combinations of measures for reduction of nox &

8/11/2019 Combinations of Measures for Reduction of NOx &

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PTNSS2011SC068

Combinations of Measures for Reduction of NOx&Nanoparticles of a Diesel Engine.

Authors:1Czerwinski, Jan

*;

2Stepien, Zbigniew;

2Oleksiak, Stanislaw;

3Otto, Andersen

1University of Applied Sciences, Biel-Bienne, Switzerland (AFHB),

2Oil and Gas Institute, Krakow, Poland (INIG)

3Western Norway Research Institute, Sogndal, Norway (Vestforsk)

ABSTRACT

Reduction of NOx- and particle emissions of Diesel en-gines is worldwide an important challenge for the engi-neers. Some unregulated components, like NO2, NH3and naoparticles NP

*)came in the focus of attention in

the last years.

Application of EGR and / or SCR can lower NOx, usingRME (Bxx) can increase NOx. What happens with NP,parameter which enters in some further steps of exhaustgas legislation in Europe?

The present paper informs about the results with EGR,B100 and SCR obtained on a medium duty Diesel en-gine in the versions: Euro 3 (w/o EGR) & Euro 4 (withEGR), both without particle filter.

The investigations were performed according to the pro-

cedures of the international network project VERT*)

dePN (de-activation, de-contamination, disposal of parti-cles & NOx).

The most important findings are:

the EGR of the new engine version E4 is active atmiddle load,

the NOx reduction potentials in ETC with combina-tions of the investigated measures are:EGR reduces NOx approx. in the same range, asB100 increases it (17-20%); SCR is the strongestreduction measure in the range of 73%.These potentials are similar at middle-load stationaryoperation.

the influences on nanoparticles counts emissions(PC) depend on different factors and can partlychange between stationary and dynamic operationand with the use of B100.

In summary: EGR and SCR can efficiently reduce NOxand overcompensate the effect of B100.EGR is most advantageous at low load, when SCR isnot active.

INTRODUCTION & OBJECTIVES

The investigations concerning the reduction potentials ofcritical emissions NOx& NP were performed with EGR /B100 / SCR and with limited variation of the injectiontiming SOI.

The exhaust gas recirculation EGR is commonly used toreduce NOx. As a drawback the increase of other emis-sions, like HC, or particle mass & counts can appearwith increasing EGR. This risk is extremely reduced withthe modern injection systems (common rail CR) with

very high injection pressures, so the EGR-rates are verymuch increased in engines of new generations. TheEGR cooling, which brings further advantages of NOxand the dynamic regulation of EGR give further chal-

lenges for developers, [1], [2].

The removal of NOxfrom the lean exhaust gases of Die-sel engines (also lean-burn gasoline engines) is an im-portant challenge. Selective catalytic reduction (SCR)uses a supplementary substance reduction agent which in presence of catalysts produces useful reactionstransforming NOxin N2and H2O.

The preferred reduction agent for toxicological andsafety reasons is the water solution of urea (AdBlue),which due to reaction with water (hydrolysis) and due tothermal decomposition (thermolysis) produces ammoniaNH3, which is the real reduction substance.

The main deNOx-reactions between NH3, NO and NO2are often mentioned in the literature [3, 4, 5, 6, 7]. Theyhave different speeds according to the temperatures ofgas and catalysts, space velocity and stoichiometry. Allthese influences cause a complex situation of reactionsduring the transient engine operation.Additionally to that there are temperature windows for

catalysts and cut off the AdBlue-injection at low exhaustgas temperatures to prevent the deposits of residues.

Several side reactions and secondary substances arepresent. An objective is to minimize the tail pipe emis-sions of: ammonia NH3, nitrous oxide N2O, isocyanicacid HNCO and ammonium nitrate NH4NO3(also knownas secondary nanoparticles).

