.0

1000.00

2000.00

3000.00

2.00

4.00

6.00

0.00

5.00

10.00

1000.00 2000.00 3000.00 2.00

4.00

6.00

0.00

5.00

10.00

RPM APP

CO2, 

g/sec CO2, 

%

APP

RPM

CO2, % -- STOCK MAP, FTP + US06 

HOLES FILLED, SMOOTHED 

APP, volts 
EXH-T after OC -- STOCK MAP, COURSE GRID 

HOLES FILLED, SMOOTHED 

Exhaust 200.00 

Temperature, °C 100.00 

2.00 

0.00 3000.00 4.00 

2000.00 

6.00 APP, V

RPM 1000.00 

APP1 

ENGINE APP, volts

SPEED,

RPM 0.53 0.70 0.87 1.03 1.20 1.37 1.53 1.70 1.87 2.03 2.20 2.37 2.53 

500 165 166 181 165 152 144 141 130 0 0 0 0 0 

750 163 147 154 165 147 148 141 130 0 0 0 0 0 

1000 167 148 149 149 148 145 131 133 127 0 0 0 0 

1250 196 151 145 154 156 147 141 127 135 0 0 0 0 

1500 216 205 208 191 187 201 188 188 200 251 252 255 0 

1750 230 235 255 262 246 215 217 233 247 249 256 264 0 

2000 259 268 290 296 279 254 238 247 228 234 257 272 273 

2250 251 274 285 294 272 270 267 248 254 243 219 264 274 

2500 242 268 233 238 257 244 225 235 254 245 249 266 275 

2750 268 267 246 226 250 234 251 249 278 266 272 267 0 

3000 0 268 268 269 251 271 271 274 267 271 270 270 0 

3250 0 268 268 263 263 264 272 273 274 270 270 270 0 

Figure 32. Engine-out CO2 concentration and instantaneous mass map over light-duty

FTP and US06 test cycles 

2 .6 

2 .4 

2 .2 

2 .0 

1 .8 

A 1 .6

P

P 1 .4

1 .2 

1 .0 

0 .8 

0 .6 

0 .5 

-200 0 2 0 0 4 0 0 6 0 0 800 1 0 00 120 0 1400 1 6 00 1 8 00 200 0 2 200 2 4 00 2 6 00 2800 3 000 3 2 00 340 0 

Engine Speed, rpm

Figure 33. Range of APP (volts) and engine speed (RPM) across the light-duty FTP and 

US06 test cycles 

60
A summary of the baseline, as-received, engine-out emissions over the light-duty FTP cycle, 

with and without EGR, is shown in Tables 16 and 17, respectively. The standard weighting of 

43% for the cold-start and 57% for the hot-start was used in calculating the composite FTP 

values. The calculated Cold-Start UDDS (Bags 1 and 2) and Hot-Start UDDS (Bags 3 and 2) 

results are also shown as it was decided to utilize these test cycles after the baseline tests had 

already been conducted. A comparison of the regulated engine-out emissions and the program 

goals (i.e., EPA Tier 2 Bin 5) are shown in Figure 33. As can be seen from this figure, meeting 

the 50K mile program goals required a 99% NOx reduction, an 84% hydrocarbon reduction, and 

an 89% PM reduction over the engine-out (no EGR) emission levels. Figures 34 through 37 

show the continuous engine-out NOx emissions and exhaust gas temperature (with and without 

stock EGR calibration) for the Cold-Start UDDS (Bags 1 and 2 of the FTP) and US06 tests, 

respectively. Given the 120,000-mile program goal of 0.07 g/mile NOx, it can be seen in Figure 

38 that the NOx target is exceeded approximately 27 seconds after the engine started. In order to 

come close to meeting the program goals, it became obvious that the system would require 

significant additional exhaust temperature (immediately after engine-start and also throughout 

the low-load operating regime) and extraordinarily high levels of emission reduction. In 

addition, it would be necessary to reduce the engine-out NOx levels to lessen the burden on the 

ECS. In order to reduce engine-out NOx levels it was decided to pursue a new EGR calibration. 

Table 16. Light-Duty FTP As-Received, Engine-Out Emissions with EGR 

Bag 1 

(grams) 

Bag 2 

(grams) 

Bag 3 

(grams) 

FTP 

Composite 

(g/mi) 

Cold-Start 

UDDS 

(g/mi) 

Hot-Start 

UDDS 

(g/mi) 

THC 1.709 1.932 1.184 0.448 0.487 0.418 

NOx 17.468 16.150 13.928 4.233 4.500 4.032 

CO 18.074 11.371 8.302 3.198 3.942 2.637 

CO2 2066 2138 1848 546 563 534 

PM 0.287 0.338 0.272 0.083 0.084 0.082 

Distance 3.60 3.87 3.59 11.06 7.47 7.46 

(Miles) (total) (total) (total) 

Table 17. Light-Duty FTP As-Received, Engine-Out Emissions without EGR 

Bag1 

(grams) 

Bag 2 

(grams) 

Bag 3 

(grams) 

FTP 

Composite 

(g/mi) 

Cold-Start 

UDDS 

(g/mi) 

Hot-Start 

UDDS 

(g/mi) 

THC 1.629 2.025 1.310 0.468 0.491 0.450 

NOx 18.740 20.98 18.14 5.304 5.346 5.272 

CO 25.918 18.120 17.460 5.282 5.927 4.795 

CO2 2138 2124 1843 551 574 535 

PM 0.360 0.311 0.335 0.088 0.090 0.087 

Distance 

(Miles) 

3.58 3.85 3.57 11.00 

(total) 

7.43 7.42 

61
0 

1 

2 

3 

4 

5 

6 

E

mis

sio

n

s (

g/mil

e) 

Stock EGR Calibration 

No EGR 

Program Goals (50k Miles) 

Program Goals (120k Miles) 

99% 

NMOG 

84% 

89% 

CO NOx THC*10 PM*25 

Figure 33. Comparison of regulated engine-out emissions to program goals (EPA Tier 2 

Bin 5) for the light-duty FTP

62
Accumulated N

OX Mass, grams 

40 

35 

Engine-Out(No EGR) 

30 Engine-Out (With EGR) 

25 

20 

15 

10 

5 

0 

0 200 400 600 800 1000 1200 1400 

Time, seconds 

Figure 34. Accumulated engine-out NOx mass over the Cold-Start UDDS cycle 

450

400

350

E

xhaust Gas Tem

perature, °C

300 

250 

200 

150 

100 

50 

0 

Downpipe (No EGR) 

Downpipe (With EGR)

0 200 400 600 800 1000 1200 1400 

Time, seconds 

Figure 35. Exhaust gas temperature (downpipe location) over the Cold-Start UDDS cycle 

63
40 

35 

Engine-Out (No EGR) 

Accumulated NOX Mass, grams 

30 Engine-Out (With EGR)

25 

20 

15 

10 

5 

0 

0 100 200 300 400 500 600 

Time, seconds 

Figure 36. Accumulated engine-out NOx mass over the US06 cycle 

450

400

350

Exhaust Gas Temperature, °

C

300 

250 

200 

150 Downpipe (No EGR) 

100 Downpipe (With EGR)

50

0

0 100 200 300 400 500 600 

Time, seconds 

Figure 37. Exhaust gas temperature (downpipe location) over the US06 cycle 

64
0 

5 

10 

15 

20 

25 

30 

35 

0 200 400 600 800 1000 1200 1400 

Accumulated NOx Mass (grams 

Vehicle Test with Stock EGR 

Target (Tier 2, Bin 5) 

LD-FTP Engine-Out Emissions vs. Goals - NOX 

>98% 

4.5 g/mi 

0.07 g/mi 

27s

Time (seconds) 

Figure 38. Continuous engine-out NOx mass and program goal over the Cold-Start UDDS 

Test cycle 

Prior to beginning any EGR calibration, testing was moved from the vehicle chassis 

dynamometer test environment to a dedicated engine test cell. This move allowed accelerated 

development of the EGR calibration and ECS control strategies; provided more repeatable test 

conditions; and shortened the test plan time line. In addition, the inherent repeatability issues of 

a human driver operating a manual transmission-equipped vehicle were eliminated. Working in 

a dedicated test cell also provided the ability to force-cool the engine, accelerating cold-start 

strategy development. However, before this move was made, it was necessary to create test cell 

control cycles that would duplicate vehicle engine operation in the test cell over the cycles of 

interest (Cold-Start UDDS, Hot-Start UDDS, HFET, and US06). 

To create an equivalent motoring dynamometer test cell cycle for the engine, data generated 

from previous light-duty vehicle tests without EGR were used to define the engine speed and 

APP signal versus time schedule (as opposed to an engine speed and torque cycle, as in the 

heavy-duty FTP test cycle). This approach was used because engine-out torque was not readily 

measurable on the vehicle chassis dynamometer; therefore, using APP as an indicator of load 

was determined to be the best alternative. The APP signal was converted to an equivalent 

indicated throttle angle for the test cell electronic control module. As the drivetrain in the 

vehicle utilizes a manual transmission, some smoothing of the engine speed trace was required to 

avoid high, transient current spikes in the dynamometer at certain shift points. The goal of the 

test cell control cycle was to operate the engine at similar conditions observed on the chassis 

dynamometer for generating similar exhaust gas temperatures, exhaust mass flow rate, engineout emissions, and fuel consumption, and thereby emulating the vehicle test. 

65
The final test cell command cycles were presented in Section 2.2.2. After the test cell command 

cycles were deemed acceptable, corresponding cycle statistics (speed, torque, and power) were 

used as a comparison for all future tests. These statistics were used to verify that the engine was 

able to follow the speed and/or torque command cycles, and to check the driveability of various 

strategy changes. The cycle statistics also provided a continual feedback of engine repeatability 

over the cycles of interests. A summary of the work for each command test cycle is shown in 

Table 18. 

Table 18. Test Cycle Work for Drive-Cycle Emulation on Motoring Dynamometer 

Cold-Start 

UDDS 

Hot-Start 

UDDS 

HFET US06 

Cycle Work, kW-hr 5.03 4.87 5.50 7.14 

3.1.2 Exhaust Gas Recirculation Calibration 

Prior to mapping the stock EGR calibration, a map of the engine-out NOx concentration as a 

function of speed and load was derived by operating the engine across a series of steady-state 

points. This map was used to identify engine operating points that would produce high levels of 

engine-out NOx (areas where increased EGR would be most beneficial). Figures 39 and 40 show 

maps of engine-out NOx concentration versus engine speed and load. 

The stock EGR system is a high-pressure loop, vacuum-actuated, cooled-EGR system, with an 

intake throttle for increasing EGR flow at low intake/exhaust flows. The recirculated exhaust 

gases pass through an EGR cooler and then enter the intake manifold downstream of the charge 

air cooler. The as-received EGR calibration on this engine provided a reduction in engine-out 

NOx of approximately 16% over the FTP-75 test cycle and 24% over the US06. After examining 

the vehicle maps, it was determined that the stock calibration was not utilizing the maximum 

available EGR from the stock system. Therefore, it was decided to assess the EGR rate and NOx 

reduction that could be achieved with the stock system. 

66
2500 

NOx Raw1 

2000

1500

 NOx, ppm 

1000

500

0

500 1000 1500 2000 2500 3000

Engine Speed

Figure 39. Measured NOx concentration as a function of engine speed (no EGR)

67
. 

NOx, ppm -- ENGINE MAP No.1: STOCK CAL, NO-EGR HOLES FILLED, SMOOTHED 

2000 

1000 

2.20

APP, volts 1.60

rpm 

1.50 1.60 1.70 1.80 1.90 2.00 2

1.80 2.00 100

2000 

NOx, ppm 

ENGINE

SPEED,

RPM

APP1, volts 

 1.40 

500 

750 

1000 1250 1500 1750 2000 2250 2500 2750 

152 130 169 388 

47 63 175 311 

8 72 171 296 

19 59 175 278 21 82 172 232 

9 54 120 191 

13 39 110 174 14 36 109 158 17 38 83 135 

1193 2190 22

821 1542 16

574 971 11

463 756 9381 658 7

363 587 6

352 494 5320 405 4

256 373 3

Figure 40. NOx concentration—stock engine calibration—no EGR 
An SwRI-developed control system, called the Emissions Reduction Integration 

Controller (ERIC), was used to create the controls for the EGR valve and intake throttle, 

allowing user-controllable operation. After verifying operation of the ERIC EGR 

controller, sweeps of engine speed, load, and EGR rate were performed. Table 19 

outlines the operating conditions that were mapped. During mapping, the following 

parameters were monitored: intake and exhaust CO2 concentrations (for calculating 

percent EGR); engine-out NOx concentration; exhaust gas temperature near the planned 

catalyst inlet location; mixed intake air temperature (after EGR added); torque; engine 

speed; fuel consumption; smoke opacity; and intake MAF. At each speed and load set 

point, the EGR rate was varied from the minimum (0% duty-cycle, valve closed) up to 

the maximum the valve would flow (100% duty cycle) while limiting mixed intake air 

temperature to a maximum of 90oC. After stabilizing the emissions systems at each 

point, data were collected at 1 Hz for a minimum of 10 seconds. Figure 41 shows the 

minimum and maximum EGR rates achieved at each tested speed and load. Table 19 

summarizes the maximum EGR rates achieved, as well as the rate-limiting factor. 

69
Table 19. EGR Mapping Points 

Engine 

Speed, RPM 

Accelerator Pedal 

Position, % 

Maximum 

EGR, % 

Limiting Factor 

Idle, 680 

0 - Valve Flow Limit 

700 10 - with intake throttle 57 Valve Flow Limit 

20 - with intake throttle 55 Valve Flow Limit 

30 - with intake throttle 39 Valve Flow Limit 

40 21 Valve Flow Limit 

50 20 Valve Flow Limit 

60 22 Intake Air Temp. 

900 10 - with intake throttle 61 Valve Flow Limit 

20 - with intake throttle 57 Intake Air Temp. 

30 32 Valve Flow Limit 

40 27 Valve Flow Limit 

50 22 Valve Flow Limit 

60 22 Valve Flow Limit 

70 22 Valve Flow Limit 

1,100 10 - Intake Air Temp. 

20 41 Intake Air Temp. 

