Atmospheric Environment 37 (2003) 949–957

A study on emission characteristics of an EFI engine withethanol blended gasoline fuels

Bang-Quan He*, Jian-Xin Wang, Ji-Ming Hao, Xiao-Guang Yan, Jian-Hua Xiao

State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China

Received 10 July 2002; accepted 22 November 2002

Abstract

The effect of ethanol blended gasoline fuels on emissions and catalyst conversion efficiencies was investigated in a

spark ignition engine with an electronic fuel injection (EFI) system. The addition of ethanol to gasoline fuel enhances

the octane number of the blended fuels and changes distillation temperature. Ethanol can decrease engine-out regulated

emissions. The fuel containing 30% ethanol by volume can drastically reduce engine-out total hydrocarbon emissions

(THC) at operating conditions and engine-out THC, CO and NOx emissions at idle speed, but unburned ethanol and

acetaldehyde emissions increase. Pt/Rh based three-way catalysts are effective in reducing acetaldehyde emissions, but

the conversion of unburned ethanol is low. Tailpipe emissions of THC, CO and NOx have close relation to engine-out

emissions, catalyst conversion efficiency, engine’s speed and load, air/fuel equivalence ratio. Moreover, the blended

fuels can decrease brake specific energy consumption.

r 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Spark ignition engine; Ethanol; Oxygenate; Catalyst; Emission; Acetaldehyde

1. Introduction

Exhaust emissions from engines are dependent on fuel

composition (DePetris et al., 1993), air/fuel equivalence

ratio (McDonald et al., 1994), driving conditions,

oxygen content and the chemical structure of additive

(Neimark et al., 1994). Since tetraethyl lead as gasoline’s

octane improver was banned in the United States on

the first day of January in 1996, oxygenates, which

have no differences in air toxicity of ozone forming

potential (Noorman, 1993), have been used to en-

hance gasoline’s octane number, reduce summertime

smog, wintertime carbon monoxide and volatile

organic compounds with the provision of more complete

fuel combustion in engines. Although the decrease

of exhaust emissions by applying oxygenates to

engines is small relative to that by catalysts (Jeffrey

and Elliott, 1993), the fuels containing oxygenates and

with aromatics replaced by isoparaffins can reduce

hydrocarbon, CO and NOx emissions (Lange et al.,

1994).

Methyl tertiary-butyl ether (MTBE) is one of oxyge-

nated fuels. To meet the Clean Air Act Amendments of

1990 and similar regulations, over 85% of reformulated

gasoline (RFG) contains MTBE because of its low cost

and good blending characteristics. By 1998, MTBE was

ranked fourth in bulk chemical production in the United

States (An et al., 2002). MTBE can remarkably reduce

exhaust emissions (Kivi et al., 1992). For example, the

fuel with 15% MTBE can reduce CO by 10–15%, NOx

by 1.0–1.7%, THC by 10–20%, and also improve

fuel consumption (Kisenyi et al., 1994). However,

MTBE is highly soluble in water. Low levels of its

concentration make drinking water unpalatable due to

its low taste and odor threshold. Moreover, MTBE is

much more difficult to be degraded than other gasoline

components. Therefore, it has been detected in surface

water and ground water because of its widespread use

*Corresponding author. Tel.: +86-10-62772515; fax: +86-

10-62785708.

E-mail address: hebq@tsinghua.edu.cn (B.-Q. He).

1352-2310/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved.

doi:10.1016/S1352-2310(02)00973-1

(Nadim et al., 2001). Besides, MTBE itself can be

presented in exhaust gas and it has irritation effects on

eyes or lungs (Poulopoulos and Philippopoulos,

2000; Flynn et al., 2001). When research animals inhale

high levels of MTBE, they will develop cancers or

experience other non-cancerous diseases. MTBE even

poses a potential for carcinogenicity to humans at

high doses (Nadim et al., 2001). Therefore, it is time

to find alternative oxygenates that have no such

disadvantages.

