NREL/CP-540-39009. Posted with permission. 

Presented at the SAE 2006 World Congress, 

April 3-6, 2006, Detroit, Michigan 2006-01-0423 

Desulfurization Effects on a Light-Duty Diesel Vehicle NOx

Adsorber Exhaust Emission Control System 

Marek Tatur, Dean Tomazic, Heather Tyrer 

FEV Engine Technology, Inc. 

Matthew Thornton 

National Renewable Energy Laboratory 

Joseph Kubsh 

Manufacturers of Emission Controls Association 

Copyright © 2006 SAE International

ABSTRACT 

The U.S. Tier 2 emission regulations require 

sophisticated exhaust aftertreatment technologies for 

diesel engines. One of the projects under the U.S. 

Department of Energy’s (DOE’s) Advanced PetroleumBased Fuels – Diesel Emission Controls (APBF-DEC) 

activity focused on the development of a light-duty 

passenger car with an integrated NOx (oxides of 

nitrogen) adsorber catalyst (NAC) and diesel particle 

filter (DPF) technology. Vehicle emissions tests on this 

platform showed the great potential of the system, 

achieving the Tier 2 Bin 5 emission standards with new, 

but degreened emission control systems. The platform 

development and control strategies for this project were 

presented in 2004-01-0581 [1]. 

The main disadvantage of the NOx adsorber technology 

is its susceptibility to sulfur poisoning. The fuel- and 

lubrication oil-borne sulfur is converted into sulfur 

dioxide (SO2) in the combustion process and is 

adsorbed by the active sites of the NAC. As a result, 

they are unavailable for NOx storage. This leads to a 

drop in system performance. In order to recover the 

active sites, the bound sulfates need to be released. The 

necessary conditions for sulfate release are relatively 

high temperatures in combination with rich exhaust gas 

conditions. This process is often referred to as 

desulfurization. 

After the completion of the development phase, the 

emission control system was aged with 15-ppm sulfur 

diesel fuel to a full useful life (120,000 miles) condition. 

During the course of this aging, intermittent 

desulfurizations were carried out. The desulfurizations 

were preceded and followed by evaluation procedures to 

allow a detailed analysis of the desulfurization effects. 

Desulfurizations were performed every 150 hours up to 

300 hours, every 100 hours up to 1,600 hours, and 

every 50 hours to the end of aging at 2,200 hours. This 

paper analyzes the effects on gaseous emissions, 

before and after desulfurization, over transient driving 

cycles such as the light-duty Federal Test Procedure 

(FTP-75). 

The results indicate a high degree of recovery, 

maintaining a low level of tailpipe emissions over the 

useful lifetime (120,000 miles) of the emission control 

system. 

INTRODUCTION 

Despite the upcoming, stringent Tier 2 emission 

standards, significant efforts are focused on the 

reintroduction of the diesel engine into the U.S. market. 

In order for these efforts to succeed, diesel powered 

vehicles will have to comply with emission standards 

while maintaining their superior fuel economy. 

Furthermore, they need to be competitive with their 

gasoline counterparts in regard to power, engine noise, 

and transient response behavior. The availability of 

technologies—such as high-pressure, common-rail fuel 

injection systems; low-sulfur diesel fuel; NACs; and 

DPFs—enable the development of powertrain systems 

that have the potential to comply with these 

requirements. 

Supporting the development of these technologies, DOE 

is engaged in several test projects under the APBF-DEC 

activity. These projects primarily address the sulfur 

tolerance and NAC/DPF system durability implications of 

varying fuel sulfur levels. A result of the project focusing 

on the passenger car platform is a fundamental 

understanding of the integrated emission control system 

(ECS) strategies and calibration. 
PROGRAM OBJECTIVES 

The main objective of the APBF-DEC activity was to 

investigate the sulfur tolerance and durability of different 

aftertreatment systems such as the NAC/DPF 

combination. 