30 36 Valve Flow Limit 

40 33 Valve Flow Limit 

50 28 Valve Flow Limit 

60 28 Valve Flow Limit 

70 29 Valve Flow Limit 

1,300 11 45 Valve Flow Limit 

20 45 Valve Flow Limit 

30 40 Valve Flow Limit 

40 35 Valve Flow Limit 

50 30 Valve Flow Limit 

60 30 Valve Flow Limit 

70 25 Valve Flow Limit 

70
Table 19. EGR Mapping Points (continued) 

Engine 

Speed, RPM 

Accelerator Pedal 

Position, % 

Maximum 

EGR, % 

Limiting Factor 

1,500 11 45 Valve Flow Limit 

20 32 Valve Flow Limit 

30 32 Valve Flow Limit 

40 30 Valve Flow Limit 

50 26 Valve Flow Limit 

60 25 Intake Air Temp. 

70 26 Intake Air Temp. 

1,700 11 37 Valve Flow Limit 

20 35 Valve Flow Limit 

30 32 Valve Flow Limit 

40 29 Valve Flow Limit 

50 25 Valve Flow Limit 

60 21 Intake Air Temp. 

70 21 Intake Air Temp. 

1,900 16 33 Valve Flow Limit 

20 30 Valve Flow Limit 

30 30 Valve Flow Limit 

40 26 Valve Flow Limit 

50 24 Valve Flow Limit 

60 20 Intake Air Temp. 

2,100 10 32 Valve Flow Limit 

20 32 Valve Flow Limit 

30 29 Valve Flow Limit 

40 26 Valve Flow Limit 

50 23 Intake Air Temp. 

60 23 Intake Air Temp. 

70 20 Intake Air Temp. 

2,300 10 34 Valve Flow Limit 

20 31 Valve Flow Limit 

30 31 Valve Flow Limit 

40 26 Intake Air Temp. 

50 23 Intake Air Temp. 

2,500 20 31 Valve Flow Limit 

30 30 Valve Flow Limit 

40 26 Intake Air Temp. 

50 23 Intake Air Temp. 

71
EGR, percent 

70 

60 

50 

40 

30 

20 

10 

0 

700-max 700-min Intake throttle closed 

900-max 900-min 

1100-max 1100-min 

1300-max 1300-min 

1500-max 1500-min 

1700-max 1700-min 

1900-max 1900-min 

2100-max 2100-min 

2300-max 2300-min 

2500-max 2500-min 

0 10 20 30 40 50 60 70 80 90 100 

% APP 

Figure 41. Maximum and minimum EGR rates as a function of engine speed and 

load 

The results of the steady-state EGR mapping of the stock system showed potential for 

significantly increasing EGR rates over the stock calibration to lower engine-out NOx 

levels. Another benefit of increased EGR rates would be higher exhaust gas 

temperatures. However, during the EGR mapping, very little of the heat generated from 

increased EGR rates was transferred to the catalyst inlet position. The intake manifold 

temperature increased up to 50oC, but this additional heat was completely lost at low 

speeds due to cooling in one or more of the following: the head, exhaust manifolds in the 

turbocharger, and downpipe. An increase in exhaust gas temperature at the catalyst inlet 

location was observed at higher speeds and loads. However, as observed during the 

baseline tests, engine operation over the FTP-75 cycle was typified by low engine speeds 

and loads. 

An EGR look-up table within the ERIC system was implemented to increase the amount 

of EGR provided to the engine at any given operating point. (From this point, the ERIC 

system was used to control the EGR valve and intake throttle during all engine 

operation.) The goal of a new EGR calibration was to reduce the engine-out NOx levels 

to reduce the burden on the ECS. An engine-out NOx level of 1.8 g/mile over the FTP-75 

cycle was targeted, as this level was to be expected from typical MY 2007 engines for 

this type of application/engine displacement. Achieving this level of engine-out NOx 

required a 66% reduction over the no EGR engine-out emissions of (13.5 grams of 

engine-out NOx mass over the Hot-Start UDDS cycle). 

72
This level of engine-out NOx mass was achieved; however, it came at the expense of 

increased engine-out PM levels. Examining the continuous smoke opacity over the HotStart UDDS cycle (shown in Figure 42), significant increases in opacity were observed 

throughout the test cycle and were attributable to APP tip-in (moderate-to-hard 

accelerations, particularly from off-idle). In order to minimize the increase in engine-out 

PM while still achieving a high-level of engine-out NOx reduction, it was decided to add 

a mode identification algorithm that would modify the EGR-duty cycle value in the lookup table. 

The different types of engine operating modes were identified as: 

• Engine crank/start 

• Idle 

• Acceleration 

• Hard acceleration 

• Cruise 

• Deceleration. 

Under acceleration and hard-acceleration modes, the amount of EGR called for by the 

look-up table was reduced in order to minimize the increase in engine-out PM. Table 20 

shows a comparison of engine-out NOx and PM mass for a number of different EGR 

calibrations/strategies for the Cold-Start UDDS cycle. Figure 43 shows the engine-out 

NOx and PM mass measured over a Hot-Start UDDS for three different strategies 

employing mode identification, along with the results using only the EGR look-up table 

and a no-EGR test. The EGR look-up table strategy resulted in reducing the engine-out 

NOx mass emissions by 64% but increased the PM mass by 93% over the base, no-EGR 

condition. Using the mode-modified EGR control strategy reduced the engine-out NOx 

mass emissions by approximately 50% while increasing the PM mass by approximately 

20%. This reduction in engine-out NOx mass equated to approximately 2.4 g/mile over 

the Hot-Start UDDS cycle, short of the desired level of 1.8 g/mile, but substantially 

below the 4.0 g/mi noted for the as-received, engine-out level with the stock EGR 

calibration. 

73
Smoke Opacity (%) - No EGR 

35 30 

Test Cell - No EGR (Cold_Rev_8) 

30 25 Test Cell - EGR Cal2 - Revised 

(Cold_Rev_8)

25 20 

20 15 

15 10 

10 5 

5 0 

0 -5 

0 200 400 600 800 1000 1200 1400 

Time (seconds) 

Figure 42. Engine-out smoke opacity over Hot-Start UDDS cycle for no EGR and

high-EGR calibration 

Table 20. NOx and PM Mass Emissions for Different EGR Calibrations

Calibration ID Cold-Start UDDS Mass Emissions, 

NOx

grams 

PM

Stock – No EGR 37.4 0.765 

Cal1-LU Table only

Cal2 w/Mode Modification-1 

Cal2 w/Mode Modification-2 

Cal2 w/Mode Modification-3 

13.1 

19.1 

18.1 

17.8 

1.600 

0.986 

1.202 

1.032 

Smoke Opacity (

%) With EG

R

Cal2 - Revised 

74
P

M Mass (grams) 

1.8 

1.6 

1.4 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

EGR Look-Up Table 

Three Different Mode 

Identification EGR Strategies 

No EGR Test 

0 5 10 15 20 25 30 35 40 

NOx Mass (grams) 

Figure 43. NOx/PM trade-off for different EGR strategies over the Hot-Start UDDS 

Test cycle 

3.2 Emissions System Calibration and Control (EGR+DPF+NAC) 

The ECS components tested in this project consisted of NACs, oxidation catalysts, and a 

catalyzed DPF. These components were integrated with the engine control to form the 

ECS. In addition to the controls/strategy developed for the ECS, a diesel-fueled burner 

was utilized to provide the heat necessary for the ECS to function in its temperature 

operating window. Section 3.2.1 describes the burner developed in this program. The 

regeneration strategies and control of the ECS are described in Section 3.2.2. The 

resultant fuel economy penalty over the test cycles of interest is discussed in Section 

3.2.3. 

3.2.1 Diesel-Fueled Burner 

A diesel-fueled burner was designed to provide supplemental heat to the ECS. However, 

because burners can typically operate across a very wide range of air-fuel ratio control, 

the burner can also provide a means for reducing exhaust gas O2 content and provide 

reductant during emissions system regeneration. The burner was created drawing on 

previous gasoline-fueled burner design experience and thorough study of a commercially 

available fuel-oil burner system. The intent was to create a fast, simplistic solution and to 

utilize commercially available parts where possible. It is a tube-type burner that operates 

in parallel to the exhaust system, minimizing back pressure increases due to the device 

75
installation. Some parts from a commercially available oil burner were combined with a 

gasoline fuel injector, an air atomizing injector holder, and a flame-stabilizing technology 

developed by SwRI (Active Porous Media Aftertreatment Control System – US Patent 

No. 5,771,68), to create the diesel burner. 

When a diesel engine is operated at loads much lower than the engine is rated for, the 

exhaust temperatures are much lower than typically required for modern day 

aftertreatment devices. Under lightly loaded engine operation it will be necessary to 

perform general thermal management as well as regeneration management for a NACbased system. When large levels of thermal management are necessary, transferring the 

supplemental heat efficiently to the catalyst system becomes the main priority in reducing 

the fuel economy penalty that will be incurred. 

One approach to thermal management is to use modified engine calibrations to generate 

the supplemental heat needed (i.e., post-injection, intake throttling, EGR). Figure 44 

shows the layout of a dual branch system that would incorporate only engine-based 

regeneration and thermal management control. For the configuration shown in Figure 44, 

supplemental heat generated by the engine has many potential heat loss paths. A major 

source of heat loss occurs in the engine during combustion of the supplemental fuel. 

After the exhaust leaves the engine, heat loss can occur in the exhaust manifolds and 

cross over pipes through the turbocharger, the downpipe, and the exhaust system that 

bends underbody into the catalyst. The heat loss paths in the exhaust are shown in red. 

90° Turn Underbody 

Engine 

NAC 

DPF 

NAC 

Flow Control Valves 

Figure 44. Heat loss paths in an engine-based regeneration and thermal 

management configuration 

Another option for supplemental heat generation would be the use a fuel burner located in 

the exhaust. A fuel burner has a very high efficiency of conversion of fuel energy to heat 

energy, and can be located in close proximity to the emissions systems, thereby reducing 

heat lost between the point of generation through transfer to the emission systems. 

Figure 45 shows a possible emissions control system configuration using a burner-based 

thermal management approach. In this configuration the combustion chamber is located 

76
inside the “Y” of the exhaust, in an underbody location. Installing the burner inside the 

exhaust allows the combusted fuel heat as well as the radiant heat emitted from the 

combustor wall to be transferred to the exhaust, limiting heat loss during the combustion 

process. The remaining heat loss paths are the exhaust pipe that transfers the heat to the 

catalyst. Figure 45 highlights this heat loss path in red. Because the heat loss path is 

confined to the exhaust system, double-walled pipe could be used to minimize heat loss 

and improve the efficiency of the heat transferred to the catalysts. 

90° Turn Underbody 

Engine 

Burner 

NAC 

DPF 

NAC 

Flow Control Valves 

Figure 45. Heat loss paths in an In-exhaust burner-based regeneration and thermal 

management configuration 

The use of a fuel burner to generate supplemental heat in close proximity to the ECSs 

creates a configuration that is more efficient at converting fuel to supplemental heat and 

transferring that heat to the emissions control systems than an engine-based approach. 

Another beneficial feature of using a fuel burner is the wide range of stable operation 

(both in airflow and fuel flow) that burners typically offer. This wide range of operation 

allows the device to provide a wide range of temperature as well as air-fuel ratio control, 

which may be a very useful feature in creating the exhaust gas composition needed to 

carry out the periodic regeneration of the NAC. The diesel engine is not well adapted to 

running under the rich conditions needed to regenerate the NAC; however, a burner lends 

itself well to rich operation. Running the burner rich will generate unburned and partially 

burned hydrocarbons, CO, and hydrogen. Running rich will also help reduce the overall 

exhaust gas oxygen content. Adding a pre-catalyst (such as a thin oxidation catalyst) can 

be useful in combusting some of the unburned hydrocarbons from the burner with the 

engine exhaust. Once overall rich conditions are achieved, the pre-catalyst can also be 

used to generate large amounts of CO from the unburned hydrocarbons and engine 

exhaust oxygen. This will help to not only create overall rich conditions, but will remove 

the excess O2 from the exhaust prior to entering the NAC. Additionally, adding SFI in 

the exhaust, upstream of the pre-catalyst, can be used to enhance the available reductant 

and to accelerate the transition from lean to rich conditions. Figure 46 shows the ECS 

77
configuration utilized in this program, which includes a burner, supplemental fuel 

injection, and a pre-catalyst before the NAC and DPF systems. 

90° Turn Underbody 

SFI 

Engine 

Burner 

SFI 

Pre-Catalyst 

NAC 

DPF 

Pre-Catalyst 

NAC 

Flow Control Valves 

HP-EGR 

Figure 46. Emissions system configuration utilizing a fuel burner, in-exhaust 

supplemental fuel injection, and pre-catalyst upstream of NAC-DPF system 

Figure 47 shows some photographs of the burner head. The injector selected was a 

Bosch K-Jetronic with fuel modulation achieved using a Bosch frequency valve. The KJetronic was selected because it offers rapid shutoff of fuel and has a poppet-valve design 

that is more heat tolerant than a needle-lift type injector. The K-Jetronic selected has an 

air-shroud bonnet installed on the injector, and for better atomization, compressed air 

flows through the bonnet while the injector is activated. To achieve this, a jacket was 

designed to hold and seal the injector, and to provide a means for injecting compressed 

air. The air jacket was also designed to provide mounting for the air-swirl bonnet and the 

electrodes. 

The flame stabilizer is a section of ceramic-foam silicon carbide, placed between the 

burner flame and exhaust flow. The foam was used to stabilize and contain the flame 

within the burner head, thus preventing the flame from contacting the catalyst face, even 

if it were to be very closely coupled to the emissions systems. It is also used to provide a 

surface for combustion of larger fuel droplets, to reduce the impact of engine exhaust 

pulsations on the burner flame structure, to flatten the burner exit temperature profile, 

and, once hot, to reignite the burner flame, if necessary. 

A control system was built to provide control over fuel injection, spark, air assist, and the 

main burner airflow rate. The controls were integrated into the ERIC, and three modes of 

operation were provided: 

78
1. Cold-start emissions system warm-up 

2. Temperature balancing 

3. Manual mode. 

Figure 47. Photographs of the diesel fuel-burner head 

The burner was installed with the combustion chamber submerged in the engine exhaust 

flow. This approach provides external cooling of the combustion chamber and reclaims 

the heat normally radiated from the combustion chamber wall, thereby improving the 

transfer efficiency of the supplemental heat to the catalyst. This configuration also 

combines all hot portions of the burner inside the exhaust. Figure 48 shows a burner 

system installed in a dual-branch configuration with an oxidation catalyst and one NAC 

catalyst. The burner is installed in a position that simulates the underbody turn of the 

exhaust on the vehicle. 

