NREL/CP-540-39228. Posted with permission. 

Presented at the SAE 2006 World Congress, 

April 3-6, 2006, Detroit, Michigan 2006-01-0425 

Fuel Sulfur Effects on a Medium-Duty Diesel Pick-Up with a 

NOX Adsorber, Diesel Particle Filter Emissions Control System: 

2000-Hour Aging Results 

Matthew Thornton 

National Renewable Energy Laboratory 

Cynthia C. Webb, Phillip A. Weber 

Southwest Research Institute 

John Orban, Elizabeth Slone 

Battelle Memorial Institute 

Copyright © 2004 SAE International 

ABSTRACT 

Increasing fuel costs and the desire for reduced 

dependence on foreign oil have brought the diesel 

engine to the forefront of future medium-duty vehicle 

applications in the United States due to its higher 

thermal efficiency and superior durability. One of the 

obstacles to the increased use of diesel engines in this 

platform is the Tier 2 emission standards. In order to 

succeed, diesel vehicles must comply with emissions 

standards while maintaining their excellent fuel 

economy. The availability of technologies—such as 

common rail fuel injection systems, low-sulfur diesel fuel, 

oxides of nitrogen (NOX) adsorber catalysts or NACs, 

and diesel particle filters (DPFs)—allows for the 

development of powertrain systems that have the 

potential to comply with these future requirements. In 

support of this, the U.S. Department of Energy (DOE) 

has engaged in several test projects under the 

Advanced Petroleum Based Fuels-Diesel Emission 

Control (APBF-DEC) activity [1, 2, 3, 4, 5]. Three of the 

APBF-DEC projects evaluated the sulfur tolerance of a 

NAC/DPF system and the full useful life implications of 

NAC desulferization. The test bed for one project in this 

activity is a 2500 series Chevrolet Silverado equipped 

with a 6.6L Duramax diesel engine certified to 2002 

model year (MY) federal heavy-duty and 2002 MY 

California medium-duty emission standards. 

While NAC systems have demonstrated extremely high 

levels of NOX reduction in steady-state laboratory 

evaluations, the application of a NAC system to an 

actual transient engine has not been demonstrated. 

Such an application requires the development of an 

integrated engine/emissions management system [6, 7, 

8, 9, 10, 11, 12, 13, 14, 15]. Two previous papers 

detailed the thermal and NOX adsorber management 

aspects of a system applied to the project test bed [1, 2]. 

The final control strategies applied to this project 

achieved over 98% reductions in tailpipe NOX mass 

emission over the hot-start Urban Dynamometer Driving 

Schedule (UDDS). This paper discusses the emission 

results of the system measured over the course of 2000 

hours of on-engine aging exposure. The system was 

evaluated over the cold-start UDDS, hot-start UDDS, 

Highway Fuel Economy Test (HFET) and US06 portion 

of the Supplemental Federal Test Procedure (SFTP). 

The discussion will cover the aging cycle utilized and its 

development, details of the desulfurization process, and 

regulated emission results over the test cycles of 

interest. After 2000 hours of on-engine aging, the 

NAC/DPF system demonstrated an average NOX

reduction of 89% and PM reduction of 94% over the 

composite Federal Test Procedure (FTP). 

INTRODUCTION 

The NAC/DPF concept has shown promising results with 

a new, but degreened emission control system (ECS). 

The platform development process and the control 

strategies were already discussed as part of SAE papers 

published last year [11, 12]. Following this development 

phase, an aging process with a target of 2000 hours was 

initiated. The 2000 hours represent the useful lifetime of 

the ECS (equivalent to 120,000 miles). Details regarding 

the aging procedure and the ECSs are provided in 

following sections. 

The aging process was interrupted by evaluation cycles 

to monitor system performance during aging. Cold- and 

hot-start UDDS (the first two bags of the FTP-75) 

simulations, as well as US06 and HFET cycle 

simulations, were tested repeatedly throughout the aging 
process to gain statistical confidence in the emission 

results. 

PROGRAM OBJECTIVES 

The main objective of the APBF-DEC activity is to 

investigate the sulfur tolerance and long term 

performance of different ECSs such as the NAC/DPF 

combination. An additional project has been initiated 

under this activity to evaluate selective catalytic 

reduction technologies. 

An integral part of the program is to demonstrate the 

capability of a state-of-the-art engine and ECS 

combination to achieve the Tier 2 Bin 5 emission levels. 

The ECS was aged up to 2000 hours with a fuel sulfur 

level of 15 ppm to allow for an assessment of its impact 

on the durability of the systems. The detailed fuel 

specifications for this project are presented in Appendix 

A. 

TEST PLATFORM 

The test vehicle for this evaluation was a 2002 Chevrolet 

Silverado 2500 Series pick-up truck equipped with a 

Duramax 6.6L engine and ZF six-speed manual 

transmission. This engine/vehicle combination met the 

California medium-duty emission requirements for 2002. 

Table 1 provides some engine specifications, and the 

test vehicle is shown in Figure 1. The stock ECS 

included a charge air cooler, turbocharger, common rail 

direct fuel injection, oxidation catalyst (OC), and highpressure exhaust gas recirculation (EGR). 

