.Reprinted with permission from SAE International. This paper may not be photocopied, e-mailed or otherwise reproduced without permission of SAE International
ABSTRACT
In order to meet the Euro V heavy-duty diesel emissionstandard legislation limits, a diesel engine can beoptimized by internal means to give low particulateemissions and lower fuel consumption. Thesemodifications of the engine lead inevitably to higher NOxemissions due to the NOx/PM trade off. An efficient UreaSCR after-treatment system is then able to reduce thehigher NOx emission to below the Euro V 2.0g/kWhlegislation limit. This paper presents tests made on a PMoptimized 12 liter heavy-duty diesel engine together witha urea SCR after-treatment system. The optimizedengine had engine out particulate emissions of about0.04 g/kWh and NOx emissions of 9 g/kWh for the ESCand 8,5 g/kWh for the ETC. The fuel consumption of theoptimized engine was 194 g/kWh for the ESC and 198g/kWh for the ETC as compared to state of the art EuroIII engines of typically 210 g/kWh for the ESC, givingsignificant fuel savings of 7.5 %.
Combining the engine with a 20 liter 300-cpsi SCRcatalyst, catalyst volume to cylinder ratio of 1.7, theparticulate emissions dropped to 0.017 g/kWh for theESC and 0.020 for the ETC. Particle size measurementsalso showed a decrease in the number of fine particles.With a urea injection corresponding to about 8-9% of thefuel flow the NOx emissions were reduced to 1.4 g/kWhfor the ESC and 1.5g/kWh for the ETC with low ammoniaslip. These reductions correspond to a NOx conversionof 84 % and 82% for the ESC and ETC respectively.
Thus the optimized engine combined with the urea SCRafter-treatment system was compliant with the Euro Vemission limits.
INTRODUCTION
In order to comply with the Euro V regulations for heavy-duty diesel engines due in 2008, both the NOx andparticulate emissions must be greatly reduced for today’sstate of the art diesel engines. The regulations of 2008,namely 2.0 g/kWh NOx and 0.02 g/kWh particulates forthe ESC and 0.03 g/kWh for the ETC driving cycles,cannot be achieved solely by engine management orimproved engines, rather some sort of aftertreatmentmust be used.
A preferred solution to comply with the Euro V emissionlimits is to optimize a diesel engine by internal means togive very low particulate emissions and considerablylower fuel consumption [1]. Due to the NOx/PM trade-offfor diesel engines this will lead to higher NOx emissions,from Euro III levels of 5-6 g/kWh to 8-10 g/kWh, thathave to be reduced with an efficient NOx aftertreatmentsystem below the 2.0 g/kWh limit, preferably Urea-SCR.The Urea SCR systems have been shown to be bothvery efficient and durable in vehicle applications[2,3,4,5,6]. The higher NOx emission of the optimizedengine therefore requires the Urea SCR system to havea high NOx conversion efficiency of about 80-85%.
The combination of the optimized engine and Urea SCRsystem eliminates the need for a particulate filter tocomply with Euro V emissions leading to a lowerpressure drop of the exhaust system and also lesscomplexity of the total system.
Furthermore the significant fuel savings of the optimizedengine compared to a standard Euro III engine couldgive a payback time for the optimized engine and theSCR system depending on the urea price and theapplication as to make the concept commerciallyinteresting even prior to the legislation limits.
This concept could also be a serious candidate for theEuro IV legislation (NOx limit of 3.5 g/kWh andparticulates the same as Euro V). The optimized engineand SCR concept has an even greater fuel savingcompared to a concept of a standard Euro III engine withEGR and particulate filter. EGR increases the fuelconsumption of the engine and the addition of theparticulate trap increases the fuel consumption further byincreasing the pressure drop giving the combination ofthe optimized engine and Urea SCR system an evengreater fuel consumption advantage.
The purpose of this work was to demonstrate a PM andfuel optimized heavy-duty diesel engine and Urea SCRconcept able to comply with the Euro V legislationemission limits. The total work consisted of 3 parts:
• SCR catalyst optimization and selection [7]
• Engine optimization
• Combination of the optimized engine with the chosenSCR system.
In previous work the catalyst selection to achieve a highNOx conversion above 80% with ammonia slip less than10 ppm and development of a novel Urea SCR injectionsystem were discussed [7]. This present paper dealswith the optimization work on the engine, performance ofthe optimized engine, final selection of catalyst and theperformance of the combination of the PM and fueloptimized engine with the efficient Urea-SCR system.
The optimization targets of the engine optimization wereto achieve low soot emissions (i.e. carbon particulatesless than 0.010/0.015 g/kWh in ESC/ETC test) byinternal means while maintaining very low fuelconsumption at engine-out NOx emissions of 8 to 10g/kWh in the ESC test.