An integral part of the program was to demonstrate the 

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

combination to achieve the Tier 2 Bin 5 emission levels 

[0.07 g/mi NOx and 0.01 g/mi particulate matter (PM)]. In 

order to meet these requirements over the lifetime of the 

ECS, the system needed to be desulfurized to allow for 

a regain in NOx conversion efficiency. 

The ECS was aged up to 2,200 hours to allow an 

assessment of the fuel effects on the durability of the 

systems. The detailed fuel specifications for this project 

are presented in Appendix A. 

HARDWARE DEFINITION 

ENGINE PARAMETERS AND CONFIGURATION 

The engine used in this project was designed to 

accommodate the increased demands of emission 

reduction development. The crankcase, crankshaft, and 

connecting rods are mass-production parts from 

Volkswagen AG, Wolfsburg. The cylinder head and the 

pistons are proprietary components developed by FEV 

Engine Technology specifically for emission reduction 

applications. Table 1 shows relevant details of this 

engine configuration [2]. 

Table 1: Diesel Future II Engine Specifications 

Arrangement In-Line 4-Cylinder 

Displacement 1.9 L 

Rated Power 100 kW @ 4000 rpm 

Max. Torque 330 Nm @ 2000 rpm 

Bore/Stroke 79.5 mm / 95.5 mm 

Turbocharger Garrett GT 17 V 

Injection System Bosch Common Rail, 2nd Gen. 

Valves 2 x Intake / 2 x Exhaust 

Compression Ratio 18.2 : 1 

Figure 1 shows the Diesel Future II engine prior to 

installation in the project test cell. With the exception of 

the components mentioned above, all other engine 

components are commercially available, including the 

electronically actuated exhaust gas recirculation (EGR) 

valve and variable nozzle geometry turbocharger visible 

in Figure 1. 

Figure 1: Diesel Future II Engine 

The combustion system was configured according to the 

required emission targets (Euro 4 NOx level < 0.4 g/mi) 

while maintaining excellent fuel economy and represents 

advanced combustion technology. 

EMISSION CONTROL SYSTEM SPECIFICATION 

The catalysts were designed and developed together 

with a MECA (Manufacturers of Emissions Controls 

Association) program participant. 

Early discussions with the catalyst supplier resolved 

initial design questions, such as dimensions and 

amounts of required catalysts. The next issue was to 

determine the positioning of the NAC and DPF. Analysis 

of similar powertrain configurations on other vehicles 

showed relatively low temperatures downstream of the 

turbine. Therefore, the decision was made to place the 

NAC upstream of the DPF. A dual-wall exhaust manifold 

and air-gap insulated exhaust piping were used to 

minimize thermal losses between components. These 

parts were also provided by a MECA project partner. 

Pre-Catalyst

Each ECS included a pre-catalyst that served several 

functions. One of its primary functions was the oxidation 

of unburned fuel introduced during post-injection events 

to increase temperature under the following three 

operating modes: 

1. Warm-up 

2. DPF regeneration 

3. Desulfurization. 

The pre-catalyst must also partially oxidize unburned 

fuel during the transition to rich mode for NOx

regeneration. This is part of the process of preparing the 

necessary NOx reduction agents [most preferably 

hydrogen (H2) or carbon monoxide (CO)]. 

Another important function of the pre-catalyst was to act 

as a sulfur trap during lean operation offering the 
underbody NAC a degree of protection from sulfur 

poisoning. 

Two ECSs, denoted as ECS-A2 and ECS-B2, were 

initially evaluated in this project. The difference between 

these systems was their pre-catalysts. ECS-A2 

comprised a pre-catalyst that was 50% DOC and 50% 

NAC, while ECS-B2 utilized a 100% NAC pre-catalyst. 

Specifications for both ECSs are summarized in Table 2. 

