Experimental Determination Of Suitable Ethanol–gasoline Blend Rate At High Compression Ratio For Gasoline Engine

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Applied Thermal Engineering 28 (2008) 396–404 www.elsevier.com/locate/apthermeng

Experimental determination of suitable ethanol–gasoline blend rate at high compression ratio for gasoline engine M. Bahattin Celik * Karabuk University, Technical Education Faculty, 78050 Karabuk, Turkey Received 17 April 2007; accepted 26 October 2007 Available 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 the gasoline engines. In this study, ethanol was used as fuel at high compression ratio to improve performance and to reduce emissions in 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 results that the most suitable fuel in terms of performance and emissions was E50. Then, the compression ratio was raised from 6/1 to 10/1. The engine 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 various speeds without any knock. The cylinder pressures were recorded for each compression ratio and fuel. The experimental results showed that engine power increased by about 29% when running with E50 fuel compared to the running with E0 fuel. Moreover, the specific fuel consumption, and CO, CO2, HC and NOx emissions were reduced by about 3%, 53%, 10%, 12% and 19%, respectively. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Ethanol; Performance; Emissions; High compression ratio

1. Introduction The increasing demand for energy and stringent pollution regulations as a result of the population growth and technological development in the world promote research on alternative fuels [1]. The investigations have concentrated on decreasing fuel consumption and on lowering the concentration of toxic components in combustion product by using non-petroleum, renewable, sustainable and non-polluting fuels [2]. The high octane ratings of the alcohols and their high heats of vaporization have made them preferred fuels for use in-high compression ratio (CR), high-output engines. High octane values which can permit significant increases of compression ratio and/ or spark advance, and high heats of evaporation which can provide fuel–air charge cooling and density increase,

*

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and thus higher mass throughput [3]. In theory, for an un-throttled Otto-cycle engine, the efficiency g can be written as g = 1 (1/ek 1), where e is compression ratio and k is specific heat ratio. If the compression ratio can be further raised, the heat efficiency and engine power output can be improved [4]. As a fuel for spark ignition engines, alcohols have some other advantages over gasoline, such as the reduction of CO and UHC emissions [5]. As ethanol fuel also has high heat of vaporization, it reduces the peak temperature 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 been converted into simple sugars. Feedstocks for this fuel include corn, barley and wheat. Ethanol can be produced from cellulose feedstock such as corn stalks, rice straw, and sugar cane which are examples of feedstock that contain sugar [7]. As ethanol can be produced from agricultural crops, its cost can be lower in the states whose economy is largely based on agriculture and it can be used

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

as alternative fuel. Thus, dependence for foreign oil is reduced in these states. The simplest approach to the use of alcohols in spark ignition (SI) engines is to blend moderate amounts of alcohols with gasoline. The second and more technically challenging option is to use alcohols essentially neatly as engine fuel [3]. Several studies have been conducted on the usage of ethanol and ethanol–gasoline blends as fuel in the SI engines. Hsieh et al. [5] investigated the engine performance and pollutant emission of an SI engine using ethanol–gasoline blends (E0, E5, E10, E20 and E30). Their experimental results indicated that torque output and fuel consumption slightly increase when using ethanol–gasoline blended fuel; CO and HC emissions decrease dramatically as a result of the leaning effect. When ethanol is added to the blended fuel, it can provide more oxygen for the combustion process and leads to the so-called ‘‘leaning effect”. In another study by Wu et al. [4], ethanol–gasoline blended fuels (E0, E5, E10, E20 and E30) were tested in a conventional engine under various air–fuel equivalence ratios for its performance and emissions. The results of the tests showed that torque output increased slightly at small throttle opening when ethanol gasoline blended fuel was used. It was also shown that CO, CO2 and HC emissions were reduced with the increase of ethanol content in the blended fuel. Yu¨ksel and Yu¨ksel [8] investigated the use of ethanol–gasoline blend (E60) as a fuel in an SI engine. In this study, it was found that using ethanol–gasoline blended fuel, the CO and HC emissions would be reduced approximately by 80% and 50%, respectively. Moreover, significant decreases in the engine power were not observed. Bayraktar [9] investigated the effects of ethanol addition (from 0% to 12%) to gasoline on an SI engine performance and exhaust emissions. The effective power and effective efficiency increased with increasing ethanol amount in the blended fuel as a result of improved combustion and CO emissions also decreased. Al-Hasan [10] investigated the effect of ethanol–unleaded gasoline blends on performance and emission. The unleaded gasoline was blended with ethanol to prepare 10 test blends ranging from 0% to 25% ethanol with an increment of 2.5%. Ethanol addition resulted in an increase in brake power, brake thermal efficiency, volumetric efficiency and fuel consumption by about 8.3%, 9%, 7% and 5.7% mean average values, respectively. Yu¨cesu et al. [11] investigated the effects of ethanol–gasoline blends (E0, E10, E20, E40, E60) on engine performance and exhaust emissions in different compression ratios (8/1–13/1). According to the results of the experiment, it was found that as the compression ratio increased, engine torque and HC emissions also increased. The fuels containing high ratios of ethanol, E40 and E60 had important effects on the reduction of CO and HC emissions. Song et al. [12] investigated the effects of the additives of ethanol (up to 9.79% ethanol) and methyl tert-butyl ether (up to 20% MTBE) in various blend ratios into the gasoline fuel on the exhaust emissions in an EFI gasoline engine. The experimental results showed that ethanol brought