Blend fuels with RME (biodiesel Bxx) have impact onemissions, which depends on the engine operating col-lective. At full load there is a tendency of increased NOxand reduced CO, HC & PM; at lower part load inversely,

[8].

*) Abbreviations see at the end of this paper


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For nanoparticles usually a bimodal particle size distribu-tion (PSD) is produced due to spontaneous condensatesin nuclei mode (the lowest size range below 30-40 nm)

with biofuels, [9, 10]. Introducing EGR provokes an in-

crease of nanoparticles count concentrations, [11, 12].

For the successful long term operation the limiting ofimpurities and phosphorus in biofuels according to thepresent standards, as well as a carefull choice of lubri-

cating oil are strongly recommended.

With SCR alone there are no differences of NOxand ofNOx reduction rate (KNOX) with increasing RME portion;there is lowering of CO & HC. With SCR catalyst there isusually a small reduction of nanoparticles concentrations(in the range of 10-20%, similar like an usual oxidation

catalyst), [13].

The objectives of the present work are to investigate theinfluences of EGR with Diesel and with B100 and thepotentials of the present SCR-system concerning deNOxrates and nanoparticles.

For comparison of potentials and drawbacks a limitedvariation of injection timing was performed, as an off-setof +/- 3 degrees CA in the engine map.

The tests were performed at the Laboratories for IC-Engines and Exhaust Emission Control of the Universityof Applied Sciences Biel, Switzerland (AFHB).

TESTED ENGINE, FUELS, LUBRICANT

Test engine

Manufacturer: Iveco, Torino ItalyType: F1C Euro 3 / Euro 4Displacement: 3.00 LitersRPM: max. 4200 rpmRated power: 100 kW @ 3500 rpmModel: 4 cylinder in-lineCombustion process: direct injectionInjection system Bosch Common Rail 1600 barSupercharging: Turbocharger with intercoolingEmission control: noneDevelopment period: until 2000 (Euro 3)

Fig. 1 shows the engine and the apparatus for nanopar-ticle analytics SMPS & NanoMet in the laboratory for IC-engines, University of Applied Sciences, Biel-Bienne.

Fuels

Following base fuels were used for the research(Table 1):

Shell Formula Diesel fuel Swiss market summerquality (10 ppm S) according to SN EN 590

Rapeseed Oil Methyl Ester RME from Flamol,

Berne, CH

Table 1 represents the most important data of the fuelsaccording to the standards and the analysis certificates.

It can be remarked, that there are differences of density,heat value, stoichiometric air requirement and boilingrange, which have influences on the engine operationand especially on the full load parameters. These chang-ing fuel parameters were taken into account by the eva-luation of measurements.

Fig.1: IVECO engine F1C and equipment for nanopar-ticle measurements in the engine room

Tabel 1: Fuel properties as per EU-standards andfurther analysis of the test fuels

Lubricant

For all tests a special lubeoil Mobil 1 ESP Formula 5W-30 was used.

Table 2 shows the available data of this oil,ACEA classes: C3, A3, B3/B4,API classes: SL / SM; CF

Tabel 2: Data of the utilized oil (* analysis, others:specifications)


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Fig. 6 shows the limited engine map and the 4 pointssteps-test.

operating point OP 3c, 20% load, 2200 rpm / 65 Nm

operating point OP 3b, 30% load, 2200 rpm / 98 Nm

operating point OP 3, 50% load, 2200 rpm / 162 Nm

operating point OP 1, 100% load, 2200 rpm / FL

These operating points were chosen in such way thatthe urea switch-on was included in the test (between20% and 30% load).The denomination of the OPs from other measuring se-ries was not changed in order to keep comparability withother projects and new OPs were named by adding aletter 3b, 3c).

For a more detailed investigation of the tested systemdifferent sampling positions (SP) were used in previousresearch, see Fig. 5. In the present works only SP 3,sampling position at tailpipe with and without aftertreat-ment system was used.