Table 2: Emission Control System Catalyst 

Specifications 

ECS A2 ECS B2 and ECS B3 

Precat UBNAC DPF Precat UBNAC DPF 

Volume [L] 1.34 2.5 4.1 1.34 2.5 4.1 

Cross 

Section [-] Round Round 

Diameter 

[in] 4.16 5.66 5.66 4.16 5.66 5.66 

Length [in] 6.00 6.00 10.00 6.00 6.00 10.00 

Substrate 

Material [-] Cord Cord SiC Cord Cord SiC 

Wall 

Thickness 

[mil] 

4.5 4.5 14 4.5 4.5 14 

Cell Density 

[cpsi] 400 400 200 400 400 200 

Pre-Cat 

Config. 50% DOC – 50% NAC 100% NAC 

Underbody Catalyst

Each ECS included an identical 2.5-liter underbody NAC 

on a Cordierite substrate. The NACs were coated with a 

formulation that maximized effectiveness at the lowest 

possible temperatures to address the typical low exhaust 

gas temperature level during FTP-75 operation. 

DPF

The selection criteria for the DPF material included 

thermal mass, backpressure characteristics, cost, and 

durability. Due to durability concerns under potential 

uncontrolled regeneration conditions, a thermally stable 

silicon carbide substrate was selected. A catalytic 

coating contributed to control of hydrocarbon (HC) and 

CO breakthrough during regeneration events. 

During testing, ECS-B2 showed the most promise in 

reducing NOx emissions. Therefore, these same 

specifications were utilized to create the aging system, 

ECS-B3. 

EMISSION CONTROL SYSTEM SETUP 

A schematic overview of the instrumented ECS is 

depicted in Figure 2. 

In the test cell, temperature and pressure measurements 

were taken at each of the exhaust locations. Emission 

measurements were taken at system inlet and system 

outlet (positions I and IV in Figure 2). A differential 

pressure transducer was installed across the DPF to 

provide feedback on its loading level. 

NOx sensors were utilized both before and after the NAC 

to provide real-time efficiency information. Engine

Exhaust

NOx

Sensor

Diff. Press.

Sensor

p p p p

p : Pressure Transducer

T T T T

T : Thermocouple

PreCatalyst

Underbody

NAC CDPF

Emission Sample Lines

I IV

λ -Sensor

Figure 2: Emission Control System Setup 

TEST ENVIRONMENT 

Emissions measured in the test cell are sampled with 

several different devices. For regulated gaseous 

emissions, such as NOx, CO, THC, and CO2, a Horiba 

emissions bench was used. NOx sensors and wide 

range lambda sensors were also utilized (Figure 2). NOx

sensors monitored real-time emissions, but the 

measurements were used for the NOx regeneration 

strategy only, not for collecting emission data. 

An Airsense 2000 mass spectrometer was used for 

unregulated gaseous emissions. During desulfurization, 

H2S and SO2 were the only sulfur species measured. 

Oxygen was also measured to allow for a time-alignment 

of the data with the emissions bench. 

DESULFURIZATION DEVELOPMENT 

Desulfurization represents one of the more challenging 

aspects of NAC strategy development. A significant 

amount of effort was invested to optimize the 

desulfurization process. Desulfurization was run at each 

designated hour mark. The frequency was every 150 

hours up to 300 hours, every 100 hours up to 1,600 

hours, then every 50 hours to the end of 2,200 hours. 

First, transient pre-desulfurization tests were run, and 
then the desulfurization was performed under steadystate conditions (2,500 rpm; 8 bar BMEP), followed by 

transient evaluation cycles (these included a preparation 

UDDS cycle). 

Previous investigations have shown that temperature 

and lambda management can be challenging during 

desulfurization conditions [3]. The return to lean 

operation at the end of the desulfurization proved 

problematic, especially since significant temperature 

spikes can lead to excessive thermal aging. Therefore, 

a 4-stage strategy was developed to address this issue: 

1. Start intake throttling. 

2. Initiate post injection to maintain target lambda of 

0.97 to 0.98 for a duration of 6 minutes. 