397

about generally lower regulated engine-out emissions (CO, THC and NOx) than MTBE did. He et al. [13] investigated the emission characteristics of an EFI engine with ethanol blended gasoline fuels. In the tests, E0, E10 and E30 fuels were used. Their results showed that the increase of ethanol content decreased THC, CO and NOx emissions. El-Emam and Desoky [14] investigated the combustion of alternative fuels theoretically and experimentally in SI engines. The results showed that there was an increase in engine thermal efficiency and decrease in NOx and CO emissions when ethanol and methanol fuels were used. Topgu¨l et al. [15] investigated the effects of ethanol– unleaded gasoline blends (E0, E10, E20, E40, E60) and ignition timing on performance and emissions. The experimental result showed that the brake torque slightly increased, and CO and HC emissions decreased when ethanol–gasoline blend was used. It was also found that blends with ethanol allowed the compression ratio to increase without any knock. Bardaie and Janius [16] investigated the conversion of SI engine for alcohol usage. They made some modifications on the carburettor. According to the experimental results, it was determined that power loss was only 3–4% when running with ethanol compared to gasoline. Abdel-Rahman and Osman [17] investigated the effect of ethanol–gasoline blends (E10, E20, E30 and E40) on engine performance and emissions at various compression ratios (8, 10, and 12). For each fuel blend, there is an optimum compression ratio that gives maximum indicated power. In this study, optimum compression ratios were found to be 8, 10 and 12 for E10, E20 and E30 fuels, respectively. Studies were also carried out regarding the use of alcohols as a fuel in the small gasoline engines (25 HP or less). Charalampos et al. [18] investigated the behavior of a small four-stroke engine when mixtures of gasoline–ethanol and gasoline–methanol were used as fuel. In the engine tests, 11 test blends ranging from 0% to 100% ethanol with an increment of 10% were used. CO emissions were decreased as ethanol content in fuel increased. Moreover, HC emissions were decreased as ethanol content in fuel increased, but HC emissions significantly increased when using E90 and E100 fuel. Jia et al. [19] investigated the emission characteristic of a four-stroke motorcycle engine using 10% ethanol–gasoline blended fuel (E10) at different driving modes on the chassis dynamometers. The results indicated that CO and HC emissions were lower when using E10 as compared to the use of unleaded gasoline. Magnusson et al. [20] investigated the regulated HC, CO and NOx emissions of a twostroke chain saw engine using ethanol, gasoline and ethanol–gasoline blends as fuel. The emissions of CO, HC and NO were reduced when the ethanol content was increased. But HC increased when using E85 and E100 fuels. When using ethanol and ethanol–gasoline blends instead of gasoline, the engine power did not vary significantly. Desoky and Rabie [21] investigated the performance of small spark ignition engines running on alcohols, gasoline and alcohol–gasoline blends. The results

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To the best of the author’s knowledge, no research has yet been carried out by increasing the compression ratio in the small engines running with ethanol. There are two aims of this study. One of them is to determine the suitable ethanol–gasoline blend rate in terms of performance and emissions for small engines. The other is to investigate experimentally the improvement of the performance and emissions by testing the engine with suitable ethanol–gasoline blend fuel at high compression ratio without any knock.

