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The Effects of Diesel-EthanolBlends on Diesel EnginePerformanceAtilla Bilgin , Orhan Durgun & Zehra SahinPublished online: 10 Nov 2010.

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Energy Sources, 24:431–440, 2002Copyright © 2002 Taylor & Francis0090-8312 /02 $12.00 C .00

The Effects of Diesel-Ethanol Blends onDiesel Engine Performance

AT ÇILLA B ÇILG ÇINORHAN DURGUNZEHRA SAHÇIN

Mechanical Engineering DepartmentKaradeniz Technical UniversityTrabzon, Turkey

The performance of a variable compression ratio compression ignition engine oper-ating on ethanol-diesel fuel blends has been evaluated experimentally. We aimed todetermine the optimum percentage of ethanol and the compression ratio of the en-gine that give the best performance and ef� ciency at the same time. The engine wasoperated with ethanol-diesel fuel blends having 2, 4, and 6% ethanol on a volumebasis as well as on diesel fuel alone. The experiments were performed for the com-pression ratios of 19, 21, and 23. Experimental results indicate that the addition of4% ethanol to diesel fuel increases power output and ef� ciency of the engine while itdecreases speci� c fuel consumption for various compression ratios. The best ef� ciencywas attained at the compression ratio of 21 with an increment ratio over 3.5%.

Keywords engine performance, ethanol-diesel blends, fuel consumption

Introduction

Although there are numerous studies on the use of alcohols in spark ignition (SI) engines(Alasfour, 1997; Gautam et al., 2000; Kiziltan, 1988; Lowry and Devoto, 1976; Rubinand McLean, 1978; Wigg and Lunt, 1974), in the past little attention has been givento the utilization of alcohols in compression ignition (CI) engines. This is due to thedif� culties encountered while attempting to use alcohols in CI engines, especially at highalcohol ratios, which are summarized as follows (Abu-Qudais et al., 2000):

1. The heating value of alcohol is less than that of diesel fuel, therefore more alcoholthan diesel fuel is required by mass and volume.

2. Large percentages of alcohol could not mix with diesel fuel homogeneously;hence use of diesel-alcohol blends at large ratios of alcohols is not suitable.Also, the blends were not stable and separate in the presence of a trace amountof water.

Received 21 April 2001; accepted 18 May 2001.This study was supported by the Karadeniz Technical University Research Fund.Address correspondence to Dr. A. Bilgin, Mechanical Engineering Department, Karadeniz

Technical University, 61080 Trabzon, Turkey. E-mail: bilgin@ktu.edu.tr

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432 A. Bilgin et al.

3. Alcohols have extremely low cetane numbers, whereas the diesel engine is knownto prefer high cetane number fuels (45–55), which auto-ignite easily and givesmall ignition delay.

4. The poor auto-ignition capability of alcohols is responsible for severe knock dueto rapid burning of vaporized alcohol and combustion quenching caused by highlatent heat of vaporization and subsequent charge cooling.

Indeed, the idea of using alcohols as a means of producing cleaner diesel engineswas introduced over 50 years ago (Choi and Reitz, 1999). The initial investigations on theuse of alcohols in CI engines were carried out in South Africa in the 1970s and during the1980s in Germany, the United States (Satge de Caro et al., 2001) and Turkey (Kiziltan,1988). Most of these works were related to the reduction of diesel emissions, such assoot and particles, and can be considered as individual investigations, although in recentyears the importance of the subject and, accordingly, studies on this area have increasedconsiderably (Abu-Quadis et al., 2000; Ajav et al.,1998, 1999; Bilgin, 2000; Satge deCaro et al., 2001; Choi and Reitz, 1999; Das and Reddy, 1996). The strong encouragementfor the use of alcohols in diesel engines can be explained in connection with an increasein prices of diesel fuel, more stringent governmental regulations on exhaust emissions,and the foreseeable future depletion of worldwide petroleum reserves.

There are several techniques involving alcohol-diesel dual fuel operation. The mostcommon methods are as follows (Abu-Quadis et al., 2000): (1) alcohol fumigation—theaddition of alcohols to the intake air charge, displacing up to 50% of diesel fuel; (2) dualinjection—separate injection systems for each fuel, displacing up to 90% of diesel fuel;(3) alcohol-diesel fuel blend—mixture of the fuels in the fuel tank, displacing up to 25%of diesel fuel.

In the study performed by Ajav et al. (1999), it was determined that if the volumepercent of ethanol is > 5%, some performance and ef� ciency losses have occurred. Inthe present study, it was our aim to determine the maximum possible replacement ofdiesel fuel by ethanol without performance losses and with a gain in ef� ciency, simulta-neously. For this reason it was predicted that the suitable percentage of ethanol would belower than 5% and, consequently, the simplest and easiest technique—alcohol-diesel fuelblend—has been preferred. In this technique, there is no need for any modi� cation ofthe engine.

Experimentation

Engine and Instrumentation

The engine used for this study is a single cylinder, 4 stroke, variable compression ratioengine. Speci� cations of the engine are presented in Table 1 (Durgun, 1995).

Calculations

Brake effective power has been calculated using the formula

Ne;1 D Md !; (1)

where ! D ¼n=30 [1/s] is angular speed of the crankshaft, n [rpm] is rotational speed ofthe crankshaft, and Md [N.m] is brake torque. Then the calculated brake effective power

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Diesel-Ethanol Blends 433

Table 1Engine speci� cations

Made by TecquipmentNo. of cylinders 1Bore ´ stroke [mm] 90 ´ 120Displacement volume [cm3] 763.4Compression ratio (variable) 7:5 ÷ 24:5Cooling system Water cooled

has been converted to the standard atmospheric conditions by taking into account thehumidity of the ambient air Xhum as (Durgun and Ayvaz, 1996)

Ne[W] D Ne;10:1013

P0

rT0

293Xhum; (2)

where T0 [K] and P0 [MPa] are measured ambient temperature and pressure, respectively.Humidity correction factor Xhum in Equation (2) is determined according to dry and wetthermometer temperature.

The stoichiometric air for the fuel mixture has been determined as follows:

hmin;mix D S .xi½ihmin;i/

S .xi½i/: (3)

In Equation (3), the volumetric percentage of fuel i, xi , is

xi [%] DVi

Vtot100; (4)

where Vi and Vtot are volume of the fuel i and total volume of the mixture, respectively.Lower heating values of the fuels have been determined from the Mendelyev for-

mula as

Hu

"MJ

kg

#D 33:91c0 C 125:6h0 ¡ 10:89.o0

y ