Produced for the U.S. Department of Energy (DOE) 

by the National Renewable Energy Laboratory (NREL),

a DOE national laboratory
DECSE Final Reports. The following three final reports contain the results of the four technologies tested in the Diesel

Emissions Control—Sulfur Effects (DECSE) project.

• Lean-NOx Catalyst and Diesel Oxidation Catalyst (DOC).

DECSE Final Report: Diesel Oxidation Catalysts and

Lean-NOx Catalysts—June 2001. 

• NOx Adsorber Catalysts DECSE Phase II Summary

Report: NOx Adsorber Catalysts—October 2000 (final

report). 

• Diesel Particulate Filters (DPFs). DECSE Program 

Phase I Interim Data Report No. 4: Diesel Particulate

Filters—January 2000 (final report for the two DPFs). 

Final DECSE Program Summary, June 2001 (a four-page

summary of final results). 

Interim DECSE Reports. These reports presented preliminary

test results before the projects were completed.

• DECSE Program Phase I Interim Data Report No. 1—August

1999 (includes descriptions of the four technologies, initial test

information, and preliminary conclusions).

• DECSE Program Phase I Interim Data Report No. 2: 

NOx Adsorber Catalysts—October 1999 (includes 

interim results and initial conclusions for the NOx

adsorber catalyst only).

• DECSE Program Phase I Interim Data Report No. 3: Diesel Fuel

Sulfur Effects on Particulate Matter Emissions—November 1999

(contains preliminary 

findings on the impacts of fuel sulfur on engine-out 

and post-catalyst emissions). 

Complete texts of DECSE final reports and preliminary 

studies are available on the World Wide Web at

http://www.ott.doe.gov/decse

DECSE Reports

For more information contact: 

Wendy Clark 

DECSE Deputy Project Manager

National Renewable Energy Laboratory

Telephone: 303-275-4468

E-mail: wendy_clark@nrel.gov

Helen Latham 

DECSE Communications

Battelle Memorial Institute

Telephone: 614-424-4062

E-mail: lathamh@battelle.org 

Photo courtesy of Chevron Phillips Chemical Company, LP, Borger, TX.
Acronyms

APBF-DEC Advanced Petroleum-Based Fuels—Diesel Emissions

Control (project)

ASTM American Society for Testing and Materials

BSFC brake-specific fuel consumption

CDPF catalyzed diesel particulate filter

CIDI compression ignition, direct injection

CO carbon monoxide

CO2 carbon dioxide

CR-DPF continuously regenerating diesel particulate filter

DECSE Diesel Emissions Control—Sulfur Effects (project)

DOC diesel oxidation catalyst

DOE U.S. Department of Energy

DPF diesel particulate filter

EPA U.S. Environmental Protection Agency

ETS Engineering Test Services

EO engine-out

FEV FEV Engine Technology

FTP Federal TestProcedure

g/bhp-hr grams/brake horsepower-hour

HC hydrocarbon(s)

HSDI high-speed, direct-injection (engine)

HT high-temperature

LNOx lean-NOx (catalyst)

LT low-temperature

N2 nitrogen

NO nitric oxide

NO2 nitrogen dioxide

NO3 nitrate

NOx nitrogen oxides

OICA Organisation Internationale des Constructeurs

d’ Automobiles

PM particulate matter

ppm parts per million

SCR selective catalytic reduction technology 

SO2 sulfur dioxide

SO4 sulfate

SOF soluble organic fraction

SUV sport utility vehicle

WVU West Virginia University

CONTENTS

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Diesel Particulate Filters . . . . . . . . . . . . . . . . . . . . 7

Lean-NOx Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . 9

Diesel Oxidation Catalysts . . . . . . . . . . . . . . . . . . 11

NOx Adsorber Catalysts. . . . . . . . . . . . . . . . . . . . . 13

Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . 15

The Next Step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1
The DECSE fuels were blended at the Chevron Phillips

Chemical Company, LP, in Borger, TX.

2

Summary of DECSE Reports

Background

This summary describes a government and industry costshared project to determine the impact of fuel sulfur levels 

on emission control systems that could be used to lower 

emissions of nitrogen oxides (NOx) and particulate matter

(PM) from compression ignition, direct injection (CIDI)

diesel-cycle vehicles. The sulfur in diesel fuel adversely affects

the operation of diesel exhaust emission control systems. Tests

were conducted and data were collected and analyzed for various combinations of fuel sulfur levels, engines, and exhaust

emission control systems.

Diesel engines are used to power most heavy vehicles, as 

well as some light trucks, minivans, and automobiles. Engine

exhaust emission standards will be more stringent for all 

vehicles, including light trucks and sport utility vehicles

(SUVs) as new federal regulations are implemented. The 

U.S. Environmental Protection Agency (EPA) has announced

emission standards for heavy-duty trucks that manufacturers

will have to meet starting in 2007. These standards require

that NOx emissions be reduced by 75%–90% and PM emissions by 80%–90%, compared with current standards. EPA

also announced lower emission standards for passenger vehicles, requiring that their emissions be 77%–95% cleaner than

current emissions and that sulfur in gasoline be reduced by as

much as 90% from today’s level. These new standards are to

be phased in beginning in 2004. 