showed that the fuel economy benefits of using alcohols gasoline blends were found to be substantial. Small spark ignition gasoline-fuelled engines can be found all over the world performing in a variety of roles including power generation, agricultural applications and motive power for small boats. To attain low cost, these engines are typically air cooled, simple carburettors are used to regulate the fuel supply and magneto ignition systems are employed [22]. As these engines run at very low compression ratio and slightly rich mixture, they have very low efficiency and high emission values. Moreover, these engines cause significant air pollution as they do not have a catalytic converter. From the above literature review, it is understood that there are slight increases or decreases in power when the ethanol and ethanol–gasoline blends are used at the original compression ratio in the engines. In addition, CO, HC, and NOx emissions decrease. However, fuel consumption increases. If ethanol and ethanol–gasoline blends are used at high compression ratio, power increases and fuel consumption decreases. The compression ratio of air-cooled small engines is low (e.g. 5/1, 6/1). In air-cooled small engines, the wall temperatures are higher than those of water-cooled engines and the knock tendency is also higher. Thus, the compression ratio is kept lower in these engines to prevent knock. Significant improvements can be obtained in power and efficiency if the small engines with low compression ratio can be run at higher compression ratios using fuels resistant to the knock. Gains of about 25–30% in power can be obtained when the compression ratio of an engine is raised from 5/1, 6/1 to 9/1, 10/1 [23,24]. Ethanol has high octane number, both permits the rising of the compression ratio and gives lower emission.

3

12

4

2. Experimental studies The experimental set-up, shown in Fig. 1, consisted of test engine, dynamometer (D.C. dynamometer), fuel and air flow meters, cylinder pressure measuring system, exhaust gas analysis system and various measuring equipments. In the tests, a single-cylinder four-stroke small engine whose original compression ratio was 6/1 was used. To increase the compression ratio, engine cylinder head was changed and the modified cylinder head was used instead of it. Thus, the compression ratio could be raised from 6/1 up to 10/1. To adjust ignition timing, electronic ignition system was used instead of magneto ignition system. Table 1 shows the specifications of the test engine. For all the tests, the ignition timing was adjusted based on maximum torque at each engine speed. The heating value of ethanol is lower than that of gasoline. Therefore, it necessitates 1.5–1.8 times more ethanol fuel to achieve the same energy output. To this effect, carburettor main jet was enlarged and the main jet cross-section was varied using a conical screw. The excess air ratio was adjusted to 1.0 for all the tests. To prevent the phase separation,

5

7

6

8

11 9

1

13

2

10

1. Engine 2. Dynamometer 3. Air flowmeter 4. Fuel flowmeter 5. Temperature indicators 6. Exhaust gas analyzer 7. Load and speed indicators

8. Dynamometer control unit

9. Pressure transducer 10. Inductive pick-up 11.Charge amplifier 12.Oscilloscope 13. Computer

Fig. 1. Test set-up.

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

Engine

Mark Engine type Engine displacement (cm3) Compression ratio Maximum speed (rpm) Ignition system type Fuel system Cooling system

Lombardini LM 250 Four-stroke, single cylinder 250 6/1–10/1 3600 Transistorized coil Carburettor Air and water cooled

ethanol with a purity of 99.5% was used in the tests. Properties of ethanol and gasoline fuels are shown in Table 2. Emissions were measured with a MRU DELTA 1600L exhaust gas analyzer. The specifications of the exhaust gas analyzer are given in Table 3. Ignition timing was measured with a Sun Equip Co. TL-06230A ignition timing measurement equipment. To measure the in-cylinder pressure of the test engine, a system was developed. The system consisted of a piezoelectric pressure transducer, inductive pick-up, charge amplifier, oscilloscope and personal computer (PC). In this study, in-cylinder pressure data was collected using a Kistler model 601A piezoelectric transducer mounted to the spark plug, Kistler model 5011 charge amplifier, a Hitachi digital oscilloscope (VC-5430) and a PC were used to record the pressure data. The data regarding the crank angles and the position of the top dead centre were transmitted to oscilloscope using an inductive pick-up. The engine tune up was checked before the test and measurements were conducted after reaching the working temperature of the engine. To determine the suitable ethaTable 2 The properties of gasoline and ethanol Fuel property

Gasoline

Ethanol

Formula Molar C/H ratio Molecular weight (kg/kmol) Latent heating value (MJ/kg) Stoichiometric air/fuel ratio Auto-ignition temperature (°C) Heat of vaporization (kJ/kg) Research octane number Motor octane number Freezing point (°C) Boiling point (°C) Density (kg/m3)