EXPERIMENTAL
ENGINE
The engine to be optimized was a direct injection 12 litreheavy-duty diesel engine with rated power of 300 kW.This engine was equipped with a modern injectionsystem, 4 valves per cylinder with central injectors, turbocharged with intercooler and high cylinder pressurepotential. The engine tested was in principle a standardEuro III engine, but already equipped with a new versionof injection system.
UREA SCR SYSTEM
The Urea-SCR system that was used is schematicallyshown in Figure 1. It is a sensor based, open loopsystem that uses real-time kinetic calculations forcontrolling the urea injection. Four sensors are used, aNOx sensor after the turbocharger, a mass airflowsensor in air intake of the engine and two temperaturesensors, before and after the catalyst. An electronic
control unit (ECU) calculates the amount of urea to beinjected based on the sensor readings and the actualinjection is carried out by means of a digital-dosingpump. The system is described further in a previouspaper [7]. The reducing agent used was a 32.5% urea-water with a density of 1.085 kg/litre.
SCR catalyst
Pump
Air Temp in
Mass air flowNOx and O2 sensor
Engine intakeairUrea
tank
CAN port
Temp out
Urea injection
TopsøeUrea-SCR
ECU
Figure 1. Urea SCR system
CATALYSTS
During previous work, different catalysts and catalystcombinations were tested in order to find suitablecatalyst combinations that had the required NOxreducing potential [7]. Since the optimized engine PM outemission was higher than the Euro IV and V levels, thecatalyst or combination of catalysts should also be ableto reduce at least 50% of the particulate matter. Fromthese previous tests [7] the following catalyst setupswere chosen for further testing, see also Figure 2 andTables 1 and 2. All SCR catalysts were corrugated fullcatalysts with a diameter of 393 mm.
A. A 15 litre 130 cpsi SCR catalyst (DNX15) combinedwith a 15 litre 130 cpsi SCR-Pd (DNX15-Pd) slipoxidation catalyst.
B. Combination A with the addition of an 8 litre (CKM)pre oxidation catalyst
C. In the previous work [7] it was also shown that thecatalyst volume could be reduced by 1/3 byincreasing the cell density from 130 to 300 cpsi.Therefore a newly developed 20 liter of 300 cpsipure SCR catalyst (DNX20) that had the requiredNOx reduction potential was included in the test.
Table 1. Catalysts used
Catalystname
Cell dens.(cpsi)
Volume(litre)
Activematerial
DNX15 130 15 V/TiO2
DNX15-Pd 130 15 V, Pd/TiO2
CKM 130 8 Pt/Al2O3
DNX20 300 20 V/TiO2
Table 2. Different catalytic setups used
Catalystsetup
Catalysts TotalVolume (l)
A DNX15+DNX15-Pd 30
B CKM+DNX15+DNX15-Pd 38
C DNX20 20
SCR catalyst130 cpsi
SCR/Oxi.catalyst
Pre oxidationcatalyst
SCR catalyst130 cpsi
SCR/Oxi.catalyst
SCR catalyst
300 cpsi
A
B
C
Figure 2. Different catalytic setups
TEST FACILITIES
All tests, with and without SCR were performed on theAVL transient test bed with CVS system. Non-regulatedemissions such as NH3 were measured with an FTIR.PM size distribution analyses were performed with aDDMPS (Dual Differential Mobility Particle Spectrometer)supplied by AVL. The CVS system consisted of full flowdilution tunnel with critical flow venturi and exhaust gasemission equipment for standard gaseous components(NOx, CO, HC, CO2) and particulates.
In order to collect a particulate sample, the dilutedexhaust gas (temperature 51.4 deg. C at the samplefilter) was drawn through a pre-weighed Teflon coatedglass fiber filter with a back-up filter of same
specifications (Pallflex TX40, 70 mm diameter). Aftersample collection, the filters were reweighed and theparticulate mass recorded. For determining thecontribution of soluble organic fraction the filters wereextracted for 2 hours using dichloromethane in a Soxhletapparatus. After drying and reweighing, the weight lossyields the amount of soluble fraction. The soluble organicfraction was further analyzed to yield the amount of fueland lube oil contribution. In a 2nd extraction of theremaining compounds (carbon, sulfates, water...), theportion of sulfates plus water (molecular bound) wasdetermined.
For the determination of particle size distribution inexhaust gas the DDMPS was used. The simultaneousmeasurement of multiple areas of the particle sizedistribution enables a time resolution of approximatelyone minute per particle size distribution of 57 particlesize classes in the diameter range of 2-600 nm. For eachoperating point and configuration 3 repeatedmeasurements were made.
FUEL SPECIFICATIONS
Two different fuels were used in the testing. The first wasstandard Austrian diesel fuel with a 230 ppm sulfurcontent. The second fuel was an ultra low sulfur dieselfuel with less than 10 ppm sulfur.