EPA has also ruled that the maximum sulfur content in 

highway diesel fuel be reduced to 15 parts per million (ppm), 

a reduction of 97% from the current maximum allowable

level of 500-ppm, beginning in mid-2006. The tests described

in this summary were conducted by the Diesel Emissions

Control—Sulfur Effects (DECSE) project, guided by a 

steering committee that included representatives of the 

U.S. Department of Energy, two national laboratories, and

manufacturers of diesel engines and emission control systems.

Collecting and analyzing data on the effects of sulfur on 

various exhaust emission systems were the key steps in a larger

cooperative research project. Results from the DECSE tests

are being used in continuing work to determine the types 

of diesel fuel, vehicle engines, and exhaust emission control

systems that, working together, will enable diesel-powered 

vehicles to meet stricter new regulations. The successor 

project is called the Advanced Petroleum-Based Fuels—

Diesel Emissions Control project (APBF-DEC).

SOURCES OF DECSE FUNDING 

AND IN-KIND SUPPORT

U.S. Department of Energy, Office of Heavy Vehicle 

Technologies, Office of Advanced Automotive 

Technologies and DOE laboratories (National 

Renewable Energy Laboratory and Oak Ridge 

National Laboratory)

Engine Manufacturers Association (representing 

original equipment manufacturers)

Manufacturers of Emission Controls Association
Displacement Peak Power Peak Torque

Engine in LIters Type kW @ rpm Nm @ rpm

Caterpillar 3126 7.2 I 6 205 (275 hp) @ 2,200 1,086 (800 ft-lb) @ 1,440

Navistar T444E 7.3 V 8 157 (210 hp) @ 2,300 70 (520 ft-lb) @ 1,500

Cummins ISM370 10.8 I 6 276 (370 hp) @ 1,800 1,830 (1,350 ft-lb) @ 1,200

DaimlerChrysler/DDC Prototype 1.9 I 4 81 (109 hp) @ 4,200 270 (199 ft-lb) @ 2,000

Table 1. DESCE Test Engines

3

Introduction

The tests conducted by DECSE were designed to provide data

on the effects of various levels of sulfur in diesel fuels on emission control systems. Fuel composition affects engine efficiency,

chemical composition of the exhaust, and the amount of a

given pollutant or proportions of types of pollutants. Previous

studies suggested that the fuel’s sulfur level can directly affect

the effectiveness of exhaust emission control devices. 

The Technologies

The following four emission control technologies tested 

included commercially available technologies as well as those

under development. 

Diesel particulate filters (DPFs)—Filters designed to remove

PM from the engine exhaust by collection on a filter element.

Laboratory: Engineering Test Services (ETS). Test program

and report completed in January 2000. Test engine: Caterpillar

3126. Examples of study questions include:

• How does the DPF affect emissions of PM and selected 

gases?

• How does fuel sulfur affect emissions (engine-out [EO] 

and post-filter)?

• Does the DPF performance degrade over time? 

Lean-NOx catalysts (LNOx)—Catalysts capable of 

converting NOx to nitrogen (N2) in the presence of oxygen.

Test program and report completed in June 2001. Laboratory:

West Virginia University (WVU). Test engines: Cummins

ISM370, Navistar T444E. Examples of study questions

include: 

• How does the catalyst affect the emissions of NOx, sulfate

(SO4), and PM?

• How does the fuel sulfur level affect the post-catalyst 

emissions?

• What is the effect of sulfur during aging on the catalyst’s 

performance? 

Summary of DECSE Reports

Diesel oxidation catalysts (DOCs)—Catalysts designed to

reduce hydrocarbon (HC), carbon monoxide (CO), and the

soluble organic compounds associated with PM emissions. 

Test program and report completed in June 2001. Test engines:

Cummins ISM370, Navistar T444E. Laboratory: WVU.

Examples of study questions include: 

• How does the catalyst affect emissions of NOx, CO, 

and PM?

• How does the fuel sulfur level affect the post-catalyst 

emissions? 

• What is the effect of sulfur during aging on the catalyst’s 

performance?

NOx adsorber catalysts—Catalysts that function by first

storing (adsorbing) NOx and then reducing the stored NOx

under fuel-rich conditions. Phase I (sulfur effects) completed

in October 1999. Phase II (regeneration/desulfurization) 

completed in October 2000. Test engine: 1.9-liter high-speed,

direct-injection (HSDI) prototype. Laboratory: FEV Engine

Technology (FEV). Tasks included:

• Develop and improve calibration to achieve maximum 

NOx reduction. 

• Map performance. 

• Develop a desulfurization process. 

• Demonstrate desulfurization. 

• Evaluate performance during repeated aging and desulfurization cycles.

The Engines

The diesel engines used for the DECSE study met specific

selection criteria. They were intended to be commercially 

available and representative of the marketplace, or the current

state of the art. They had to represent light-, medium-, or

heavy-duty applications, operating within the range of exhaust

temperatures and emissions levels typical of roadway duty

cycles (generally of 1998 or 1999 model year). Three met the

criteria; the engine used in the NOx adsorber test was a prototype. (See Table 1.) The engines and related emission control

hardware selected were: 
• Control technology inlet and outlet temperature and pressure, space velocity and exhaust components such as NOx,

HC, CO, CO2, PM and sulfur dioxide (SO2). (See Table 3.)