79
Engine Exhaust In 

Combustion Chamber Location 

Oxidation Catalyst 1 - NAC 

Engine Exhaust Flow 

Combustion Chamber 

Burner Head 

Figure 48. Photographs of the burner installed in the engine exhaust with an 

oxidation catalyst and one NAC 

3.2.2 Emission Control System Regeneration Control/Strategy 

The ECS was a dual-leg NAC with a single DPF downstream of the combined flow after 

the NACs. There were also oxidation catalysts installed upstream of each NAC and in 

front of the DPF. The dual leg NAC configuration allowed reduced flow regeneration 

(compared to a single leg, full-flow system), and used exhaust valves to direct flow 

during regeneration and desulfurization. This particular system included a single diesel 

fuel burner used for thermal management and to produce reductants for regeneration. 

SFIs were installed in each exhaust leg to allow additional control of the regeneration 

reductant. Figure 49 shows a schematic of the ECS evaluated in this project. 

80
 81

Figure 49. Schematic of an ECS 

Control Strategy Overview 

The controller strategy developed to manage the ECS consisted of three main software 

“controllers” or elements. Each controller was a piece of software that was developed to 

monitor and control the hardware associated with a specific subsystem. All software 

controllers interacted and exchanged information with each other to create an integrated 

solution. In the SwRI approach, there were three main controllers: the EGR controller, 

the ECS controller, and the burner controller. A schematic overview of the emissions 

controller is shown in Figure 50. 

The EGR controller was responsible for the proportional control of the EGR valve and 

intake throttle. EGR control was modified to reduce flow during cold starting and 

acceleration conditions. The EGR controller communicated information about EGR flow 

to the ECS controller. EGR calibration was described earlier in Section 3.1. 

The ECS controller was responsible for estimating engine-out NOx mass, running the 

NOx mass model for each NAC, determining the NAC regeneration state of the system, 

tracking engine load to determine if additional heat from the burner was needed, and 

calculating the amount of reductant needed for each regeneration. The ECS controller 
communicated information about pre-burn needs and regeneration state to the burner 

controller. 

The burner controller was responsible for tracking when the engine started, controlling 

engine-start ECS warm-up schedules, and for monitoring data from the ECS controller to 

determine when burner pre-heating would be required prior to NAC regeneration. 

The full transient control strategy can be broken down into three areas: 

1. NOx regeneration management 

2. General thermal management 

3. Cold-start thermal management. 

82
Regeneration Reductant Mass Calculation 

MODE = Crank 

ECS Strategy Activated 

EGR Controller 

Look-up 

Table 

APP RPM 

Duty 

Cycle 

Crank Timer 

Look-up 

X Start Multiplier 

Mode 

Modifier 

Mode 

multiplier X 

EGR 

Valve 

Control 

Intake 

Throttle 

Control 

Look-up 

Table 

APP RPM 

NOx 

Concentration 

1 

X MAF Constants X EGR Mult. = EO Mass 

2 

I 

II 

mNOx Leg1 = [EO Mass X (0, 0.5, 1)] + MNOx Leg1 Last 

mNOx Leg2 = [EO Mass X (0, 0.5, 1)] + MNOx Leg2 Last 

Valve Position Multiplier 

3 

Regen 

Control 

mNOx 1 mNOx 2 

Mode 

Target 

mNOx 

Current Regeneration State 

Regeneration State 

0 = Normal 1 = Regen Leg1 2 = Regen Leg2 

Calc 

mRed 

mNOx 1 mNOx 2 

mRed 

mNOx 

SFI Injection Time Leg1 SFI Injection Time Leg2 

Regeneration Controller 

Normal State 

Regenerate Leg1 (or 2) State 

Calc 

Preburn 

Time Since Last Burned 

Preburn 

Leg1/Leg2 

1 Control Pre-Burn 

2 Store Regeneration Information 

3 Calculate Regeneration Cycle 

4 Control regeneration cycle and 

output exhaust valve and SFI controls. 

5 Reset NOX mass to zero (MNOx Last = 0). 

Reset regeneration mode to ‘normal.’ 

EGR= 

NOX Mass Calculation 

Regeneration State Control 

Look-up 

Table 

APP RPM 

IT = Duty Cycle 

Determine Mode 

4 Regeneration Cycle Output Control 

SFI1 SFI2 Exhaust Valve 

Control Control Position Control 

Figure 50. Schematic overview of software controller designed for ECS management 

83
NOx Regeneration Management 

The following section describes how regeneration was carried out in this system and the 

catalysts’ interaction. During normal operation (adsorbing mode), both exhaust flow control 

valves were open, and the exhaust was free to flow down both legs (refer to Figure 49 for the 

ECS schematic). The NOx mass model continually estimated the mass of NOx trapped in each 

NAC. Once a predetermined mass of NOx was reached, a regeneration event was triggered. The 

NAC controller first determined if the burner needed to be operated to increase the ECS 

temperature. If necessary, the burner was operated for a fixed period of time prior to continuing 

with the regeneration sequence. The exhaust flow control valve in the leg to be regenerated then 

closed, directing all of the exhaust flow through the opposite leg. After a short period of time, 

the supplemental, in-exhaust fuel injection was activated in the leg to be regenerated. The 

exhaust flow control valve in the regenerating leg remained closed for a period of time after the 

supplemental fuel was injected. Following this time period, the exhaust flow control valve 

opened, and the exhaust flowed down both legs. This sequence repeated, alternating legs for 

regeneration as controlled by the NOx mass model. Using this approach to regeneration allowed 

at least one leg of the system to always be adsorbing. 

During regeneration, the overall rich mixture first entered the oxidation catalyst, where the fuel 

was partially oxidized to form lighter hydrocarbons and CO while simultaneously removing 

excess O2 in the feed stream. The other function of the oxidation catalyst was to absorb the very 

high exotherm resulting from the oxidation of the injected fuel and O2 remaining in the exhaust 

stream. This catalyst was more thermally stable than the NAC, and by absorbing this release of 

heat, it provided some thermal protection for the NAC. 

A NOx mass model was created to predict the level of NOx stored in the adsorber system and 

predict when each adsorber was in need of regeneration. The NOx mass model estimated the 

amount of NOx stored in the adsorbers in real-time, integrating the instantaneous NOx mass 

entering each adsorber and assumed 100% adsorption. The model also assumed that during 

regeneration, 100% of the stored NOx was removed from the adsorber. The concept of this 

model is shown in Figure 51. 

The NOx concentration used in this model was based on a look-up table of measured NOx 

concentration as a function of engine speed and load. The NOx map was generated under steadystate conditions, and as such there was some error associated with transient operation. An 

alternative to using a NOx mass look-up table would be to use an exhaust NOx sensor to measure 

engine-out NOx directly. This method would provide a more direct and perhaps more accurate 

result. However, in production, if a sensor would be used, it would most likely need a NOx 

concentration look-up table as a back-up alternative in the event of sensor failure. 

84
0.00 50.00 100.00 

1000 

2000 

1000 

2000 

RPM 

NOx, ppm 

NOX Mass Concentration Map 

APP 

[NOX] x MAF = Inst. NOX Mass 

NOX Mass Stored = 

Inst. NOX Mass - NOX Mass Removed 

Figure 51. NOx mass model concept 

General Thermal Management. 

Examination of the baseline temperature data across the FTP test cycle showed that the measured 

exhaust gas temperature at the catalyst inlet location averaged only 165°C, well below the 275°C 

to 400°C temperature range recommended by the catalyst supplier for efficient NAC operation. 

Examination of the data revealed three main areas of engine operation that presented special 

thermal management needs: 

1. Cold-start - to create rapid warm-up for ensuring that the emission systems are active within 

10 to 20 seconds after engine start 

2. Deceleration and idle – to prevent rapid cooling during deceleration and increasing low idle 

temperatures 

3. Cruise – to increase the average exhaust gas temperature under steady-state, lightly loaded 

operation. 

Due to the large difference between the normal operating temperature of the engine and the 

required temperature for high-efficiency catalyst performance, it became obvious that a large 

amount of supplemental heat would need to be added to the system to achieve the desired 

performance. The large amount of supplemental heat required indicated that a large fuel penalty 

would be incurred in creating the necessary heat, and the most fuel efficient solution for the 

application was sought to minimize the fuel economy penalty. The results of a heat loss analysis 

led to the conclusion that for the engine operating over lightly loaded conditions (i.e., the FTP85
75), the temperature requirements may be extremely difficult and costly to meet using an enginebased approach alone (an exhaustive study of several options showed that up to 75% of the 

supplemental heat generated at the engine could be lost before the catalyst inlet). It was decided 

that the source of heat necessary to achieve the temperature window should come from an 

external source (e.g., electric heater or fuel burner) installed in close proximity to the catalysts. 

Due to the energy requirements needed to raise the exhaust gas temperature during general 

operation and particularly during a cold start, a decision was made to use a fuel burner. It was 

also felt that the fuel for the burner should come from the same source as the engine (diesel) to 

maintain fuel singularity in the application. 

A fuel burner was created for this application and installed in the exhaust of the Duramax (as 

was shown in Figure 49). The burner control was designed to monitor engine and exhaust 

conditions, detect cold-start or temperature balancing needs, and self activate when conditions 

indicated a need to increase the exhaust gas temperature. Figure 52 shows the temperature at the 

oxidation catalyst inlet location for the Cold-Start UDDS (Bags 1 and 2 of the FTP-75), the 

stock, no-EGR configuration, and for using the burner in combination with HP-EGR and intake 

throttling (all other temperature management controls were eliminated). The additional fuel

consumed by the burner was used to calculate the efficiency of the conversion of fuel to heat 

energy and the transfer of that heat to the catalyst. This burner-based approach was found to be 

90% efficient.

Burner + EGR + IT 400 

300 

200 

Stock Temperature 100 

Vehicle Speed

0 

0 200 400 600 800 1000 1200 1400 

Time, seconds

Figure 52. Exhaust gas temperature at catalyst inlet location for burner + oxidation

catalyst and stock, no-EGR configuration 

Cold-Start Thermal Management

In the absence of any cold-start strategy, the temperature in the front of the first catalyst

(oxidation catalyst) would not exceed 200°C for well over 200 seconds over the Cold-Start 

UDDS cycle and never exceeded 300°C. In order to achieve high conversion efficiencies, the 

front oxidation and NACs needed to be at operating temperature (275°C - 405°C) as soon as 

Vehicle Speed, mph 

 Gas Temperature at Catalyst , °

C

 86
possible (preferably in under 20 seconds) after engine start. During this work, several cold-start 

strategies were developed. 

Cold-start strategy 1 (S1) involved activating the burner and running it in thermal balancing

mode for 120 seconds. Using this strategy, the front of the NACs (2.5-cm deep on the centerline 

of the NAC substrate) did not reach over 300°C until 75 seconds after cold start, and the back of 

the adsorber, NAC5 (12.7-cm deep on the centerline), did not exceed 300°C until 180 seconds 

into the cycle. Figure 53 shows the NAC bed temperatures for the base system, S1. 

To further improve cold-start emissions performance, it was necessary to accelerate the heat up 

of the NAC to operating temperature. The cold-start strategy was modified to improve burner 

output and to add additional energy to the NAC. Cold-start strategy 2 (S2) increased burner 

airflow from 226 l/min to 263 l/min, and added short bursts of SFI to add chemical energy to the 

NACs. The increased burner airflow improved burner temperature output and resulted in 

increased temperature at the inlet to the oxidation catalysts. Once the oxidation catalysts had 

reached sufficient temperature, the SFI (in-exhaust injection) was activated, supplying short 

bursts of fuel to each leg under full-flow conditions. 

600

NAC1-1”

400

200

NAC1-5”

0

050100150200

Time, seconds

Figure 53. NAC1 bed temperature for S1 

When examining the results of S2, it can be seen that supplemental heat was getting into the 

front of the NAC, but was not being transferred throughout the NAC. In order to raise the 

temperature at the back of the NAC, more exhaust flow was required to push the energy through 

the catalyst. Cold-start strategy 3 (S3) was developed to target transferring heat through the 

NAC. Under S3, EGR was eliminated for the first 120 seconds after cold-start. EGR originally

was reduced under cold-start for driveability reasons, but was maintained at a low level for NOx

control. Figure 54 shows that strategy S3 worked well to accelerate the heat-up of the entire 

NAC, and that NAC5 achieved 300°C in 120 seconds (compared to 180 seconds with S1). S3 

also achieved substantially accelerated warm-up of the DPF (see Figure 55).

T

e

mperatur

e, °C

T

e

mperatur

e, °C

 87
T

emper

ature, °C

T

emper

ature, °C

600

NAC1-1”

S3

400 S2 S1

S3 S2

200S1

NAC1-5”

0

0 5 0 100 150 200

Time, seconds

Figure 54. Effect of cold-start strategy on NAC1 bed temperatures 

Using a burner to rapidly add heat energy to the exhaust emission components accelerated 

catalyst light-off to less than 20 seconds for the oxidation pre-catalysts and to 50 seconds for the 

front of the NAC. In operating situations in which supplemental heat is required, the burner 

system provides an efficient means for maintaining the temperature window for efficient

operation of the ECS. 

88
 89

Figure 55. Impact of accelerated NAC S4 on DPF warm up 

3.2.3 Fuel Economy Penalty Associated with Emission Control System Operation 

A fuel penalty is incurred whenever energy is put into the system beyond that which is necessary 

to power the engine/vehicle over the desired operating cycle. In this project, the magnitude of 

fuel economy penalty was a function of the thermal penalty (energy added to increase the ECS 

temperature sufficiently) and the regeneration penalty (fuel used for removing NOx from the 

NAC). The total thermal penalty was a function of the engine-out exhaust temperature, the 

exhaust mass flow rate, and the efficiency of converting fuel chemical energy to heat at the ECS. 

The regeneration fuel penalty was a function of the engine-out NOx mass, NAC volume, the 

reductant type, and the level of NOx reduction required from the ECS (the emissions goal). 