The dynamic testing was performed with the ETC (Euro-pean Transient Cycle), which in this work was defined onthe basis of the non limited engine operation map(NEM), for the engine version E3, Fig. 7. The definitionof ETC was not changed, to keep a better comparabilitywith the previous results.

Fig.7: Torque & speed in ETC IVECO F1C

The tests have shown that the backpressure at dynamicoperation is generally lower, as at stationary operationand therefore the dynamic tests were performed withETC adapted to the entire engine operation map.

The tests were driven after a warm-up phase, when the

engine coolant temperature and lube oil temperaturereached their stationary values (stationary points tests).

Before the start of each dynamic cycle the same proce-dure of conditioning was used to fix as well as possiblethe thermal conditions of the exhaust gas aftertreatmentsystem.This conditioning was: 5 min pt. 1 and 0.5 min idling.

The test program consisted of:

test procedures: steps-tests at 2200 rpm and ETC

(NEM);

aftertreatment systems: without, with SCR only;

fuels: Diesel (ULSD) & B100;

with/without EGR (engine versions E4 / E(4))

TESTED SCR SYSTEM

The SCR exhaust gas aftertreatment system was in-stalled on the IVECO research engine in the ICE-laboratory in Biel, CH.This system is designed for dynamic on-road applica-tions.The filters and catalysts are exchangeable moduls, forSCR alone the DPF modulus was removed.

The investigations in the present work were performedwithout DPF, with the Vanadium-based SCR catalystdownstream of the urea injection point (see schemeFig. 5).Additionally to the elements in the engine exhaust sys-tem an Ad Blue-tank and Ad Blue injection unit withpump, sensors and electronic control were installed inthe laboratory.

There are following sensors, which enable the open-loopcontrol of urea dosing:

2x Temperature sensors (PT200)

1x AdBlue level sensor 1x Mass Air Flow sensor

2x NOxsensors (upstream & downstream DPF)Optional: 1x NOxsensor downstream SCR catalysts formonitoring of performance.

Urea dosing and control unit has an open loop control.

Optional: GPRS Flight recorder enables:

data logging of system performance, state andalarms on a remote server/database

changing and checking of configuration parametersof urea dosing unit via internet.

The SCR-system, which was investigated in the presentwork is without mixer (only mixing tube 1.0 m).

RESULTS

Steady state operation, 4 pts-test

In this research 4 operating points (OP) were used.

At the lowest load (20%, OP3c) SCR is not active due tolower exhaust gas temperatures and urea cut off.

All part load operating points (OP3c, OP3b, OP3) wererealized at exactly the same speed & torque. In contrarythe full load points (OP1) were driven at different torquesaccording to the used fuel (same engine speed).

With the used EGR map at full load (OP1) EGR is al-most switched off with Diesel and completely closed withB100. Therefore, in the variant with EGR the full loadpoint (OP1) is de facto without EGR.

Except of influences of EGR the following figures showalso the influences of B100 (RME) and of SCR.

Effect of EGR at middle engine load (OP3, 50%) onsome control- and emissions parameters is demonstrat-ed in Fig. 8. Looking on these plots from right to left itcan be summarized that EGR lowers the NOx-emissions


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and increases the NP-emissions (PAS & DC) (compari-son E(4)-E4). With EGR there is less gas flow throughthe engine, lower boost pressure and lower backpres-sure. At higher engine loads there are also higher engineout exhaust gas temperatures with EGR.

Fig.8: Switch off EGR mode at 2200 rpm / 162 Nm,

Iveco F1C E4; diesel; w/o exhaust gas after-treatment system

PAS (photoelectric aerosol sensor) is sensitive to thesurface of particulates and to the chemical properties ofthe surface. It indicates the solid carbonaceous particles.DC (diffusion charging sensor) measures the total activeparticle surface independent of the chemical properties.It indicates the solids and the condensates.