Tests were conducted on the emission control technologies 

to measure and compare the effects of as many as 250 hours

of aging on engines using diesel fuel containing varying 

levels of sulfur (see Table 4). In addition, for the NOx adsorber catalyst project, tests were conducted to improve the 

NOx regeneration calibration to achieve a greater than 80%

NOx conversion between operating temperatures of 250°C

and 500°C and to develop a desulfurization process to restore

NOx conversion efficiency lost to sulfur contamination. 

Table 4 summarizes the DECSE test components.

In general, the DECSE data show the effects that fuel-borne

sulfur has on the performance of emission control systems.

The reports providing the results of these tests can be found at

http://www.ott.doe.gov/decse. This document is an executive

summary of the results of the DECSE tests.

DECSE DECSE

Fuel Property ASTM a Goal Measured

Density, kg/m3 D4052 820–850 826.1

Viscosity @ 40C, mm2/s D445 >2.0 2.4

Distillation IBP, C D86 171–182 185

10% recovery, C D86 210–226 207

50% recovery, C D86 254–271 259

90% recovery, C D86 310–321 314

FBP, C D86 326–360 350

Sulfur, ppm D5453 <10 3.1

Aromatics, vol. % D1319 25–32 27.0

Olefins, vol. % D1319 1–3 2.3

Saturates, vol. % D1319 55–70 70.7

Aromatics, wt. % D5186 28.5

Polyaromatics, wt. % D5186 3–10 9.6

Non-aromatics, wt. % D5186 71.2

Cetane number D613 42–48 45

Cetane index D976 53.6

HFRR lubricity, um D6079 635/355b

a American Society for Testing and Materials

b Values without/with 55-ppm Octel 35a and 211-ppm OLI-9000 additives

Emissions benches like this one at WVU were used to collect

data during the tests.

Navistar T444E engine/low-temperature lean-NOx catalysts

and DOC

Caterpillar 3126 engines/DPFs

DaimlerChrysler/DDC 1.9L HSDI engine/NOx adsorber 

catalyst

Cummins ISM370/high-temperature lean-NOx catalysts and

DOC. 

The Fuels

Chevron Phillips Chemical Company, LP, provided the 

base fuel, which was similar to commercially available fuel, 

except for sulfur content, and with limited representation of

specific compounds within a class, such as aromatics and 

polyaromatics.

Fuels for the tests were then formulated by:

• Blending the base fuel to contain 3-ppm of sulfur.

• Adding incremental amounts of a representative mix of sulfur compounds (doping) to create more fuel formulations

with sulfur content levels at 16- and 78-ppm (NOx adsorber catalyst project only), 30-, 150-, and 350-ppm (the

then-current average sulfur content in on highway diesel

fuels). Table 2 lists the major properties of the fuels.

The Tests

Three independent testing laboratories—WVU, FEV, and

ETS—gathered data on the engines and emission control

technologies as follows: 

• Engine speed and load, fuel rate, oil temperature and 

pressure, compressor/turbine pressure and temperature,

exhaust temperatures, and oil consumption. 

Table 2. Major Fuel Properties—DECSE Base Fuel

4

Summary of DECSE Reports
DOC

Active LNOx 

CR-DPF and 

CDPFb

NOx 

Adsorber

Special Navistar aging cycle

Modified OICAa aging cycle

Special Navistar aging cycle

Modified OICA aging cycle

No aging test, used special

tests to determine

regeneration temperatures and

emissions

3-hour and 10-hour aging cycle

using 9 temperature points in

sequence

Navistar 9-mode and

simulated FTP-75

Stabilized OICA and 

heavy-duty FTP

Navistar 9-mode

Stabilized OICA

Steady-state exhaust

temperature tests and 

stabilized OICA

Phase 1: NOx conversion 

every 50 hours

Phase 2: before and after

desulfurization

High precious

metal loading

Low precious

metal loading

LT

catalyst

HT

catalyst

Determine

sulfur effect on

regeneration

temperature

150- and 350-

ppm fuel not 

used based on 

initial results on

lower sulfur

levels

T444E

(Navistar)

ISM 370

(Cummins)

T444E

ISM 370

3126

(Caterpillar)

HSDI

(DaimlerChrysler/

DDC prototype)

250 Hours Aging

Technology at various fuel-sulfur levels Evaluation

Table 3. Summary of DECSE’s Experimental Designs

Engine Remarks

3 16 30 78 3 16 30

a A test cycle developed during European work; OICA is the International

Organization of Motor Vehicle Manufacturers (Organisation Internationale

des Constructeurs d’Automobiles)

b Continuously regenerating diesel particulate filters (CR-DPFs) and 

catalyzed diesel particulate filters (CDPFs).