The thermal fuel economy penalty was the energy input to the system in order to raise the 

temperature of the ECS system into its operating window and is summarized in Equation 1. 
Energy = m& ×c p 

×ΔT (Eq. 1) 

m& = exhaust mass flow rate 

cp = specific heat of exhaust gas 

ΔT = desired temperature – engine provided temperature 

λ = efficiency in converting fuel energy to heat at the ECS 

As discussed in Section 3.1, the average exhaust gas temperature was less than 165°C across the 

Cold-Start UDDS, significantly below the NAC operating window of 275-400°C necessary to 

achieve the high levels of NOx reduction required to meet the project goals, as shown in Figure 

56. EGR was used to reduce the exhaust mass flow ( m& ) to lessen the energy required. The 

average exhaust flow rate over the Cold-Start UDDS was reduced by 33% through the use of 

EGR, as shown in Figure 57. A diesel-fueled burner was used to supply the necessary heat 

directly to the exhaust gas upstream of the NACs (ΔT). The burner was found to be the most 

efficient method for increasing the exhaust temperature as compared to other strategies such as 

intake throttling and turbo-charger by pass systems. The entire fuel economy penalty associated 

with the thermal requirements only brought the ECS into its operating window; it did not directly 

contribute to NOx reduction. 

The fuel economy penalty associated with actually reducing the NOx with the ECS was referred 

to as the regeneration fuel economy penalty. The regeneration fuel economy penalty was a 

function of: 

• Engine-out NOx mass 

• Reductant type 

• NAC volume 

• NAC efficiency 

• Exhaust environment at regeneration initiation 

• Emissions goal. 

90
Figure 56. Exhaust gas temperature over the Cold-Start UDDS and desired operating 

window for ECS 

400 

ECS Desired Operating Window for >90% Efficiency 

350 

300 

250 ΔT 

200 

150 

Exhaust 

100 

Gas Temperature, °C 

50 Turbocharger Downpipe Location, Average =153°C 

0 

0 200 400 600 800 1000 1200 1400 

Time, seconds 

91
250 

Average 33% Reduction in Flow

200 No EGR 

With EGR 

150 

Intake Mass Air Flow Rate, g/sec. 

100 

50 

0 

0 200 400 600 800 1000 1200 1400 

Time, seconds 

Figure 57. Exhaust mass flow rate over the Cold-Start UDDS with and without EGR 

Higher levels of NOx mass emitted from the engine, requires more frequent regenerations for a

given level of NOx reduction efficiency. Figure 58 shows an example of the NOx reduction 

efficiency (at steady-state) for different levels of NOx concentration at constant NAC

temperature. Certain reductants are more efficient at regenerating the NAC (i.e., hydrogen, CO) 

while others are less efficient (diesel fuel, larger hydrocarbons). Thus, the type of reductant will 

have a direct impact on the efficiency of the ECS, and subsequently, on the amount of reductant 

required for a given level of NOx reduction. As diesel fuel was used as the reductant in this 

program, the regeneration frequency had a direct impact on the fuel economy penalty. The 

NACs ability to store NOx is reduced as NOx is stored on the NAC, thus, the volume of the NAC 

directly affects the frequency of regeneration for a given level of NOx reduction. This ability to 

store NOx is also a function of the NAC formulation and operating temperature as shown in 

Figure 59. Thus, the efficiency of the NAC to store NOx also directly affects the frequency of 

regeneration. When a regeneration is initiated, it is necessary to achieve overall reducing

conditions in the NAC. Therefore, the exhaust environment will have a direct impact on the

amount of reductant required to achieve overall reducing conditions (exhaust oxygen 

concentration and mass flow). Ultimately, the most important factor affecting the regeneration 

fuel economy penalty is the desired emissions goal. Achieving a tailpipe NOx emissions level 

that requires a 95% reduction over the engine-out emissions will result in a fuel economy penalty

substantially larger than one associated with achieving a NOx reduction of 75% over the engineout emissions. 

92
100 

98 

96 

Burner SP =300°C, SV = 25k

94 

92 

150 ppm NOx Inlet 

90 280 ppm NOx Inlet

415 ppm NOx Inlet

88 

86 

0.0 0.5 1.0 1.5 2.0 2.5 3.0 

NOx Mass Stored (grams) 

Figure 58. NOx reduction for various NOx inlet concentrations at constant inlet

temperature NO t

o NO2 Conversion Efficienc

y (Percent)

 93
100 

90 

70 

80

NO to NO2 Conversion Efficiency (

Percent)

SV = 25k, Inlet NOx = 280 ppm 

50 

60 

300°C Burner SP 

350°C Burner SP 

375°C Burner SP 

40 

0.0 

Figure 59. NOx

temperature 

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 

NOx Mass Stored (grams) 

 reduction for various NOx inlet concentrations at constant inlet 

5.0 

Figure 60 summarizes the fuel economy penalty due to EGR, regeneration, and thermal 

management for the Hot-Start UDDS, HFET, and US06 cycles. This figure shows that the total 

fuel economy penalty for the Hot-Start UDDS cycle is high (18%) due to the level of NOx 

reduction required (>98%), and the low average exhaust gas temperature (thermal penalty 

contributes over half the total fuel economy penalty). As the cycle work increases (UDDS < 

HFET < US06), the total fuel economy penalty decreased (as does the overall NOx reduction 

efficiency). Figure 61 summarizes the fuel penalty attributable to regeneration and the overall 

NOx reduction (after 300 hours of aging) for the Hot-Start UDDS, HFET, and US06. Figure 60 

and 61 both show that high levels of NOx reduction can be achieved with a relatively small total 

fuel economy penalty (90% reduction over the US06 for a 4% fuel economy penalty) when 

minimal additional thermal energy is required by the ECS. However, when the engine-out 

exhaust gas temperature is far below the necessary operating window and extremely high levels 

of NOx reduction are required (such as the Hot-Start UDDS), the fuel economy penalty can be 

quite high. These results imply that a more appropriately sized engine/vehicle combination has 

potential for reasonable fuel economy penalties over certification cycles and real-world driving. 

94
95

Figure 60. Fuel economy penalty and source over Hot-Start UDDS, HFET, and US06

0

1

2

3

4

5

6

7

HLA-4 HFET US06 Regeneration Fuel Penalty, %

8 6

8 8

9 0

9 2

9 4

9 6

9 8

100 NOx Reduction, %

Fuel Penalty

NOx Reduction

Figure 61. Regeneration penalty and associated NOx reduction for the Hot-Start UDDS, 

HFET, and US06 

Hot Start 

UDDS
3.3 Development of Desulfurization Process 

One of the drawbacks to a NAC-based aftertreatment system is the requirement to intermittently 

“desulfate” the adsorber due to its high affinity for adsorbing sulfur oxides. The accumulation of 

sulfur on the available adsorption sites inhibits the NAC’s ability to reduce NOx by reducing its 

NO to NO2 conversion performance and blocking NO2 adsorption sites. In order to maintain a 

high level of NOx reduction, the NAC must be intermittently cleansed of this sulfur 

accumulation. 

For this program, after every 100 hours of aging, approximately 660 kilograms of fuel were 

consumed upstream of the NACs (engine, burner, and SFI). Given a fuel sulfur level of 15 ppm, 

there was a total fuel sulfur mass exposure of approximately 9.9 grams total over 100 hours. 

This mass of sulfur is assumed to be split evenly between the two exhaust legs, resulting in a fuel 

sulfur mass exposure for each NAC of approximately 4.95 grams. The engine oil consumption 

rate was approximately 0.35 liters (315g) every 100 hours. An oil sulfur level of 6,400 ppm 

results in a total oil sulfur mass exposure of approximately 2 grams for 100 hours of aging (1g 

for each leg). Therefore, the total sulfur mass exposure for each NAC over 100 hours of aging 

was approximately 6 grams (assuming an equal split of exhaust between the two exhaust legs). 

In general, desulfurization of most NACs requires elevated bed temperatures (>650°C) and 

overall reducing conditions (lambda < 1). Four different on-engine desulfurization strategies 

were developed during this program. Each strategy attempted to create specific conditions 

within the catalyst in order to remove the stored sulfur, while minimizing thermal damage to the 

catalyst or engine. All desulfurization strategy development was conducted on the first 

generation NACs. 

Ultimately, based on input from the ECS supplier, an off-line desulfurization process was 

developed on a gasoline engine. This option was accepted due to the limited availability of 

NACs, the potential for thermally damaging aged NACs during desulfurization, delays in 

receiving the second generation components, and the necessity to achieve extremely high levels 

of NOx reduction. This cycle used a rich/lean pertubated approach and desulfated one NAC at a 

time. The gasoline SI engine was run at a constant speed and load with an exhaust flow rate of 

approximately 52 g/s. The fuel sulfur content was less than 30 ppm. The engine was run under 

rich conditions (lambda = 0.9) during the warm-up phase until the three NAC bed temperatures 

(1”, 3”, and 5” in) reached 600°C. At this point the engine air-fuel ratio was then pertubated 

between lambda of 0.9 and 1.05 (five seconds at each air-fuel ratio). The measured NAC bed 

temperatures typically reached 650°C (the desired desulfurization temperature) approximately 2 

minutes after beginning the perturbation. The air-fuel perturbation was continued for an 

additional 5 minutes, after which it was ceased and the engine held at lambda of 0.9 for 

approximately 90 seconds. At this point in time the engine was brought to idle conditions (still 

at lambda of 0.9) and allowed to idle until the NAC bed temperatures dropped below 520°C (the 

typical peak temperature observed during transient emission evaluations). This idle period 

typically lasted 800-900 seconds. The entire process was then repeated on the second 

DOC/NAC combination. 

The DOC/NACs were first subjected to desulfurization after 200 hours of aging. After this 

point, a desulfurization was conducted every 100 hours of aging after the pre-desulfurization 

emission evaluations had been completed. A “dummy” DOC/NAC was always run prior to the 

actual test parts to warm-up the engine and ensure the operating conditions were repeatable. An 

96
example of the engine-out lambda and NAC system temperatures during a desulfurization is 

shown in Figure 62. 

0.80 

0.85 

0.90 

0.95 

1.00 

1.05 

1.10 

1.15 

1.20 

1.25 

1.30 

Lambda 

520 

540 

560 

580 

600 

620 

640 

660 

680 

700 

720 

T

emperat

ure, °C 

Lambda Inlet Oxi2-1" 

NAC2-1" NAC2-3" NAC2-5" 

900 910 920 930 940 950 960 

Time, seconds 

Figure 62. Example of engine-out lambda and NAC system temperatures during 

desulfurization 

During the course of the program, an attempt was made to quantify the amount of sulfur (in the 

form of SO2 and H2S) released from the NAC system during a typical desulfurization or during 

each desulfurization. For the 1,300- and 1,400-hour desulfurizations, raw exhaust after the NAC 

system was pulled through impingers using the same sampling procedures as detailed in Section 

2.2.3 for SO2 and H2S. Sampling began when the NAC bed temperatures reached 600°C 

(immediately before beginning the rich/lean cycling) and continued for approximately 2 minutes 

after cycling ceased (total sample time of 540 seconds). Table 21 summarizes the sulfur mass 

measured (in the form of H2S and SO2) during the 1,300- and 1,400-hr desulfurizations. Also 

this table provides an estimate of the total sulfur mass consumed in the engine, burner, and SFI 

for both the fuel and oil (theoretically the largest mass of sulfur that could be deposited on the 

NAC). After completing the 1,400-hour desulfurization and bringing the engine to idle 

conditions, a strong H2S smell was observed in the test cell long after sampling had ceased, 

indicating that sulfur was still being removed from the NAC. In addition, condensed water was 

observed in the sample line immediately before the impinge. As H2S is highly soluble in water, 

it is likely that a significant portion of the H2S emitted was not collected. Modifications were 

made to the sample cart in an effort to increase the sample volume to maintain the sample 

temperature above the water condensation temperature. 

97
The H2S sampling period was subsequently increased and broken into four distinct periods. The 

first sampling period began during the warm-up phase, approximately 420 seconds prior to the 

NAC bed temperatures reaching 600°C. All sampling periods were 420 seconds in duration. 

The second sampling period began when the air-fuel perturbation was initiated. The third 

sampling period followed immediately thereafter when the air-fuel perturbation ceased, and the 

engine was brought to idle conditions. The fourth sampling period covered the last portion of the 

idle period. The 420-second sample duration was chosen in an effort to eliminate sample 

saturation and minimize lost periods of sampling due to bubbler changeover. However, for the 

third sampling period (first idle period at rich conditions), the primary and secondary samples 

were both found to be saturated, indicating a probable loss of sample. Due to the extremely high 

levels of H2S emitted during the idle period, the established sampling and analytical procedures 

were not adequate to accurately quantify the mass of H2S being emitted. Table 2 summarizes the 

H2S mass measured at the 1,600-hour desulfurization point using the modified sampling 

procedures (a problem was encountered during the analysis for the first sample for NAC2 and no 

quantification of H2S mass was possible). After this aging point, no further attempts to quantify 

the sulfur removal were made as the 1,600-hour results indicated a substantial portion of the 

maximum theoretical mass of sulfur deposited on the NACs was being removed during the 

desulfurization procedure. Substantial modifications to the sampling and analysis system would 

have been required to accurately quantify the H2S mass emitted during desulfurization and was 

beyond the scope of this program. 

Table 21. Sulfur Mass Summary for 1,300- and 1,400-Hour Desulfurizations 

NAC1 

1,300 

Hours 

NAC1 

1,400 

Hours 

NAC2 1,300 

Hours 

NAC2 

1,400 

Hours 

SO2 Mass, g 0.829 0.610 1.047 0.524 

H2S Mass, g 2.696 2.649 2.618 2.629 

Total S Mass, g 2.952 2.797 2.987 2.747 

Estimated Fuel + Oil Sulfur Mass 

For 100 Hours of Aging, g 5.95 5.95 

Sulfur Removal 50% 47% 50% 46% 

Table 22. H2S Mass Measured during 1,600-Hour Desulfurization 

 Sample 

Period 1 

H2S Mass, 

g 

Sample 

Period 2 

H2S Mass, 

g 

Sample 

Period 3 

H2S Mass, 

g 

Sample 

Period 4 

H2S Mass, 

g 

Total Sulfur 

Mass 

Contribution 

from H2S, g 

NAC1 1.503 2.456 0.826 0.219 5.005 

NAC2 No Data 3.134 1.378 0.525 5.037 

98
Section 4: Results

Study results of the demonstration phase are organized around four sets of study questions. 

