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Development of an indicator for the emission controlof diesel passenger cars

Efthimios Zervas *

Department of Environmental Engineering, Democritus University of Thrace, Vas. Sofias 12, 67100 Xanti, Greece

Received 20 June 2007; accepted 23 September 2007Available online 29 September 2007

Abstract

An indicator for the CO and HC emission control, based on the instant values of exhaust temperature and engine-out emissions of COand HC, is developed in the case of Euro4 diesel engines. For a certain level of tail-pipe emissions and for a given diesel oxidation cat-alyst, this indicator can estimate the necessary catalytic volume to satisfy the regulation limits. More than this, it can also indicate theparts of NEDC that mainly contribute to this catalytic volume because of their low temperature or high engine-out CO or HC emissionsor a combination of both of them. This indicator can help engine-developing engineers to find out how they can to minimize the totalcatalytic volume, by controlling HC and CO engine-out emissions and exhaust temperature at certain parts of NEDC. This indicator canalso be used to minimize the number of necessary tests during engine development by directly comparing two engine tunings from thepoint of view of CO and HC emission control and thus estimate the necessary catalytic volume for each tuning.2007 Elsevier Ltd. All rights reserved.

Keywords: Diesel; Oxidation catalyst; Modeling; Exhaust temperature; CO; HC; Exhaust emissions; NEDC

1. Introduction

To find out the severity of emission control in the case ofdiesel CO and HC exhaust emissions control, three parame-ters are currently in use: average temperature on the urbandriving cycle (ECE) of the new European driving cycle(NEDC), and the engine-out CO and HC emissions. Theseparameters are used for a given catalyst and a given regula-tion emission level (Euro3, Euro4, . . .). The one real indi-cator enveloping the above three parameters is the necessarycatalytic volume to satisfy the given regulation limits. How-

ever, this volume is not directly linked with instant exhausttemperature and instant engine-out CO and HC emissionsand does not give any information of the parts of the cyclethat contribute more or less at the final tail-pipe emissions.

Several articles use models to describe the operation ofan oxidation catalyst [13]. All these models use more orless complex equations for the oxidation of CO and HC

on the oxidation catalyst. However, literature does notreport a simple model that relates the engine-out CO andHC emissions, the exhaust temperature and the necessarycatalytic volume to satisfy a certain level of regulations.

This article describes a simple indicator based on theinstant values of exhaust temperature and CO and HCengine-out emissions. For a given level of tail-pipe regulatedemissions level (Euro3, Euro4, Euro5,. . .) and a given oxida-tion catalyst, thisindicator can very easily estimate the neces-sary catalytic volume and also indicate the parts of NEDCthat mainly contribute to this volume because CO and HC

engine-out emissions are high at these parts or becauseexhaust temperature is not high enough to oxidize them.

2. Experimental

2.1. Methodology for the development of this indicator

The main factors influencing the necessary catalytic vol-ume for CO and HC oxidation in the case of diesel enginesare:

1359-4311/$ - see front matter 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.applthermaleng.2007.09.008

* Tel.: +30 24510 79392.E-mail address:[email protected]

www.elsevier.com/locate/apthermeng

Available online at www.sciencedirect.com

Applied Thermal Engineering 28 (2008) 14371442
mailto:[email protected]:[email protected]



1. The regulation limits (Euro3, Euro4, Euro5, . . .) and thesafety target used (usually 20% lower than the regulationlimits).

2. The performances of the oxidation catalyst (wash coat,Pt load, . . .)

3. The level of CO and HC engine-out emissions.

4. The level of exhaust gas temperature.5. The space velocity, which for a given catalytic volumedepends on the exhaust gas flow and finally on theengine displacement.

In this work, Euro4 limits are used as regulatory limitsand the safety target is defined as 20%, which gives a levelof tail-pipe emissions of 0.4 and 0.04 g/km for CO and HCemissions, respectively. A standard commercial catalystwith 50 g Pt/ft3 is used for these tests.

