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Applied Thermal Engineering 28 (2008) 396–404

Experimental determination of suitable ethanol–gasoline blend rateat high compression ratio for gasoline engine

M. Bahattin Celik *

Karabuk University, Technical Education Faculty, 78050 Karabuk, Turkey

Received 17 April 2007; accepted 26 October 2007Available online 19 November 2007

Abstract

Ethanol produced from biomass has high octane number and gives lower emissions. Therefore, it is used as alternative fuel in thegasoline engines. In this study, ethanol was used as fuel at high compression ratio to improve performance and to reduce emissionsin a small gasoline engine with low efficiency. Initially, the engine whose compression ratio was 6/1 was tested with gasoline, E25(75% gasoline + 25% ethanol), E50, E75 and E100 fuels at a constant load and speed. It was determined from the experimental resultsthat the most suitable fuel in terms of performance and emissions was E50. Then, the compression ratio was raised from 6/1 to 10/1. Theengine was tested with E0 fuel at a compression ratio of 6/1 and with E50 fuel at a compression ratio of 10/1 at full load and variousspeeds without any knock. The cylinder pressures were recorded for each compression ratio and fuel. The experimental results showedthat engine power increased by about 29% when running with E50 fuel compared to the running with E0 fuel. Moreover, the specific fuelconsumption, and CO, CO2, HC and NOx emissions were reduced by about 3%, 53%, 10%, 12% and 19%, respectively.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Ethanol; Performance; Emissions; High compression ratio

1. Introduction

The increasing demand for energy and stringent pollu-tion regulations as a result of the population growth andtechnological development in the world promote researchon alternative fuels [1]. The investigations have concen-trated on decreasing fuel consumption and on loweringthe concentration of toxic components in combustionproduct by using non-petroleum, renewable, sustainableand non-polluting fuels [2]. The high octane ratings ofthe alcohols and their high heats of vaporization havemade them preferred fuels for use in-high compressionratio (CR), high-output engines. High octane values whichcan permit significant increases of compression ratio and/or spark advance, and high heats of evaporation whichcan provide fuel–air charge cooling and density increase,

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

doi:10.1016/j.applthermaleng.2007.10.028

* Tel.: +90 370 4338200; fax: +90 370 4338204.E-mail address: mbcelik@gmail.com

and thus higher mass throughput [3]. In theory, for anun-throttled Otto-cycle engine, the efficiency g can be writ-ten as g = 1 � (1/ek�1), where e is compression ratio and k

is specific heat ratio. If the compression ratio can be furtherraised, the heat efficiency and engine power output can beimproved [4]. As a fuel for spark ignition engines, alcoholshave some other advantages over gasoline, such as thereduction of CO and UHC emissions [5]. As ethanol fuelalso has high heat of vaporization, it reduces the peak tem-perature inside the cylinder and hence reduces the NOx

emissions [6].Ethanol is an alcohol-based alternative fuel produced

by fermenting and distilling starch crops that have beenconverted into simple sugars. Feedstocks for this fuelinclude corn, barley and wheat. Ethanol can be producedfrom cellulose feedstock such as corn stalks, rice straw,and sugar cane which are examples of feedstock that con-tain sugar [7]. As ethanol can be produced from agricul-tural crops, its cost can be lower in the states whoseeconomy is largely based on agriculture and it can be used

M.B. Celik / Applied Thermal Engineering 28 (2008) 396–404 397

as alternative fuel. Thus, dependence for foreign oil isreduced in these states. The simplest approach to theuse of alcohols in spark ignition (SI) engines is to blendmoderate amounts of alcohols with gasoline. The secondand more technically challenging option is to use alcoholsessentially neatly as engine fuel [3].