Section 4.1 addresses the initial performance of the ECS through the first 300 hours of testing, 

and Section 4.2 describes the performance of the desulfurization process as well as the long-term 

aging performance of the ECS. The interaction of sulfur with ECS performance and the potential 

impacts of fuel properties on tailpipe emissions are presented in Sections 4.3 and 4.4, 

respectively. Finally, Section 4.5 discusses some technical problems that were encountered and 

the remedial actions that were taken. Unregulated emissions results are presented in a separate 

report that incorporates findings from other APBF-DEC studies. 

4.1 Initial Performance 

This section describes the performance of the ECS during the initial 300 hours of aging, focusing 

on the initial impact of the ECS on regulated emissions and fuel economy and the impact of 

sulfur on a fresh ECS. The following study questions are addressed: 

Q1.1 Can the system meet the 2007-2010 regulated emissions levels for NOx, NMHC, and 

PM? 

Q1.2 What is the impact on other regulated emissions (THC and CO) and fuel economy? 

Q1.3 How does system performance change during the early life (under 300 hours) of the 

system? 

Q1.4 Are there similar patterns for various transient duty cycles (Cold- and Hot-Start UDDS, 

US06, HFET)? 

At the start of the demonstration phase, three pairs of engine-out emissions tests were performed, 

one with each of the three test fuels (i.e., D8, D15, and BP15). Each series consisted of a ColdStart UDDS test cycle followed by a Hot-Start UDDS, USO6, and HFET. These baseline tests 

were performed without EGR. In addition, a single series of baseline engine-out tests was 

performed with EGR activated. Following the installation of a fresh ECS, a triplicate series of 

tests was performed using the D15 fuel. After 50 hours of aging, the system was re-evaluated. 

This evaluation process was repeated every 50 hours using either a duplicate or triplicate series 

of tests until the first desulfurization event at 200 hours. All tests with the ECS were performed 

with EGR activated. These tailpipe results are compared to both sets of baseline engine-out 

emissions in order to characterize the NOx reduction performance of the total system (ECS + 

EGR) as well as the NOx reduction efficiency of the ECS relative to engine-out emissions with 

comparable EGR. During each test with the ECS, the total amount of engine-out accumulated 

NOx was recorded along with the total tailpipe NOx. It was confirmed that the engine-out results 

were consistent with the single series of engine-out measurements taken prior to the installation 

of a fresh ECS at the start of the study. 

Table 23 shows the average composite FTP emissions from the seven engine-out tests (six 

without EGR and one with EGR) and the 18 tailpipe tests conducted prior to the first 

desulfurization, along with 95% confidence intervals. Emission reductions are calculated 

99
relative to engine-out with and without EGR. Note that emission reduction does not necessarily 

equate to NOx conversion efficiency because the back pressure caused by the ECS affects 

engine-out emissions by changing the amount of EGR in use. 

The reductions in NOx, NMHC, CO, and PM emissions due to the ECS were all statistically 

significant, as was the reduction in fuel economy (18.7% relative to engine-out without EGR and 

16.7% relative to engine-out with EGR). Tailpipe emissions for THC were significantly greater 

than engine-out THC emissions due to the fuel used as a reductant and use of a burner to increase 

the temperature of the exhaust. 

Table 23. Average Engine-Out and Initial Tailpipe Composite FTP Regulated Emissions 

and Fuel Economy—with 95% Confidence Intervals 

Engine Out Tailpipe (0-200 Hours) w/ EGR 

Emission 

Parameter Unit EGR Average1 

95% Confidence 

Interval Average2 

95% 

Confidence 

Interval 

Percent 

Reduction 

Regulated 

Emission 

Standard3 

Without 4.38 (4.34, 4.42) 97.8% NOx g/mi 

With 2.12 -

4 0.095 (0.069, 0.12) 

95.5% 

0.07 

Without 0.198 (0.19, 0.207) 16.7% NMHC g/mi 

With no data -

0.165 (0.145, 0.186) 

-

0.09 

Without 0.204 (0.194, 0.213) -126.9% THC g/mi 

With 0.264 -

0.463 (0.434, 0.491) 

-75.1% 

N/A 

Without 2.02 (1.85, 2.18) 87.2% CO g/mi 

With 4.43 -

0.258 (0.215, 0.301) 

94.2% 

4.2 

Without 0.065 (0.056, 0.074) 91.6% PM g/mi 

With 0.145 -

0.005 (0.004, 0.007) 

96.2% 

0.01 

Fuel Without 18.4 (18.2, 18.6) 18.7% 

Economy 

mi/gal With 18.0 -

15.0 (14.8, 15.1) 

16.7% 

N/A 

1

 Engine-out average without EGR is based on 6 tests; engine-out average with EGR is based on 

one test. 

2

 Average of 18 tests performed prior to first desulfurization at 200 hours 

3

 Tier 2 Bin 5 full useful life 

4

 Confidence intervals cannot be determined based on a single test; however, the values are 

generally consistent with the average engine-out results obtained during testing with the ECS. 

N/A = Not applicable 

Although the average tailpipe NOx emissions of 0.095 g/mi were higher than the regulated 

emissions standard of 0.07 g/mi, the difference was not statistically significant. Nevertheless, 

the reduction efficiency of 97.8% relative to engine-out without EGR was encouraging. That is, 

even though the NOx emissions target was not reached, the high-efficiency performance of the 

ECS showed promise for this technology. With more control over the engine controls and 

combustion process engine out emissions levels could be reduced to a level where these NOx 

conversion efficiencies would lead to a system that would meet the project goals. Average 

NMHC emissions of 0.165 g/mi were 83% higher than the applicable standard, again due to the 

100
use of the diesel fuel burner. It is anticipated that a production system with finer thermal 

management control and lower engine-out NOx will not experience this problem. Average PM 

emissions were 50% lower than the applicable standard, well within the project’s emissions 

target. 

Figure 63 shows the average FTP composite NOx emissions and reduction efficiency relative to 

engine-out emissions without EGR during the first 300 hours of aging. The error bars on the 

emissions plot indicate the range of values observed among the duplicate or triplicate 

measurements. Prior to the first desulfurization there was no particular trend in tailpipe 

emissions; however, a trend is evident between 200 hours and 300 hours. Performance improved 

significantly following the desulfurization at 300 hours. This is discussed more fully in 

Section 4.2. 

NOx Reduction Efficiency 

90% 

92% 

94% 

96% 

98% 

100% 

0 50 100 150 200 250 300 350 

Age (hours) 

NOx Reduction 

FTP Composite (D15) FTP Composite (BP15) Standard-D 15 

Desulfurization 

NOx Emissions 

0.0 

0.1 

0.2 

0.3 

0.4 

0.5 

0 50 100 150 200 250 300 350 

Age (hours) 

Catalyst Out

NOx (g/mi) 

FTP Composite (D15) FTP Composite (BP15) 

Desulfurization 

Figure 63. NOx Composite FTP emissions and reduction efficiency during the first 300 

hours of aging 

Figure 64 displays the average NOx emissions and reduction efficiency relative to engine-out 

without EGR for each of the four test cycles. Generally there are similar patterns among the four 

test cycles; however, the US06 emissions are consistently higher. Strong evidence that NOx 

emissions from the US06 and HFET tests were increasing prior to the first desulfurization event 

at 200 hours was also observed. This is likely due to the fact that the catalyst used during the 

aging portion of the testing were not de-greened, and their performance had not stabilized at this 

early point in the aging process. 

101
NOx Reduction Efficiency 

75% 

80% 

85% 

90% 

95% 

100% 

0 50 100 150 200 250 300 350 

Age (hours) 

NOx Reduction 

Cold UDDS (D15) Hot UDDS (D15) US 06 (D15) HFET (D15) 

Cold UDDS (BP15) Hot UDDS (BP15) US 06 (BP15) HFET (BP15) 

NOx Emissions 

0.0 

0.3 

0.6 

0.9 

1.2 

1.5 

0 50 100 150 200 250 300 350 

Age (hours) 

Catalyst Out

NOx (g/mi) 

Cold UDDS (D15) Hot UDDS (D15) US 06 (D15) HFET (D15) 

Cold UDDS (BP15) Hot UDDS (BP15) US 06 (BP15) HFET (BP15) 

Desulf urization 

Figure 64. NOx emissions and NOx reduction efficiency during the Cold-Start UDDS, HotStart UDDS, US06, and HFET test cycles over the first 300 hours of aging 

Figure 65 shows the average FTP composite emissions of NMHC, CO, and PM, and fuel 

economy during the first 300 hours of aging. Except for a slight increase in CO after 100 hours, 

there were no significant trends. Also, the desulfurization events at 200 and 300 hours had no 

impact on these emissions or fuel economy. 

102
NMHC Emissions 

0.0 

0.1 

0.2 

0.3 

0.4 

0.5 

0 50 100 150 200 250 300 350 

Age (hours) 

Catalyst Out

NMHC (g/mi) 

FTP Composite (D15) FTP Composite (BP15) 

PM Emissions 

0.000 

0.003 

0.006 

0.009 

0.012 

0.015 

0 50 100 150 200 250 300 350 

Age (hours) 

Catalyst Out

PM (g/mi) 

FTP Composite (D15) FTP Composite (BP15) 

Fuel Economy 

14.0 

14.5 

15.0 

15.5 

16.0 

16.5 

0 50 100 150 200 250 300 350 

Age (hours) 

Catalyst Out

FE (mi/gal) 

FTP Composite (D15) FTP Composite (BP15) 

CO Emissions 

0.0 

0.1 

0.2 

0.3 

0.4 

0.5 

0 50 100 150 200 250 300 350 

Age (hours) 

Catalyst Out

CO (g/mi) 

FTP Composite (D15) FTP Composite (BP15) 

Figure 65. Composite FTP emissions of NMHC, CO, and PM and fuel economy during the 

first 300 hours of aging 

4.2 Aging and Desulfurization (300 to 2,000-hours) 

This section addresses the impact of 2,000-hours of aging and sulfur accumulation on ECS 

performance and the effectiveness of periodic desulfurizations for restoring NOx reduction 

performance. The long-term impact on regulated emissions and fuel economy are also 

described. The following study questions are addressed: 

Q2.1 How do NOx emissions change as the system ages? Specifically, how do the maximum 

(pre-desulfurization), minimum (post-desulfurization), and average NOx levels change? 

Q2.2 Is the increase in NOx emissions between consecutive desulfurizations constant over 

time? 

Q2.3 How effective is desulfurization at restoring the initial NOx reduction performance of the 

system (initially and over time)? 

Q2.4 Does the performance of the system stabilize within the first 2,000-hours? If so, at what 

point does this occur? 

103
Q2.5 Are there temporal trends with respect to other regulated emissions or fuel economy? 

The durability portion of the study was conducted using the D15 fuel during aging, as well as for 

the evaluations performed immediately before and after the desulfurization events. These events 

were scheduled every 100 hours. Each evaluation consisted of a duplicate or triplicate series of 

motoring dynamometer engine tests, each emulating a Cold-Start UDDS followed by Hot-Start 

UDDS, US06, and HFET duty cycles. 

4.2.1 Average NOx Emissions and Reduction Efficiency over 2,000-hours 

The results are summarized in Figure 66. The upper graph shows the average NOx FTP 

composite emissions for each evaluation. The vertical lines identify the desulfurization events, 

and the error bars denote the minimum and maximum measurements within each evaluation 

period. The lower graph displays the same results in terms of NOx reduction efficiency relative 

to engine-out emissions both with and without EGR. The Tier 2 Bin 5 NOx emissions standard 

of 0.07 g/mi corresponds to a target NOx reduction efficiency of 98.4% relative to engine-out 

without EGR and 96.7% relative to engine-out with EGR. 

0.0 

0.2 

0.4 

0.6 

0.8 

1.0 

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

NOx (g/mi) 

Desulfurization NOx Mean 

0.07 g/mi 

80% 

84% 

88% 

92% 

96% 

100% 

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

EO without EGR 

59% 

67% 

75% 

83% 

92% 

100% 

NOx Reduction Efficiency with

Respect to

EO with EGR 

NOx Mean Standard Desulfation 

NOx Reduction Efficiency with

Respect to

Figure 66. NOx emissions (FTP composite) and NOx reduction efficiency versus ECS age 

(vertical lines identify desulfurization events) 

104
These plots show that NOx reduction efficiency decreases during the first 1,000 hours of aging. 

Initially the reduction efficiency relative to engine-out without EGR is relatively steady at 98%; 

however, by 1,000 hours the efficiency ranges from 84% immediately before the desulfurization 

event to about 90% immediately after the event. 

4.2.2 Performance Degradation and Desulfurization Effectiveness 

Figure 67 illustrates the degradation in catalyst performance between desulfurizations and the 

effectiveness of the desulfurization process at restoring performance. The upper graph 

demonstrates that the loss in NOx reduction efficiency (FTP composite) between desulfurizations 

is generally about 6% of the engine-out without EGR emissions, with a slight trend ranging 

between 4% and 6%. The lower graph demonstrates that there is also a 6% improvement in NOx 

reduction efficiency at each desulfurization event, with a slight trend ranging between 3% and 

6%. Although these trend lines, based on log-linear models, show slight changes in NOx 

reduction efficiency, the slopes of the regression lines were not statistically different from zero. 

Combined, these graphs indicate that the desulfurization process generally compensates for the 

increased degradation in catalyst performance between desulfurizations throughout the 2,000­

hour test. Nevertheless, the cumulative effect of the initial 1% change between desulfurizations 

was found to be significant as is shown in the following analysis. 

Change in NOX Reduction Efficiency (% of Engine Out NOX) Between Desulfurizations 

0.0% 

-2.0% 

-4.0% 

-6.0% 

-8.0% 

-10.0% 

-12.0% 

-14.0%

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

Age (hours) 

Difference Difference Trend 

10.0% 

8.0% 

6.0% 

4.0% 

2.0% 

0.0% 

-2.0%

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

Age (hours) 

Difference (Post-Pre) Difference Trend 

NOX Reduction Efficiency NOX Reduction Efficiency 

Increase in NOX Reduction Efficiency (% of Engine Out NOX) at Each Desulfurization 

Figure 67. Effectiveness at desulfurization and deterioration of the catalyst between 

desulfurizations for FTP composite NOx emissions compared to aging hours (Trends for 

these were not statistically significant.) 