The first step for the development of this indicator is tofind some quite simple relationships between the necessarycatalytic volume to satisfy the regulatory standards and

exhaust emissions and temperature. Next, these equationscan be combined to form a global equation which can beused as this indicator. Using several experimental points,three figures are traced (not presented here). The first figureis the catalytic volume versus the average temperature ofexhaust gas on the urban part of NEDC for iso-engine-out emissions. These data reveal a relationship of a qua-dratic form

Volume aT2 bTc 1

withTthe average temperature of exhaust gas on the urbanpart of NEDC. This equation can be used to relate the cat-

alytic volume with exhaust temperature. The second figurerelates the necessary catalytic with the exhaust HC emis-sions at iso-temperature and iso-CO emissions. The thirdone relates the necessary catalytic with the exhaust COemissions at iso-temperature and iso-HC emissions. Onceagain, a quadratic form arrears for these data. The similarequations

Volume aCO2 bCOc 2

and

Volume aHC2 bHCc 3

are also used at iso-temperature and iso-HC or iso-CO en-gine-out emissions on the NEDC, respectively, (with COand HC engine-out emissions in g/km). Combining thesethree equations, the global equation, called indicator

Volume aT2 bTcCO2 dCOeHC2 fHCg

4

can be used to link the necessary catalytic volume with ex-haust temperature, CO and HC engine-out emissions.However, no information for each part of the NEDC is gi-ven. For this reason the instant values ofT, CO and HC

are used in the empirical equation, called instant indicator

VolumeX

aT2 bT cCO2 dCO eHC2 fHCg

5

with CO and HC in g/s, Tin C and volume in l, which isused to link T, CO and HC at each part of the cycle, whilethe necessary catalytic volume is estimated from the aver-

age of the sum of this equation at each second of the cycle.The instant value of this equation is the proposed indicatorat each point of he NEDC, while the global value is the glo-bal indicator, which corresponds to the catalytic volume.

The parameters ag are firstly estimated using severalvehicles tested on the NEDC. The catalytic volume esti-mated from this function is then compared with the realused catalytic volume. At a second stage, the analysis ofthis function during the NEDC is performed. Space veloc-ity is also an important parameter [4]; however, the addi-tion of exhaust gas flow (F)to form the following equation:

Volume

X

aT2 bT bCO2 dCOeHC2 fHCgF2 hF i

6

gives practically the same results as Eq.(5) (differences lessthan 0.1%), so this last parameter is ignored.

Other empirical equations are also tested; however, theobtained results are either not satisfactory, as in the caseof the equations

VolumeX

aCObHCcTd 7

and

VolumeX

aCObHCcT273d 8

or give practically the same results (differences less than0.5%) with those of Eq. (5) having more parameters, asthe equations:

VolumeX

aTbcT dCOefCOgHCh iHCj

9

Volume

X

aT2 bT bCO2 dCO eHC2 fHCghF2 iF k

10

andVolume

X

aT2 bT bCO2 dCOeHC2 fHCg=hF2 iF k

11

For this reason only the results of Eqs.(4) and (5) will bepresented here.

2.2. Vehicles/engines used

Ten passenger cars, named PC1PC10, were used in thiswork. Each one performed one new European driving cycle

according to official European regulations [5]. These 10

1438 E. Zervas / Applied Thermal Engineering 28 (2008) 14371442



NEDC were used to determine the parameters agof thisindicator. The passenger cars used are equipped with differ-ent commercial or experimental Euro4 diesel engines andare all equipped with the same type of diesel oxidation cat-alyst (50 g Pt/ft3). To obtain different values of exhaustemissions and exhaust temperature, the tuning of someengines is modified and the necessary catalytic volume tosatisfy Euro4 emission standards is adjusted.Table 1showsthe average, on the urban part of NEDC (ECE), exhaust

gas temperature and engine-out CO and HC emissions ofthese engines/vehicles.