TEST CYCLES
The test cycles used in the project were the standardEuropean cycles used for emission certification of heavy-duty diesel engines, ETC and ESC. The ETC cycle is a1800 s transient driving cycle that comprises of three 600s parts. The parts correspond to urban driving, ruraldriving and highway driving conditions. The ESC is a 13-mode stationary test cycle. The test cycles wereconducted according to regulations. In order to evaluatethe optimized engines transient operation the EuropeanLoad Response (ELR) cycle was also used.
Besides the ETC and ESC a bus cycle was used forfurther evaluation. This bus-cycle was an adaptation ofthe Munich and Belgium real world bus-cycles into acombined 1200 s cycle for this particular engine. Thespeed and torque of the adapted cycle are presented inFigure 3. The engine was preconditioned at 1400 rpmand 110 kW, a typical road-load point of this engine classbefore starting the bus cycle.
0
500
1000
1500
2000
2500
0 200 400 600 800 1000 1200
Time(s)
Spee
d (rp
m)
Combined Munich-Belgium bus cycle
-5000
5001000150020002500
Torq
ue (N
m)
Figure 3. Speed and Torque for the combined Munich-Belgium Bus cycle
RESULTS
ENGINE OPTIMIZATION WORK
The combustion of this engine was to be optimized forlow soot emissions (i.e. carbon particulates less than0.010/0.015 g/kWh in ESC/ETC test) by internal meanswhile maintaining very low fuel consumption at engine-out NOx emissions of 8 to 10 g/kWh in ESC test.
The original engine tested was in principle a standardEuro III engine, but already equipped with a new versionof injection system. Also advanced timing was applied tothe engine application ECU to see the effect on sootemission and fuel consumption. The ESC test resultsdemonstrated with the original engine were 199 g/kWhBSFC at a NOx level of 6.5 g/kWh and 194 g/kWh BSFCat a NOx level of 8.7. But in both cases the sootemission was too high to be able to meet EU5 particulatetargets without a filter. An interesting fact was, that noimprovement in soot emissions could be observed withadvanced timing.
After the baseline testing the engine was rebuilt to a firstversion for Euro V emission compliance by changingdifferent engine components.
Modifications on the following parts were carried out:
• Injection system type
• Injection cam profile and position
• Injection nozzle
• Combustion bowl shape
• Compression ratio
• Intake swirl number
• Turbo charger match
• Adaptation of engine management control functionsfor injection timing, fuel and boost control duringtransients
All engine components which were changed or adaptedfor the optimized combustion system were coming fromserial parts, which makes this optimized engineappropriate for serial application.
The first test results showed significant improvement insoot emission at a NOx level of about 9 g/kWh, but stilltoo high ESC fuel consumption of 199 g/kWh. Furtheroptimization work such as turbocharger matching andapplying a completely new injection timing map to theECU made it possible to demonstrate the lowest sootemissions (0.0048 g/kWh) and cycle fuel consumption of194 g/kWh in the ESC. The NOx and soot emissions ofthe engine for the different optimization steps arepresented in Figure 4.
0
0,005
0,01
0,015
0,02
4 5 6 7 8 9 10 11 12
NOx (g/kWh)
SOOT TARGET
NOx TARGET RANGE
2
3
1
1: BASELINE EURO 3 ENGINE, BUT WITH NEW INJECTION SYSTEM2: AS 1, BUT ADVANCED TIMING3: NEW ENGINE CONFIGURATION (AVL) 4: OPTIMIZED ENGINE CONFIGURATION
4
(BSFC= 198,9 g/kWh)
(BSFC= 194,4 g/kWh)
(BSFC= 199,3 g/kWh)
(BSFC= 194,8 g/kWh)
*: Soot calculated acc. MIRA correlation
Figure 4. Summary of optimization work of the engine.
With the final engine hardware configuration theelectronic engine management now had to be optimizedfor transient operation in ELR and ETC. In addition theusual demands for reasonable smoke limiter times hadto be considered to get an excellent driveability of theengine in the vehicle. With the new smoke limiterinterfere times programmed to the engine ECU andoperating the engine in the ELR according to the EU4/5legislation a light absorption coefficient of 0.093 1/mcould be demonstrated (EU5 limit = 0.5 1/m). The lightabsorption recording from the ELR test is presented inFigure 5.
ELR test
00,020,040,060,080,1
0,120,140,16
0 100 200 300 400
Time
Ligh
t abs
orpt
ion
coef
ficie
nt (1
/m)
Engine Speed
A
C
B
Weighed Result
0.093 1/m
Figure 5. Light absorption coefficient for ELR test on theoptimized engine.
The optimized engine was tested under the ESC andETC cycles with both standard and ultra low sulfur fuel toget the baseline engine-out emissions of the engine. Theresults of the gaseous emissions and fuel consumptionaveraged from 3 cycles each are presented in Table 3.The particulate mass and the composition of theparticulate mass are presented for the same cycles inTable 4.
Table 3. Baseline emissions and fuel consumption of theoptimized engine with both fuels.