Several studies have been conducted on the usage of eth-anol and ethanol–gasoline blends as fuel in the SI engines.Hsieh et al. [5] investigated the engine performance andpollutant emission of an SI engine using ethanol–gasolineblends (E0, E5, E10, E20 and E30). Their experimentalresults indicated that torque output and fuel consumptionslightly increase when using ethanol–gasoline blended fuel;CO and HC emissions decrease dramatically as a result ofthe leaning effect. When ethanol is added to the blendedfuel, it can provide more oxygen for the combustion pro-cess and leads to the so-called ‘‘leaning effect”. In anotherstudy by Wu et al. [4], ethanol–gasoline blended fuels (E0,E5, E10, E20 and E30) were tested in a conventional engineunder various air–fuel equivalence ratios for its perfor-mance and emissions. The results of the tests showed thattorque output increased slightly at small throttle openingwhen ethanol gasoline blended fuel was used. It was alsoshown that CO, CO2 and HC emissions were reduced withthe increase of ethanol content in the blended fuel. Yukseland Yuksel [8] investigated the use of ethanol–gasolineblend (E60) as a fuel in an SI engine. In this study, itwas found that using ethanol–gasoline blended fuel, theCO and HC emissions would be reduced approximatelyby 80% and 50%, respectively. Moreover, significantdecreases in the engine power were not observed. Bayrak-tar [9] investigated the effects of ethanol addition (from0% to 12%) to gasoline on an SI engine performance andexhaust emissions. The effective power and effective effi-ciency increased with increasing ethanol amount in theblended fuel as a result of improved combustion and COemissions also decreased. Al-Hasan [10] investigated theeffect of ethanol–unleaded gasoline blends on performanceand emission. The unleaded gasoline was blended with eth-anol to prepare 10 test blends ranging from 0% to 25% eth-anol with an increment of 2.5%. Ethanol addition resultedin an increase in brake power, brake thermal efficiency,volumetric efficiency and fuel consumption by about8.3%, 9%, 7% and 5.7% mean average values, respectively.Yucesu et al. [11] investigated the effects of ethanol–gaso-line blends (E0, E10, E20, E40, E60) on engine perfor-mance and exhaust emissions in different compressionratios (8/1–13/1). According to the results of the experi-ment, it was found that as the compression ratio increased,engine torque and HC emissions also increased. The fuelscontaining high ratios of ethanol, E40 and E60 had impor-tant effects on the reduction of CO and HC emissions.Song et al. [12] investigated the effects of the additives ofethanol (up to 9.79% ethanol) and methyl tert-butyl ether(up to 20% MTBE) in various blend ratios into the gasolinefuel on the exhaust emissions in an EFI gasoline engine.The experimental results showed that ethanol brought

about generally lower regulated engine-out emissions(CO, THC and NOx) than MTBE did. He et al. [13] inves-tigated the emission characteristics of an EFI engine withethanol blended gasoline fuels. In the tests, E0, E10 andE30 fuels were used. Their results showed that the increaseof ethanol content decreased THC, CO and NOx emis-sions. El-Emam and Desoky [14] investigated the combus-tion of alternative fuels theoretically and experimentally inSI engines. The results showed that there was an increase inengine thermal efficiency and decrease in NOx and COemissions when ethanol and methanol fuels were used.Topgul et al. [15] investigated the effects of ethanol–unleaded gasoline blends (E0, E10, E20, E40, E60) andignition timing on performance and emissions. The exper-imental result showed that the brake torque slightlyincreased, and CO and HC emissions decreased when eth-anol–gasoline blend was used. It was also found thatblends with ethanol allowed the compression ratio toincrease without any knock. Bardaie and Janius [16] inves-tigated the conversion of SI engine for alcohol usage. Theymade some modifications on the carburettor. According tothe experimental results, it was determined that power losswas only 3–4% when running with ethanol compared togasoline. Abdel-Rahman and Osman [17] investigated theeffect of ethanol–gasoline blends (E10, E20, E30 andE40) on engine performance and emissions at various com-pression ratios (8, 10, and 12). For each fuel blend, there isan optimum compression ratio that gives maximum indi-cated power. In this study, optimum compression ratioswere found to be 8, 10 and 12 for E10, E20 and E30 fuels,respectively.

Studies were also carried out regarding the use of alco-hols as a fuel in the small gasoline engines (25 HP or less).Charalampos et al. [18] investigated the behavior of a smallfour-stroke engine when mixtures of gasoline–ethanol andgasoline–methanol were used as fuel. In the engine tests, 11test blends ranging from 0% to 100% ethanol with an incre-ment of 10% were used. CO emissions were decreased asethanol content in fuel increased. Moreover, HC emissionswere decreased as ethanol content in fuel increased, but HCemissions significantly increased when using E90 and E100fuel. Jia et al. [19] investigated the emission characteristic ofa four-stroke motorcycle engine using 10% ethanol–gaso-line blended fuel (E10) at different driving modes on thechassis dynamometers. The results indicated that CO andHC emissions were lower when using E10 as compared tothe use of unleaded gasoline. Magnusson et al. [20] investi-gated the regulated HC, CO and NOx emissions of a two-stroke chain saw engine using ethanol, gasoline and etha-nol–gasoline blends as fuel. The emissions of CO, HCand NO were reduced when the ethanol content wasincreased. But HC increased when using E85 and E100fuels. When using ethanol and ethanol–gasoline blendsinstead of gasoline, the engine power did not vary signifi-cantly. Desoky and Rabie [21] investigated the perfor-mance of small spark ignition engines running onalcohols, gasoline and alcohol–gasoline blends. The results