3 30 150 350 3 30 150 350 

5

Summary of DECSE Reports
Emissions Measureda

Catalyst Age Fuel Sulfur Gases and Fuel Particulate

Engine Test Method (hours) ppm Economy Matter

Cummins OICA modes 2, 3, 10, 11 0, 50, 150, 250 3, 30, 150, 350 EO, DOC, LNOx

ISM370 OICA 4-mode wtd. 0, 50, 150, 250 3, 30, 150, 350 EO, DOC, LNOx EO, DOC, LNOx

OICA mode 2 (w/filter) 0 3, 30, 150, 350 EO, DOC, LNOx EO, DOC, LNOx

FTP hot 0, 50, 150, 250 3, 30, 150, 350 EO, DOC EO, DOC

Navistar Nav-9 modes 2, 3, 7, 9 0, 50, 150, 250 3, 30, 150, 350 EO, DOC, LNOx

T444E Nav-9 (4-mode) wtd. 0, 50, 150, 250 3, 30, 150, 350 EO, DOC, LNOx EO, DOC, LNOx

Nav-9 mode 9 (w/filter) 0 3, 30, 150, 350 EO, DOC, LNOx EO, DOC, LNOx

FTP 75 0, 50, 150, 250 3, 30, 150, 350 EO, DOC EO, DOC

Caterpillar OICA modes 1-13 Noted3, 30, 150, 350 EO, CDPF, CRDPF

3126 Noted30 EO, CDPF, CRDPF

OICA 13-mode wtd. Noted3, 30, 150, 350 EO, CDPF, CRDPF EO, CDPF, CRDPF

Noted30 EO, CDPF, CRDPF EO, CDPF, CRDPF

OICA mode 2 (w/filter) Noted3, 30, 150, 350 EO, CDPF, CRDPF EO, CDPF, CRDPF

OICA mode 4 (w/filter) Noted3, 30, 150, 350 EO, CDPF, CRDPF EO, CDPF, CRDPF

1.9L Performance mapping As long as 250 3, 16, 30, 78 EO, NOx EO, NOx

HSDI @ 3000 rpm over range Adsorber Adsorber

prototype of temperatures Catalyst Catalyst

Table 4. Summary of DECSE Test Components

6

a Entries identify source from which emissions data were obtained for each combination of catalyst/filter age and fuel sulfur level.

EO = engine-out; DOC = diesel oxidation catalyst; LNOx = lean-NOx catalyst; CDPF = catalyzed diesel particulate filter; CR-DPF = continuously 

regenerating diesel particulate filter

b HC, NOx, CO, CO2, BSFC (a measure of engine efficiency).

c Total PM, SOF, SO4, NO3. 

d The same CDPF and CR-DPF filters were used throughout the test program. The 30-ppm sulfur fuel was tested after approximately 100 hours and 

425 hours of use to evaluate aging effects.

The Navistar T444E test engine. The Cummins ISM370 test engine.

Summary of DECSE Reports
engine (which has a relatively low temperature exhaust) was

tested using the OICA 13-mode test procedure and tests at

peak-torque and “road-load” steady-state conditions. Regeneration temperatures were determined at selected engine

speeds by measuring the change in pressure across the DPFs

while operating the engine at different temperature and

torque settings.

Key Results

• Increasing the fuel sulfur level from 3- to 350-ppm produced an essentially linear 29% increase in the EO PM

emissions. No significant changes in the EO gas phase

emissions or baseline fuel consumption were observed 

as a result of increasing the fuel sulfur level.

• Fuel sulfur had significant effects on post-DPF total PM

emissions. Both DPFs effectively reduced PM emissions

(95% over the OICA cycle), when used with 3-ppm sulfur

fuel. With 30-ppm sulfur fuel, the PM reduction efficiencies dropped to 73%. When tested with the 150-ppm sulfur fuel, PM reduction efficiency was nearly zero. With the

350-ppm sulfur fuel, PM increased by more than 100% 

(see Figure 1).

• Fuel sulfur levels lower than 150-ppm were required to

achieve any reduction in total PM. Similarly, a sulfur level

of 3-ppm was required to achieve the total PM emissions

target of the 0.01 grams per brake horsepower-hour 

(g/bhp-hr) standard for the 2007 federal regulation.

• Approximately 40%–60% of fuel sulfur was converted to 

SO4 PM as measured over the 13-mode cycle for both DPFs.

Figure 1. Engine-out and post-DPF emissions of total PM 

and components as a function of fuel sulfur level for the

OICA cycle (with 95% confidence intervals on estimated PM)

Diesel Particulate Filters

Test Design

DPFs remove PM from engine exhaust by collecting it on a

filter—in this test, a ceramic element. Sulfur in the exhaust

can be oxidized over these filters, forming sulfates that are

measured as PM. The exhaust gas temperature and fuel sulfur

level are critical factors that affect the performance of DPFs.

Two types of DPFs—a continuously regenerating DPF 

(CR-DPF) and a catalyzed DPF (CDPF)—were evaluated. 

The critical role of these technologies is to clean (or regenerate) the DPF by oxidizing the collected PM to prevent the

device from becoming plugged. The CR-DPF regenerates the

DPF by continuously generating nitrogen dioxide (NO2),

with the help of a DOC upstream of the filter. The CDPF

regenerates the DPF by using a catalyst coating on the filter

element to promote oxidation of the collected PM.

Two types of tests—emission tests (PM and selected gases)

and experiments to measure the effect of fuel sulfur level on

the regeneration temperature of the DPFs—were conducted

using the OICA’s 13-mode test procedure. Fuels used had 

sulfur levels ranging from 3- to 350-ppm. A Caterpillar 3126

B) CR-DPF

12.0”

10.5”

4.0

A) CDPF

6.0” 12.0”

10.5”

4.0

Precious Metal-Coated Ceramic

Wall-Flow Filter; 100 cpsi

17 mil Wall Thickness

Oxidation Catalyst

400CPSI

Uncoated Ceramic 

Wall-Flow Filter,100 cpsi, 

17 mil Wall Thickness

Exhaust Gas

Exhaust Gas

7

Two types of DFPs were tested in this project.