Ethanol is a promising alternative biomass fuel

because of its biodegradable and regenerative character-

istic. The use of ethanol to substitute for MTBE in RFG

has some benefits in reducing water contamination and

poses no significant adverse impacts on public health

and environment (Nadim et al., 2001). CO2 released by

burned ethanol can be fixed by growing plants and

therefore makes no net greenhouse gas contribution to

global warming (Wheals et al., 1999). Since oxygen

content by weight in an ethanol molecule is approxi-

mately twice that of MTBE, less ethanol is required to

meet specified oxygen content in fuel. However, the heat

value of ethanol is less than that of gasoline. Conse-

quently, the heat value of ethanol blended gasoline fuels

will decrease when the proportion of ethanol increases

(Hsieh et al., 2002). Addition of ethanol to gasoline not

only increases Reid vapor pressure (RVP) of the blended

fuel (Pumphrey et al., 2000), but also alters the fuel’s

distillation curve and composition (Hsieh et al., 2002;

D’Ornellas, 2001). Hence, additional costly steps are

needed to reduce evaporative emissions from ethanol

blended gasoline fuels. Furthermore, ethanol blended

gasoline fuels will yield high unburned ethanol

and acetaldehyde emissions (Poulopoulos et al., 2001;

Zervas et al., 2002) and acetic acid emissions (Zervas

et al., 2001).

Ethanol content and engine operating conditions

influence exhaust emissions. Therefore, much attention

is paid to regulated and unregulated emissions from a

spark ignition engine in this experiment.

2. Experimental equipment and procedure

The engine used in this experiment is a multi-point

port injection gasoline engine with a cylinder bore of

90.82mm, a stroke of 76.95mm and a compression ratio

of 8.2. Its rated power is 66 kW at 5000 rpm and the

speed of maximum torque is 3000 rpm.The EFI system

will choose a close-loop control mode at part engine

loads to keep the engine operating near stoichoimetric

air/fuel ratio and then change to an open-loop control

mode at full engine loads to produce maximum power.

A Pt/Rh based three-way catalytic converter was

installed in the tailpipe.

Exhaust gases were sampled from the inlet and outlet

of the catalytic converter and then were measured on

line by an AVL exhaust analyzer. THC was analyzed

with a flame ionization detector (FID). CO was analyzed

with a non-dispersive infrared analyzer (NDIR). NOx

was analyzed with a chemiluminescent detector (CLD).

CO, THC and NOx emissions were average values of the

acquired data within 20 s for each stable operating

condition. Unburned ethanol and acetaldehyde were

measured in a GC-17A gas chromatography equipped

with a 30m long, 0.32mm inner diameter GS-Q type

capillary column and a FID.

3. Experimental results and discussions

3.1. Properties of ethanol blended gasoline fuels

Three test fuels were used in this study. The first was

unleaded gasoline (E0) as a base fuel for ethanol blended

gasoline fuels. The second and the third were ethanol

blended gasoline fuels containing 10% ethanol (E10)

and 30% ethanol (E30) by volume, respectively. Some of

the combustion-related properties concerning the three

fuels have been summarized in Table 1.

Table 1 shows research octane number (RON), motor

octane number (MON) and distillation temperature

including initial boiling temperature (IBT), 10%, 50%,

90% distillation temperatures and final distillation

temperature. As shown in Table 1, RON and MON

increase with the increase of ethanol concentration.

Compared to E0, RON of the blended fuels is increased

by 2.6 and 7.3, respectively. It can also be observed that

the addition of ethanol to gasoline increases IBT, but

10%, 50%, 90% and final distillation temperatures

decrease; The distillation temperatures below 50% of

E10 are lower than those of E30 and then become higher

than those of E30, which indicates that distillation

temperatures of ethanol blended fuels are dependent on

the evaporation of ethanol.

Table 1

Properties of ethanol blended gasoline fuels

Property items E0 E10 E30

Density (kg/l at191C) 0.736 0.741 0.751

RON 92.4 95.0 99.7

MON 81.2 82.3 86.6

Distillation temperature (1C)

IBP 36.0 37.5 40.0

10 vol% 55.2 49.0 52.7

50 vol% 92.5 73.2 72.5

90 vol% 153.7 149.8 145.7

End point 184.5 181.0 181.5

B.-Q. He et al. / Atmospheric Environment 37 (2003) 949–957950

3.2. Regulated engine emission characteristics and

catalyst conversion efficiencies

To analyze emissions and catalyst conversion effi-

ciencies, the relationship between air/fuel equivalence

ratio (l) and brake mean effective pressure (BMEP) is

presented in Fig. 1. It can be seen that l is almost the

same quantity at most operating conditions. The spark

ignition engine operates near stoichiometric air/fuel

ratio at part loads and burns rich mixture at full loads.

Fig. 2 shows CO emissions under different loads and

speeds. It can be seen that ethanol can decrease engine-

out CO emissions. Compared to E0 at full loads, at

2000 rpm, E10 and E30 decrease engine-out CO emis-

sions by 4.7% and 5.8%, respectively; At 3000 rpm,

engine-out CO emissions decrease by 5.7% and 3.1%,

respectively, which can be explained by the fact that the

oxygen atom in ethanol molecule is more effective in

improving combustion in rich mixture than that in air.