C8H18 0.445 114.18 44 14.6 257 305 88–100 80–90 40 27–225 765

C2H5OH 0.333 46.07 26.9 9 425 840 108.6 89.7 114 78 785

Table 3 The specifications of the exhaust gas analyzer

CO (vol.%) CO2 (vol.%) HC (ppm) NOx (ppm) O2 (vol.%)

Measurements range

Accuracy

0–15 0–20 0–20000 0–4000 0–25

0.01 0.01 1 1 0.1

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 1.0 with E0, E25, E50, E75 and E100 fuels. The obtained results are given below. 3.1. The effects of various fuels on engine performance Fig. 2 shows the effect of various fuels on power and specific fuel consumption (SFC). As the ethanol content in 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 higher than that of gasoline. High heat of evaporation can provide fuel–air charge to cool and density to increase, thus higher power output is obtained to some extent [3]. However, power increase starts to decrease when ethanol content is raised to more than 50%. When running with E100 fuel, it is seen that a 4% decrease in power takes place in comparison with E0 fuel. Owing to the fact that the heating value of ethanol is lower than that of gasoline, the SFC increases as the ethanol content in blend increases (Fig. 2). Increases of 10%, Full throttle opening, 2000 rpm, CR=6/1 2.2

700

Power SFC

2.1

650

2

600

1.9

550

1.8

500

1.7

450

1.6

SFC (g/kWh)

Items

nol–gasoline blend rate in terms of performance and emissions, 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 (gasoline), E25 (75% gasoline + 25% ethanol), E50, E75 and E100 (ethanol) fuels. All the data for engine power, specific fuel consumption, spark timing, exhaust gas temperature, HC, CO, CO2 and NOx emissions were collected. The cylinder pressures were recorded for each compression ratios and fuels. At all the tests, all values were recorded after allowing sufficient time for the engine to stabilize.

Power (kW)

Table 1 Specifications of the test engine

399

400 E0

E25

E50

E75

E100

Fuel 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 running 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 incomplete combustion. When ethanol containing oxygen is mixed with gasoline, the combustion of the engine becomes better and therefore CO emission is reduced [18]. As seen from Fig. 3, the values of CO emission are about 3.76%, 2.65%, 2.06%, 1.24% and 0.73% for E0, E25, E50, E75 and E100 fuels, respectively. In addition, the decreases in CO2 emission are observed when ethanol is used. Carbon dioxide is non-toxic but contributes to the greenhouse effect. Because the ethanol contains lower C atom than gasoline, it gives off lower CO2 [4]. The values of CO2 are about 13.25%, 12.14%, 11.62%, 10.25% and 9.51% with E0, E25, E50, E75 and E100 fuels, respectively (Fig. 3). The effect of various fuels on HC and NOx emissions is given in Fig. 4. Ethanol contains an oxygen atom in its Full throttle opening, 2000 rpm, CR=6/1 5

20

17

CO CO2

3

14 2

CO2 (%)

CO (%)

4

11

1 0

8 E0

E25

E50

E75

E100

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

Full throttle opening, 2000 rpm, CR=6/1 600

2500

HC NO x

2000

400

1500

300

1000

200

500

100

NOx (ppm)

HC (ppm)