The optimized engine exhibits excellent fuel consumptionof 194 g/kWh for the ESC and 198 g/kWh for the ETCregardless of the fuel used. As is commonly known, theaverage of the fuel consumption of Euro III engines inthe market place is about 210 g/kWh for the ESC. Theoptimized engine thus has a significant fuel saving ofapproximately 7.5 % compared to todays Euro IIIengines.
The NOx emissions are approximately 9 g/kWh for theESC and 8.6 g/kWh for the ETC cycle and are practicallythe same for both fuels. The NOx emission of the engineis within the optimization target. The insoluble part of theparticulates is below the 0.01 and 0.015 g/kWhoptimization targets for the ESC and ETC respectively forboth fuels. However the total particulate emission was
above the Euro V limits due to the relatively highcontribution of the soluble content on the totalparticulates namely 80% for the ESC and 60% for theETC.
From the baseline emissions of the engine it was evidentthat the SCR system, apart from reducing the NOxcontent of the exhaust by at least 80%, also should beable to reduce the total particulate mass by about 50% inorder for the whole concept to comply with the Euro Vemission limits.
CATALYST SELECTION TO REDUCE PARTICULATES
In order to investigate the PM reduction potential of thedifferent catalysts, tests were conducted with the threedifferent catalyst combinations without urea injection forboth ESC and ETC cycles and for both high and lowsulfur fuels. The particle sample filters were subjected tostandard chemical analysis as specified previously inorder to determine the composition of the particulatemass. For the higher sulfur fuel the results are presentedin Figure 6 and 7 for the ESC and ETC respectively.
Particulate emissions ESC 230 ppm S
0
0,005
0,010,015
0,02
0,025
0,030,035
0,04
0,045
w/o catalyst A B C
PM (g
/kW
h)SO4&H20FuelLubeCarbon
Figure 6. Particulates for ESC with 230 ppm S fuel andthe three different catalytic setups without urea injection
Particulate emissions ETC 230 ppm S
0
0,0050,01
0,015
0,020,025
0,03
0,0350,04
0,045
w/o catalyst A B C
PM (g
/kW
h)
SO4&H20FuelLubeCarbon
Figure 7. Particulates for ETC with 230 ppm S fuel andthe three different catalytic setups without urea injection
It can be seen that all three catalyst combinations reducethe total particulate mass. The largest reduction of theparticulates comes from the reduction of the solublefraction (characterized as lube and fuel). It can also beseen that setup C, the DNX20 pure SCR catalyst, is asgood as the other two combinations in reducing thesoluble fraction, even though it contains no preciousmetals.
In the ETC all three catalyst combinations reduce theparticulates below the 0.03 g/kWh limit with a goodmargin. However, the ESC 0.02 g/kWh limit is not metwith any combination. Catalyst combination B with bothpre and slip oxidation catalyst and thus a lot of preciousmetal has large sulfate formation and thus highparticulate mass. However the same effect but lesspronounced can be seen with the pure SCR catalyst.
Since the future fuel sulfur specification in Europe islikely to be below 10 ppm sulfur it was decided toconduct tests with the ultra low sulfur fuel. The results ofthe ESC and ETC measurements of particulate mass forthe different catalyst combinations with the ultra lowsulfur fuel are presented in Figures 8 and 9 respectively.
Particulate emissions ESC <10 ppm S
0,0000
0,0050
0,0100
0,0150
0,0200
0,0250
0,0300
0,0350
0,0400
w/o catalyst A B C
PM (g
/kW
h)
SO4&H20FuelLubeCarbon
Figure 8. Particulates for ESC with <10 ppm S fuel andthe three different catalytic setups without urea injection
Particulate emissions ETC <10ppm S
0,0000
0,0050
0,0100
0,0150
0,02000,0250
0,0300
0,0350
0,0400
0,0450
w/o catalyst A B C
PM (g
/kW
h)
SO4&H20FuelLubeCarbon
Figure 9. Particulates for ETC with <10 ppm S fuel andthe three different catalytic setups without urea injection
As with the high sulfur fuel the general trend is the samewith a reduction in particulate mass for all catalystcombinations. The ETC PM limit of 0.03 g/kWh is easilymet. Furthermore it can be seen that setup C, theDNX20 pure SCR catalyst, is below the limit of 0.02g/kWh on the ESC. The particulate mass wasconsistently below the 0.02 g/kWh limit for all testsconducted with the DNX20 on the ESC with the ultra lowsulfur fuel. The other two combinations were also veryclose to the emission limits on the ESC, but it wasdecided to continue the tests with the 20 litre DNX20catalyst together with the ultra low sulfur fuel.
The choice of setup C, the 20 liter DNX20 catalyst, wasan obvious one to continue the test work with since it hadthe best particulate reduction, and also had the leastvolume of all catalyst combinations.