3 30 150 350 30

Fuel Sulfur Level (ppm)

PM Emissions (g/bhp-hr)

Repeat Test 

After 400 

Engine Out

Hours

CDPFCR-DPF

Other

Sulfate 0.25

0.20

0.15

0.10

0.05

0

Summary of DECSE Reports
temperature of the CDPF averaged 66°C higher than the

regeneration temperature for the CR-DPF. 

• Fuel consumption increases of up to 2% above the baseline were measured when operating with the DPFs. This

increase, which resulted from the additional exhaust backpressure created by the DPFs, was generally larger with 

the CR-DPF than with the CDPF.

• The performance of the DPFs when exposed to 400 hours

of testing with the higher sulfur levels did not degrade (see

Figure 1 on previous page).

8

• The exhaust temperature required to regenerate the DPF

devices increased by about 25°C when changing from 

3- to 30-ppm sulfur fuel. The regeneration temperature

remained stable at 150- and 350-ppm fuel sulfur level for

the CDPF. 

• Within the range of fuel sulfur levels required to achieve

any PM reduction (less than 150-ppm), the temperature

required for filter regeneration was consistently higher for

the CDPF than for the CR-DPF. The average difference

when operating with the 3-ppm sulfur fuel was 54°C.

When operating with 30-ppm sulfur fuel, the regeneration

Summary of DECSE Reports
Lean-NOx Catalysts

Test Design

Lean-NOx catalysts can reduce diesel NOx emissions with the

assistance of a supplementary reductant (such as diesel fuel)

under a lean (oxygen-rich) exhaust. The main concern about

sulfur in diesel fuel is that the sulfates produced during combustion can be adsorbed on the active catalyst surface and

block the adsorption of NOx and HC. This results in a

decrease in the catalyst’s efficiency in reducing NOx and an

increase in fuel consumption and HC slip. (This refers to the

amount of HC that is more than what is needed to reduce the

NOx. The unconsumed HC is then exhausted into the air.)

The two lean-NOx catalysts used were performance tested

only at steady-state test cycles and before, during, and after a

250-hour aging cycle using four fuel sulfur levels. Two types

of lean-NOx catalysts—a high-temperature lean-NOx catalyst

and a low-temperature catalyst were chosen for the study.

Both catalysts require a reductant (supplemental HC) in the

exhaust stream to reduce the NOx emissions. 

The diesel test fuel was used as the reductant. The injection

rate was optimized for peak NOx reduction without exceeding

4% of the total fuel consumption. The high-temperature

(360°–600°C) catalyst was evaluated on a Cummins ISM370

engine and the low-temperature (170°–300°C) catalyst was

evaluated on a Navistar T444E engine, which was chosen to

provide a range of exhaust temperatures. Four steady-state

modes were selected from the OICA 13-mode steady-state 

test cycle for the high-temperature catalyst tests. The lowtemperature catalysts were evaluated using selected modes

from the Navistar 9-mode cycle.

The Navistar T444E engine was installed on a GE-2000 DC

dynamometer at WVU’s test facility.

Gaseous and PM emissions were sampled in the exhaust

before and after the catalysts to determine reduction efficiencies. PM breakdown analyses were also conducted.

Key Results

• Fresh lean-NOx catalysts achieved NOx reduction peak 

efficiencies of less than 20% with a maximum fuel penalty

of 4% for all catalysts during the defined steady-state test

cycles. However, reductions of more than 50% and 30%

NOx were observed at specific operating temperatures for

the low-temperature and high-temperature catalysts, respectively (see Figure 2). The effect of the fuel sulfur level on

NOx reduction efficiency was not statistically significant.

• There was a significant increase in the catalyst-out SO4

emissions when operating with fresh low-temperature leanNOx catalysts under the high-temperature, steady-state test

mode (405°C) at higher fuel sulfur levels (150- and 350-

ppm sulfur) (see Figure 3 on the next page). 

• The high-temperature lean-NOx catalyst was vulnerable to

HC slip (more than 50% of injected fuel in certain test

modes) with all fuels tested. The low-temperature lean-NOx

catalyst more effectively controlled HC and CO slip, but

only when using low-sulfur fuels (3- and 30-ppm sulfur).

• Catalyst aging (as long as 250 hours) had no apparent effect

on the NOx reduction efficiency of the low-temperature

and high-temperature lean-NOx catalysts, independent of

fuel sulfur level.

Figure 2. NOx reduction efficiency of low-temperature

(Navistar) and high-temperature (Cummins) lean-NOx

catalysts at selected catalyst inlet temperatures (with 

95% confidence intervals)

9

Summary of DECSE Reports

100 200 300 400 500 600

Catalyst Inlet Temperature (Degree C)

Lean-NOx Catalyst

NOx Reduction Efficiency (%)

70

60

50

40

30

20

10

0

-10

LT Catalyst

HT Catalyst
• PM emissions from aged (50 hours) low-temperature leanNOx catalysts increased significantly, mainly because of

higher SO4 emissions with higher sulfur fuels (150- to 350-

ppm) (see Figure 4). Thermal aging seems to be the primary

reason for the increase of PM with the lower sulfur levels.