All signals of PAS and DC in this figure are converted tothe values responding to the undiluted volume concen-trations in the exhaust gas.

The NanoMet results usually confirm the findings fromSMPS and are regarded, especially DC, as parameterssubstituting the NP-count concentration measurement.

Fig. 9 gives an example of some NOx-related emissionvalues depending on B100 and SCR, all with EGR.It can be remarked, that:B100: increases NOxat higher part load and full load in

the range of 10-15%, reduces strongly HC andincreases CO (not represented here).

SCR: reduces strongly NOx& NO2, is source of NH3inthe range up to 20 ppm at full load, reduces HC.

The resulting average EGR rates for both fuels arerepresented in this figure. They are different for Dieseland for B100 because of different injection duration and

air consumption and different settings of the presentEGR control system.

Fig.9: Influences of B100 & SCR on NOx emissions in4pts.-test, Iveco F1C E4; 2200rpm

Identical tests were also performed without EGR.

Table 3 summarizes the relative changes of NOx-emissions, as averages of 4 points. It results, that EGRreduces NOxapproximately in the same range (15%) asB100 increases it (12%). SCR is the strongest reductiontool in the range of 60% (by averaging only OPs withSCR active 80%).

Tabel 3: Relative changes of NOx-emissions (FTIR),average of 4 pts.

Fig. 10 gives example of SMPS PSD-specta with differ-ent engine variants at middle load (OP3, 50% load). ThePSD are represented in linear and in logarithmic scale to

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EGR increases PC by 29%. Looking separately on thetwo fuels this increase is much stronger with Diesel fuel,than with B100.B100 reduces PC for this engine and test procedure by72% and SCR reduces PC by 15%,

Dynamic operation, ETC

Fig. 13 shows examples of NOx-traces in a part of

ETC, comparing the effects of:EGR, SCR, EGR+SCR, B100 and B100+EGR+SCR the NOx-differences caused by the different measuresare well demonstrated.

Fig.13: Influences of EGR, B100 & SCR on NOx-tracesin ETC

*), Iveco F1C E4

Fig. 14 represents the average emissions in ETC of:NOx, NO2, NH3and CPC (all with EGR).Again it is confirmed, that:

- B100: increases NOx, but reduces NO2 and NP

(CPC)

- SCR: reduces strongly NOx & NO2, increases NH3,reduces slithly CPC with Diesel (no reduction withB100).

Identical tests have also been performed without EGR.

Table 5 summarizes the average reduction or increaserates of NOxin ETC with the investigated measures.

Similar statements like for the stationary operation canbe made for the results in ETC:EGR reduces NOxapprox. in the same range (17%), asB100 increases it (10%); SCR is the strongest reductionmeasure in the range of 72%.

Table 6 gives an analogous information for CPC in-crease, or CPC-reduction rates in ETC.

With EGR the total NP-counts are much less increasedwith B100, than with standard Diesel fuel. This is veryplausible, since B100 produces lower total particle num-bers with more spontaneous condensates in nucleimode, which are much more lost, or agglomerated onthe way from engine exhaust to the engine intake.

Fig.14: Average emissions in ETC, Iveco F1C E4; withdiesel & B100; with and w/o SCR

Tabel 5: Reduction rates of NOx in ETC

With B100 the NP-emissions are reduced w/o SCR, butincreased with SCR. The reason for that is the interac-tion of secondary nanoparticles from SCR with the aero-sol coming from the engine.With B100 the exhaust gas contains much more heavyHCs, which are ready for spontaneous condensationand the secondary NPs from SCR give a seeding ef-

fect for that, [13].

Regarding the CPC RR with SCR (Tab. 6) the differencebetween Diesel and B100 is also extremely pronounced.


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Tabel 6: Relative changes of summary particle counts

(PC) in ETC

In summary regarding the Diesel fuel only it can bestated, that EGR increases NP /CPC by 44% and SCRreduces it by 15%.