NOX REDUCTION PERFORMANCE
With the selection of the 20 litre DNX20 catalyst and theultra low sulfur fuel, tests were conducted with the ETCand ESC in order to optimize the real time urea injectionalgorithms. The aim was to achieve NOx emissionsbelow the 2.0 g/kWh legislation limits of Euro V whilemaintaining the NH3 slip below 10 ppm on average.
ETC test cycle
The NOx reduction over the DNX20 catalyst for an ETCcycle is presented in Figure 10 while the NH3 slip fromthe same test is presented in Figure 11. The NOxconversion is high for all parts of the ETC while the NH3slip peaks do not exceed 10ppm. For this ETC cycle theNOx emission was reduced to 1.55g/kWh with anammonia slip of 6ppm on average.
NOx reduction during ETC
0
0,002
0,004
0,006
0,008
0,01
0,012
0,014
0,016
0,018
0,02
0 200 400 600 800 1000 1200 1400 1600 1800
Time (s)
Flow
(mol
e/s)
NOx InNOx Out
Figure 10. NOx flow with and without DNX20 catalyst forETC
NH3 slip during ETC
0
2
4
6
8
10
12
14
16
18
20
0 500 1000 1500 2000
Time (s)
NH
3 sl
ip (p
pm)
Figure 11. Ammonia slip for ETC
ESC test cycle
The stationary ESC tests were carried out using thesame injection strategy as for the transient tests. TheNOx reduction over the DNX20 catalyst for the ESCcycle is presented in Figure 12 while the NH3 slip fromthe same test is presented in Figure 13.
NOx reduction during ESC
0
0,002
0,004
0,006
0,008
0,01
0,012
0,014
0,016
0,018
0,02
0 200 400 600 800 1000 1200 1400 1600Time (s)
Flow
(mol
e/s)
NOx InNOx Out
Figure 12. NOx flow with and without DNX20 catalyst forESC
NH3 slip during ESC
0123456789
10
0 500 1000 1500Time (s)
NH
3 sl
ip (p
pm)
Figure 13. Ammonia slip during ESC
The NOx emission for this ESC cycle was 1,40 g/kWhand the ammonia slip was considerably lower than forthe ETC cycle with peaks of up to 4-5 ppm only on thefirst portion of the ESC. This injection strategy wastherefore adequate to meet the NOx reduction requiredto comply with the Euro V NOx limits for both cycles,while having a slip below 10 ppm on average.
SUMMARY OF REGULATED EMISSIONS
The regulated emissions for the chosen injection strategyare presented in Tables 5 and 6 for the ESC and ETCcycles respectively and summarized in Figure 14. Theresults are averaged from 2 repeated measurementsthat had very consistent emission levels.
ESC test cycle
For the ESC the NOx emission with the SCR catalyst is1.38 g/kWh, well below the 2,0 g/kWh EuroV limit. Thiscorresponds to a NOx conversion of nearly 85% with aurea solution consumption of 9% (gravimetric) comparedto the fuel flow.
The hydrocarbons of the exhaust are reduced with 82 %over the SCR catalyst whereas the CO is increased withabout 60%. This is the standard behavior of pure SCRcatalyst, which is also a good partial oxidation catalyst.The hydrocarbons are readily oxidized but some formCO instead of CO2. The increase in CO is however notcrucial for the Euro V CO emission limit on the ESC thatis 1.5 g/kWh.
The 54% reduction of PM over the catalyst is, asdiscussed earlier mainly due to the removal of thesoluble fraction bringing down the PM below the 0.02g/kWh limit to 0.017 g/kWh. The injection of urea doesnot affect the particulate mass which is indicated by thefact that the PM levels do not increase as compared withthe tests conducted without urea injection.
The fuel consumption remains practically constant withthe addition of the DNX20 catalyst as can be seen inFigure 14, implying that there is no significant fuelpenalty by adding the SCR system to the engine.
Table 5: Regulated emissions with DNX20 catalyst andultra low sulfur fuel for the ESC
For the ETC the NOx emission of the engine is reducedby 82% to 1.54 g/kWh with a urea solution consumptionof 8% of the fuel flow, comfortably below the Euro V 2,0g/kWh limit. The reduction of NOx is comparable for bothtest cycles and shows that one setting of the urea
injection system is sufficient for both stationary andtransient operation.
Like for the ESC the hydrocarbons are greatly reduced,by 83%, while there is an increase in CO of 60%. Againboth HC and CO emissions are well below the Euro Vlimits.
The decrease in PM in the ETC is approximately 45% toa level of 0.02 g/kWh compared to the legislative limit of0.03 g/kWh. The fuel consumption is the same afteradding the SCR system, as for the ESC.
Table 6 : Regulated emissions with DNX20 catalyst andultra low sulfur fuel for the ETC
1: AVERAGE OF 2 TESTS - ESC; w/o SCR (CVS INSOL LUBE FUEL2: AVERAGE OF 2 TESTS - ESC; with SCR; (CVS3: AVERAGE OF 2 TESTS - ETC; w/o SCR (CVS EU5 Limits
4:AVERAGE OF 2 TESTS - ETC; with SCR; (CVS
Figure 14: Summary of regulated emissions with DNX20catalyst and ultra low sulfur fuel for ESC and ETC.