The overall trends in FTP composite NOx emissions between 300 and 2,000 hours of aging were 

also modeled using a log-linear model, as shown in the upper graph in Figure 68. To account for 

105
the effects of the desulfurization process, separate models were fit to three sets of NOx emissions 

data: (1) measurements made before a desulfurization event, (2) measurements made after a 

desulfurization event, and (3) the average of measurements made at the beginning (postdesulfurization) and end (pre-desulfurization) of each 100-hour aging period. The latter results, 

plotted at the midpoint of the aging period, represent the best estimate of the average emissions 

over time; however, we could not verify that the increase in NOx emissions within an aging 

period is linear. The lower graph in Figure 68 shows the same trends in terms of NOx reduction 

efficiency relative to engine-out with and without EGR. All three of the regression lines shown 

in Figure 68 were found to have statistically significant trends at the 95% confidence level. 

0.0 

0.2 

0.4 

0.6 

0.8 

1.0 

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

NOx (g/mi) 

Pre Desulfurization Average Post Desulfurization 

Pre Trend Average Trend Post Trend 

80% 

84% 

88% 

92% 

96% 

100% 

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

NOx Reduction Efficiency with

Respect to EO

without EGR 

59% 

67% 

75% 

83% 

92% 

100% 

NOx Reduction Efficiency with

Respect ro EO

with EGR 

Pre Desulfurization Average Post Desulfurization 

Pre Trend Average Trend Post Trend 

Figure 68. NOx emissions (FTP composite) and NOx reduction efficiency (FTP composite) 

versus ECS age with statistical trend lines: pre-desulfurization, post-desulfurization, and 

average results 

4.2.3 Determination of System Stabilization 

Additional analyses were performed to determine if there were persistent trends in emissions 

results over time. As illustrated in Figure 69, this analysis was accomplished by iteratively 

truncating the left-most data from each of the three data sets, refitting the regression model, and 

evaluating the significance of the regression slope parameter. This analysis determined that the 

trends are not statistically significant after 800 to 900 hours of aging. 

106
0.0 

0.2 

0.4 

0.6 

0.8 

1.0 

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

NOx (g/mi) 

Pre Desulfurization Average Post Desulfurization 

Pre Trend Average Trend Post Trend 

80% 

84% 

88% 

92% 

96% 

100% 

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

NOx Reduction Efficiency 

Pre Desulfurization Average Post Desulfurization 

Pre Trend Average Trend Post Trend 

Figure 69. Statistical trends in FTP composite NOx emissions and NOx conversion at predesulfurization, post-desulfurization, and midpoint between desulfurizations are not 

statistically significant after 800, 900, and 850 hours, respectively 

4.2.4 Trends in Other Regulated Emissions and Fuel Economy 

Figures 70 to 74 display the trends in the other average FTP composite regulated emissions of 

NMHC; percent NMHC in THC, CO, and PM; and fuel economy for each data set versus time. 

There were some anomalies in the data. For example, at 700 hours, there was a spike in NMHC 

pre- and post-desulfurization measurements; between 700 and 800 hours, CO was relatively 

elevated and FE was relatively low; and between 1,100 and 1,200 hours, CO was relatively low. 

Despite these anomalies, the fitted curves representing average emissions or fuel economy at the 

beginning, midpoint, and end of each 100-hour aging period are virtually identical, indicating 

that sulfur accumulation on the catalyst has no effect on these emissions. Using the same 

iterative approach described above, we found that there are statistically significant trends in 

NMHC and CO emissions through 1,400 hours; but there are no trends in PM emissions. Percent 

NMHC and fuel economy increase steadily through about 1,100 hours. 

107
0.0 

0.1 

0.2 

0.3 

0.4 

0.5 

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

NMHC (g/mi) 

Pre Desulfurization Average Post Desulfurization 

Pre Trend Average Trend Post Trend 

Figure 70. FTP composite NMHC emissions compared to aging hours: preDesulfurization, post-desulfurization, and average results (Trend is statistically 

significant through 1,400 Hours.) 

0% 

10% 

20% 

30% 

40% 

50% 

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

Percent NMHC 

Pre Desulfurization Average Post Desulfurization 

Pre Trend Average Trend Post Trend 

Figure 71. FTP composite percent NMHC emissions compared to aging hours: predesulfurization, post-desulfurization, and average results (Trend is not statistically 

significant after 1,100 hours.) 

0.75 

0.60 

0.00 

0.15 

0.30 

0.45 

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

CO (g/mi) 

Pre Desulfurization Average Post Desulfurization 

Pre Trend Average Trend Post Trend 

Figure 72. FTP composite CO emissions compared to aging hours: pre-desulfurization, 

post-desulfurization, and average results (Trend is statistically significant through 1400 

hours.) 

108
0.000 

0.002 

0.004 

0.006 

0.008 

0.010 

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

PM (g/mi) 

Pre Desulfurization Average Post Desulfurization 

Pre Trend Average Trend Post Trend 

Figure 73. FTP composite PM emissions compared to aging hours: pre-desulfurization, 

post-desulfurization, and average results (Trend is not statistically significant.) 

14.0 

14.4 

14.8 

15.2 

15.6 

16.0 

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 

Age (hours) 

FE (mi/gal) 

Pre Desulfurization Average Post Desulfurization 

Pre Trend Average Trend Post Trend 

Figure 74. FTP composite FE compared to aging hours: pre-desulfurization, postdesulfurization, and average results (Trend is statistically significant through 1100 

hours.) 

Table 24 compares the average composite FTP emissions from the seven engine-out tests (six 

without EGR and one with EGR) with the estimated FTP composite emissions measured at 1950 

hours. The 1,950-hour estimates were based on the regression model derived from the 

measurements taken between 350 and 1,950 hours. For each estimate, 95% confidence intervals 

are provided. As before, emission reductions were calculated relative to engine-out with and 

without EGR. The reductions in NOx, CO, and PM emissions due to the ECS were all 

statistically significant, as was the reduction in fuel economy (16.0% relative to engine-out 

without EGR and 13.9% relative to engine-out with EGR). 

109
Table 24. Average Engine-Out and Estimated 1,950-Hour Average Tailpipe Composite 

FTP Regulated Emissions and Fuel Economy—with 95% Confidence Intervals 

Engine Out Tailpipe Average (1950 Hours) w/ EGR 

Emission 

Parameter Unit EGR Average1 

95% 

Confidence 

Interval Average2 

95% 

Confidence 

Interval 

Percent 

Reduction 

Regulated 

Emission 

Standard3 

Without 4.38 (4.34, 4.42) 85.9% NOX g/mi 

With 2.12 -

4 0.616 (0.558, 0.675) 

70.9% 

0.07 

Without 0.20 (0.19, 0.207) -87.6% NMHC g/mi 

With no data -

0.372 (0.349, 0.395) 

-

0.09 

Without 0.20 (0.194, 0.213) -257.8% THC g/mi 

With 0.26 -

0.730 (0.695, 0.764) 

-176.2% 

N/A 

Without 2.02 (1.85, 2.18) 69.3% CO g/mi 

With 4.43 -

0.620 (0.571, 0.669) 

86.0% 

4.2 

Without 0.07 (0.056, 0.074) 91.8% PM g/mi 

With 0.15 -

0.005 (0.005, 0.006) 

96.3% 

0.01 

Fuel Without 18.40 (18.2, 18.6) 16.0% 

Economy 

mi/gal With 17.95 -

15.453 (15.312, 15.594) 

13.9% 

N/A 

1 Engine-out average without EGR is based on 6 tests; engine-out average with EGR is based on 1 test. 

2 Estimates based on the regression model derived from measurements taken between 350 and 1,950 

 hours. 

3 Tier 2 Bin 5 full useful life 

4 Confidence intervals cannot be determined based on a single test; however, the values are generally

 consistent with the average engine-out results obtained during testing with the ECS.

 N/A = Not applicable 

4.2.5 Soluble Organic Fraction and Sulfate Emissions 

Figure 75 displays the average emissions of sulfate measured in PM samples collected at the 

beginning and end of alternate 100-hour aging cycles. Results are presented for each of the four 

test cycles (Cold-Start UDDS, Hot-Start UDDS, US06, and HFET) as well as the calculated FTP 

composite. The average emissions of sulfate are fairly consistent across the four transient cycles; 

however, there appears to be an increasing trend in Composite FTP sulfate emissions starting at 

approximately 1,400 hours. The apparent decrease in sulfate measurements between 400 and 

900 hours is due to measurements at or below the detection limits due to high background levels 

during this period. Over the whole program, the sulfate emissions only account for about 1% of 

the total PM mass, which were all below 0.10 g/mi. The apparent upward trend in sulfate 

emissions in the 1,500- to 2,000-hour range, while not significant, may be due to the release of a 

small amount stored sulfur in the catalysts. 

110
Engine Out 

SO4 (mg/mi) 

SO4 Emissions 

0.00 

0.07 

0.14 

0.21 

0.28 

0.35 

0.00 

0.02 

0.04 

0.06 

0.08 

0.10 

Figure 75. Sulfate emissions (Cold-Start UDDS, Hot-Start UDDS, US06, HFET, and FTP 

composite) versus ECS age (vertical lines identify desulfurization events) 

Figure 76 displays the average percentage of SOF emissions measured in PM samples collected 

at the beginning and end of alternate 100-hour aging cycles. Results are presented for each of the 

four test cycles (Cold-Start UDDS, Hot-Start UDDS, US06, and HFET) as well as the calculated 

FTP composite mode. Average emissions of SOF are fairly consistent across the four transient 

cycles, and the average emissions of Composite FTP SOF are fairly consistent at approximately 

80% after the desulfurization at 400 hours. 

111

Age (hours) 

EO/Cold UDDS(D15) EO/Hot UDDS(D15) EO/US 06(D15) EO/HFET(D15) 

EO/Cold UDDS(BP15) EO/Hot UDDS(BP15) EO/US 06(BP15) EO/HFET(BP15) 

Cold UDDS (D15) Hot UDDS (D15) US 06 (D15) HFET (D15) 

Cold UDDS (BP15) Hot UDDS (BP15) US 06 (BP15) HFET (BP15) 

Composite FTP SO4 Emissions 

0.00 

0.07 

0.14 

0.21 

0.28 

0.35 

-50

0

50

100150200250300350400450500550600650700750800850900950

1000105011001150120012501300135014001450150015501600165017001750180018501900195020002050 

Age (hours) 

Engine Out 

SO4 (mg/mi) 

0.00 

0.02 

0.04 

0.06 

0.08 

0.10 

Catalyst Out

SO4 (mg/mi) 

EO/FTP Composite (D15) EO/FTP Composite (BP15) 

FTP Composite (D15) FTP Composite (BP15) 

EO -50

0

50

100150200250300350

EO 

400450500550600650700750800850900950

1000105011001150120012501300135014001450150015501600165017001750180018501900195020002050 

Catalyst Out

SO4 (mg/mi)
Engine Out

Percent SOF 

Percent SOF Emissions in Composite PM 

0% 

20% 

40% 

60% 

80% 

100% 

0% 

20% 

40% 

60% 

80% 

100% 

Figure 76. Percent SOF emissions (Cold-Start UDDS, Hot-Start UDDS, US06, HFET, and 

FTP composite) versus ECS age (Vertical lines identify desulfurization events.) 

4.3 Sulfur Mass Balance 

Understanding the mechanisms by which sulfur from the fuel and lubricants interacts with the 

ECS is important for designing an effective and durable system. This section presents a mass 

balance approach to gain insight on the disposition of sulfur in the system. The following study 

questions are addressed: 

Q3.1 How much sulfur is emitted during the desulfurization process? 

Q3.2 How does the amount of sulfur emitted during the aging cycle compare to the amount 

emitted during the desulfurization process? Do these rates change over time? 

Q3.3 What happens to the differences between these amounts? 

Although there were no plans to routinely monitor sulfur emissions during aging or 

desulfurization events, special tests were performed periodically to measure the mass of SO2 and 

H2S emitted during desulfurization events. These results were used to estimate total sulfur 

accumulation on the catalysts for comparison with estimated engine-out emissions based on 

measured fuel and oil consumption. 

As described in Section 3.3, measurements of SO2 and H2S were made during the desulfurization 

events at 1,300 and 1,400 hours. The SO2 measurements are believed to be accurate; however, it 

was suspected that a significant portion of the H2S emissions was not captured. Therefore, the 

112

650700750800850900

Percent Composite FTP SOF Emissions in Composite PM 

0% 

20% 

40% 

60% 

80% 

100% 

-50

0

50

100150200250300350400450500550600650700750800850900950

1000105011001150120012501300135014001450150015501600165017001750180018501900195020002050 

Age (hours) 

Engine Out

Percent SOF 

0% 

20% 

40% 

60% 

80% 

100% 

Catalyst Out 

Percent SOF 

EO/FTP Composite (D15) EO/FTP Composite (BP15) 

FTP Composite (D15) FTP Composite (BP15) 

EO 

Age (hours) 

EO/Cold UDDS(D15) EO/Ho t UDDS(D15) EO/US 06(D15) EO/HFET(D15) 

EO/Cold UDDS(BP15) EO/Hot UDDS(BP15) EO/US 06(BP15) EO/HFET(B P15) 

Cold UDDS (D15) Hot UDDS (D15) US 06 (D15) HFET (D15) 

Cold UDDS (BP15) Hot UDDS (BP15) US 06 (BP15) HFET (BP15) 

-50

0

50

100150200250300

EO 

350400450500550600950

1000105011001150120012501300135014001450150015501600165017001750180018501900195020002050 

Catalyst Out

Percent SOF
sampling method for H2S was modified before it was used again during the 1,600-hour 

desulfurization event. 

The calculations summarized in Table 25 demonstrate that nearly all of the sulfur emitted during 

the 100-hour aging cycle, as estimated by measured fuel and oil properties and consumption 

rates, is accounted for by the measured emissions of SO2 and H2S. 

Table 25. Sulfur Mass Balance between Engine-Out and Desulfurization Emissions 

Catalyst 

Measured Sulfur Mass from 

Desulfurization Events (g) 

Estimated Sulfur Mass 

from Engine-Out 

Emissions 

(g/100 hrs) 

Percent 

Recovery 

Average 

SO2 

(note 1) 

Average 

H2S 

(note 2) 

Total 

Sulfur 

Sulfur 

from 

Oil3 

Sulfur 

from 

Fuel4 

Total 

Sulfur 

NAC1 0.720 5.004 5.068 1.008 5.025 6.033 84% 

NAC2 0.786 7.199 7.167 1.008 5.025 6.033 119% 

Total 1.506 12.203 12.235 2.016 10.05 12.066 101% 

1 Average SO2 measured during 1,300- and 1,400-hour desulfurizations using measurement methods described in 

Section 2.2.3 

2 Average H2S measured during 1,600-hour desulfurization using modified methods (See Section 3.3.) 

3 Oil consumption = 0.0035 liter/hr. Oil density = 0/9kg/liter. Sulfur concentration = 6,400 ppm. Assumes equal 

exposure to the two catalysts. 