Tailpipe CO emissions are also decreased except for few

operating conditions.

From engine-out emissions and tailpipe emissions,

catalyst conversion efficiency of emissions can be

calculated. Fig. 3 presents catalyst conversion efficiency

of CO. Compared to E0, at part loads, ethanol can

enhance CO conversion at 2000 rpm and only E30 has

higher CO conversion at 3000 rpm. However, at full

loads, the conversion of CO decreases at above two

speeds. Because exhaust temperature of the catalytic

converter inlet in Fig. 4 exceeded the catalyst light-off

temperature of 3501C, the space velocity of the catalytic

converter was between 40 000 h�1 and 120 000 h�1 at all

2000 rpm

0.0

0.5

1.0

1.5

0.20 0.32 0.48 0.64 0.80BMEP (MPa)

E0 E10 E303000 rpm

0.0

0.5

1.0

1.5

0.20 0.35 0.54 0.69 0.86BMEP (MPa)

E0 E10 E30

λ λ

Fig. 1. The relationship between l and BMEP.

2000 rpmEngine-out

0

1

2

3

4

0.20 0.32 0.48 0.64 0.80

BMEP (MPa)

CO

(%

)

0

1

2

3

4

CO

(%

)

E0

E10

E30

2000 rpmTailpipe

0.20 0.32 0.48 0.64 0.80

BMEP (MPa)

E0

E10

E30

3000 rpmEngine-out

0

1

2

3

4

5

0.20 0.35 0.54 0.69 0.86BMEP (MPa)

CO

(%

)

0

1

2

3

4

5

CO

(%

)

E0E10E30

3000 rpmTailpipe

0.20 0.35 0.54 0.69 0.86BMEP (MPa)

E0

E10

E30

(a)

(b)

Fig. 2. (a) CO emissions at 2000 rpm and (b) CO emissions at 3000 rpm.

B.-Q. He et al. / Atmospheric Environment 37 (2003) 949–957 951

2000 rpm

0

20

40

60

80

100

0.20 0.32 0.48 0.64 0.80BMEP (MPa)

CO

con

vers

ion

(%)

CO

con

vers

ion

(%)

E0

E10

E30

3000 rpm

0102030405060708090

100

0.20 0.35 0.54 0.69 0.86BMEP (MPa)

E0

E10

E30

Fig. 3. CO conversion.

2000 rpm

0

200

400

600

800

1000

0.20 0.32 0.48 0.64 0.80BMEP (MPa)

Tem

pera

ture

(°C

)

0

200

400

600

800

1000

Tem

pera

ture

(°C

) E0 E10 E303000 rpm

0.20 0.35 0.54 0.69 0.86BMEP (MPa)

E0 E10 E30

Fig. 4. Exhaust temperature of catalytic converter inlet.

2000 rpmEngine-out

0

500

1000

1500

2000

2500

0.20 0.32 0.48 0.64 0.80BMEP (MPa)

0.20 0.32 0.48 0.64 0.80BMEP (MPa)

TH

C (

ppm

)

0

500

1000

1500

2000

2500

TH

C (

ppm

)

E0 E10 E30 2000 rpmTailpipe

E0

E10

E30

3000 rpmEngine-out

0

500

1000

1500

2000

2500

0.20 0.35 0.54 0.69 0.86BMEP (MPa)

0.20 0.35 0.54 0.69 0.86BMEP (MPa)

TH

C (

ppm

)

0

500

1000

1500

2000

2500

TH

C (

ppm

)

E0 E10 E30 3000 rpmTailpipe

E0

E10

E30

(b)

(a)

Fig. 5. (a) THC emissions at 2000 rpm and (b) THC emissions at 3000 rpm.

B.-Q. He et al. / Atmospheric Environment 37 (2003) 949–957952

2000 rpm

0

20

40

60

80

100

0.20 0.32 0.48 0.64 0.80BMEP (MPa)

TH

C c

onve

rsio

n (%

)

TH

C c

onve

rsio

n (%

)

0

20

40

60

80

100

E0

E10

E30

3000 rpm

E0

E10

E30

0.20 0.32 0.48 0.64 0.80BMEP (MPa)

Fig. 6. THC conversion.