EFFECT OF SULFUR CONTENT ON REGULATEDEMISSIONS
To evaluate the effect of fuel sulfur content on theemissions, ETC and ESC were also run with thestandard 230 ppm sulfur fuel and the 20 litre SCRcatalyst. The comparisons of the results for the differentfuels are presented in Figures 15 and 16 for the ESC andETC respectively.
0,0
2,0
4,0
6,0
8,0
10,0
12,0
1 2 30,00
0,05
0,10
0,15
0,20
0,25
0,30
1 2 30,00
0,20
0,40
0,60
0,80
1,00
1 2 3185
190
195
200
1 2 3
NOx(g/kWh)
HC(g/kWh)
CO(g/kWh)
BSFC(g/kWh)
0,000
0,010
0,020
0,030
0,040
1 2 3
PM(g/kWh)
1: Without SCR and <10 ppm S Carbon Lube Fuel SO4/H2O2: With DNX20 and <10ppm S 3: With DNX20 and 230 ppm S
Figure 15 Comparison of ESC emissions with DNX20catalyst and both high and low sulfur fuel.
0,0
2,0
4,0
6,0
8,0
10,0
12,0
1 2 30,00
0,05
0,10
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1 2 30,00
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1,00
1 2 30,000
0,010
0,020
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1 2 3185
190
195
200
1 2 3
HC(g/kWh)
CO(g/kWh)
PM(g/kWh)
BSFC(g/kWh)
NOx(g/kWh)
1: Without SCR and <10 ppm S Carbon Lube Fuel SO4/H2O2: With DNX20 and <10ppm S 3: With DNX20 and 230 ppm S
Figure 16 Comparison of ETC emissions with DNX20catalyst and both high and low sulfur fuel.
It can be seen that the NOx, hydrocarbon and COemissions are practically unaffected by the sulfur contentof the fuel for both test cycles. The gaseous emissionsare comfortably below the Euro V limits also with thehigher sulfur fuel. However, with the higher sulfur fuel, asinvestigated previously, the particulate mass emission ishigher than the limit for the ESC cycle mainly due to thesulfate formation over the catalyst. For the ETC cycle theparticulate mass is practically the same for both fuelsand below the legislation limit. Here the sulfate formationis not as pronounced as for the ESC cycle. This could beexplained by the higher exhaust temperature levels ofthe ESC cycle as compared to the ETC cycle. Highertemperature favors the formation of sulfate over thecatalyst.
MUNICH-BELGIUM BUS CYCLE
With the final settings of urea injection and the 20 l SCRcatalyst and the ultra low sulfur fuel, the combinedMunich-Belgium real world buscycle was also run. TheNOx conversion and ammonia slip for the buscycle arepresented in Figures 17 and 18 respectively. The NOx
conversion is not as high at the first part of the cycle dueto starting the cycle at colder conditions as compared tothe ETC. After the first 200 seconds the NOx conversionis high and stays at a high level for the duration of the1200 s cycle. The ammonia slip is comparable to that ofthe ETC. The results for gaseous emissions and PM aresummarized in Table 7.
Combined Munich-Belgium Bus cycle
0
0,002
0,004
0,006
0,008
0,01
0,012
0,014
0,016
0,018
0,02
0 200 400 600 800 1000 1200
Time (s)
Flow
(mol
e/s)
NOx In
NOx Out
Figure 17. NOx flow with and without DNX20 catalyst forcombined Munich-Belgium bus-cycle
NH3 slip during combined Munich-Belgium bus cycle
0
2
4
6
8
10
12
14
16
18
20
0 200 400 600 800 1000 1200
Time (s)
NH
3 sl
ip (p
pm)
Figure 18. Ammonia slip during combined Munich-Belgium bus-cycle
Table 7: Emissions with DNX20 catalyst and ultra lowsulfur fuel for the combined Munich-Belgium bus cycle.
The results for the bus-cycle are similar to those for theETC and ESC. A high NOx conversion is achievedthroughout the cycle of approximately 79%. Thehydrocarbon oxidation is high over the SCR catalyst witha total of 77 % reduction. The same levels of COincrease are observed as with the ETC and ESC. Theparticulate mass is reduced by 20%.
PARTICLE SIZE DISTRIBUTION W/WO SCR SYSTEM
Particulate size distribution measurements wereperformed for all the ESC operating points (except foridle) with 3 different configurations i.e. without SCR, withSCR but without urea injection and with SCR with ureainjection. Three repeated tests were performed for eachoperating point and configuration and the averages arepresented in Figures 19,20 and 21.
It can be seen for all operating points that there is a vastreduction, in some areas by two orders of magnitude, inthe number of particles by adding the DNX20 SCRcatalyst in the exhaust. The most significant reduction inparticle number occurs in the size range of approximately2-30 nm. The decrease in particle number is lessprofound for the size range from 30-100 nm but is stillevident. Above 100 nm the particle numbers are virtuallyunaffected by the SCR system.
Hence even if the SCR catalyst does not decrease thelarger solid particles that contribute the most to theinsoluble particulate mass, it has a large effect on thenanoparticles that are attributed with the adverse healtheffects of diesel exhaust PM.
Additionally it can be seen that the numbers of particlesare practically the same for the SCR catalyst with andwithout urea injection implying that there are no ureadroplets or urea bi-products that pass through thecatalyst.
Engine speed: 1851 rpm / 17 bar (C 100 %)
1E+04
1E+05
1E+06
1E+07
1E+08
1E+09
1 10 100 1000
Dp [nm]
dN /
dl(D
p) [/
cm3]
1.with SCR2. with SCR & Urea inj.3. w/o SCR
Engine speed: 1851 rpm / 13 bar (C 75 %)
1E+04
1E+05
1E+06
1E+07
1E+08
1E+09
1 10 100 1000
Dp [nm]
dN /
dl(D
p) [/
cm3]
1. with SCR2. with SCR & Urea inj.3. w/o SCR
Engine speed: 1851 rpm / 8 bar (C 50 %)
1E+04
1E+05
1E+06
1E+07
1E+08
1E+09
1 10 100 1000
Dp [nm]
dN /
dl(D
p) [/
cm3]
1. with SCR2. with SCR & Urea inj.3. w/o SCR
Engine speed: 1851 rpm / 4 bar (C 25 %)
1E+04
1E+05
1E+06
1E+07
1E+08
1E+09
1 10 100 1000
Dp [nm]
dN /
dl(D
p) [/
cm3]
1. with SCR2. with SCR & Urea inj.3. w/o SCR
1.
2.
3.
3.
3.
3.
1.
2.
1.
2.2.
1.
Figure 19. Particle size distribution for 1850 rpm withand without catalyst DNX20
Engine speed: 1537 rpm / 20 bar (B 100 %)
1E+04
1E+05
1E+06
1E+07
1E+08
1E+09
1 10 100 1000
Dp [nm]
dN /
dl(D
p) [/
cm3]
1. with SCR2. with SCR & Urea inj.3. w/o SCR
Engine speed: 1537 rpm / 10 bar (B 50 %)
1E+04
1E+05
1E+06
1E+07
1E+08
1 10 100 1000
Dp [nm]
dN /
dl(D
p) [/
cm3]
1. with SCR2. with SCR & Urea inj.3. w/o SCR
Engine speed: 1537 rpm / 15 bar (B 75 %)
1E+04
1E+05
1E+06
1E+07
1E+08
1 10 100 1000
Dp [nm]
dN /
dl(D
p) [/
cm3]
1. with SCR2. with SCR & Urea inj.3. w/o SCR
Engine speed: 1537 rpm / 5 bar (B 25 %)
1E+04
1E+05
1E+06
1E+07
1E+08
1 10 100 1000
Dp [nm]
dN /
dl(D
p) [/
cm3]
1. with SCR2. with SCR & Urea inj.3. w/o SCR
3.
1.
2.
3.
1.
2.
1.
2.
3.
1.
3.
1.
2.
Figure 20. Particle size distribution for 1537 rpm withand without catalyst DNX20
Engine speed: 1223 rpm / 20 bar (A 100 %)
1E+03
1E+04
1E+05
1E+06
1E+07
1E+08
1E+09
1E+10
1 10 100 1000
Dp [nm]
dN /
dl(D
p) [/
cm3]
1. with SCR2. with SCR & Urea inj.3. w/o SCR
Engine speed: 1223 rpm / 5 bar (A 25%)
1E+03
1E+04
1E+05
1E+06
1E+07
1E+08
1E+09
1 10 100 1000
Dp [nm]
dN /
dl(D
p) [/
cm3]
1. with SCR2. with SCR & Urea inj.3. w/o SCR
Engine speed: 1223 rpm / 15 bar (A 75%)
1E+03
1E+04
1E+05
1E+06
1E+07
1E+08
1 10 100 1000
Dp [nm]
dN /
dl(D
p) [/
cm3]
1. with SCR2. with SCR & Urea inj.3. w/o SCR
Engine speed: 1223 rpm / 10,3bar (A 50%)
1E+03
1E+04
1E+05
1E+06
1E+07
1E+08
1 10 100 1000
Dp [nm]
dN /
dl(D
p) [/
cm3]
1. with SCR2. with SCR & Urea inj.3. w/o SCR
3.
2.1.
3.
1.
2.
3.
1.
2.
3.
1.
2.