4 Fuel consumption = 6.7 kg/hr. Sulfur concentration = 15 ppm. Assumes equal exposure to the two catalysts. 

Tailpipe emissions of SO2 and H2S were not routinely measured, except as part of the 

unregulated emissions tests performed at 100, 300, 900, 1,500, and 2,000-hours. H2S levels were 

consistently below the detection limits of the analytical method. SO2 levels were measured at 

less than 0.5 mg/mi, which corresponds to less than 0.025 grams of sulfur per 100 miles. This is 

consistent with achieving an estimated 100% recovery of sulfur from the desulfurization events. 

4.4 Fuel Effects on Regulated Emissions (D15 vs. BP15) 

Two different ultra-low-sulfur diesel fuels, ranging from 3 ppm to 30 ppm, were tested. This 

section investigates whether the fuels or fuel sulfur levels have direct impacts on regulated 

emissions or fuel economy. The following study questions are addressed: 

Q4.1 Are there differences in emissions from DECSE and BP fuels? 

Q4.2 If such differences exist, are they consistent over time? 

Analysis of variance models were used to compare the two test fuels in terms of the average 

emissions of NOx, hydrocarbon, PM, and fuel economy. The model was used to calculate 

average emissions for each combination of fuel type, aging time, and test cycle (Cold-Start 

UDDS, Hot-Start UDDS, US06, and HFET). A 95% confidence interval was computed for each 

estimate in order to assess the differences between the fuels. 

113
Figure 77 displays the average NOx emissions with BP15 and D15 fuels at 100, 300, 900, 1,500, 

and 2,000 hours of testing under the FTP composite, Cold-Start UDDS, Hot-Start UDDS, US06, 

and HFET test cycles. The error bars represent 95% confidence bounds on the estimated average 

emissions. Statistical tests were performed to determine if the differences in average emissions 

at various combinations of test cycles and aging times were statistically significant. While there 

were a few instances in which the differences were statistically significant, there was no 

consistent pattern over time. Similar comparisons were performed on the PM and NMHC 

emissions and fuel economy. Again, there were no consistent patterns in the differences in 

emissions or fuel economy between tests run on the two fuels. 

114
Cold LA4 

0.0 

0.1 

0.2 

0.3 

0.4 

0.5 

BP15 D15 BP15 D15 BP15 D15 BP15 D15 BP15 D15 

100 300 Pre 900 Post 1500 Post 2000 Post 

Fuel / Age (hours) 

NOx (g/mi) 

Hot LA4 

0.00 

0.16 

0.32 

0.48 

0.64 

0.80 

BP15 D15 BP15 D15 BP15 D15 BP15 D15 BP15 D15 

100 300 Pre 900 Post 1500 Post 2000 Post 

Fuel / Age (hours) 

NOx (g/mi) 

US06 

0.3 

0.5 

0.7 

0.9 

1.1 

1.3 

1.5 

BP15 D15 BP15 D15 BP15 D15 BP15 D15 BP15 D15 

100 300 Pre 900 Post 1500 Post 2000 Post 

Fuel / Age (hours) 

NOx (g/mi) 

HFET 

0.1 

0.2 

0.3 

0.4 

0.5 

0.6 

BP15 D15 BP15 D15 BP15 D15 BP15 D15 BP15 D15 

100 300 Pre 900 Post 1500 Post 2000 Post 

Fuel / Age (hours) 

NOx (g/mi) 

LA4 Composite 

0.00 

0.12 

0.24 

0.36 

0.48 

0.60 

BP15 D15 BP15 D15 BP15 D15 BP15 D15 BP15 D15 

100 300 Pre 900 Post 1500 Post 2000 Post 

Fuel / Age (hours) 

NOx (g/mi) 

Figure 77. Average NOx emissions with 95% confidence intervals by fuel type and ECS 

age 

115
4.5 Discussion of Technical Problems and Remedial Actions 

A number of different problems arose during the course of the program. Some of the main 

problems encountered and the solutions devised are discussed below. In addition, some 

proposed modifications for improved performance of the design/strategy utilized are also 

discussed. 

4.5.1 Second-Generation Emission Control System Components 

The initial system evaluated (first-generation System B shown in Figure 78) utilized relatively 

small-diameter (14.4-cm diameter, 7.6-cm length), high precious metal content oxidation 

catalysts mounted upstream of each NAC and upstream of the DPF (15.2-cm length). The intent 

for these catalysts was to break down the diesel fuel used as a reductant into smaller (more NAC 

friendly) hydrocarbons and CO. The oxidation catalyst upstream of the DPF was intended to 

minimize any hydrocarbon slip resulting from “overfueling” during regeneration. 

Due to the high level of NOx reduction required to meet the program goal, it was anticipated that 

overfueling would be needed to ensure maximum NOx reduction under all possible regeneration 

conditions. While the small diameter (14.4-cm) pre-NAC oxidation catalysts produced high 

levels of CO upon in-exhaust injection (greater than 3% into the NAC), they caused 

unacceptably high engine exhaust back pressure during high-load conditions due to their small 

frontal area. As a result, the designated ECS supplier provided new oxidation catalysts (identical 

loading, but 24.1-cm in diameter and 7.6-cm length) which were delivered in late June 2003. 

Figure 79 shows the second-generation System B utilizing the new components. 

The new oxidation catalysts resulted in a significant volume increase (3.8 times), adding 

additional thermal mass upstream of the NACs. As all strategy development/optimization had 

been performed on the first-generation system, the additional volume and mass of the secondgeneration, pre-NAC oxidation catalysts introduced a number of issues related to the ECS 

performance. 

Due to the increased pre-NAC oxidation catalyst mass, substantially more heat was required 

from the burner to quickly bring the ECS to operating temperature following a cold start. This 

requirement led to increased THC emissions from the burner as it was being operated at its 

upper-functional limit. The EGR calibration was also modified at idle conditions in an effort to 

transfer more heat to the pre-NAC oxidation catalysts through increased exhaust mass flow. 

116
EGR 

VALVE 

6600 Duramax 

INTAKE 

THROTTLE 

AIR 

FILTER 

Air Charge Cooler 

SFI 

SFI 

Diesel Fuel 

Burner 

DPF 

DPF 

#1 OC NAC

F

#1C

DPF 

#1 OC NAC

F 

#1C

OC

Figure 78. First-generation System B 

117
EGR 

VALVE 

6600 Duramax 

INTAKE 

THROTTLE 

AIR 

FILTER 

Air Charge Cooler 

SFI 

SFI 

Diesel Fuel 

Burner 

SFI 

OC DPF 

DPF OC N#1AC 

DPF OC N#1AC 

Figure 79. Second-generation System B 

During warmed-up, transient operation, the second-generation system exhibited higher levels of 

NOx reduction than the first-generation system; however, during the aging portion of the cycle, 

plugging of the oxidation catalysts was observed, as shown in Figure 80. As this phenomenon 

was not observed with the first-generation system, it appeared that the combination of increased 

thermal mass and reduced space velocity due to the larger pre-NAC oxidation catalysts had an 

undesirable effect. 

The cause for the plugging was theorized to result from low temperatures at the edge of the 

catalyst when fuel was injected during regeneration. At low-load, low-temperature exhaust 

conditions (i.e., idle), if a regeneration was initiated (preceded by burner preheating), insufficient 

heat was transferred to the periphery of the pre-NAC oxidation catalyst, resulting in an 

interaction between the raw fuel and PM present in the exhaust, causing a carbonaceous buildup 

on the face of the catalyst. After this buildup or face plugging began, it continued growing 

inward, even if the catalyst was brought to temperatures in excess of 600°C during the aging 

cycle. 

In an attempt to minimize or eliminate the face plugging, the order of the aging cycle modes was 

modified prior to the 500-hour aging block to eliminate extended periods at low exhaust 

temperature (i.e., idle followed by low-load, low-speed conditions). In addition, the burner 

118
preheating time was slightly increased in an attempt to raise the pre-NAC bed temperature. 

Using a combination of these approaches, the face plugging was reduced, but not completely 

eliminated. Face plugging of the pre-NAC oxidation catalyst continued to be a problem 

throughout the program, specifically in Leg 2, which required cleaning approximately every 50 

hours. The pre-NAC oxidation catalyst in Leg 1 was cleaned as a precautionary measure every 

100 hours, even though it typically showed minimal plugging/edge discoloration after this 

duration. 

Thermocouple 

Substrate 

Cell 

Plugging 

Figure 80. Face plugging of pre-NAC oxidation catalyst 

In addition to the pre-NAC oxidation catalyst face plugging observed with the second-generation 

components, the DPF was no longer passively regenerating during the aging cycle. The exact 

cause of this problem was unknown; however, the increased efficiency of the second-generation, 

pre-NAC oxidation catalysts and NACs may have contributed to this problem, significantly 

reducing the amount of NO/NO2 available for PM oxidation in the DPF. A third in-exhaust 

119
injector was added to the system to ensure continuous regeneration of the DPF by raising its 

operating temperature. As this problem arose fairly late in the program, no optimization of the 

DPF regeneration fuel usage was performed. Sufficient fuel was provided to ensure that the DPF 

reached at least 625°C during the steady-state portion of the aging cycle. This third, in-exhaust 

injector was utilized only during the aging cycle and increased fuel consumption by 

approximately 8% (the fuel used by this injector was not included when calculating the total fuel 

sulfur exposure of the NACs during aging). This injector was activated for approximately 

1 second out of every 7 seconds during the aging cycle (14% duty cycle). 

The new, larger pre-NAC oxidation catalysts also required increased burner run time prior to a 

burner-assisted regeneration in order to raise the temperature of the larger thermal mass. This 

change led to occasional high-temperature spikes (850°C) in the pre-NAC oxidation catalysts 

when the exhaust flow rate was suddenly lowered during a regeneration preheating cycle (e.g., 

deceleration to an idle period). Upon the next increase in exhaust flow (i.e., acceleration), the 

temperature “wave” within the pre-NAC oxidation catalyst was passed on to the NAC (albeit 

with a reduced peak temperature typically no greater than 550°C), often resulting in thermal 

desorption of NO2 from the NAC. 

4.5.2 Diesel-Fueled Burner 

The diesel-fueled burner described earlier was a laboratory-built unit fabricated within the 

limited time frame of this program. As a laboratory prototype the unit experienced multiple 

failures during the 2,000-hour aging portion of the program. A maintenance schedule was 

developed in order to minimize burner system component failure and its subsequent effect on the 

system performance. 

The electrodes were found to be the weakest component of the burner and were replaced after 

every 100-hour aging block, regardless of whether or not they exhibited cracking. Cracked 

electrodes led to burner misfires, which, if they occurred during an emission test, invalidated the 

test (and required repeating the entire prep sequence). Thus, the electrodes were replaced prior 

to beginning a sequence of emission tests after aging. 

The silicon carbide foam used as a flame holder also exhibited poor durability related to the 

mounting system. As a result, the foam was only used during the emission tests and removed for 

aging. The fuel injector in the burner also required periodic cleaning (approximately every 500 

hours of operation) to maintain its spray pattern. 

The fuel pumps used to supply the necessary 470kPa of pressure to the burner and in-exhaust 

injectors suffered failures after 1,000 to 1,200 hours of total run time. These failures led to no 

fuel being injected during regeneration, in the case of the in-exhaust injectors, or complete 

misfires of the burner, resulting in no additional heat being added to the system. 

The current-to-pressure regulator used for controlling the airflow to the burner failed due to the 

presence of water in the air system between the 1,000-hour, pre- and post-desulfurization 

evaluations. This failure led to intermittently reduced burner airflow that resulted in “dirty” 

burner operation and intermittent misfires. 

120
4.5.3 In-Exhaust Injectors 

The water-cooled, in-exhaust injectors also exhibited durability problems during the aging 

portion of the program. PM would collect on the tip of the injector, resulting in poor fuel 

distribution. The tips of the injectors were cleaned after every 100-hour aging block as part of 

routine maintenance. 

There appeared to be some cross talk between the two exhaust legs during a regeneration (i.e., 

fuel injected into the regenerating leg would also be observed in the opposite leg). Placing the 

exhaust flow control valves upstream of the in-exhaust injection probably would have eliminated 

this problem. However, the durability of the valves in this position would have been 

questionable. 

4.5.4 Exhaust System and Flow Maldistribution 

The prototype, hand-fabricated, air-gap exhaust manifolds failed after 800 hours of aging, 

causing damage to the turbocharger, necessitating a replacement. As no air-gap manifold 

replacements were readily available, the stock, cast iron exhaust manifolds were reinstalled. As 

the diesel-fueled burner supplied the majority of temperature to the ECS for the configuration 

utilized, no significant change in ECS performance was observed due to this change. 

The dual-leg exhaust configuration had an inherent flow distribution problem. As the exhaust 

from the engine encountered the burner flow stream orthogonally, the exhaust mass flow rate 

affected the burner distribution to the two exhaust legs. At low engine exhaust flow rates, the 

burner output was relatively well distributed to the two exhaust legs. However, at higher engine 

exhaust flow rates, the burner flow stream would be “converted” towards Leg 1, affecting the 

temperature and oxygen concentration in each leg prior to a burner-assisted regeneration. A total 

redesign and fabrication of the exhaust system would have been required to eliminate this issue. 

In order to minimize the effect of this maldistribution, the DOC/NAC combination was switched 

from one leg to the other every 100 hours of aging. 

The wiring for the exhaust valve position switch (used as feedback to the control system) was 

broken during one of the many NAC system position swaps (affecting the 148-hour emission 

evaluations). In an attempt to minimize fuel penalty during regeneration, this system was used to 

time the in-exhaust injection to avoid injecting fuel into the regenerating leg prior to the exhaust 

valve closing. A timer safety had been incorporated in the regeneration controller, so that if no 

valve closure signal was received 2 seconds after the valve closure command was issued, fuel 

was injected into the leg to be regenerated. No significant change in ECS performance was 

observed for the tests in which the valve position switch was inoperable. 