Table 1. Engine Specifications for MY2002 6.6L 

Duramax 

Rated Speed (rpm) 3000 

Rated Power (hp) 300 ± 12 

Rated Torque Speed (rpm) 1800 

Rated Torque (ft-lb) 520 ± 20 

Low idle (rpm) 680 ± 25 

Figure 1. Project Test Vehicle—2500 Series Chevrolet 

Silverado 

EMISSIONS CONTROL SYSTEM 

The ECS components tested in this project consisted of 

NACs, OCs, and a catalyzed DPF. These components 

were integrated with the engine control to form the ECS. 

The final ECS configuration utilized in this program was 

a dual-leg NAC with a single DPF downstream of the 

combined flow after the NACs. There were also OCs 

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 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 for producing reductants for regeneration. 

Supplemental fuel injectors (SFIs) were installed in each 

exhaust leg to allow control of the regeneration 

reductant. An additional injector was installed upstream 

of the DPF to allow for active regeneration. Figure 2 

shows a schematic of the ECS evaluated in this project. 

The rationale for the configuration selected and details 

of the ECS and the temperature management control 

strategies are outlined in SAE 2004-01-0584 and 2004-

01-0585 [11, 12]. 
EGR 

VALVE

6600 Duramax

INTAKE 

THROTTLE 

AIR 

FILTER

Air Charge Cooler

SFI

SFI

Diesel Fuel

Burner

SFI

OC DPF

DPF OC NAC #1

DPF OC NAC #1

OC = 3.5L NAC = 7L DPF = 12.5L 

Figure 2. Schematic of Emissions Control System 

TEST PROCEDURES 

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 UDDS, the HFET, 

and the US06 portion of the SFTP. 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 soak-time, 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 Appendix B. 

Table 2 shows a comparison of the maximum speed, 

average speed, maximum acceleration, distance 

traveled and time for the different cycles. As can be 

seen in this table, the UDDS is a lightly loaded cycle 

where the engine spends significant time at idle 

conditions. 

Table 2. Operational Characteristics of Select LightDuty Chassis Dynamometer Test Cycles 

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 

BASELINE EMISSIONS 

A summary of the baseline, as-received engine-out 

emissions over the light-duty FTP cycle, with and without 

EGR is shown in Tables 3 and 4, respectively. The 

engine-out emissions are presented in this fashion in 

order to provide an appropriate baseline for evaluating 

the NAC performance versus the overall ECS 

performance. All of the emissions results presented in 

the following ‘TEST RESULTS’ section include EGR. 

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 these were the test cycles 

utilized in this program. Figure 3 shows a comparison of 

the regulated engine-out emissions and the program 

goals [i.e., U.S. Environmental Protection Agency (EPA) 

Tier 2 Bin 5]. As can be seen from this figure, meeting 

the 50K mile program goals required a 99% NOX

reduction, an 84% HC reduction, and an 89% particulate 

matter (PM) reduction over the engine-out (no EGR) 

emission levels. Appendix B shows the continuous 

engine-out NOX emissions and exhaust gas temperature 

(with and without stock high-pressure EGR) for the coldstart UDDS. 

 

Table 3. Composite LD-FTP As-Received Engine-Out 

Emissions with EGR 

 FTP 

Composite 

(g/mi) 

Cold-Start 

UDDS (g/mi) 

Hot-Start 

UDDS (g/mi)

THC 0.448 0.487 0.418 

NOX 4.233 4.500 4.032 

CO 3.198 3.942 2.637 

CO2 546 563 534 

PM 0.083 0.084 0.082 

Distance 

(Miles) 

11.06 

(total) 

7.47 

(total) 

7.46 

(total) 
Table 4. Composite LD-FTP As-Received Engine-Out 

Emissions without EGR 

FTP 

Composite 

(g/mi) 

Cold-Start 

UDDS (g/mi) 

Hot-Start 

UDDS (g/mi)

THC 0.468 0.491 0.450 

NOX 5.304 5.346 5.272 

CO 5.282 5.927 4.795 

CO2 551 574 535 

PM 0.088 0.090 0.087 

Distance 

(Miles) 

11.00 (total) 7.43 (total) 7.42 (total) 

0

1

2

3

4

5

6

Emissions (g/mile)

CO NOx THC*10 PM*25

Stock EGR Calibration

No EGR

Program Goals (50k Miles)

Program Goals (120k Miles)

99%

NMOG

84%

89%

Figure 3. Comparison of Regulated Engine-Out 

Emissions to Program Goals (EPA Tier 2 Bin 5) for the 

Light-Duty FTP 

TEST CELL CONTROL CYCLES 

In order to speed the development of the NAC system 

control strategy, provide more repeatable test 

conditions, and conduct multiple cold-start tests in a 

single day, tests on the vehicle were dropped and the 

project was moved into a transient-capable test cell. 

The test cell was equipped with a General Electric Direct 

Current Dynamometer, capable of absorbing 350 hp and 

motoring 225 hp and an exhaust dilution tunnel with a 

nominal flow rate of 28 m3

/min. The test cell was also 

equipped with various raw and dilute emission 

equipment to measure regulated and unregulated 

species. 