With 350-ppm sulfur fuel, the effects of thermal aging

seemed essentially additive. Unlike the low-temperature

lean-NOx catalyst, the aging process had only a slight effect

on catalyst-out PM emissions with the high-temperature

lean-NOx catalyst. 

Figure 3. Engine-out and post-lean-NOx catalyst (fresh) 

emissions of PM and components under low-temperature

(Navistar) applications using a Nav-9 mode 9 test (with 95%

confidence intervals on estimated PM)

3 30 150 350

0.20

0.16

0.12

0.08

0.04

0

Fuel Sulfur Level (ppm)

NAV-9 Mode 9

PM (g/bhp-hr)

Hydrated SO4

SOF

Cat_in Temp. = 405 C Other

Engine Out

Post Catalyst

• Thermal aging was also the main contributor to the

increase of HC slip with the low-temperature lean-NOx

catalyst. Thermal aging could be making the catalyst more

vulnerable to sulfur inhibition, resulting in the higher HC

slippage with high-sulfur fuels. The HC slip from the hightemperature lean-NOx catalysts also increased after aging.

• For the low-temperature lean-NOx catalyst, the adverse

aging effects on PM emissions and HC slip were reversed

within 50 hours of operation with 30-ppm sulfur fuel. This

suggests that the catalyst had not been permanently deactivated. For the high-temperature lean-NOx catalyst, HC slip

increased after switching from high-sulfur fuel (350-ppm)

to low-sulfur fuel (30-ppm).

Figure 4. Engine-out and fresh, aged lean-NOx emissions 

of PM under low-temperature (Navistar) applications

using the Nav-9 weighted 4-mode test cycle (with 95%

confidence intervals)

3 30 150 350

Fuel Sulfur Level (ppm)

NAV-9 4-Mode Weighted

PM (g/bhp-hr)

0.6

0.5

0.4

0.3

0.2

0.1

0

Engine Out

Fresh Catalyst

Aged Catalyst

10

Summary of DECSE Reports
PM measured at EO. The increase is due almost exclusively

to the increase in SO4 fraction. The effect is seen only with

the 150- and 350-ppm sulfur fuels (see Figure 5).

• The catalyst response over the transient evaluation cycles

differed from the steady-state tests. In the transient tests

(FTP-75 mimicry) with the Navistar engine (see Figure 6),

the DOC reduced the SOF of the PM by 70%–85% and

PM by 35%–45%. The reductions in SOF and PM were

statistically significant. Fuel sulfur content did not affect

Diesel Oxidation Catalysts

Test Design 

DOCs reduce HC, CO, and the soluble organic fraction

(SOF) of PM by oxidation over a precious metal catalyst. 

A concern with higher precious metal loadings is the DOC’s

tendency to convert SO2 in the exhaust gas to SO4. Testing

was performed to assess fresh catalyst performance and its 

performance after aging.

The performance of the base metal, fresh high-temperature

DOCs was evaluated on a Cummins ISM370 engine using a

3-ppm sulfur base fuel and fuels with 30-, 150-, and 350-ppm

sulfur. The precious metal-coated low-temperature DOC catalysts were aged and evaluated using a Navistar T444E engine

operating on the same fuels. CO, HC, and PM emissions were

analyzed before and after the high-temperature DOC using

the heavy-duty Federal Test Procedure (FTP) transient test

cycle. Similarly, the low-temperature DOCs were evaluated

using the FTP-75 transient test procedure. Both the hightemperature and low-temperature DOCs were tested using

four steady-state modes from the OICA 13-mode test cycle.

Gaseous and PM emissions were sampled in the exhaust

before and after the catalysts to determine their efficiency 

in reducing the CO, HC, and PM emissions.

Key Results

• At the high exhaust temperature (405°C) steady-state

modes (at or near peak torque), there was a statistically 

significant increase in post-DOC PM over and above the

The exhaust gas recirculation system was tested on the

Navistar T444E engine at WVU’s test facility.

Figure 6. Engine-out and post-DOC emissions of PM and 

components under low-temperature (Navistar) applications

using the FTP-75 mimicry transient cycle (with 95% confidence intervals on estimated PM)

3 30 150 350

0.25

0.20

0.15

0.10

0.05

0

Fuel Sulfur Level (ppm)

FTP-75 Mimicry

PM (g/bhp-hr)

Hydrated SO4

SOF

Other

Engine Out

Post Catalyst

Figure 5. Engine-out and post-DOC (fresh) emissions 

of total PM and components under low-temperature

(Navistar) applications using a Nav-9 mode 9 test 

(with 95% confidence intervals on estimated PM)

3 30 150 350

0.30

0.25

0.20

0.15

0.10

0.05

0

Fuel Sulfur Level (ppm)

NAV-9 Mode 9

PM (g/bhp-hr)

Hydrated SO4

SOF

Other

Cat_in Temp. = 405 C

Engine OutPost Catalyst

11

Summary of DECSE Reports
• The steady-state PM emissions from the low-temperature

DOC aged with 350-ppm sulfur fuel exceeded those measured when the catalyst was fresh (0.20 versus 0.14 g/bhphr). A much smaller aging effect on total PM was observed

with the lower sulfur fuels (see Figure 7).