398 M.B. Celik / Applied Thermal Engineering 28 (2008) 396–404

showed that the fuel economy benefits of using alcoholsgasoline blends were found to be substantial.

Small spark ignition gasoline-fuelled engines can befound all over the world performing in a variety of rolesincluding power generation, agricultural applications andmotive power for small boats. To attain low cost, theseengines are typically air cooled, simple carburettors areused to regulate the fuel supply and magneto ignition sys-tems are employed [22]. As these engines run at very lowcompression ratio and slightly rich mixture, they have verylow efficiency and high emission values. Moreover, theseengines cause significant air pollution as they do not havea catalytic converter.

From the above literature review, it is understood thatthere are slight increases or decreases in power when theethanol and ethanol–gasoline blends are used at the originalcompression ratio in the engines. In addition, CO, HC, andNOx emissions decrease. However, fuel consumptionincreases. If ethanol and ethanol–gasoline blends are usedat high compression ratio, power increases and fuel con-sumption decreases. The compression ratio of air-cooledsmall engines is low (e.g. 5/1, 6/1). In air-cooled smallengines, the wall temperatures are higher than those ofwater-cooled engines and the knock tendency is also higher.Thus, the compression ratio is kept lower in these engines toprevent knock. Significant improvements can be obtained inpower and efficiency if the small engines with low compres-sion ratio can be run at higher compression ratios usingfuels resistant to the knock. Gains of about 25–30% inpower can be obtained when the compression ratio of anengine is raised from 5/1, 6/1 to 9/1, 10/1 [23,24]. Ethanolhas high octane number, both permits the rising of the com-pression ratio and gives lower emission.

543

1. Engine 2. Dynamometer 3. Air flowmeter 4. Fu6. Exhaust gas analyzer 7. Load and speed in9. Pressure transducer 10. Inductive pick-up 11.

1

9

1112

10

13

Fig. 1. Test

To the best of the author’s knowledge, no research hasyet been carried out by increasing the compression ratioin the small engines running with ethanol. There are twoaims of this study. One of them is to determine the suitableethanol–gasoline blend rate in terms of performance andemissions for small engines. The other is to investigateexperimentally the improvement of the performance andemissions by testing the engine with suitable ethanol–gaso-line blend fuel at high compression ratio without anyknock.

2. Experimental studies

The experimental set-up, shown in Fig. 1, consisted oftest engine, dynamometer (D.C. dynamometer), fuel andair flow meters, cylinder pressure measuring system,exhaust gas analysis system and various measuring equip-ments. In the tests, a single-cylinder four-stroke smallengine whose original compression ratio was 6/1 was used.To increase the compression ratio, engine cylinder headwas changed and the modified cylinder head was usedinstead of it. Thus, the compression ratio could be raisedfrom 6/1 up to 10/1. To adjust ignition timing, electronicignition system was used instead of magneto ignition sys-tem. Table 1 shows the specifications of the test engine.For all the tests, the ignition timing was adjusted basedon maximum torque at each engine speed. The heatingvalue of ethanol is lower than that of gasoline. Therefore,it necessitates 1.5–1.8 times more ethanol fuel to achievethe same energy output. To this effect, carburettor mainjet was enlarged and the main jet cross-section was variedusing a conical screw. The excess air ratio was adjustedto 1.0 for all the tests. To prevent the phase separation,

876

2

el flowmeter 5. Temperature indicatorsdicators 8. Dynamometer control unit

Charge amplifier 12.Oscilloscope 13. Computer

set-up.