Different test cell control cycles for the cold-start UDDS, 

hot-start UDDS, HFET, and US06 were developed in 

order to duplicate engine operation in the vehicle. The 

vehicle was first operated on the chassis dynamometer 

over the test cycles of interest while recording important 

operational information such as engine speed, 

accelerator pedal position, manifold absolute pressure, 

intake mass airflow, 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 

Appendix B. These data were then utilized to develop a 

desired torque/engine speed control cycle for use in the 

test cell. These control cycles resulted in engine-out 

emissions, fuel consumption, and exhaust gas 

temperatures similar to those observed on-vehicle. 

Appendix B also shows a comparison of the engine-out 

accumulated NOX mass, carbon dioxide (CO2) mass, 

and exhaust gas temperature for a cold-start UDDS on 

the vehicle and in the test cell.. A summary of the cycle 

work for the different test cycles is shown in Table 5. 

Table 5. Equivalent Test Cycle Work for Light-Duty 

Chassis Dynamometer Test Cycles 

Test Cycle Work (hp-hr) 

Equivalent 

Distance 

(miles) 

Cold UDDS 6.67 7.5 

Hot UDDS 6.53 7.5 

HFET 7.39 10.26 

US06 9.57 8.01 

DESULFURIZATION 

One of the drawbacks to a NAC-based aftertreatment 

system is the requirement to intermittently “desulfurize” 

or “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 nitric oxide to nitrogen 

dioxide (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. 

During this program approximately 660 kg of fuel were 

consumed upstream of the NACs (engine, burner, and 

SFI) over the course of every 100 hours of aging. A fuel 

sulfur level of 15 ppm, this resulted in a total fuel sulfur 

mass exposure of approximately 9.9 g total over 100 

hours. This mass of sulfur was assumed to be split 

evenly between the two exhaust legs, resulting in a fuel 

sulfur mass exposure for each NAC of approximately 

4.95 g. The engine oil consumption rate was 

approximately 0.35 liters (315 g) every 100 hours. 

Given an oil sulfur level of 6400 ppm, this resulted in a 

total oil sulfur mass exposure of approximately 2 g for 

100 hours of aging (1 g for each leg). Therefore the total 

sulfur mass exposure for each NAC over 100 hours of 

aging was approximately 6 g (assuming an equal split of 

exhaust between the two exhaust legs). 

The desulfurization process was conducted off-line on a 

gasoline engine. This was done in order to maintain 

precise and efficient desulfurization control. This cycle 

used a rich/lean perturbated approach and desulfated 

one NAC at a time. The 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 (2.5 cm, 7.5 cm, and 12.5 cm 

deep) reached 600°C. At this point the engine air-fuel 

ratio was then perturbated between lambda of 0.9 and 

1.05 (5 seconds at each air-fuel ratio). The measured 

NAC bed temperatures (at a depth of 2.5 cm) typically 

reached approximately 650-660°C (the desired 

desulfurization temperature) 2 minutes after beginning 

the perturbation. The air-fuel perturbation was 

continued for an additional 5 minutes, after which it was 

stopped, 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 oxi-cat/NAC 

combination. An example of the engine-out lambda and 

NAC system temperatures during desulfurization is 

shown in Figure 4. 

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

1.25

1.30

920 930 940 950 960 970 980

Time, seconds

Lambda

520

540

560

580

600

620

640

660

680

700

720

Temperature, °C

Lambda Inlet NAC2-2.5cm

NAC2-7.5cm NAC2-12.5cm

Figure 4. Example of Engine-Out Lambda and NAC 

System Temperatures during Desulfurization

SUMMARY OF TEST PLAN 

In order to evaluate the effectiveness of the 

aftertreatment system after exposure to sulfur over an 

extended period of time, emission tests were conducted 

at regular intervals. Initially, emissions evaluations were 

conducted at intervals of every 50 hours through the first 

300 hours of aging. During this time desulfurization was 

only conducted after the 200- and the 300-hour aging 

points. Starting with the 300-hour aging point, the 

frequency of desulfurizations and emissions evaluations 

was timed to occur at intervals of every 100 hours of 

aging until a total of 2000 hours of aging had been 

completed. Emissions tests were conducted both before 

and after every desulfurization. 

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 light-dutybased 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 automated 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 top ten modes of operation [engine 

speed and accelerator pedal position (APP)] during a 

vehicle test operating over the California Air Resource 

Board (CARB) Unified Driving Cycle (speed versus time 

trace shown in Figure 5). 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 Driving 

Cycle on a chassis dynamometer to obtain engine 

operating information (speed, APP, exhaust 

temperatures, etc.). Table 6 shows a summary of the 

frequency of operation for various engine speed and 

APP “bins” 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 dynamometerbased 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. 
0

10

20

30

40

50

60

70

80

0 300 600 900 1200 1500

Time, seconds

Vehicle Speed, mph

Target Vehicle Speed

Duration = 1435 seconds

Total Distance = 9.82 miles

Average Speed = 24.6 mi/hr

Figure 5. Vehicle Speed versus Time for CARB Unified 

Driving Cycle Schedule 

Table 6. RPM and APP Analysis of the CARB Unified 

Driving Cycle for Test Vehicle 

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% 

1050 2.7% 3.6% 4.0% 2.7% 0.8% 0.3% 0.0% 0.0% 0.0% 0.0% 

1350 4.0% 6.0% 8.0% 8.2% 6.8% 3.7% 0.3% 0.0% 0.0% 0.0% 

1650 1.6% 1.5% 1.5% 2.4% 3.1% 4.3% 1.1% 0.1% 0.0% 0.0% 

1950 0.6% 0.3% 1.7% 5.5% 5.7% 3.1% 1.1% 0.4% 0.0% 0.0% 

2250 0.1% 0.1% 0.1% 0.4% 0.4% 0.2% 0.3% 0.3% 0.1% 0.0% 

2550 0.0% 0.0% 0.0% 0.0% 0.0% 0.1% 0.0% 0.2% 0.1% 0.0% 

2850 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.1% 0.0% 

3150 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

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 and their relative weighting, but was expanded to 

include a steady-state evaluation point. The selected 

steady-state evaluation point was the highest speed and 

load point of the 10 cycle modes (1950 rpm and 45% 

APP or 244 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 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 7 provides the operating characteristics of the 

steady-state evaluation point. Figure 6 shows the 

percentage of time spent at each operating point for the 

aging cycle as a four-hour set (22, 10-minute cycles plus 

one 20-minute evaluation). 

Table 7. Summary of Modified CARB Unified Driving 

Cycle Based Aging Cycle Operating Conditions and 

Mode Order 

Step 

Original 

Mode 

Number 

Engine 

Speed, 

rpm 

APP 

(%) 

% of 

CARB 

Unified 

Cycle 

% of 

Aging 

Cycle 

Mode 

Time, 

sec 

1 1 680 0 9.2 12.8 84 

2 Ramp 680-

1950 

0-35 - - - 0.8 5 

3 9 1950 35 5.5 7.8 51 

4 Ramp 1950-

1050 

35-15 - - - 0.8 5 

5 2 1050 15 3.6 4.9 32 

6 Ramp 1050-

1650 

15-55 - - - 0.8 5 

7 8 1650 55 4.3 6.0 39 

8 Ramp 1650-

1050 

55-25 - - - 0.8 5 

9 3 1050 25 4.0 5.5 36 

10 Ramp 1050-

1350 

25-45 - - - 0.8 5 

11 7 1350 45 6.8 9.6 63 

12 Ramp 1350-

1350 

45-15 - - - 0.2 1 

13 4 1350 15 6.0 8.4 55 

14 Ramp 1350 15-35 - - - 0.2 1 

15 6 1350 35 8.2 11.6 76 

16 Ramp 1350 35-25 - - - 0.2 1 

17 5 1350 25 8.0 11.3 74 

18 Ramp 1350 25-45 - - - 0.2 5 

19 10 (SS) 1950 45 5.7 16.3 52 

20 Ramp 1950-

680 

45-0 - - - 0.8 5 

Totals - - - - - - 61.3 100 600 

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500

Engine Speed (rpm)

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

Figure 6. Aging Cycle Operating Points with SteadyState Evaluation Point (Based on CARB Unified Driving 

Cycle) 
TEST RESULTS 

ENGINE DYNAMOMETER TEST CELL 

The average NOX emission results are displayed in 

Figures 7 and 8. Observations at the beginning and end 

of a single aging cycle are connected. Tier 2 Bin 5 

useful life standards are included for reference and 

appear as a horizontal line. 

Cold- and hot-start UDDS (or LA4) cycles were 

performed at the aging marks depicted in Figure 7. 

The composite FTP emissions, which comprised 43% 

cold-start emissions and 57% hot-start emissions, are 

illustrated in Figure 8. 

With the given desulfurization frequency, the composite 

FTP tailpipe NOX emission number post desulfurization 

after 2000 hours could not be maintained below the 

emission standard for 120,000 miles of 0.07 g/mi beyond 

the first 2500 hours of aging. A detailed statistical 

analysis of NOX emissions results from the test cell is 

discussed in the ‘STATISTICAL ANALYSIS’ section. 

NOx Emissions

0.00

0.25

0.50

0.75

1.00

1.25

0 250 500 750 1000 1250 1500 1750 2000

Age (hours)

NOx (g/mi)

Cold UDDS Hot UDDS

i

Figure 7: Cold and Hot UDDS NOX Emissions 

FTP Composite NOx Emissions

0.00

0.25

0.50

0.75

1.00

1.25

0 250 500 750 1000 1250 1500 1750 2000

Age (hours)

NOx (g/mi)

Figure 8: Composite FTP Emissions 

The evaluation of the PM filters showed the high degree 

of filtration efficiency of the DPF. In all instances 

throughout the aging, the average composite PM 

numbers were below the emission standard of 0.01 g/mi. 

The remaining UDDS-regulated emissions and fuel 

economy results, as well as the results for the US06 and 

HFET simulation cycles, are presented in Appendix C. 

Composite FTP Particulate Matter Emissions

0.000

0.003

0.006

0.009

0.012

0.015

0 250 500 750 1000 1250 1500 1750 2000

Age (hours)

PM (g/mi)

Figure 9: Composite PM Emissions 

STATISTICAL ANALYSIS 

Statistical analyses were performed to characterize 

trends in emissions levels over the 2000 hours of 

testing. The trend analysis was performed using only 

the data collected after the second desulfurization at 300 

hours. Prior to 300 hours, evaluations were performed 

every 50 hours. After 300 hours, the data were collected 

using a 100-hour aging/desulfurization cycle. 