4.5.5 Particle Sampling 

Due to the extremely low levels of PM measured after the DPF, it was decided to sample 

multiple runs (two or three, depending on test matrix) of a particular test cycle (i.e., Cold-Start 

UDDS, Hot-Start UDDS, etc.) on a single 90-mm filter. While this approach doubled or tripled 

the mass collected on a single filter, it also introduced sample handling errors resulting from 

installing and removing the filter itself from the holder assembly multiple times. 

121
4.5.6 Engine-Related Components 

The stock EGR valve failed after 700 hours, most likely due to excessive temperatures found 

after the EGR cooler caused by the high levels of EGR demanded by the new calibration. The 

EGR cooler was cleaned when the EGR valve was replaced as a precautionary measure. A 

larger EGR cooler probably would have prevented the EGR valve failure. However, due to 

packaging constraints, a larger cooler was not installed. 

4.5.7 Test Cell Equipment 

The direct-current electric dynamometer used for simulating the vehicle load in the testing 

suffered an armature failure, necessitating replacement prior to the 248-hour emission 

evaluations. The replacement dynamometer was unable to perform at the same level, requiring 

modification to the control cycle and resulting in engine speeds higher than commanded during 

the high-load transient portion of the US06 cycle. 

4.5.8 Emission Control System Components/Regeneration Control System 

Performance 

As the ECS aged, the pre-NAC oxidation catalysts appeared to require higher operating 

temperatures to effectively break down the injected fuel needed for regeneration and to maintain 

their NO to NO2 reduction efficiency. However, at the same time, the NACs appeared to 

become more sensitive to higher temperatures after aging, thermally desorbing NO2 at 

temperatures above 450°C. 

Throughout the emission evaluations performed in this program, a large variation in test-to-test 

repeatability was observed. This variation became more pronounced as the aging progressed. . 

An analysis of the second-by-second data revealed that a large portion of this variability was 

attributable to differences in the timing of regenerations for a particular test cycle. As the NOx 

mass model target for regeneration is a “floating” variable (based on accumulated NOx mass 

upper and lower limits and operating mode), regeneration can occur at different times during a 

particular test cycle due to small differences in accelerator pedal position. In addition, the 

regeneration controller has a floating NOx mass target for regeneration, which is affected by 

mode type. 

As an example, the lower NOx mass limit for regeneration initiation is increased by 0.3 grams if 

the mode is identified as hard acceleration. The purpose of this strategy was to delay 

regeneration during less favorable modes (e.g., hard acceleration) and encourage it during more 

desirable modes (e.g., cruise). If the NOx mass model accumulation passed the 1.5-gram lower 

limit threshold, and the mode was “cruise,” regeneration would be initiated. However, if the 

mode was designated as “acceleration” or “hard acceleration” during this transition past 1.5 

grams of accumulated NOx, the regeneration would be delayed until the upper limit of the NOx 

mass window was reached, or the operating mode changed to one more favorable for 

regeneration (e.g., cruise). 

122
If a regeneration typically occurred immediately before a deceleration/idle period, a small 

change in engine operation could result in this particular regeneration being delayed until the 

next acceleration event. This change in timing could then affect the timing of subsequent 

regenerations. The efficiency of a particular regeneration is linked to the engine operating 

condition at the time the regeneration event is initiated. A change in the timing of a particular 

regeneration event could result in different exhaust flow rates, temperatures, and exhaust 

composition at the initiation of regeneration. All of these factors affect the efficiency of the 

regeneration event. In addition, a single incomplete regeneration could impact all subsequent 

regenerations as the NAC would not necessarily be at the same condition (level of loading) when 

the next regeneration was initiated. These factors all affected the test-to-test repeatability. 

An example of a difference in regeneration timing is shown for three repeat Hot-Start UDDS 

tests conducted after 1,500 hours of aging. In this case, Runs 1 and 2 had the first regeneration 

of the cycle occur for Leg 2 while the third test had its first regeneration occur on Leg 1. This 

resulted in significantly different regeneration timing for the three repeat tests with a subsequent 

impact in system NOx reduction efficiency. Figure 81 shows the NOx mass model accumulation 

for Leg 1 for the three repeat tests. In this figure, it can be seen that the “reset” of accumulated 

NOx mass (corresponding to a regeneration) for the third run occurred approximately 75 seconds 

into the cycle, while for Runs 1 and 2 the first regeneration for Leg 1 occurred approximately 

115 seconds after engine-start. This difference resulted in the Leg 1 regenerations for Run 3 

being “out of phase” with the regenerations for Runs 1 and 2, as shown in Figure 81. The 

resultant accumulated tailpipe NOx for the three “repeat” tests is shown in Figure 82. From this 

figure it can be seen that this difference in regeneration timing had a significant impact on the 

NOx reduction efficiency of the system. The timing of regenerations for Run 3 was obviously 

less favorable and resulted in higher tailpipe NOx mass. 

123
2.5 

Run #1 - Leg 1 NOx Mass Model 

Run #2 - Leg 1 NOx Mass Model 

2.0 

Run #3 - Leg 1 NOx Mass Model

1.5 

1.0 

0.5 

0.0 

0 200 400 600 800 1000 1200 1400

Time, seconds

Figure 81. NOx mass model accumulation for Leg 1 over Hot-Start UDDS NOX Mass Model, Leg 1 Accumulation, grams

 124
4 

5 

X Mass, grams 

Run #1 - TP NOx 

Run #2 - TP NOx 

Run #3 - TP NOx 

3 

2

Accumulated Tailpipe N

O

1 

0 

0 200 400 600 800 

Time, seconds 

1000 1200 1400 

Figure 82. Accumulated tailpipe NOx mass for three repeat runs after 1,500 hours of aging 

(post-desulfurization) for Hot-Start UDDS 

4.5.9 Possible Improvements to Emission Control System/Exhaust Configuration 

The extremely high levels of NOx reduction required to meet the program goals (99% over the 

FTP), and the low exhaust temperature (average of less than 165°C at the catalyst inlet location 

over the FTP), resulted in many system design constraints and requirements. The need for a 

fully functional ECS within seconds after engine-start required an auxiliary heating device 

(diesel-fueled burner) and the placement of this device immediately upstream of the NACs. In 

order to make use of the heat generated by the diesel-fueled burner, it was decided to place the 

DPF after the NACs. However, in this configuration the DPF did not assist in NO to NO2 

conversion, placing this burden on the pre-NAC oxidation catalysts and the NACs themselves. 

In addition, there was minimal NO2 available to the DPF for passive PM reduction due to the 

high level of NOx reduction required by the upstream NACs. 

An improved system design may have been to move the DPF upstream of the NACs and burner 

(as shown in Figure 83), utilizing in-cylinder post injection to provide heat to the DPF when 

needed for regeneration. This placement would allow the DPF to assist in NO to NO2 

conversion, allow passive regeneration at a lower temperature due to the increased NO2/PM 

ratio, and perhaps most importantly, act as a thermal capacitor. In the System B configuration, 

the pre-NAC oxidation catalysts and NACs themselves were subjected to large swings in exhaust 

temperature. This required activating the burner more frequently in order to ensure that the 

125
oxidation catalysts would be sufficiently active to break down the fuel injected during a 

regeneration. Placing the large DPF upstream of these components would significantly dampen 

these temperature fluctuations, helping maintain the oxidation catalysts and NACs at a more 

uniform temperature; however, the burner would still be required to rapidly heat the NACs to 

operating temperature after a cold start. 

For the test cell evaluations, the NOx mass model introduced significant variability from test to 

test due to its real-time determination of the need for regeneration. A fixed regeneration strategy 

versus time may have produced more repeatable results; however, this approach would 

essentially lock in the regeneration strategy for a given test cycle, being unrepresentative of 

actual in-use need. While the “cycle-beater” approach was advocated by some due to its more 

research-oriented perspective, the more production-like approach described was favored by the 

bulk of the steering committee. 

EGR 

VALVE

6600 Dur

a

max 

INTAKE 

THROTTLE 

AIR 

FILTER 

Air Charge Cooler 

EGR

VALVE

6600 Dur

a

max

INTAKE 

THROTTLE

AIR

FILTER

Air Charge Cooler

SFI 

SFI 

OC 

DPF 

DPF OCN#1 ACF N#1AC

DPF OCN#1 ACF 

Diesel Fuel N#1AC

Burner 

Figure 83. Possible improved system design configuration 

126
Section 5: Conclusions 

The goal of this project was to demonstrate the ability of an NAC/DPF ECS to meet Tier 2–Bin 5 

standards with FTP transient test limits of 0.07 g/mi NOx and 0.01 g/mi PM in an SUV/pick-up 

truck vehicle platform without producing unreasonably high emissions during other modes of 

operation. Additionally, hydrocarbon and CO emissions standards had to be met while 

minimizing impacts on fuel economy. 

The test was performed for 2,000-hours with evaluations performed before and after 

desulfurizations that were performed every 100 hours. The majority of the testing was performed 

with 15-ppm sulfur fuel developed for the DECSE program. Additionally, an 8-ppm sulfur fuel 

was evaluated. Unregulated emissions tests were performed; however, these results are to be 

presented in a separate report that incorporates findings from other APBF-DEC projects. 

Objectives 

The objectives of this project are to 

1. Demonstrate the emissions potential of advanced fuels, engines, and ECSs for meeting 

federal Tier 2–Bin 5 emissions standards 

2. Evaluate the effect of fuel sulfur level on emissions and fuel economy, ECS performance, 

and catalyst degradation. 

The federal standards, being implemented between 2004 and 2009, are as follows: PM of 0.01 

g/mi, NOx of 0.07 g/mi, and NMHC of 0.09 g/mi. These standards are to be met when testing 

over the FTP-75 test cycle at a full useful life of 120,000 miles. 

The following is a summary of the significant conclusions from the study. Further details are 

provided in Section 4 of the report. 

Initial Performance 

• During the first 200 hours of testing, tailpipe emissions of NOx averaged 0.095 g/mi (+/­

0.026 g/mi with 95% confidence) using the FTP composite test cycle. Although higher than 

the regulated emissions limit of 0.07 g/mi, the estimated NOx emissions were 97.8% lower 

than engine-out emissions without EGR and 95.5% lower than engine-out emissions with 

EGR. Figure 63 presents the NOx emissions and reduction efficiency results during the first 

300 hours of testing. 

• The ECS reductions in NOx (97.8%), CO (87.2%), and PM (91.6%) emissions were 

statistically significant, as was the reduction in fuel economy (18.7%). The 16.7% decrease 

in NMHC emissions (from 0.198 to 0.165 g/mi) was also statistically significant. Initial 

tailpipe emissions of CO and PM were below the regulated limits; however, the engine-out 

and tailpipe emissions of NMHC were above the Tier 2–Bin 5 limit of 0.09 g/mi. These test 

results are shown in Figure 65. 

127
Aging and Desulfurization 

• The loss in NOx reduction efficiency of the catalysts between consecutive desulfurization 

events increased slightly from 4% to 6% throughout the 2,000-hour test. However, the 

desulfurization process was effective at restoring catalyst performance. The desulfurization 

process produced an improvement in NOx reduction efficiency that changed from 3% at the 

beginning of the test to 6% at end of the 2,000-hour test. 

• Although there was a decrease in NOx reduction efficiency during the early aging periods, 

Figure 69 illustrates that the increase in NOx emissions—or decrease in NOx reduction 

efficiency—was not statistically significant after approximately 850 hours of testing. 

• There were statistically significant increases in NMHC and CO emissions, and fuel 

consumption during the 2,000-hour test; but there was no significant change in PM 

emissions. Table 24 compares the initial estimated engine-out regulated emissions and fuel 

economy (with and without EGR) with the estimated tailpipe emissions at 1,950 hours— 

midway between the last two desulfurization events. The system achieved emissions 

reduction efficiencies of 85.9% for NOx, 69.3% for CO, and 91.8% for PM. Fuel economy 

decreased by 16%, and NMHC emissions increased by 87.6% partially due to the use of the 

diesel fuel burner and the diesel fuel used as a reductant for catalyst regeneration. 

• A comparison of measured sulfur emissions with the amount of sulfur contained in the fuel 

and lubricant demonstrated that nearly all of the sulfur accumulated on the catalysts was 

effectively removed during the desulfurization process. 

Fuel Effects on Regulated Emissions 

• There were no consistent significant differences in the emissions from tests conducted with 

the DECSE and BP fuels. 

Unregulated Emissions 

• Unregulated emissions results are presented in a separate report. 

Future Work 

The results of this work have identified a number of areas worthy of additional study. These 

include further evaluation of the NAC desulfurization process analyzing both deterioration 

mechanisms and the composition of the liberated sulfur compounds, and the evaluation of other 

fuel formulations on the performance of emission control devices (e.g., the impact of biodiesel 

blends on NACs and DPFs). One specific area of research is related to the impact of biodiesel 

blends on DPF regeneration temperature. 

128
References 

Dzubay, T.G.; Nelson, R.O. (1975) “Self Absorption Corrections for X-Ray Fluorescence 

Analysis of Aerosols.” Pickles, W.L. et al. ed. Advances in X-Ray Analysis. New York, 

NY: Plenum Publishing Corp. Vol. 18. p. 619. 

Diesel Emissions Control – Sulfur Effects Project (DECSE) Summary of Reports (February 

2002). U.S. Department of Energy. NREL/TP-540-31600. Golden, CO: National 

Renewable Energy Laboratory. Available at: 

http://www.nrel.gov/docs/fy02osti/31600.pdf 

Siegl, W.O.; Richert, J.F.O.; Jensen, T.E.; Schuetzle, D.; Swarin, S.J.; Loo, J.F.; Prostak, A.; 

Nagy, D.; Schlenker, A.N. (1993) “Improved Emissions Speciation Methodology for 

Phase II of the Auto/Oil Air Quality Improvement Research Program – Hydrocarbon and 

Oxygenates.” Society of Automotive Engineers. SAE Paper 930142. 

U.S. Patent No. 6,742,328, System B3, (June 2004). 

U.S. Patent No. 5,771,68, Active Porous Media Aftertreatment Control System, (June 1998). 

129
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A Strong Energy Portfolio for a Strong America 

Energy efficiency and clean, renewable energy will mean a stronger econ 

omy, a cleaner environment, and greater energy independence for America. 

Working with a wide array of state, community, industry, and university 

partners, the U.S. Department of Energy’s Office of Energy Efficiency and 

Renewable Energy invests in a diverse portfolio of energy technologies. 

Produced for the U.S. Department of Energy by the 

National Renewable Energy Laboratory 

For more information contact: 

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March 2007 

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