3. Terminate post-injection. 

4. De-throttle following 5-10 second delay. 

Stages 3 and 4 were critical as they provided the system 

with time to purge unburned HC before excess oxygen 

became available. This process is illustrated in Figure 3. Lambda [-] 0.90

0.95

1.00

1.05

1.10

1.15

1.20

1.25

1.30

1.35

1.40

0 25 50 75 100 125 150 175

Time [s]

500 525 550 575 600 625 650 675 700

1st Stage:

- Throttling to lambda 1.1

2nd Stage:

- Apply post-injection

- Lambda control between 0.96 and 0.98

3rd Stage:

- Disable post-injection

4th Stage:

- Dethrottle after 5-10 seconds waiting period

Figure 3: 4-Stage Desulfurization Strategy 

AGING AND EVALUATION CYCLE DEFINITION 

Aging of the ECS was accomplished by alternating aging 

and evaluation cycles. The typical test matrix consisted 

of 100 hours of aging cycles, followed by a transient predesulfurization cycle, desulfurization, and finally a 

transient post-desulfurization evaluation. 

AGING CYCLE 

The aging cycle used was based on the LA92 driving 

cycle (shown in Figure 4). This is a high-speed/highacceleration driving cycle developed by the California Air 

Resources Board. 

Time [s]

Speed [mi/h]

Figure 4: LA92 Driving Cycle 

The test was adapted into 14 steady-state points to 

determine and optimize engine-out emissions. Each of 

the points was run 43 seconds to accumulate the 

desired cycle time of 10 minutes. The cycle was then 

repeated until the subsequent hour mark for the 

evaluation tests was reached. 

During the aging cycles, it became apparent that the 

ECS was exposed to higher temperatures with the 

adapted steady-state cycle than with the original 

transient LA92. Therefore, the points with temperatures 

above 450oC were moved toward a higher engine speed 

and lower load. This lead to a lower pre-catalyst inlet 

temperature while maintaining the same fuel flow. Figure 

5 shows the 14 steady-state points during the 10-minute 

aging cycle. Speed [rpm]

0

500

1000

1500

2000

2500

3000

3500

Time [sec]

0 100 200 300 400 500 600

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

BMEP [Bar]

Figure 5: Speed and BMEP of Steady-State Aging 

Cycle 

EVALUATION CYCLES 

When the desired ECS age was reached with the aging 

cycles, transient evaluation tests were run to determine 

the efficiency of the system. Several procedures were 

created for different purposes. Each procedure 

consisted of at least one of each of the following tests: 

cold and hot UDDS (bags 1 and 2 of the FTP-75), US06, 
and HFET. Procedures differed by the amount of times 

these tests were repeated. 

The UDDS cycle is run twice. The first ‘cold UDDS’ is 

performed after the overnight soaking period while the 

second ‘hot UDDS’ is performed following a 10-minute 

hot soak. The duration of the UDDS is 1,369 seconds, 

with a distance covered of approximately 7.45 miles. 

The US06 cycle was developed to address 

shortcomings in the FTP-75 in regard to representing 

aggressive acceleration and deceleration, as well as 

high-speed driving. The cycle covers a distance of 8.01 

miles over a duration of 596 seconds. In comparison to 

the FTP-75 cycle, the engine speed and load profile of 

this test are significantly higher. 

The HFET was initially developed to quantify the 

deterioration in fuel economy of light-duty vehicles. It is a 

light load and low speed test without any additional lowidle phases. The overall duration of the test cycle is 765 

seconds, covering 10.26 miles in distance. 

TEST RESULTS 

DEVELOPMENTAL RESULTS 

Investigations were conducted with desulfurization 

temperatures ranging from 580°C to 725°C. Figure 6 

documents the steps that were taken to determine the 

minimum desulfurization temperature for further 

investigations. During preliminary tests with 

developmental catalysts, the largest increase in catalyst 

capacity was found at a desulfurization temperature of 

700°C. Experience from numerous desulfurizations has 

demonstrated the capability to achieve 95% and greater 

recovery of NOx storage capacity. 