Table 1Specifications of the test engine

Items Engine

Mark Lombardini LM 250Engine type Four-stroke, single cylinderEngine displacement (cm3) 250Compression ratio 6/1–10/1Maximum speed (rpm) 3600Ignition system type Transistorized coilFuel system CarburettorCooling system Air and water cooled

M.B. Celik / Applied Thermal Engineering 28 (2008) 396–404 399

ethanol with a purity of 99.5% was used in the tests. Prop-erties of ethanol and gasoline fuels are shown in Table 2.Emissions were measured with a MRU DELTA 1600Lexhaust gas analyzer. The specifications of the exhaustgas analyzer are given in Table 3. Ignition timing was mea-sured with a Sun Equip Co. TL-06230A ignition timingmeasurement equipment.

To measure the in-cylinder pressure of the test engine, asystem was developed. The system consisted of a piezoelec-tric pressure transducer, inductive pick-up, charge ampli-fier, oscilloscope and personal computer (PC). In thisstudy, in-cylinder pressure data was collected using a Kis-tler model 601A piezoelectric transducer mounted to thespark plug, Kistler model 5011 charge amplifier, a Hitachidigital oscilloscope (VC-5430) and a PC were used torecord the pressure data. The data regarding the crankangles and the position of the top dead centre were trans-mitted to oscilloscope using an inductive pick-up.

The engine tune up was checked before the test andmeasurements were conducted after reaching the workingtemperature of the engine. To determine the suitable etha-

Table 2The properties of gasoline and ethanol

Fuel property Gasoline Ethanol

Formula C8H18 C2H5OHMolar C/H ratio 0.445 0.333Molecular weight (kg/kmol) 114.18 46.07Latent heating value (MJ/kg) 44 26.9Stoichiometric air/fuel ratio 14.6 9Auto-ignition temperature (�C) 257 425Heat of vaporization (kJ/kg) 305 840Research octane number 88–100 108.6Motor octane number 80–90 89.7Freezing point (�C) �40 �114Boiling point (�C) 27–225 78Density (kg/m3) 765 785

Table 3The specifications of the exhaust gas analyzer

Measurements range Accuracy

CO (vol.%) 0–15 0.01CO2 (vol.%) 0–20 0.01HC (ppm) 0–20000 1NOx (ppm) 0–4000 1O2 (vol.%) 0–25 0.1

nol–gasoline blend rate in terms of performance and emis-sions, the test engine was run at a compression ratio of 6/1,2000 rpm, MBT (minimum spark advance for best torque),full throttle opening, over a k – value of 1.0; with E0 (gas-oline), E25 (75% gasoline + 25% ethanol), E50, E75 andE100 (ethanol) fuels. All the data for engine power, specificfuel consumption, spark timing, exhaust gas temperature,HC, CO, CO2 and NOx emissions were collected. The cyl-inder pressures were recorded for each compression ratiosand fuels. At all the tests, all values were recorded afterallowing sufficient time for the engine to stabilize.

3. Results and discussion

The tests were performed at two stages. At first stage,the engine was tested at original compression ratio (6/1),2000 rpm, full throttle opening and air excess ratio of 1.0with E0, E25, E50, E75 and E100 fuels. The obtainedresults are given below.

3.1. The effects of various fuels on engine performance

Fig. 2 shows the effect of various fuels on power andspecific fuel consumption (SFC). As the ethanol contentin the blend fuel increases, power also slightly increases.When compared to E0 fuel, the power increases of 3%,6% and 2% are obtained with E25, E50 and E75 fuels,respectively. The heat of evaporation of ethanol is higherthan that of gasoline. High heat of evaporation can providefuel–air charge to cool and density to increase, thus higherpower output is obtained to some extent [3]. However,power increase starts to decrease when ethanol content israised to more than 50%. When running with E100 fuel,it is seen that a 4% decrease in power takes place in com-parison with E0 fuel.

Owing to the fact that the heating value of ethanol islower than that of gasoline, the SFC increases as the etha-nol content in blend increases (Fig. 2). Increases of 10%,

Full throttle opening, 2000 rpm, CR=6/1

1.6

1.7

1.8

1.9

2

2.1

2.2

E0 E25 E50 E75 E100

Fuel

Pow

er (k

W)

400

450

500

550

600

650

700

SFC

(g/k

Wh)

PowerSFC

Fig. 2. The effect of various fuels on power and specific fuel consumption(SFC).

400 M.B. Celik / Applied Thermal Engineering 28 (2008) 396–404

19%, 37% and 56% in the SFC were observed when run-ning with E25, E50, E75 and E100 fuels, respectively.