Figure 10 illustrates the degradation in catalyst 

performance between desulfurizations. A log-linear 

model was fit to estimate average trends and evaluate 

statistical significance. 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%. Figure 11 

illustrates the effectiveness of the desulfurization 

process at restoring performance. There is a 6% 

improvement in NOX reduction efficiency at each 

desulfurization event, with NOX a slight trend ranging 

between 3% and 6%. Although these trend lines show 

slight changes in NOX reduction efficiency, the slopes of 

the regression lines were not statistically different from 

zero. Combined, these figures indicate that after 300 

hours of aging, the desulfurization process generally 

compensates for the increased degradation in catalyst 

performance between desulfurizations throughout the 

2000-hour test. 
Change in NOX Reduction Efficiency (% of Engine Out NOX) 

Between Desulfurizations

-14.0%

-12.0%

-10.0%

-8.0%

-6.0%

-4.0%

-2.0%

0.0%

300 600 900 1200 1500 1800 2100

Age (hours)

Change in NOx Reduction 

Efficiency

Difference Difference Trend

Figure 10: Change in NOX Reduction Efficiency between 

Desulfurization over Time 

Increase in NOX Reduction Efficiency (% of Engine Out NOX) 

at Each Desulfurization

-2.0%

0.0%

2.0%

4.0%

6.0%

8.0%

10.0%

300 600 900 1200 1500 1800 2100

Age (hours)

Increase in NOx Reduction 

Efficiency

Difference (Post-Pre) Difference Trend

Figure 11: Increase in NOX Reduction Efficiency at 

Desulfurizations over Time 

The trends in FTP composite NOX emissions between 

300 hours and 2000 hours of aging are shown in Figure 

12, and trends in FTP composite NOX reduction 

efficiency relative to engine-out between 300 hours and 

2000 hours of aging are shown in Figure 13. To account 

for the effects of the 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 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. 

0.0

0.2

0.4

0.6

0.8

1.0

300 600 900 1200 1500 1800 2100

Age (hours)

NOx (g/mi)

Pre Desulfurization Average Post Desulfurization

Pre Trend Average Trend Post Trend

Figure 12: NOX Emission Trends over Time 

80%

84%

88%

92%

96%

100%

300 600 900 1200 1500 1800 2100

Age (hours)

NOx Reduction Efficiency

Pre Desulfurization Average Post Desulfurization

Pre Trend Average Trend Post Trend

Figure 13: NOX Reduction Efficiency Trends over Time 

The plots in Figures 12 and 13 show the performance 

stabilization for the system over time. All three of the 

regression lines were found to have statistically 

significant trends at the 95% confidence level. However, 

because of the curvature in the trends, we performed 

additional analyses to determine if there were any 

persistent trends in the emissions results over time. 

This was accomplished by iteratively truncating the 

leftmost data from each of the three data sets; then 

refitting the regression model and evaluating the 

significance of the regression slope parameter. Through 

this process we determined that when the analysis is 

applied to data collected after 800 or 900 hours, the 

trends were no longer statistically significant. 

A similar analysis strategy was applied to the observed 

fuel efficiency and CO, PM, and HC emissions results. 

There was a statistically significant increase in fuel 

efficiency and THC, NMHC, and CO emissions over the 

300- to 2000-hour aging period; however, using the 

same iterative analysis approach described above, the 

trend in fuel economy was not statistically significant 

using only the data collected after 1100 hours; and the 

trends in THC, NMHC, and CO emissions were not 

statistically significant using only the data collected after 

1400 hours. There were no observed trends for 

observed PM emissions. 
Table 8 shows the average composite FTP emissions 

from the seven engine-out tests (six without EGR and 

one with EGR); the 18 tailpipe tests conducted prior to 

the first desulfurization at 200 hours; and the estimated 

FTP composite emissions results at 1950 hours as 

determined by the average trend line based upon 

measurements taken between 350 and 1950 hours. 

Emission reductions are calculated relative to engine-out 

with and without EGR. Emission reduction does not 

necessarily equate to NOX conversion because back 

pressure affects engine-out emissions by changing the 

amount of EGR in use. 

The initial and 1950-hour estimated reductions in NOX, 

carbon monoxide (CO), and PM emissions due to the 

ECS were all statistically significant, as was the 

reduction in fuel economy (initially 18.7% relative to 

engine-out without EGR and 16.7% relative to engineout with EGR). Although initially 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. The 1950-

hour estimate of 0.616 g/mi was significantly above the 

standard. Initial average non-methane hydrocarbon 

(NMHC) emissions of 0.165 g/mi was 83% higher than 

the applicable standard and the estimated 1950-hour 

average NMHC of 0.372 g/mi was over four times the 

applicable standard. Tailpipe emissions for total 

hydrocarbon (THC) were greater than engine-out THC 

emissions, and average PM emissions were 50% lower 

than the applicable standard throughout. 