While the majority of development was conducted with 

zero ppm sulfur fuel, the ECS was intentionally sulfur 

poisoned using standard premium diesel fuel with a 

sulfur content of 350 ppm in order to conserve valuable 

test cell time. The engine was operated under moderate 

load conditions with representative NAC regenerations 

for 5 hours. This resulted in a massive decrease in 

catalyst activity in terms of NOx storage and conversion 

efficiency. The pre-catalyst was rendered virtually 

ineffective, while the underbody catalyst NOx storage 

capacity was reduced by 64%. 

The gradual increase in desulfurization temperature 

showed improving efficiencies up to the desulfurization 

temperature of 720°C. In order to limit the effects of 

thermal aging throughout the useful life of the catalyst 

system, the more conservative desulfurization 

temperature level of below 700°C was chosen for the 

durability testing. 

560 580 600 620 640 660 680 700 720 740

20

40

60

80

1 100

2

3

4

5

6

 Capacity compared to aged catalyst

 NOx Storage Capacity [%]

Desulfurization Temperature [°C]

Capacity aged catalyst

NOx Storage Capacity [g]

Capacity sulfur-poisoned catalyst

Figure 6: Determination of Minimum Desulfurization 

Temperature 

Figure 7 shows temperature profiles during a typical 

desulfurization. An exotherm of approximately 50°C was 

generated over the pre-catalyst during the extended rich 

operation. The inlet temperature of the underbody 

catalyst was comparable to the inlet temperature of the 

pre-catalyst. 

Figure 7: Temperature Profiles during Desulfurization 

No temperature spike is visible at the transition to lean 

operation at the end of the desulfurization event due to 

the 4-stage transition strategy that was employed. 

The final developmental desulfurization strategy utilized 

a 700°C catalyst inlet temperature, a rich lambda of 

0.98, and a duration of 6 minutes. However, later tests 

showed that this was not long enough to fully purge the 

system of sulfur. Therefore, sulfur was monitored at real 

time downstream from the ECS, and desulfurization was 

discontinued when the sulfur release was no longer 

significant (below 15 ppm), which was approximately 8 

to 13 minutes. 
AGING RESULTS 

Fresh-Catalyst Effects

Initial developmental desulfurizations were performed on 

a slightly aged ECS. The operating conditions that gave 

the desired temperatures were developed based on that 

ECS’s characteristics. During the first desulfurizations 

on the test systems, it was found that these conditions 

were too severe for a fresh catalyst. The same 

developmental inlet temperature resulted in a much 

higher exotherm (over 100°C) on the aging ECS-B2. It 

was believed that these high temperatures may have 

severely thermally aged the catalysts. Therefore, aging 

with ECS-B3 first used much lower pre-catalyst 

exotherms. 

Figure 8 shows the higher exotherm across the precatalyst as compared to the development system (Figure 

7). Temperature [°C]

300

350

400

450

500

550

600

650

700

750

800

Time [s]

0 100 200 300 400 500 600 700

Temperatures 

 before Turbine

 before CCC

 after CCC

 before DPF

 after DPF

Lambda [-]

0.95

1.05

1.15

1.25

1.35

1.45

Exotherm

Desulfurization ECS-B2

after 150 hours

Operating conditions:

2500 rpm / 8 bar BMEP

Duration

Figure 8: First Desulfurization on a Fresh Catalyst 

Desulfurization during Aging

Table 3 shows the desulfurization characteristics for 

ECS-A2 and ECS-B2. These systems utilized the initial 

conditions set by the developmental catalysts. 

Therefore, these systems were subject to the higher 

exotherms due to the fresh-catalyst effects. Each system 

was desulfurized only twice before the aging was 

discontinued. 

Desulfurizations at 150 hours on each system had an 

exotherm of about 150°C (Figure 8). Since these 

conditions were much too extreme, the calibration was 

changed at 300 hours to allow for lower pre-catalyst 

outlet temperatures (i.e., lower exotherm across the precatalyst). 

However, it was believed that the systems were already 

severely thermally aged. Tests have shown that NACs 

suffer a loss in conversion efficiency when exposed to 

high-temperature, lean-rich conditions. This loss 

becomes greater as temperature increases [4]. 