3.2. The effects of various fuels on exhaust emissions

Fig. 3 shows the effect of various fuels on CO and CO2

emissions. CO is a toxic gas that is the result of incompletecombustion. When ethanol containing oxygen is mixedwith gasoline, the combustion of the engine becomes betterand therefore CO emission is reduced [18]. As seen fromFig. 3, the values of CO emission are about 3.76%,2.65%, 2.06%, 1.24% and 0.73% for E0, E25, E50, E75and E100 fuels, respectively. In addition, the decreases inCO2 emission are observed when ethanol is used. Carbondioxide is non-toxic but contributes to the greenhouseeffect. Because the ethanol contains lower C atom thangasoline, it gives off lower CO2 [4]. The values of CO2 areabout 13.25%, 12.14%, 11.62%, 10.25% and 9.51% withE0, E25, E50, E75 and E100 fuels, respectively (Fig. 3).

The effect of various fuels on HC and NOx emissions isgiven in Fig. 4. Ethanol contains an oxygen atom in its

Full throttle opening, 2000 rpm, CR=6/1

100

200

300

400

500

600

E0 E25 E50 E75 E100

Fuel

HC

(ppm

)

0

500

1000

1500

2000

2500

NO

x (pp

m)

HCNOx

Fig. 4. The effect of various fuels on HC and NOx emissions.

Full throttle opening, 2000 rpm, CR=6/1

0

1

2

3

4

5

E0 E25 E50 E75 E100Fuel

CO

(%)

8

11

14

17

20

CO

2 (%

)

COCO2

Fig. 3. The effect of various fuels on CO and CO2 emissions.

basic form; it can be treated as a partially oxidized hydro-carbon when ethanol is added to the blended fuel. There-fore, CO and HC emissions decrease [8]. As seen fromthis figure, HC decreases to some extent as ethanol addedto gasoline increases. The value of HC declines to271 ppm and 245 ppm with E25 and E50 fuels, respectively,from 331 ppm with E0. But the significant increases areseen in the HC emissions when running with E75 andE100 fuels. The value of HC rises to 340 ppm and483 ppm with E75 and E100 fuels, respectively. The pureethanol and higher ethanol content blends reduce the cylin-der temperature as the heat of vaporization of ethanol ishigher when compared to gasoline. The lower temperaturecauses misfire and/or partial burn in the regions near thecombustion chamber wall. Therefore, HC emissionsincrease, and engine power can slightly decreases.

As the ethanol content in the blend increases, NOx

decreases (Fig. 4). The value of NOx declines to 1711ppm, 1434 ppm, 1150 ppm and 988 ppm with E25, E50,E75 and E100 fuels, respectively, from 2152 ppm with E0fuel. Since ethanol has a higher heat of vaporization relativeto that of base gasoline, the mixture’s temperature at theend of intake stroke decreases and finally causes combus-tion temperature to decrease. As a result, engine-out NOx

emissions decrease [13].According to the results of experiment carried out at

first stage, it was determined that the most suitable fuelwas E50 in terms of power and HC emission. CO, CO2

and NOx were low with E100 fuel also. But HC increased;power decreased and SFC increased extremely with E100fuel. HC is a very important emission because it increaseswith the fuels containing high ratios of ethanol such asE75 and E100. HC value of E50 fuel was the lowest whencompared to the other fuels.

At second stage, the compression ratio was raised from6/1 to 8/1 and 10/1 and the engine was tested with E50 andE0 fuels for comparison. These tests were performed at fullload in the ranges of 1500–4000 rpm at intervals of 500 rpmand excess air ratio of 1.0. The experimental data could notbe recorded when running with gasoline due to knock at acompression ratio of 8/1, full throttle opening and lowspeeds (1500 rpm and 2000 rpm). As maximum air–fuelmixture went into the engine at full throttle opening-lowspeeds, the knock tendency became higher. However, theengine could be run with E50 fuel without knock atcompression ratios of 8/1 and 10/1, at full throttle open-ing-all speeds. The knock was determined from the pres-sure–time curves. The knock also showed itself with aspecific knock voice and engine malfunction. The obtainedresults are given below.