Figure 21. Particle size distribution for 1223 rpm withand without catalyst DNX20
CONCLUSION
The 12 litre heavy-duty diesel engine was optimized byinternal means to achieve low soot emissions and lowfuel consumption while keeping the NOx emissionsbelow 10 g/kWh. For the ESC and a NOx emission of 9.1g/kWh, low insoluble content of below 0.01 g/kWh wasachieved. For the ETC the engine out NOx emission was8.6 g/kWh while the insoluble content of the particulateswas below 0.015 g/kWh. Total particulate mass washowever 0.038 g/kWh for the ESC and 0.039 g/kWh forthe ETC, higher than the Euro V legislation limits. TheSCR system thus had to be able to reduce a large part ofthe PM, around 50%, for the ESC.
Excellent fuel consumption could be achieved with theoptimized engine of 194 g/kWh and 198 g/kWh for theESC and ETC respectively. Compared to standard EuroIII engines that have an average fuel consumption ofabout 210 g/kWh for the ESC, the optimized engineexhibits considerable fuel savings of about 7.5 %.
20 litres of newly developed 300-cpsi SCR catalyst weresufficient to reduce the NOx levels of the 12 litre PM andfuel optimized engine below the EuroV 2.0 g/kWh forboth ESC and ETC. With a catalyst to cylinder ratio ofonly 1.7 the NOx reduction was 84 % and 82% for theESC and ETC respectively with ammonia slip below 10ppm on average and the same urea injection algorithms.This NOx reduction was achieved by having a ureasolution injection of 9% and 8% of the fuel flow for theESC and ETC respectively.
Furthermore the 20 litre 300-cpsi SCR catalyst is capableof reducing approximately 80% of the hydrocarbonswhile having an increase in CO due to partial oxidation ofhydrocarbons over the catalyst. This CO increase is notcritical since the CO emissions are well below the Euro Vlimits.
The 20 litre SCR catalyst is also able to reduce theparticulate mass by 54% on the ESC and 45% on theETC to 0.017 g/kWh and 0.02 g/kWh respectively withthe ultra low (<10 ppm) sulfur fuel. For both cycles theemissions of PM are well below the Euro V legislationlimits. The large reduction in particulate mass isattributed mainly to the oxidation of the soluble fraction.
The combination of the 12 litre PM and fuel optimizedengine with the 20 litre 300 cpsi SCR catalyst iscompliant with the EuroV emission limits using ultra low(<10ppm) sulfur fuel.
With the standard Euro III (230 ppm) sulfur fuel the PMemissions are slightly above the 0.02 g/kWh limit for theESC namely 0.022-0.025 g/kWh. Concerning the ETCthe PM emission limit is easily met also with the standardsulfur fuel. The sulfur content of the fuel is shown not toinfluence the performance of the SCR catalystconcerning NOx and hydrocarbon reduction.
Particle size distribution measurements show that thereis a considerable decrease of particles in the size rangeof 2-30 nm over the SCR catalyst, with and without ureainjection. There is also a decrease in the size range of30-100 nm. No significant difference is found whencomparing particle numbers after the SCR system withand without urea injection.
Further improvements of the whole concept are tooptimize the engine further in order to lower the baselineNOx emission while keeping the particulates and fuelconsumption at the same low levels. With lower NOxbaseline emissions the urea consumption required toreach the legislation limits would be lower making thewhole concept more economical in operation.
ACKNOWLEDGMENTS
The authors would like to acknowledge the work of TineLadefoged and Viggo Hansen in preparing the SCRsystem and the work of Mr Kreiner and Mr Simic duringthe engine testing. A special thanks to Ms Neunteufel forextracting data from the engine testing.
REFERENCES
1. Cartellieri et al., “Development of a Fuel EfficientEU5 Heavy Duty Diesel Engine with Urea-SCRExhaust Aftertreatment System”, VDA TechnicalCongress, 28. -29. Sept. 2000, Frankfurt.
2. Walker et al, “Development of an Ammonia/SCRNOx Reduction System for a Heavy Duty NaturalGas Engine”, SAE paper 921673.
3. Gabrielsson et al, Combined Silencers and Urea-SCR Systems for the Heavy-duty Diesel Vehicles for
OEM and Retrofit Markets, SAE paper 2001-01-0517.
4. Havenith et al, “Transient Performance of a UreadeNOx Catalyst for Low Emissions Heavy-DutyDiesel engines”, SAE paper 970185.
5. Fritz et al, “On-Road Demonstrations of NOxEmissions Control for Diesel Trucks with SINOXUrea SCR System”, SAE paper 1999-01-0111
6. Gabrielsson et al, “Urea-SCR NOx RemovalEfficiency For a Diesel Engine in the SuggestedEuropean ETC Test Cycle”, 32nd ISATA Conference,14th – 18th June 1999 –Vienna- Austria
7. Gekas et al, “Urea-SCR Catalyst System Selectionfor Fuel and PM Optimized Engines and aDemonstration of a Novel Urea Injection System”,SAE paper 2002-01-0289