3. Results and discussion

3.1. Comparison between the catalytic volumes estimated

from the indicator and the used one

Fig. 1shows the catalytic volume used to satisfy Euro4limits minus the safety limit of 20% and the catalytic pointestimated from this indicator (Eq.(4)). It can be seen that,for each experimental point used, there is a very goodagreement between the estimated and experimental values.The next step was the validation of this indicator. Thisindicator is applied to three NEDC tests of other passengercars, not used for the estimation of the indicator parame-tersag.Fig. 1shows the used and estimated catalytic vol-umes for these three points (square points), where a goodagreement is also observed. These results show that thisindicator in the global form of Eq. (4) can be used forthe rapid estimation of the necessary catalytic volume ofa certain type of catalyst and a certain level of tail-pipeemissions.

3.2. Evolution of the indicator on the NEDC

Fig. 2 shows the shape of this indicator (in its instantform, Eq.(5)) on the NEDC for the new European drivingcycles of three characteristic passenger cars: PC2PC4. Amore detailed analysis follows.

Fig. 3shows the same results asFig. 2, but is focused onthe first 200 s of the NEDC. The indicator follows thecycle, because exhaust temperature (Fig. 3) and CO andHC engine-out emissions (Fig. 4) also follow it. The indica-tor starts from zero and then increases because CO and HCengine-out emissions increase. All three engines show twopeaks at the first two bumps of NEDC, indicating that

there is an increased need for emission control (increased

catalytic volume), due to the two peaks of CO and HCemissions, while exhaust temperature is not high enough

to oxidize them.

Table 1Average, on the ECE, exhaust gas temperature and engine-out CO and HC emissions of the 10 NEDC used

PC1 PC2 PC3 PC4 PC5 PC6 PC7 PC8 PC9 PC10

Engine displacement (l) 1.2 1.9 1.2 1.6 1.2 1.2 1.2 1.6 1.9 1.6Vehicle weight (g) 1020 1360 1020 1130 1020 1020 1020 1130 1360 1130Average temperature on ECE (C) 163 177 159 151 163 163 163 155 164 170Engine-out CO on NEDC (g/km) 1.03 1.17 1.08 1.15 1.03 0.83 1.34 1.11 1.16 1.10

Engine-out HC on NEDC (g/km) 0.226 0.174 0.136 0.133 0.271 0.226 0.226 0.135 0.154 0.200

0 200 400 600 800 1000 1200

Time (s)

-20

-10

0

10

20

Indicator

0

40

80

120

Speed(km/h)

Speed

PC2

PC3

PC4

Fig. 2. The instant indicator for the PC2PC4 on the entire NEDC.

0.5 1 1.5 2 2.5

Used catalytic volume (L)

0.5

1

1.5

2

2.5

Estimated

catalyticvolume(L)

Estimated/used volumes

Validation points

Fig. 1. Necessary catalytic volume to satisfy Euro420% for the differentpassenger cars tested. Estimated from the indicator catalytic volumeversus used catalytic volume (round points) and validation of thisindicator using three other passenger cars (square points).

E. Zervas / Applied Thermal Engineering 28 (2008) 14371442 1439



There are significant local differences between the indi-cator of the three engines. The two peaks of PC2 are quitehigher than those of the two other engines, because even ifexhaust temperature of this engine is not very differentfrom the exhaust temperature of the other two engines(Fig. 3), engine-out CO emissions, but especially engine-out HC emissions are significantly higher than the emis-sions of the other two engines (Fig. 4).