Variation of start of injection SOI +/- 3CA was per-formed to show the magnitude of positive and negative

effects. This was done by introducing an offset in theengine operation map.

SOI is the start of main injection quantity. If there is apreinjection, it is always kept at the same distance fromthe main injectors.

The name SOI was introduced to simplify the under-standing. In fact this is the start of energizing the injec-tors.

Fig.15: Variation of start of injection (SOI): Comparisonof NOx-plots in ETC

*), Iveco F1C E(4); diesel;

w/o exhaust gas aftertreatment system

Fig. 15 shows the NOx- and NO2plots in an interval ofETC with different SOI. As usual the earlier injection tim-ing results in higher NOx.

The way to reduce NOxis the late injection, which in turncauses higher fuel consumption.

Other test with B100 at stationary and dynamic engineoperation were performed with variation of SOI. They arenot further described here, but the findings are includedin conclusions.

Combinations of measures

In Figures 16 & 17 the effects of the investigated mea-

sures (B100, SOI, EGR, SCR) on NOx, NP and e are

summarized. The effective engine efficiency e is in-versely proportional to the fuel consumption.

At low load (OP3c), Fig. 16, there is no influence of B100on NOx.Reducing NOx by retarding SOI is disadvantageous forthe effective efficiency (higher fuel consumption).EGR reduces NOx in the same magnitude, like retardedSOI, but without the draw-back of efficiency. SCR has a

little effect on NOxbecause of urea cut-off. All variantswith B100 have lower NP-emissions than Diesel andthere are only little differences between them concerningNPs.

Fig.16: Influences of combinations of measures onemissions NOx & NP and on the effective engineefficiency, Iveco F1C E4; EGR, B100; SOI

*),

SCR

At transient operation (ETC), Fig. 17, the influences onNOxare similar as at stationary points: slight increase ofNOxby B100, reduction by EGR and significant reduc-tion by SCR. The NP-emission level (CPC) with B100 is

higher than with Diesel.


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Fig.17: Influences of combinations of measures on

emissions NOx & NP and on the effective engineefficiency, Iveco F1C E4; EGR, B100; SOI

**),

SCR

CONCLUSIONS

From the present tests performed at stationary engineoperation in steps-tests and at dynamic engine operation

in ETC several results can be remarked. The most im-portant are:

General influences of EGR

EGR, which is active at middle load of version E4 hasfollowing effects:

EGR lowers NOx and increases CO, PAS & DC(NP),

EGR reduces the gas throughput through the en-gine,

EGR lowers the boost pressure and the backpres-

sure, EGR increases the exhaust gas temperature.

These effects are confirmed in dynamic operation (ETC).

Stationary engine operation, 4 pts tests, EGR, B100,SCR

EGR: lowers NOx, but does not impact NO2(NO2/NOx-ratio increases), lowers slightly NH3(which ispresent only with SCR), increases the NP countsin average of 4 pts 43% with Diesel & 16% withB100,

B100: increases NOxat higher part load and full load inthe range of 10-15%,reduces the NP counts in average of 4 pts by72%.

SCR: reduces strongly NOx& NO2, is source of NH3 in therange up to 20 ppm at full load, reduces HC,reduces the NP counts in average of 4 pts by15%.

The average NOxreduction potentials with EGR, B100 &SCR are: EGR reduces NOx approximately in the samerange (15%) as B100 increases it (12%). SCR is thestrongest reduction tool in the range of 60% (by ave-

raging only OPs with SCR active 80%).

Transient engine operation, ETC, EGR, B100, SCR

EGR : reduces NOx(with Diesel) by 23%, no clear influ-ence on NO2increases the NP counts in averageby 44% (with Diesel),

B100: increases NOxby 10%; no clear influence on NO2reduces PC with Diesel by 6%,

SCR: reduces NOx(in average of all variants) by 73%and eliminates nearly NO2(by 95-100%); withSCR there are: an average NH3-emission up to12 ppm (LDS), reduces PC with Diesel (~ 15%);

with B100 there is lower reduction, (3%).