Table 8. Average Engine-Out, Initial, and Estimated 

1950 Hour Tailpipe Composite FTP Regulated 

Emissions and Fuel Economy 

Engine 

Out 

Tailpipe 

(0-200 Hours) 

Tailpipe Average 

(Post-Pre) 

(1950 Hours) 

Emission 

Parameter EGR Avg.1 Avg.2

Percent 

Reduction Avg.3

Percent 

Reduction

Regulated 

Emission 

Standard 4

Without 4.38 97.8% 85.9% NOx 

(g/mi) With 2.12 

0.095 

95.5% 

0.616 

70.9% 

0.07 

Without 0.198 16.7% -87.6% NMHC 

(g/mi) With Missing 

0.165 

Missing 

0.372 

Missing 

0.09 

Without 0.204 -126.9% -257.8% THC 

(g/mi) With 0.264 

0.463 

-75.1% 

0.730 

-176.2% 

N/A 

Without 2.02 87.2% 69.3% CO 

(g/mi) With 4.43 

0.258 

94.2% 

0.620 

86.0% 

4.2 

Without 0.065 91.6% 91.8% PM 

(g/mi) With 0.145 

0.005 

96.2% 

0.005 

96.3% 

0.01 

Without 18.4 18.7% 16.0% FE 

(mi/gal) With 18.0 

15.0 

16.7% 

15.5 

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

 Average of 18 tests performed prior to first desulfurization at 200 hours 3

 Estimate at 1950 hours based upon the trend of average results between 350 

and 1950 hours 

4

 Tier 2 Bin 5 Full Useful Life 

N/A = Not applicable 

CONCLUSION 

During the course of this program, it was demonstrated 

that the NAC/DPF system evaluated, in conjunction with 

a 15 ppm sulfur fuel and appropriate control strategies 

and calibrations, could achieve high NOX and PM 

reduction efficiencies. After 2000 hours of on-engine 

aging, the NAC/DPF system demonstrated an average 

NOX reduction of 89% and PM reduction of 94% over the 

composite Federal Test Procedure (FTP). While the PM 

emissions were below the Tier 2 Bin 5 emission 

standard, the NOX emissions were outside of this limit 

after full aging. The desulfurization strategy employed 

was successful in recovering NOX adsorber performance 

with some deterioration through 2000 hours of aging. 

ACKNOWLEDGMENTS 

The authors would like to thank the members of the 

APBF-DEC Steering Committee, the ABPF-DEC NOX 

Adsorber Workgroup, Oak Ridge National Laboratory, 

and the DOE for their support and guidance. The 

authors would also like to acknowledge General Motors 

and members of the Manufacturers of Emission Controls 

Association for their hardware contributions to this 

project. This project and all of the ABPF-DEC activities 

were conducted with the cooperation of engine and 

vehicle manufacturers, emission control device 

manufacturers, energy and additive companies, 

California state agencies, and the EPA. Representatives 

from all of these organizations and their member 

companies are part of the steering committee and 

workgroups. This project would not have been possible 

without their help and technical support. 

REFERENCES 

1. Webb, C., Weber, P., Thornton, M. “Achieving Tier 2 

Bin 5 Emission Levels with a Medium-Duty Diesel 

Pick-Up and a NOX Adsorber, Diesel Particulate 

Filter Emissions System—Exhaust Gas 

Temperature Management,” SAE 2004-01-0584, 

2004. 

2. Webb, C., Weber, P., Thornton, M. “Achieving Tier 2 

Bin 5 Emission Levels with a Medium-Duty Diesel 

Pick-Up and a NOX Adsorber, Diesel Particulate 

Filter Emissions System—NOX Adsorber 

Management,” SAE 2004-01-0585, 2004. 

3. Tomazic D., Tatur M., Thornton M. “Development of 

a Diesel Passenger Car Meeting Tier 2 Emissions 

Levels,” SAE Paper 2004-01-0581, March 2004, 

Detroit, Michigan. 

4. Tomazic D., Tatur M., Thornton M. “APBF-DEC NOx

Adsorber/DPF Project: Light-Duty Passenger Car 

Platform,” DEER Paper, August 2003, Newport, 

Rhode Island 

5. Whitacre, S., et al. “Systems Approach to Meeting 

EPA 2010 Heavy-Duty Emission Standards Using a 

NOx Adsorber Catalyst and Diesel Particle Filter on 

a 15l Engine” SAE Paper 2004-01-0587. 
6. Diesel Emission Control – Sulfur Effects (DECSE) 

Program: NOx Adsorber Catalysts; Phase II 

Summary Report; U.S. Department of Energy, Office 

of Transportation Technologies, U.S. Government 

Printing Office: Washington, D.C., October 2000.

7. Clark, W., Sverdrup, G., Goguen, S., Keller, G., 

McKinnon, D., Quinn, M., Graves, R. “Overview of 

Diesel Emission Control – Sulfur Effects Program,” 

SAE 2000-01-1879, 2000. 

8. Ketfi-Cherif, A., et al. “Modeling and Control of a 

NOX trap Catalyst,” SAE 2000-01-1199, 2000. 

9. Guyon, M., et al. “NOX –Trap System Development 

and Characterization for Diesel Engines Emission 

Control,” SAE 2000-01-2910, 2000. 

10. Schenk, C., et al. “High-Efficiency NOX and PM 

Exhaust Emission Control for Heavy-Duty OnHighway Diesel Engines,” SAE 2001-01-1351, 2001. 

11. Hachisuka, H., et al. “Deactivation Mechanism of 

NOX Storage-Reduction Catalyst and Improvement 

of Its Performance,” SAE 2000-01-1196, 2000. 