3.3. The effect of E0 and E50 fuels on performance

The knock was observed when running with E0 at acompression ratio of 8/1-low speeds (1500 rpm and2000 rpm). The knock was deduced from the pressure–timecurves. The knock also showed itself with specific knock

5

10

15

20

Cyl

inde

r pre

ssur

e (b

ar)

0

25

30

35

E0, CR=6/1

E50, CR=6/1

E50, CR=10/1

M.B. Celik / Applied Thermal Engineering 28 (2008) 396–404 401

voice and engine malfunctions. Fig. 5 shows the superim-posed pressure–time curves of the two fuels at the samecompression ratio (8/1). The tests were not performed atcompression ratios of 8/1 and 10/1 with E0 fuel owing toknock. The knock did not occur at the compression ratioof 10/1 with E50 fuel.

Fig. 6 shows the effect of E0 and E50 fuels on power atvarious compression ratios. The power obtained with E50fuel is about 6% higher than that with E0 at the same com-pression ratio. The engine could be run with E50 fuel with-out knock at the compression ratio of 10/1 and a powerincrease of 29% was obtained when compared to the run-ning with E0 at the compression ratio of 6/1. Fig. 7 showsthe superimposed pressure–time curves of the two differentfuels at various compression ratios. The maximum cylinderpressure is obtained with E50 fuel at the compression ratioof 10/1 and the knock does not occur. The value of this

0 20 4020 60

5

10

15

20

Crank angle (deg)

Cyl

inde

r pre

ssur

e(ba

r)

0

tdcbtdc atdc

25

30CR=8/1

E50

E0

Fig. 5. The superimposed pressure–time curves of E0 and E50 fuel (fullthrottle opening, 2000 rpm, CR = 8/1).

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

1500 2000 2500 3000 3500 4000Engine speed (rpm)

Pow

er (k

W)

E50, CR=10/1

E50, CR=6/1

E0, CR=6/1

Fig. 6. The effect of E0 and E50 fuels on power at various compressionratios.

0 20 4020 60

Crank angle (deg)tdcbtdc atdc

Fig. 7. The superimposed pressure–time curves of two different fuels atvarious compression ratios (full throttle opening, 2000 rpm).

pressure is about 31 bar. It is seen that the values of pres-sures are about 22 bar and 21 bar at the same compressionratio (6/1) with E50 and E0, respectively. When Figs. 6 and7 are examined together, it is seen that there is parallelismbetween power increase and cylinder pressure increase.

The effect of E0 and E50 fuels on SFC at various com-pression ratios are given in Fig. 8. The value of minimumSFC with E0 fuel is 411 g/kWh at the compression ratioof 6/1 and 2500 rpm. When the engine runs with E50 fuelat same compression ratio, SFC increases by about 19%.Owing to the fact that the heating value of ethanol is lowerthan that of gasoline, the SFC increases. When the engineruns with E50 fuel at the compression ratio of 10/1, theSFC decreases by about 3%. The SFC increases due toE50 fuel were recovered by increasing the compression

300

400

500

600

700

1500 2000 2500 3000 3500 4000

Engine speed (rpm)

SFC

(g/k

Wh)

E50, CR=6/1

E0, CR=6/1

E50, CR=10/1

Fig. 8. The effect of E0 and E50 fuels on SFC at various compressionratios.

402 M.B. Celik / Applied Thermal Engineering 28 (2008) 396–404

ratio from 6/1 to 10/1. In addition, 3% decrease in SFC wasobtained.

3.4. The effect of E0 and E50 fuels on exhaust emissions

Fig. 9 shows the effect of E0 and E50 fuels on CO emis-sion. CO emission obtained with E50 at the same compres-sion ratio (6/1) is about 45% lower than that with E0 fuel.CO emissions essentially depend on air–fuel ratio. With theincrease of ethanol content, CO emission is reduced due tooxygen enrichment resulting from ethanol. When theengine is run with E50 fuel at the compression ratio of10/1, a 13% lower CO emission is seen when comparedto the running with E50 fuel at the compression ratio of6/1. CO emission obtained with E50 fuel at the compres-sion ratio of 10/1 is about 53% lower than that with E0 fuelat the compression ratio of 6/1.