2000 rpmEngine-out

0

500

1000

1500

2000

2500

0.20 0.32 0.48 0.64 0.80

BMEP (MPa)

0.20 0.32 0.48 0.64 0.80BMEP (MPa)

NO

x (p

pm)

0

500

1000

1500

2000

2500

NO

x (p

pm)

E0

E10

E30

2000 rpmTailpipe

E0

E10

E30

3000 rpmEngine-out

0

500

1000

1500

2000

2500

3000

3500

0.20 0.35 0.54 0.69 0.86BMEP (MPa)

0.20 0.35 0.54 0.69 0.86BMEP (MPa)

NO

x (p

pm)

0

500

1000

1500

2000

2500

3000

3500

NO

x (p

pm)E0

E10

E30

3000 rpmTailpipe E0

E10

E30

(a)

(b)

Fig. 7. NOx emissions at 2000 rpm and (b) NOx emissions at 3000 rpm.

2000 rpm

0

20

40

60

80

100

120

0.20 0.32 0.48 0.64 0.80BMEP (MPa)

0.20 0.32 0.48 0.64 0.80BMEP (MPa)

NO

x co

nver

sion

(%

)

NO

x co

nver

sion

(%

)

0

20

40

60

80

100

120E0 E10 E30 3000 rpm E0 E10 E30

Fig. 8. NOx conversion.

B.-Q. He et al. / Atmospheric Environment 37 (2003) 949–957 953

operating conditions, the catalyst conversion efficiency

reaches its maximum and keeps constant. As a result,

tailpipe CO emissions have close relations with engine-

out emissions, operating conditions (loads and speeds),

ethanol content in the blended fuels and l.THC emissions are illustrated in Fig. 5. Compared to

E0, engine-out THC emissions of E10 and E30 are

reduced by 6–13% and 15–29.5% at 2000 rpm, respec-

tively and reduced by 5–15.3% and 22.1–25.8% at

3000 rpm, respectively. Those results indicate that

ethanol can significantly reduce engine-out THC emis-

sions.

Fig. 6 presents THC conversion efficiencies. It can be

seen that although the conversion of THC of E10 and

E30 is less than that of E0 at most operating conditions,

tailpipe THC emissions of E10 and E30 is low since

engine-out THC emissions of E10 and E30 are far less

those of E0; The degree of THC reduction by catalysts is

far more than that by ethanol.

NOx emissions are illustrated in Fig. 7. It can be seen

that ethanol can decrease engine-out NOx emissions.

The main reason is attributed to the properties of

ethanol blends. In order to produce the same power at

part loads, electronic control unit will decrease the

amount of intake air and increase the amount of injected

fuel to maintain air/fuel equivalence ratio near 1.0. At

full loads, to maintain the maximum power of the

engine, more blended fuel is injected. Since ethanol has

higher latent heat relative to that of base gasoline, the

mixture’s temperature at the end of intake stroke

decreases and finally causes combustion temperature to

decrease. As a result, engine-out NOx emissions

decrease.

NOx conversion efficiencies are shown in Fig. 8.

Because of high oxygen concentration in the exhaust

when ethanol is used, the NOx conversion of E10 and

E30 is lower relative to that of E0 at most operating

conditions. But tailpipe NOx emissions of the three fuels

are quite close.

Engine-out emissions at idle speed are presented in

Fig. 9. The emissions of E0 are assumed to be 100%

here. The emissions of E10 and E30 are relative values to

E0. It can be seen that E10 slightly decreases CO, THC

and NOx emissions, but E30 can reduce CO, THC and

NOx by 35.7%, 53.4% and 33%, respectively, which

indicates that the fuel with high oxygen content can

improve combustion.

0

25

50

75

100

CO THC NOx

%

E0

E10

E30

Fig. 9. Engine-out emissions at idle speed.

2000 rpmEngine-out

01020304050607080

0.20 0.32 0.48 0.64 0.80BMEP (MPa)

0.20 0.32 0.48 0.64 0.80BMEP (MPa)

Eth

anol

(pp

m)

01020304050607080

Eth

anol

(pp

m)

E10

E302000 rpmTailpipe

E10E30

3000 rpmEngine-out

0

10

20

30

40

50

60

70

0.20 0.35 0.54 0.69 0.86BMEP (MPa)

0.20 0.35 0.54 0.69 0.86BMEP (MPa)

Eth

anol

(pp

m)

0

10

20

30

40

50

60

70

Eth

anol

(pp

m)

E10 E30 3000 rpmTailpipe

E10 E30

(a)

(b)

Fig. 10. (a) Unburned ethanol emissions at 2000 rpm and (b) Unburned ethanol emissions at 3000 rpm.