Emissions before desulfurization at 300 hours showed a 

steep increase in NOx. Figure 9 illustrates the NOx

emissions for ECS-B2 during hot UDDS tests. 

Maximum

Average 

Minimum

Figure 9: NOx Emissions for ECS-B2 for Hot LA4 

Table 3 shows the desulfurization characteristics for 

ECS-A2 and ECS-B2. While all desulfurizations result in 

a gain in NOx conversion efficiency, both systems are 

over the composite FTP-75 emission limits before 

desulfurization at 300 hours. 

Table 3: Desulfurization Characteristics for ECS-A2 and 

ECS-B2 

Composite

FTP75 NOx

300 6.70 614 653 1.70 0.103 0.061

150 6.85 661 748 * 0.067 0.020

[Hours] [min] [°C] [°C] [grams] [g/mi] [g/mi]

After

Desulf

Before

Desulf

Sulfur 

Released

Average Temp

after CCC

Average 

System

Inlet Temp

Desulf Duration

ECS-A2

Composite

FTP75 NOx

300 6.29 661 708 1.17 0.109 0.027

150 6.70 678 789 * 0.035 0.017

[Hours] [min] [°C] [°C] [grams] [g/mi] [g/mi]

After

Desulf

Before

Desulf

Sulfur 

Released

Average Temp

after CCC

Average 

System

Inlet Temp

Desulf Duration

ECS-B2

* No data available

Secondary air injection upstream the DPF was used 

during the 150-hour desulfurizations for ECS-A2 and 

ECS-B2 to allow for a DPF regeneration. The air 

injection eliminated the possibility to detect H2S and SO2

in the exhaust as those species react the oxygen and 

form other species that were not captured with the 

measurement equipment. This procedure was used 

initially to prove the concept, however was discontinued 
to allow real-time sulfur release analysis during the 

desulfurization event. 

Due to variation in engine behavior and fresh-catalyst 

effects, calibration for ECS-B3 was redeveloped. Table 4 

shows the desulfurization characteristics for ECS-B3 up 

to 2,200 hours. 

Table 4: Desulfurization Characteristics for ECS-B3 

At 1600 hours, the decision was made to increase the 

desulfurization frequency from every 100 hours to every 

50 hours to improve NOx emissions over the life of the 

system. Those cells highlighted show before and after 

desulfurization results for the hot UDDS only, not the 

combined composite FTP-75. 

While the desulfurization at 150 hours released a large 

amount of sulfur, the composite FTP-75 emissions 

actually increased (over the average). This is most likely 

because the emissions at this age were initially very low. 

The sulfur released at 300, 400, and 500 hours was 

much lower. However, the system showed an 

improvement in NOx conversion efficiency. 

At 600 hours, it was decided to increase the system inlet 

temperature to release more sulfur. Since the system 

had been aged to approximately one-quarter of its life, 

fresh-catalyst effects were not anticipated to be an 

issue. Engine speed and load were increased to raise 

the system inlet temperature. Desulfurizations at 600 

and 800 hours showed a significant regain in NOx

conversion efficiency. 

Desulfurizations at 800 and 900 hours resulted in higher 

sulfur release. At 1,000 hours, it was noticed that a 

lower system inlet temperature resulted in a decreased 

amount of released sulfur. With that in mind, efforts 

were made to keep the inlet temperature high, but with 

an open-loop control, the temperature varied from test to 

test. 

At 1,300 hours, the post-desulfurization test was 

conducted with NOx regenerations disabled. This 

resulted in higher NOx emissions, therefore giving a 

negative percent improvement. Sulfur release and 

duration were relatively constant throughout the 

remainder of the system’s lifetime. 