It must be noticed that exhaust temperature of PC2 ishigher than that of the other two engines at 6590 s. At thispart of NEDC, CO engine-out emissions of this vehicle isslightly higher than the CO engine-out emissions of theother two vehicles; however, its HC engine-out emissions

are significantly higher. The emission control need (whichcan be translated by the necessary volume of oxidation cat-alyst) is higher due to increased HC emissions and to rela-tively low exhaust temperature, below the light-off of theoxidation catalyst. This indicator shows quite clearly thisneed and can help to find the parts of NEDC where the

emissions of a vehicle are quite high relatively to exhausttemperature, and mostly contribute to the catalytic volume.Fig. 5illustrates another example of PC2 at the part of

300400 s of the NEDC. Between 320 and 340 s, engine-outemissions show a slight increase, but as exhaust gas temper-ature increases more rapidly, the instant indicatordecreases, because exhaust temperature is high enough totreat CO and HC engine-out emissions. At this region ofNEDC, an engine tuning of lower fuel consumption orlower NOx/PM emissions could be applied, even if thistuning increases CO and HC engine-out emissions, becauseexhaust temperature is sufficient for the oxidation catalystto oxidize them. Instead, at the part of 375385 s, CO

engine-out emissions, in combination with the quite lowexhaust temperature, show a quite high peak increasingthe value of this instant indicator and thus the need for cat-alytic volume.

Figs. 6 and 7show the instant indicator, exhaust temper-ature and CO and HC engine-out emissions at the part200800 s of the NEDC. Exhaust temperature of each pas-senger car follows quite well the driving cycle. However, itcan be seen that PC2 exhaust gas is hotter than the exhaustgas of PC3 (18 C in average on the ECE), while those ofPC4 are less hot than those of PC3 (8 C in average onthe ECE). Average exhaust temperature on the ECE is

not the only parameter influencing CO and HC conversionefficiency, but the instant temperature also plays an impor-tant role[4]. The instant high temperature of PC2 is abovecatalyst light-off temperature and thus leads to high CO

0 50 100 150 200

Time (s)

0

4

8

12

Indicator

0

30

60

Speed(km/h)

Speed

PC2

PC3

PC4

0

100

200

300

Temperature(C)

Fig. 3. The indicator for the PC2PC4 on the first 200 s of the NEDC(lower curves) and exhaust temperature of the same vehicles (uppercurves).

0 50 100 150 200

0

2

4

6

8

10

HC(mg/s)

0

25

50

Speed

PC2

PC3

PC4

0

2

4

6

8

10

CO/10(mg/s)

Time (s)

Speed(km

/h)

Fig. 4. CO (lower curves) and HC (upper curves) engine-out emissions for

the PC2PC4 on the first 200 s of the NEDC.

300 350 400

Time (s)

0

1

2

3

4

5

HC(mg/s),CO(mg/s

/10),Indicator

0

100

200

300

Speed(km/h),Tem

perature(C)

Speed

Temp.

HC

CO

Indicator

Fig. 5. Exhaust temperature, CO and HC engine-out emissions and

instant indicator for the PC2 on the 300400 s of the NEDC.




and HC conversions, even if engine-out emissions arehigher (Fig. 7).

As exhaust temperature is now higher than at the begin-ning of the NEDC and the oxidation catalyst is activated,the instant indicator (Eq. (5)) is generally quite low, indi-cating that even a small catalytic volume could be sufficientto oxidize these emissions. However, there are some partsof the cycle where some peaks of the indicator can beobserved: the indicator of PC2 shows three low peaksdue to high exhaust temperature at the points of 50 km/hwhere very high conversion efficiencies can be observed;PC3 shows some high peaks at the beginning of some accel-

erations due to high HC and CO instant emissions, while

exhaust temperature is not as high as needed; PC4 showstwo peaks at the third and fourth steady speed of 30 km/h, due to quite low temperature of this part and to quitehigh CO and HC engine-out emissions, especially at650 s. Once more, this indicator can help to find out whichpart of NEDC contributes to the catalytic volume and can

help to apply a different engine tuning to control engine-out emissions or increase exhaust temperature at thesepoints.

Fig. 8 shows the shape of this indicator at the EUDC.This indicator goes to negative values a little after 800 sand is lower when exhaust temperature is higher. This isdue to the following reason: even in the case of high

200 400 600 800

0

4

8

12

0

30

60

Speed

PC2

PC3

PC4

80

120

160

200

240

280

Time (s)

Indicator

Speed(km

/h)

T

emperature(C)

Fig. 6. The indicator for the PC2PC4 on the 200800 s of the NEDC

(lower curves) and exhaust temperature of the same vehicles (uppercurves).