12. Dou, D., Balland, J. “Impact of Alkali Metals on the 

Performance and Mechanical Properties of NOX

Adsorber Catalysts,” SAE 2000-01-0734, 2000. 

13. Hachisuka, H., et al. “Improvement of NOX StorageReduction Catalyst,” SAE 2002-01-0732, 2000. 

14. Hodijati, Sh., et al. “Impact of Sulphur on the NOX

Trap Catalyst Activity – Poisoning and Regeneration 

Behaviour,” SAE 2000-01-1874, 2000. 

15. Asik, J., Meyer, G., Dobson, D. “Lean NOX Trap 

Desulfation through Rapid Air Modulation,” SAE 

2000-01-1200, 2000. 

CONTACTS 

Matthew Thornton 

National Renewable Energy Laboratory 

617 Cole Boulevard 

Golden, Colorado 80401 

Email: matthew_thornton@nrel.gov 

Work Number: (303) 275-4273 

FAX Number: (303) 275-4415 

Cynthia C. Webb 

Southwest Research Institute 

Department of Emissions Research 

6220 Culebra Road 

San Antonio, Texas 78228-0510 

Email: cwebb@swri.org

Work Number: 210-522-5873 

FAX Number: 210-522-3950 

Phillip A. Weber 

Southwest Research Institute 

Department of Engine and Emissions Research 

6220 Culebra Road 

San Antonio, Texas 78228-0510 

Email: pweber@swri.org

Work Number: 210-522-5872 

FAX Number: 210-522-3950 

DEFINITIONS, ACRONYMS, ABBREVIATIONS 

APBF-DEC: Advanced Petroleum Based FuelsDiesel Emission Control Activity 

APP: Accelerator Pedal Position 

C: Celsius 

CARB: California Air Resources Board 

CM: Centimeter 

CO: Carbon Monoxide 

CO2: Carbon Dioxide 

DESCE: Diesel Emission Control Sulfur Effects 

Program 

DOE: U.S. Department of Energy 

DPF: Diesel Particulate Filter 

ECS: Emission Control System 

EGR: Exhaust Gas Recirculation 

EPA: U.S. Environmental Protection Agency 

FTP Federal Test Procedure 

FTP-75: Light-Duty Federal Test Procedure 

G: Gram 

G/MI: Gram per Mile 

G/S: Gram per Second 

HC: Hydrocarbon 

HFET: Highway Fuel Economy Test 

KG: Kilogram 

LA-4: Bag 1 and Bag 2 of the FTP-75 Cycle 

MY: Model Year 

NAC: NOX Adsorber Catalyst 

NMHC: Non-Methane Hydrocarbon 

NOx: Oxides of Nitrogen 

NO2: Nitrogen Dioxide 

OC: Oxidation Catalyst 

PM: Particulate Matter 

RPM: Revolutions per Minute (engine speed) 

SFI: Supplemental Fuel Injectors

SUV: Sport Utility Vehicle 

THC: Total Hydrocarbon 

UDDS: Urban Dynamometer Driving Schedule 

US06: An aggressive chassis dynamometer 

emissions test procedure, part of the 

 Supplemental FTP 
APPENDIX A: FUEL PROPERTIES 

The base fuel used in this study is an ultra-low sulfur (0.6-ppm) fuel with properties that are representative of diesel fuels 

used in the United States, except for its sulfur content. Table A-1 summarizes the properties of the fuel. To achieve higher 

sulfur levels, without otherwise impacting other fuel properties, a mixture of the sulfur containing compounds (listed in 

Table A-2) typically found in diesel fuel is doped into the base fuel. The dopant mixture contains a variety of classes of 

sulfur containing molecules that is in the same boiling range as diesel fuel, with an emphasis on thiophenes. Careful 

addition of this dopant mixture yields fuels containing 8 ppm and 15 ppm sulfur for use in the catalyst aging experiments 

that follow this development activity. 

Table A-1. Test Fuel Properties 

Fuel Property ASTM 

Method 

Base Fuel BP15 

Density (kg/m3) D4052 826.2 837.1 

Viscosity @40oC (mm2/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 A-2. 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 
APPENDIX B 

0

10

20

30

40

50

60

70

0 500 1000 1500 2000 2500 3000 3500

Time, seconds

Vehicle Speed, mph

CLA-4

HLA-4

Cold Start UDDS 10-Minute Hot Start UDDS

Soak Period

FTP-75

Figure B-1. Indicated Vehicle Speed versus Time for Cold-Start UDDS and Hot-Start UDDS Driving Schedules 

0

10

20

30

40

50

60

70

0 200 400 600 800 1000 1200 1400 1600

Time, seconds

Indicated Vehicle Speed, mph

HFET Prep and Test Sequence

Prep Sequence Test Sequence

Figure B-2. Indicated Vehicle Speed versus Time for HFET Prep and Test Driving Schedule 
0

10

20

30

40

50

60

70

80

90

0 200 400 600 800 1000 1200

Time, seconds

Indicated Vehicle Speed, mph

US06 Prep and

Test Sequence

Prep Sequence Test Sequence

Figure B-3. Indicated Vehicle Speed versus Time for US06 Prep and Test Driving Schedule 

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 200 400 600 800 1000 1200 1400