Figure 10 shows the duration, system inlet temperature, 

sulfur released, and percent improvement of NOx for all 

desulfurizations for ECS-B3. Duration [min]

0

4

8

12

16

20

Avg Inlet Temp [C]

600

620

640

660

680

700

720

740

Sulfur Released [g]

0

1

2

3

4

5

Percent Improvement [%]

-20

0

20

40

60

80

100

Aging Hours

100200300400500600700800900

1000110012001300140015001600170018001900200021002200

Figure 10: ECS-B3 Desulfurization Overview 

Over 100 hours of aging, the ECS is exposed to 

approximately 6 g of sulfur. With an average 

improvement of over 40% in NOx conversion efficiency, 

it is likely that the majority of the trapped sulfur is 

released during desulfurization. Therefore, the catalyst 

traps approximately 30% of the sulfur in the exhaust. It 

is also possible that sulfur was released in forms other 

than H2S and SO2, which would increase the degree of 

retention stated above. The desulfurization results show 

that a greater gain in NOx conversion efficiency is found 

at lower releases of the measured sulfur. Presumably, 

more efficient desulfurization conditions release other 

forms of sulfur than H2S and SO2, which is subject to 

further investigations. 

Emissions during desulfurization were measured 

downstream from the ECS (tailpipe). Figure 11 shows 

lambda, oxygen, CO, THC, and NOx for a typical 

desulfurization. 
NOx [ppm]

0

200

400

600

800

1000

Time [sec]

0 100 200 300 400 500 600 700

Lambda [-]

0.95

1.05

1.15

1.25

1.35

1.45

O2 [%]

0

2

4

6

8

CO [%]

0

100

200

300

400

500

THC [ppm]

0

100

200

300

400

500

Figure 11: Tailpipe Emissions during Desulfurization 

When the engine is operating in a rich or stoichiometric 

condition, the NAC acts as a three-way catalyst. NOx is 

reduced by splitting the molecules into nitrogen and 

oxygen. This oxygen is then used to oxidize CO and HC. 

However, since there is not enough oxygen to fully 

oxidize all the species, some CO and HC slip through, 

leaving no oxygen downstream from the ECS. 

DPF REGENERATION DURING DESULFURIZATION 

The remaining element of the strategy development and 

calibration effort consisted of evaluating the required 

frequency and efficiency of DPF regeneration events. 

The quantity of DPF regenerations required over the 

lifetime of the ECS can have a significant impact on fuel 

consumption. Therefore, a significant effort was invested 

in optimizing the efficiency of the DPF regeneration. 

During the first desulfurization, air was injected upstream 

the DPF to aid in DPF regeneration. At high 

temperatures, the limited addition of oxygen allows the 

soot to burn at a controlled rate. Figure 12 shows the 

drop in differential pressure and the associated 

temperature during desulfurization. This allows the 

majority of the soot to oxidize before returning to lean 

conditions, therefore preventing a temperature spike and 

possible thermal damage. 

This method was used on both the ECS-A2 and ECS-B2 

at the 150-hour desulfurizations. While air was injected 

upstream the DPF, sulfur emissions were being 

measured downstream the DPF (ECS outlet). However, 

no sulfur was measured during either desulfurization, so 

it is believed that the air injection interfered with the 

production of H2S and SO2. Most likely, the addition of 

oxygen allowed for the formation of other sulfur 

compounds, such as sulfuric acid, that were not being 

measured. 

0

50

100

150

200

250

300

350

0 100 200 300 400 500 600 700 800

Time [sec]

DPF Diff Press [mbar]

0

100

200

300

400

500

600

700

800

900

Temp After DPF [C]

Start of Desulfurization 

and Air Injection

End of Desulfurization 

and Air Injection

Figure 12: Differential Pressure Drop during 

Desulfurization 

Initially, it was believed that the DPF would need 

regeneration throughout the aging process. However, 

early tests showed that the DPF would self-regenerate 

over the developed aging cycle. As the DPF was selfregenerating during aging, and reading sulfur release 

during desulfurization was more important, air injection 

during desulfurization was discontinued after the 150-

hour event. 

CONCLUSION 

Development studies have proven that the NAC in 

combination with DPF technology has considerable 

potential in meeting future Tier 2 emissions regulations. 

However, NACs must also combine desulfurization 

strategies to regain the lost NOx storage sites due to 

sulfur poisoning. 