The NOxreduction potentials with combination of EGR,B100 & SCR are:

EGR reduces NOxapprox. in the same range (17%), asB100 increases it (10%); SCR is the strongest reductionmeasure in the range of 72%.

Variation of SOI & combinations

After the tests with Diesel and B100 with variation of SOIfollowing statements can be made:

for fuels with different heat values, like Diesel

and B100, there are different injection durations

for the same power and the ECU sets differently

the injection timing map,

NOx-emissions generally increase with advan-

cing the SOI. At full load NOx-values are clearly

higher for B100,

the influence of SOI on the integrated NP-

emissions depends on engine load:

o at lower OP3c there is a tendency of increas-

ing NP with advancing SOI,

o at higher OP1 the NP with Diesel decrease

with advancing SOI, with B100 there is no in-

fluence of SOI,

o at dynamic operation (ETC) the nanoparticles

emissions are not influenced by the SOI,

with combination of different measures the in-

crease of NOxcaused by B100 can be compen-

sated by EGR & SCR,

EGR is particularly useful at lower load, when

SCR is still inactive, reducing NOx by means of retarding SOI has a

disadvantage of higher energy consumption.


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Finally it can be stated, that the combination of EGR andSCR is a very important way to reduce NOxwithout draw-backs for: the fuel-consumption, for other emission com-ponents and nanoparticles.

ACKNOWLEDGEMENT

The authors want to express their gratitude to IVECOSwitzerland for the research engine and help with engine

settingMr. M. Signer, Mr. E. Mathis, Mr. R. Zellweger.

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ferenz, Dresden, Nov. 2006, p. 155.

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ABBREVIATIONS

AFHB Abgasprfstelle FH Biel, CHAir min stoichiometric air requirementBAFU Bundesamt fr Umwelt, CH (Swiss EPA)Bxx blend fuel with biocomponent share xx%CFPP cold filter plugging pointCLD chemoluminescence detectorCNC condensation nuclei counterCPC condensation particle counterDC Diffusion Charging SensordePN de Particles + deNOxDI Direct Injection

DMA differential mobility analyzerDPF Diesel Particle FilterE3 engine version Euro3 w/o EGRE4 engine version Euro4 with EGRE(4) engine version Euro4 closed EGRECU electronic control unitEGR exhaust gas recirculationEPA Environmental Protection AgencyETC European Transient CycleFAME Fatty Acid Methyl EsterFE filtration efficiencyFID flame ionization detectorFL full load

FOEN Federal Office of Environment (BAFU)FTIR Fourrier Transform Infrared SpectrometerHD heavy dutyHu lower calorific value


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ICE internal combustion enginesIR increase rateKx conversion rate of xLDS Laser Diode Spectrometer (for NH3)LEM limited engine mapLRV LuftreinhalteverordnungMD19 heated minidiluterNanoMet NanoMet nanoparticle summary surface

analyser (PAS + DC + MD19)

NEM nonlimited engine mapNP nanoparticles < 999 nm (SMPS range)OAPC Ordinance on Air Pollution ControlOP operating pointPAS Photoelectric Aerosol SensorPC particle countsPM particulate matter, particle massPSD particle size distributionRE reduction efficiencyRME rapeseed oil methyl ester

RR reduction rateSCR selective catalytic reductionSMPS Scanning Mobility Particle SizerSOI start of injectionSP sampling positionTC thermoconditioner.ULSD ultra low sulfur DieselVERT Verminderung der Emissionen von Real maschinen in Tunelbau

Verification of Emission Reduction Tech nologiesVERTdePN VERT DPF + VERT deNOx

feed factor of urea dosing;ratio: urea injected / urea stoichio-metric; calculated by the ECU.

here = 0.9

combinations of measures for reduction of nox &

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