Time, seconds

Engine Speed, rpm

-500

-400

-300

-200

-100

0

100

200

300

400

Torque, lbf-ft

Command Cycle Engine Speed

Command Cycle Engine Torque Output

Figure B-4. Test Command Cycle (Engine Speed and Torque) for Cold-Start UDDS Cycle 
500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 200 400 600 800 1000 1200 1400

Time, seconds

Engine Speed, rpm

-400

-300

-200

-100

0

100

200

300

400

500

Torque, lbf-ft

Command Cycle Engine Speed

Command Cycle Engine Torque Output

Figure B-5. Test Cell Command Cycle (Engine Speed and Torque) for Hot-Start UDDS 

500

1000

1500

2000

2500

3000

3500

4000

4500

0 100 200 300 400 500 600 700 800

Time (seconds)

Engine Speed (rpm)

-400

-300

-200

-100

0

100

200

300

400

Torque (ft-lbs)

Command Cycle Engine Speed

Command Cycle Engine Torque Output

Figure B-6. Test Cell Command Cycle (Engine Speed and Torque) for HFET Cycle 
500

1500

2500

3500

4500

5500

6500

0 100 200 300 400 500 600

Time, seconds

Engine Speed, rpm

-500

-300

-100

100

300

500

700

Torque, lbf-ft

Command Cycle Engine Speed

Command Cycle Engine Torque Output

Figure B-7. Test Cell Command Cycle (Engine Speed and Torque) for US06 Cycle 

0

5

10

15

20

25

30

35

40

45

0 200 400 600 800 1000 1200 1400

Time (seconds)

Raw Accumulated NOx Mass (grams

Vehicle Test - No EGR

Test Cell - No EGR (Cold_Rev_8)

Test Cell Cycle (Cold_Rev_8) Results in 

7% Lower NOx Compared to Vehicle Test

Figure B-8. Comparison of Accumulated Engine-Out NOX Mass over the Cold-Start UDDS for a Vehicle Test and Test 

Cell Run 
0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 200 400 600 800 1000 1200 1400

Time (seconds)

Raw Accumulated CO2 Mass (grams

Vehicle Test - No EGR

Test Cell - No EGR (Cold_Rev_8)

Test Cell Cycle (Cold_Rev_8) Results in 

2% Lower CO2 Compared to Vehicle Test

Figure B-9. Comparison of Accumulated Engine-Out CO2 Mass over the Cold-Start UDDS for a Vehicle Test and Test 

Cell Run 

0

50

100

150

200

250

300

0 200 400 600 800 1000 1200 1400

Time (seconds)

Temperature (°C)

Vehicle Test - No EGR

Test Cell - No EGR (Cold_Rev_8)

Figure B-10. Comparison Exhaust Gas Temperature over the Cold-Start UDDS for a Vehicle Test and Test Cell Run 
APPENDIX C: TEST CELL EMISSION RESULTS 

NOx Emissions

0.0

0.5

1.0

1.5

2.0

2.5

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Age (hours)

NOx (g/mi)

Cold UDDS Hot UDDS US 06 HFET

Burner Misfiring @

US 06 (last 2 tests) & HFET 

(first 2 tests)

Figure C-1. NOx Emissions versus ECS Age (Vertical Lines Identify Desulfurization Events) by Test Cycle 

PM Emissions

0.000

0.005

0.010

0.015

0.020

0.025

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Age (hours)

PM (g/mi)

Cold UDDS Hot UDDS US 06 HFET

Figure C-2. PM Emissions versus ECS Age (Vertical Lines Identify Desulfurization Events) by Test Cycle 
NMHC Emissions

0.00

0.25

0.50

0.75

1.00

1.25

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Age (hours)

NMHC (g/mi)

Cold UDDS Hot UDDS US 06 HFET

Figure C-3. NMHC Emissions versus ECS Age (Vertical Lines Identify Desulfurization Events) by Test Cycle 

Composite FTP NMHC Emissions

0.0

0.2

0.4

0.6

0.8

1.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Age (hours)

NMHC (g/mi)

Figure C-4. FTP Composite NMHC Emissions versus ECS Age (Vertical Lines Identify Desulfurization Events) 
CO Emissions

0.00

0.35

0.70

1.05

1.40

1.75

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Age (hours)

CO (g/mi)

Cold UDDS Hot UDDS US 06 HFET

Figure C-5. CO Emissions versus ECS Age (Vertical Lines Identify Desulfurization Events) by Test Cycle 

Composite FTP CO Emissions

0.00

0.25

0.50

0.75

1.00

1.25

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Age (hours)

CO (g/mi)

Figure C-6. FTP Composite CO Emissions versus ECS Age (Vertical Lines Identify Desulfurization Events) 
Fuel Economy

10

14

18

22

26

30

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Age (hours)

FE (mi/gal)

Cold UDDS Hot UDDS US 06 HFET

Figure C-7. Fuel Economy Emissions versus ECS Age (Vertical Lines Identify Desulfurization Events) by Test 

Cycle

FTP Composite Fuel Economy

10

14

18

22

26

30

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Age (hours)

FE (mi/gal)

Figure C-8. FTP Composite Fuel Economy Emissions versus ECS Age (Vertical Lines Identify Desulfurization 

Events)