500

0 E0

E25

E50

E75

E100

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

basic form; it can be treated as a partially oxidized hydrocarbon when ethanol is added to the blended fuel. Therefore, CO and HC emissions decrease [8]. As seen from this figure, HC decreases to some extent as ethanol added to gasoline increases. The value of HC declines to 271 ppm and 245 ppm with E25 and E50 fuels, respectively, from 331 ppm with E0. But the significant increases are seen in the HC emissions when running with E75 and E100 fuels. The value of HC rises to 340 ppm and 483 ppm with E75 and E100 fuels, respectively. The pure ethanol and higher ethanol content blends reduce the cylinder temperature as the heat of vaporization of ethanol is higher when compared to gasoline. The lower temperature causes misfire and/or partial burn in the regions near the combustion chamber wall. Therefore, HC emissions increase, and engine power can slightly decreases. As the ethanol content in the blend increases, NOx decreases (Fig. 4). The value of NOx declines to 1711 ppm, 1434 ppm, 1150 ppm and 988 ppm with E25, E50, E75 and E100 fuels, respectively, from 2152 ppm with E0 fuel. Since ethanol has a higher heat of vaporization 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 [13]. According to the results of experiment carried out at first stage, it was determined that the most suitable fuel was 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 E100 fuel. HC is a very important emission because it increases with the fuels containing high ratios of ethanol such as E75 and E100. HC value of E50 fuel was the lowest when compared to the other fuels. At second stage, the compression ratio was raised from 6/1 to 8/1 and 10/1 and the engine was tested with E50 and E0 fuels for comparison. These tests were performed at full load in the ranges of 1500–4000 rpm at intervals of 500 rpm and excess air ratio of 1.0. The experimental data could not be recorded when running with gasoline due to knock at a compression ratio of 8/1, full throttle opening and low speeds (1500 rpm and 2000 rpm). As maximum air–fuel mixture went into the engine at full throttle opening-low speeds, the knock tendency became higher. However, the engine could be run with E50 fuel without knock at compression ratios of 8/1 and 10/1, at full throttle opening-all speeds. The knock was determined from the pressure–time curves. The knock also showed itself with a specific knock voice and engine malfunction. The obtained results are given below. 3.3. The effect of E0 and E50 fuels on performance The knock was observed when running with E0 at a compression ratio of 8/1-low speeds (1500 rpm and 2000 rpm). The knock was deduced from the pressure–time curves. The knock also showed itself with specific knock

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voice and engine malfunctions. Fig. 5 shows the superimposed pressure–time curves of the two fuels at the same compression ratio (8/1). The tests were not performed at compression ratios of 8/1 and 10/1 with E0 fuel owing to knock. The knock did not occur at the compression ratio of 10/1 with E50 fuel. Fig. 6 shows the effect of E0 and E50 fuels on power at various compression ratios. The power obtained with E50 fuel is about 6% higher than that with E0 at the same compression ratio. The engine could be run with E50 fuel without knock at the compression ratio of 10/1 and a power increase of 29% was obtained when compared to the running with E0 at the compression ratio of 6/1. Fig. 7 shows the superimposed pressure–time curves of the two different fuels at various compression ratios. The maximum cylinder pressure is obtained with E50 fuel at the compression ratio of 10/1 and the knock does not occur. The value of this

E50, CR=10/1

Cylinder pressure (bar)

30

25 E50, CR=6/1 20 15

E0, CR=6/1

10

5

0 20 btdc

0 tdc

60

atdc

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

E50 20 15

E0

10

5 0 20 btdc

0 tdc

40

20

60

atdc

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

pressure is about 31 bar. It is seen that the values of pressures are about 22 bar and 21 bar at the same compression ratio (6/1) with E50 and E0, respectively. When Figs. 6 and 7 are examined together, it is seen that there is parallelism between power increase and cylinder pressure increase. The effect of E0 and E50 fuels on SFC at various compression ratios are given in Fig. 8. The value of minimum SFC with E0 fuel is 411 g/kWh at the compression ratio of 6/1 and 2500 rpm. When the engine runs with E50 fuel at same compression ratio, SFC increases by about 19%. Owing to the fact that the heating value of ethanol is lower than that of gasoline, the SFC increases. When the engine runs with E50 fuel at the compression ratio of 10/1, the SFC decreases by about 3%. The SFC increases due to E50 fuel were recovered by increasing the compression 700

4.5

E50, CR=6/1

4 3.5

E0, CR=6/1

600

SFC (g/kWh)

Power (kW)

40

20

Crank angle (deg)

25

Cylinder pressure(bar)

35

CR=8/1

30

401

3 2.5 2

E50, CR=10/1

1.5

E50, CR=6/1

1

E50, CR=10/1 500

400

E0, CR=6/1

0.5 300

0 1500

2000

2500

3000

3500

4000

Engine speed (rpm) Fig. 6. The effect of E0 and E50 fuels on power at various compression ratios.

1500

2000

2500

3000

3500

4000

Engine speed (rpm) Fig. 8. The effect of E0 and E50 fuels on SFC at various compression ratios.