200 250 300 350 400 450 500 550 600 650 700 750 800

0

1

2

3

4

5

6

0

25

50

Speed

PC2

PC3

PC4

0

2

4

6

8

10

HC(mg/s)

CO/10(mg/s)

Time (s)

Speed(km/h)

Fig. 7. CO (lower curves) and HC (upper curves) engine-out emissions forthe PC2PC4 on the 200800 s of the NEDC.

800 900 1000 1100 1200

-20

-10

0

0

30

60

90

120

Speed

PC2

PC3

PC4

0

100

200

300

400

500

Time (s)

Indicator

Speed(km/h)

Temperature(C)

Fig. 8. Instant indicator (lower curves) and exhaust temperature (uppercurves) for the PC2PC4 on the EUDC.

800 900 1000 1100 1200

0

2

4

0

30

60

90

120

Speed

PC2

PC3

PC4

0

2

4

6

HC(mg/s)

CO/10(mg/s)

Time (s)

Speed(km/h)

Fig. 9. CO (lower curves) and HC (upper curves) engine-out emissions for

the PC2PC4 on the EUDC.

E. Zervas / Applied Thermal Engineering 28 (2008) 14371442 1441



engine-out emissions (Fig. 9), CO and HC oxidation effi-ciencies are near 100% due to high exhaust temperature.For this reason, EUDC practically does not add supple-mentary CO and HC emissions to NEDC emissions. How-ever, the regulatory limits are expressed on g/km and arebased on the 11 km of NEDC. As the 7 km of EUDC do

not contribute on the total CO and HC tail-pipe emissions(because the oxidation efficiency is almost 100%), practi-cally the total emissions can come from the 4 km of theECE part of the cycle. For this reason, the global indicatormust substrate the emissions corresponding to EUDC fromtotal NEDC emissions.

4. Conclusions

An indicator, based on the instant values of exhausttemperature and engine-out emissions of CO and HC isdeveloped to estimate the necessary catalytic volume fora certain level of emission limits and to reveal the parts

of NEDC that contribute to this catalytic volume. Thisfunction can help to find out which parts of NEDC musthave lower emissions in order to minimize the total cata-

lytic volume. This function can be used during the enginedevelopment to directly compare two engine tunings fromthe point of view of CO and HC emission control and thusestimate the necessary catalytic volume for each tuningwith fewer tests.

References

[1] A.M. Stamatelos, G.C. Koltsakis, I.P. Kandylas, G.N. Pontikakis,Computer aided engineering in diesel exhaust aftertreatment systemsdesign, Proc. Inst. Mech. Eng., Part D: J. Automob. Eng. 213 (6)(1999) 545560.

[2] D. Chalet, J. Galindo, H. Climent, One dimensional modeling ofcatalyst for internal combustion engine simulation, in: Proceedings ofthe Spring Technical Conference of the ASME Internal CombustionEngine Division, 2006, pp. 129135.

[3] Y. Tanaka, T. Hihara, M. Nagata, N. Azuma, A. Ueno, Modeling ofdiesel oxidation catalyst, Ind. Eng. Chem. Res. 44 (22) (2005) 82058212.

[4] E. Zervas, Impact of different configurations of a diesel oxidationcatalyst on the CO and HC tail-pipe emissions of a Euro4 passenger

car, Appl. Therm. Eng. 28 (89) (2008) 962966.[5] Directive 70/220. .

http://ec.europa.eu/enterprise/automotive/directives/vehicles/dir70_220_cee.htmlhttp://ec.europa.eu/enterprise/automotive/directives/vehicles/dir70_220_cee.htmlhttp://ec.europa.eu/enterprise/automotive/directives/vehicles/dir70_220_cee.htmlhttp://ec.europa.eu/enterprise/automotive/directives/vehicles/dir70_220_cee.html

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