Desulfurization strategies utilized on these ECSs 

showed that a significant amount of NOx conversion 

efficiency could be recovered. Both test cell and vehicle 

results show that after desulfurization at 120,000 miles 

(full useful life), the test ECS was able to meet the Tier 2 

Bin 5 standard for NOx and PM emissions. 

For the most thorough desulfurization, a more 

sophisticated desulfurization strategy needs to be 

developed that not only considers the degree of sulfur 

poisoning, but also uses the temperatures during the 

desulfurization as feedback signal and adjusts the 

parameters accordingly. It was found that fresh catalysts 

react significantly different to the same engine 

parameter settings than moderately aged catalysts. 

Furthermore, the sulfur release effects could be subject 

to other studies. A more detailed chemical analysis of 

the exhaust would show if there is any existence of 

sulfur other than H2S and SO2. Also, an evaluation of 

the regain in NOx conversion efficiency versus the type 

of sulfur released would give more insight into the most 

desirable desulfurization conditions. 
ACKNOWLEDGMENTS 

The authors would like to thank the members of the 

APBF-DEC Steering Committee, ABPF-DEC NOx

Adsorber Workgroup, National Renewable Energy 

Laboratory, Oak Ridge National Laboratory, MECA, and 

DOE for their support and guidance. This project and all 

of the ABPF-DEC activities are being conducted with the 

cooperation of engine and vehicle manufacturers, 

emission control device manufacturers, energy and 

additive companies, California State agencies, and the 

U.S. Environmental Protection Agency. Representatives 

from all of these organizations and their member 

companies are represented on the steering committee 

and the workgroups. This project would not be possible 

without their help and technical support. 

REFERENCES 

1. 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. 

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

Adsorber/DPF Project: Light-Duty Passenger Car 

Platform,” DEER Paper, August 2003, Newport, 

Rhode Island. 

3. Geckler S., Tomazic D., et al. “Development of a 

Desulfurization Strategy for a NOx Adsorber Catalyst 

System,” SAE Paper 2001-01-0510, March 2001, 

Detroit, Michigan. 

4. Fang H., Wang J., Yu R., Wan C., Howden K. 

“Sulfur Management of NOx Adsorber Technology 

for Diesel Light-Duty Vehicle and Truck 

Applications.” SAE Paper 2003-01-3245, October 

2003, Pittsburgh, Pennsylvania. 

CONTACT 

Marek Tatur, FEV Engine Technology, Senior Engineer 

Diesel Combustion Systems. E-Mail: tatur@fev-et.com

DEFINITIONS, ACRONYMS, ABBREVIATIONS 

APBF-DEC: Advanced Petroleum-Based Fuels – Diesel 

Emissions Control 

BTDC: Before Top Dead Center 

CA: Crank Angle 

CO: Carbon Monoxide 

CO2: Carbon Dioxide 

DOE U.S. Department of Energy 

DPF: Diesel Particle Filter 

ECM: Electronic Control Module 

ECS: Emission Control System 

ECU: Engine Control Unit 

EGR: Exhaust Gas Recirculation 

EPA: Environmental Protection Agency 

ETK: Emulator Task Kopf 

FSN: Filter Smoke Number 

FTP: Federal Test Procedure 

FTP-75:Light-Duty Federal Test Procedure 

HC: Hydrocarbon 

HFET: Highway Fuel Economy Test 

HSDI: High-Speed Direct Injection 

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

MECA: Manufacturers of Emissions Controls 

Association 

NAC: NOx Adsorber Catalyst 

NMHC: Non-Methane Hydrocarbon 

NO: Nitric Oxide 

NO2: Nitrogen Dioxide 

NOx: Oxides of Nitrogen 

O2 Oxygen 

OEM: Original Equipment Manufacturer 

PM: Particulate Matter 

RPM: Revolutions per Minute (engine speed) 

SC03: Air Conditioning Test 

SCR: Selective Catalytic Reduction 

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 are doped into the base fuel. The dopant mixture contains a variety of classes of S 

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

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

development activity. 

Table B-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 B-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