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ratio from 6/1 to 10/1. In addition, 3% decrease in SFC was obtained. 3.4. The effect of E0 and E50 fuels on exhaust emissions Fig. 9 shows the effect of E0 and E50 fuels on CO emission. CO emission obtained with E50 at the same compression ratio (6/1) is about 45% lower than that with E0 fuel. CO emissions essentially depend on air–fuel ratio. With the increase of ethanol content, CO emission is reduced due to oxygen enrichment resulting from ethanol. When the engine is run with E50 fuel at the compression ratio of 10/1, a 13% lower CO emission is seen when compared to the running with E50 fuel at the compression ratio of 6/1. CO emission obtained with E50 fuel at the compression ratio of 10/1 is about 53% lower than that with E0 fuel at 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-

pression ratio of 10/1 is about 10% lower than that with E0 fuel at the compression ratio of 6/1. CO and CO2 have complementary correlation, that is, with increasing CO emission the amount of CO2 decreases. When Fig. 9 and 10 are examined together, it is seen that CO2 increases as CO decreases with increasing engine speed. CO2 emission depends on air–fuel ratio and CO emission concentration [4]. The effect of E0 and E50 fuels on HC emissions is given in 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 chamber surface/volume ratio also increases and this, in turn, increases HC [23]. When running with E50 at high compression ratio (10/1), HC decreases by about 12% compared to the running with E0 at compression ratio of 6/1. 400

4.5 350

E50, CR=10/1

E50, CR=6/1

3.5

HC (ppm)

2.5 2

E50, CR=6/1

300

E50, 10/1

3

CO (%)

E0, CR=6/1

E0, CR=6/1

4

1.5 1

250 200 150

0.5 100

0 1500

2000

2500

3000

3500

1500

4000

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

3000

3500

4000

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

15

2600

14

2200

NOx (ppm)

CO2 (%)

2500

Engine speed (rpm)

Engine speed (rpm)

13

12

1800

1400

E0, CR=6/1 11

2000

E0, CR=6/1

E50, CR=10/1

1000

E50, CR=10/1

E50, CR=6/1

E50, CR=6/1

10

600 1500

2000

2500

3000

3500

4000

Engine speed (rpm) Fig. 10. The effect of E0 and E50 fuels on CO2 at various compression ratios.

1500

2000

2500

3000

3500

4000

Engine speed (rpm) Fig. 12. The effect of E0 and E50 fuels on NOx emissions at various compression ratios.

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NOx emission obtained with E50 fuel at the same compression ratio (6/1) is about 33% lower than that with E0 fuel. For E50 fuel, NOx increases by about 22% with increasing the compression ratio from 6/1 to 10/1. As the compression ratio increases, the combustion temperature also increases and this, in turn, increases NOx. When running with E50 at high compression ratio (10/1), NOx decreases by 19% compared to the running with E0 fuel at a compression ratio of 6/1 (Fig. 12). 4. Conclusions In this study, ethanol was used as a fuel at a high compression ratio (10/1) to improve performance and to reduce emissions in a small engine with low efficiency. To this effect, the engine’s compression ratio was raised from 6/1 to 10/1 and the engine could be run with suitable ethanol–gasoline blend without any knock at full load. The tests were performed at two stages. Initially, the engine was tested at the original compression ratio (6/1), 2000 rpm, full throttle opening and air excess ratio of 1.0 with E0, E25, E50, E75 and E100 fuels. According to the results of these tests, it was found that the most suitable fuel in terms of power and HC emission was E50 fuel. Afterward, the engine was tested with E0 and E50 at compression ratios of 6/1, 8/1 and 10/1. In this stage, the tests were performed at full load in the ranges of 1500–4000 rpm at intervals of 500 rpm. But the experimental data could not be recorded when running with E0 due to knock at a compression ratio of 8/1, full throttle opening and low speeds (1500 rpm and 2000 rpm). Therefore, the engine was tested with E0 fuel only at the compression ratio of 6/1. E50 fuel enabled the engine to run without any knock at a high compression ratio (10/1) at full load and all speeds. From the experimental results, it was determined that the engine power increased by about 29% when running with E50 fuel at high compression ratio compared to the running with E0 fuel. At the same time, the specific fuel consumption, CO, CO2, HC and NOx emissions were reduced by about 3%, 53%, 10%, 12% and 19%, respectively. As the compression ratio is increased, engine power increases and SFC decreases. However, HC and NOx emissions increase. In this study, thanks to the usage of E50 fuel, the negative effect of compression ratio on HC and NOx was recovered and decreases in HC and NOx were obtained. When E50 fuel instead of E0 fuel is used, the SFC increases. Thanks to increases in compression ratio, the negative effect of E50 on the SFC was recovered and some decreases in SFC were also obtained. The test results showed that both significant performance improvement and emission reduction in the small engines can be obtained if these engines with low compression ratio could be run at higher compression ratios using alternative clean fuels resistant to the knock.

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