• After aging, the high-temperature catalysts more efficiently

reduced the SOF and resulted in greater PM reduction efficiency than the fresh catalyst. This improvement was

observed with catalysts aged with 30-, 150-, and 350-ppm

sulfur fuel, though the level of sulfur in the fuel did not

affect the magnitude of the improvement.

• The CO reduction efficiency of the high-temperature catalysts dropped 10 percentage points after aging. This effect

was independent of the level of fuel sulfur.

SOF emissions or the DOC’s SOF suppression efficiency.

Although there is some statistical evidence that SO4 emissions increased with higher sulfur fuel, the resulting impact

on PM (either EO or post-catalyst) was negligible and not

statistically significant.

• Under the transient test conditions, the low-temperature

DOCs on the T444E engine more effectively reduced 

PM SOF than the high-temperature DOCs used on the

ISM370. The performance difference can be attributed to

the higher platinum loading on the low-temperature catalysts, which are more active at the characteristically low

exhaust temperatures of the transient test cycles.

• The low-temperature DOC’s HC reduction efficiency was

90%–100% under steady-state and transient conditions. 

No sulfur effect was observed in either EO or post-catalyst

HC emissions from the T444E.

• A statistically significant increase in the high-temperature

DOC’s HC emissions (both EO and post-catalyst) was

observed during FTP transient tests with high-sulfur fuels

(150- and 350-ppm sulfur). HC reduction efficiency during the FTP declined from near 100% with 3-ppm sulfur

fuel to approximately 91% with 350-ppm sulfur fuel. 

• Low-temperature DOCs were 90%–99% effective in 

reducing CO concentrations at steady-state and 88%–92%

effective during the transient tests. The high-temperature

DOCs were 78%–84% effective in CO reduction at

steady-state but only 41%–45% effective during the 

transient tests. There is no statistical evidence that sulfur

affects CO emissions or the CO reduction efficiency of 

the DOC in any operating mode.

12

Figure 7. Engine-out and fresh, aged DOC emissions of PM

under low-temperature (Navistar) applications using the

Nav-9 weighted 4-mode test cycle (with 95% confidence

intervals)

Summary of DECSE Reports

3 30 150 350

Fuel Sulfur Level (ppm)

NAV-9 4-Mode Weighted

PM (g/bhp-hr)

0.30

0.25

0.20

0.15

0.10

0.05

0

Engine Out

Fresh Catalyst

Aged Catalyst
Key Results

• The improved lean/rich engine calibration achieved as a

part of this test resulted in NOx conversion efficiencies

exceeding 90% over a catalyst inlet operating temperature

window of 300°–450°C (see Figure 8). This was achieved

while staying within the 4% fuel economy penalty target

defined for the regeneration calibration. This calibration 

was developed using 3-ppm sulfur level fuel.

NOx Adsorber Catalysts

Test Design

A NOx adsorber catalyst is a flow-through emission control

device that temporarily stores NO2 emissions during the operation of a diesel engine. Before the NOx adsorbent becomes

saturated, engine operating conditions and fueling rates are

adjusted to produce a fuel-rich exhaust. Under these conditions, the stored NOx is released from the adsorbent and

reduced to N2 over three-way precious metal catalyts. 

The NOx adsorber test was designed to address the following

questions: 

• What NOx conversion efficiency is possible with an

improved lean/rich regeneration calibration?

• Can a practical on-engine desulfurization cycle be 

developed? 

• What effect does the desulfurization process have on the

long-term performance of the NOx adsorber, and does it

vary with the fuel sulfur level?

The NOx adsorber tests were conducted on duplicate systems

(see photo) using a three-step process. First, the calibration of

the engine management system was improved, which resulted

in an NOx conversion efficiency of at least 80% across engine

operating temperatures of 250°–500°C, using the 3-ppm sulfur base fuel. This was achieved with no more than a 4% 

average increase in fuel consumption.

Next, the test focused on desulfurizing the NOx adsorber 

catalyst by controlling the air/fuel ratio and catalyst inlet temperatures to achieve the high temperatures required to release

the sulfur from the device. The desulfurization process was

demonstrated by running it on the catalysts periodically 

over 250 hours with varying sulfur-level fuels.

The final step included: 

• A series of aging, performance mapping, and desulfurization cycles.

• Multiple consecutive desulfurizations to determine the

effect of the high temperature exposure on the catalyst’s

durability.

Figure 8. The NOx conversion efficiency of the fresh 

NOx adsorber catalyst under improved lean/rich engine 

calibration 

NOx adsorber catalysts were installed in this test cell at FEV 13

in Auburn Hills, MI.

250 300 350 400 450 500

Catalyst Inlet Temperature (C)

NOx Conversion Efficiency (%)

100

80

60

40

20

0

Summary of DECSE Reports
level of performance. Exposing the catalyst repeatedly to 

the desulfurization procedure caused a continued decline 

in the catalyst’s desulfurized performance (see Figure 10).

Additional work will be necessary to identify the cause of

this decline.

• The rate of sulfur contamination during aging with 78-

ppm sulfur fuel increased with repeated aging/desulfurization cycles (from 10% per 10 hours to 18% per 10 hours).