Fig. 10 shows the effect of E0 and E50 fuels on CO2

emission. CO2 emission obtained with E50 fuel at the com-

10

11

12

13

14

15

1500 2000 2500 3000 3500 4000

Engine speed (rpm)

CO

2 (%

)

E0, CR=6/1

E50, CR=10/1

E50, CR=6/1

Fig. 10. The effect of E0 and E50 fuels on CO2 at various compressionratios.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

1500 2000 2500 3000 3500 4000Engine speed (rpm)

CO

(%)

E0, CR=6/1

E50, CR=6/1

E50, 10/1

Fig. 9. The effect of E0 and E50 fuels on CO at various compressionratios.

pression ratio of 10/1 is about 10% lower than that with E0fuel at the compression ratio of 6/1. CO and CO2 havecomplementary correlation, that is, with increasing COemission the amount of CO2 decreases. When Fig. 9 and10 are examined together, it is seen that CO2 increases asCO decreases with increasing engine speed. CO2 emissiondepends on air–fuel ratio and CO emission concentration[4].

The effect of E0 and E50 fuels on HC emissions is givenin Fig. 11. HC emission obtained with E50 is about 26%lower than that with E0 fuel at the same compression ratio(6/1). For E50 fuel, HC emission increases by about 19%with increase in the compression ratio from 6/1 to 10/1.As the compression ratio increases, the combustion cham-ber surface/volume ratio also increases and this, in turn,increases HC [23]. When running with E50 at high com-pression ratio (10/1), HC decreases by about 12% com-pared to the running with E0 at compression ratio of 6/1.

100

150

200

250

300

350

400

1500 2000 2500 3000 3500 4000

Engine speed (rpm)

HC

(ppm

) E0, CR=6/1E50, CR=10/1

E50, CR=6/1

Fig. 11. The effect of E0 and E50 fuels on HC emissions at variouscompression ratios.

600

1000

1400

1800

2200

2600

1500 2000 2500 3000 3500 4000Engine speed (rpm)

NO

x (pp

m)

E0, CR=6/1E50, CR=10/1

E50, CR=6/1

Fig. 12. The effect of E0 and E50 fuels on NOx emissions at variouscompression ratios.

M.B. Celik / Applied Thermal Engineering 28 (2008) 396–404 403

NOx emission obtained with E50 fuel at the same com-pression ratio (6/1) is about 33% lower than that with E0fuel. For E50 fuel, NOx increases by about 22% withincreasing the compression ratio from 6/1 to 10/1. As thecompression ratio increases, the combustion temperaturealso increases and this, in turn, increases NOx. When run-ning with E50 at high compression ratio (10/1), NOx

decreases by 19% compared to the running with E0 fuelat a compression ratio of 6/1 (Fig. 12).

4. Conclusions

In this study, ethanol was used as a fuel at a high com-pression ratio (10/1) to improve performance and to reduceemissions in a small engine with low efficiency. To thiseffect, the engine’s compression ratio was raised from 6/1to 10/1 and the engine could be run with suitable etha-nol–gasoline blend without any knock at full load.

The tests were performed at two stages. Initially, theengine was tested at the original compression ratio (6/1),2000 rpm, full throttle opening and air excess ratio of 1.0with E0, E25, E50, E75 and E100 fuels. According to theresults of these tests, it was found that the most suitablefuel in terms of power and HC emission was E50 fuel.Afterward, the engine was tested with E0 and E50 at com-pression ratios of 6/1, 8/1 and 10/1. In this stage, the testswere performed at full load in the ranges of 1500–4000 rpmat intervals of 500 rpm. But the experimental data couldnot be recorded when running with E0 due to knock at acompression ratio of 8/1, full throttle opening and lowspeeds (1500 rpm and 2000 rpm). Therefore, the enginewas tested with E0 fuel only at the compression ratio of6/1. E50 fuel enabled the engine to run without any knockat a high compression ratio (10/1) at full load and allspeeds.

From the experimental results, it was determined thatthe engine power increased by about 29% when runningwith E50 fuel at high compression ratio compared to therunning with E0 fuel. At the same time, the specific fuelconsumption, CO, CO2, HC and NOx emissions werereduced by about 3%, 53%, 10%, 12% and 19%,respectively.

As the compression ratio is increased, engine powerincreases and SFC decreases. However, HC and NOx emis-sions increase. In this study, thanks to the usage of E50fuel, the negative effect of compression ratio on HC andNOx was recovered and decreases in HC and NOx wereobtained. When E50 fuel instead of E0 fuel is used, theSFC increases. Thanks to increases in compression ratio,the negative effect of E50 on the SFC was recovered andsome decreases in SFC were also obtained.

The test results showed that both significant perfor-mance improvement and emission reduction in the smallengines can be obtained if these engines with low compres-sion ratio could be run at higher compression ratios usingalternative clean fuels resistant to the knock.

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