B.-Q. He et al. / Atmospheric Environment 37 (2003) 949–957954

3.3. Unregulated engine emission characteristics

Unregulated emissions such as unburned ethanol and

acetaldehyde were measured. Unburned ethanol emis-

sions are shown in Fig. 10. It is evident that there are

engine-out unburned ethanol emissions at various

operating conditions when ethanol is used. Engine-out

unburned ethanol emissions of E30 are more than two

times those of E10; Tailpipe unburned ethanol emissions

are high, which means that the conversion of ethanol is

low in the catalysts.

Fig. 11 shows acetaldehyde emissions. It is clear that

engine-out acetaldehyde emissions increases as the

proportion of ethanol increases. The maximum engine-

out acetaldehyde emissions of E30 are reached at

0.48MPa/2000 rpm and 0.2MPa/3000 rpm, respectively.

While engine-out acetaldehyde emissions of E0 are quite

low relative to those of the blended fuels, which

indicates that more acetaldehyde emissions are formed

due to the oxidation of ethanol. But tailpipe acetalde-

hyde emissions are low except few operating conditions.

Those results show that Pt/Rh based catalysts are

2000 rpmEngine-out

0

20

40

60

80

100

0.20 0.32 0.48 0.64 0.80

BMEP (MPa)

0.20 0.32 0.48 0.64 0.80

BMEP (MPa)

Ace

tald

ehyd

e (p

pm)

0

20

40

60

80

100

Ace

tald

ehyd

e (p

pm)

E0 E10 E302000 rpmTailpipe

E0E10E30

3000 rpmEngine-out

0

20

40

60

80

100

120

0.20 0.35 0.54 0.69 0.86BMEP (MPa)

0.20 0.35 0.54 0.69 0.86

BMEP (MPa)

Ace

tald

ehyd

e (p

pm)

0

20

40

60

80

100

120

Ace

tald

ehyd

e (p

pm)

E0 E10 E30 3000 rpmTailpipe E0 E10 E30

(b)

(a)

Fig. 11. (a) Acetaldehyde emissions at 2000 rpm and (b) acetaldehyde emissions at 3000 rpm.

0.2 0.4 0.6 0.8

300

350

400

450

500

E0 E10 E30

2000 rpm

BS

FC

(g/

kW h

)

300

350

400

450

500

BS

FC

(g/

kW h

)

BMEP (MPa)0.2 0.4 0.6 0.8

BMEP (MPa)

3000 rpm

E0 E10 E30

Fig. 12. BSFC of ethanol blended gasoline fuels.

B.-Q. He et al. / Atmospheric Environment 37 (2003) 949–957 955

effective in converting acetaldehyde emissions when

compared to the conversion of unburned ethanol.

3.4. Fuel consumption

Brake specific fuel consumption (BSFC) is presented

in Fig. 12. Since ethanol has low heat value, in order to

produce the same power at the same operating condi-

tions, more fuel will be burned as the proportion of

ethanol increases. As a result, BSFC increases. To

properly evaluate combustion efficiency of the blended

fuels, brake specific energy consumption (BSEC) is

introduced in Fig. 13. As shown, ethanol can decrease

BSEC except for low load using E10 at 2000 rpm. BSEC

can be decreased up to 4% for E30. Those results show

that ethanol can improve combustion efficiency.

4. Conclusions

From the discussions above, we can conclude that:

1. The addition of ethanol to gasoline fuel enhances

octane number of the blended fuels and decreases

distillation temperature except for IBP.

2. At operating conditions, ethanol blended fuels

slightly decrease engine-out CO and NOx emissions,

but they can significantly reduce engine-out THC

emissions. At idle, E10 has little effect on the

decrease of engine-out CO, THC and NOx emissions,

but E30 can drastically reduce engine-out CO, THC

and NOx emissions.

3. At most cases, ethanol blended fuels can decrease

tailpipe CO, THC and NOx emissions. The tailpipe

emissions have close relations to engine-out emis-

sions, conversion efficiencies, engine operating con-

ditions (speeds and loads), ethanol content and air/

fuel equivalence ratio.

4. With the increase of ethanol content, engine-out

unburned ethanol and acetaldehyde emissions in-

crease. Pt/Rh based three-way catalysts can effec-

tively convert acetaldehyde emissions, but the

conversion of unburned ethanol is low.

5. Ethanol blended fuels can decrease BSEC.

Acknowledgements

This study was financially supported by the National

Natural Science Foundation of China under the

contract No. 50136040.

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