This was not observed with the 3-ppm fuel, where the rate

of decline during aging was fairly constant at approximately

2% per 10 hours.

Figure 9. Comparison of NOx conversion efficiency before

and after desulfurization for catalysts aged as long as 250

hours with 3-, 16-, and 30-ppm sulfur level fuels 

14 Figure 10. Regression model (with 95% confidence interval)

of post-desulfurization NOx conversion efficiency versus

total desulfurization time. Data for catalyst pair aged on 

78-ppm sulfur level fuel.

• The desulfurization procedure recovers efficiency of at least

85% NOx conversion from fuel sulfur levels of 3-, 16-, and

30-ppm for as long as 250 hours over a catalyst inlet operating temperature window of 300°–450°C (see Figure 9). 

• This desulfurization procedure has the potential to meet 

in-service engine operating requirements and acceptable 

drivability conditions.

• Aging with 78-ppm sulfur fuel reduced NOx conversion

efficiency more than aging with 3-ppm sulfur fuel as a 

result of sulfur contamination. However, the desulfurization

events restored the conversion efficiency to nearly the same

250 300 350 400 450 500

Catalyst Inlet Temperature (C)

A, B, C after 

desulfurization

B = 16 ppm 

for 200 hours

C = 30 ppm 

for 150 hours

A = 3 ppm 

for 250 hours

NOx Conversion Efficiency (%)

100

80

60

40

20

0

Summary of DECSE Reports

0 50 100 150 200 250 300 350 400

Desulfurization Time (minutes)

Integrated NOx Conversion Efficiency (%)

120

100

80

60

40

20

0

Regression Fit

Catalyst 1 

Catalyst 2

95% Limit
Recommendations

By 2007, EPA emission standards for heavy-duty diesel

engines will require that NOx and PM emissions be reduced

by 90% below current limits. Passenger vehicles will need to

be 77%–95% cleaner than those now on the road and refiners

will need to reduce the sulfur content of diesel fuel by as

much as 97%. Beginning in 2004, this tailpipe standard will

also limit NOx emissions to an average of 0.07 grams per mile

for all classes of passenger vehicles, including all light-duty

trucks and the largest SUVs. 

Diesel Oxidation Catalyst

DECSE tests demonstrated that the DOC does not control

PM emissions well enough to meet the EPA’s 2007 standards.

However, it could be useful in an emission control system 

to clean up the HC emissions during rich regeneration. 

The DOC may be effective when used in combination with

selective catalytic reduction (SCR), either as a pre-catalyst 

for converting NO to NO2 or as a post-catalyst to control

ammonia slip. 

Lean-NOx Catalyst

With its limited reduction efficiency (~20%), this technology

cannot meet the EPA’s 2007 emission standards. But it could

meet the 2004 emission regulations for light- and heavy-duty

diesel engines. A DOC could be used to clean up HC slip

when this approach is used. 

NOx Adsorber Catalyst 

This technology is promising for meeting future NOx standards. However, more study is needed to investigate the frequency of desulfurization and to more accurately characterize

thermal degradation associated with the high-temperature

desulfurization cycle. More detailed studies are also needed to

address the long-term operation of the NOx adsorber catalyst,

including the durability of the engine and catalyst, and other

exhaust constituents—such as smoke levels during regeneration—and on which trade-offs are required to reduce or keep

them low. 

Diesel Particulate Filter

When used with low-sulfur fuel, this technology is capable 

of meeting future PM standards. Research is needed to

demonstrate that DPFs can be beneficial in combination,

respectively, with SCR and a NOx adsorber. Additional 

research should be conducted on measurements for PM 

mass, size, and composition, as well as for air toxics.

The Next Step

Results and test experiences from the DECSE project are

being used by its successor, the APBF-DEC project, to identify the optimal combinations of fuels, lubricants, diesel

engines, and emission control systems to meet projected EPA

emission standards for 2002 to 2010. APBF-DEC also will

identify properties of fuels and vehicle systems that could lead

to even lower emissions beyond 2010. 

The APBF-DEC project selected two emission control technology systems for further study: 

Selective Catalytic Reduction/

Diesel Particulate Filter

The SCR is an emissions reduction device that, combined

with a DPF and advanced fuel formulations, may reduce 

regulated (especially NOx), unregulated, and toxic emissions.

Two types of SCR-based catalysts are being evaluated in 

combination with DPFs and possibly DOCs.

NOx Adsorber Catalyst/

Diesel Particulate Filter 

The NOx adsorber may significantly reduce NOx, HC, and

CO emissions from diesel engine exhaust. Combined with a

DPF, the NOx adsorber can also effectively oxidize the PM

and other unregulated emissions from diesel exhaust. Two 

systems are being evaluated on light-, medium-, and heavyduty engines and light- and medium-duty vehicles.

For detailed information about the progress of the APBF 

project, visit http://www.ott.doe.gov/apbf. Direct your 

questions about the DECSE or APBF-DEC to: 

Wendy Clark

DECSE Deputy Project Manager

National Renewable Energy Laboratory

Phone 303-275-4468 

E-mail: wendy_clark@nrel.gov

15

Summary of DECSE Reports
Summary of DECSE Reports

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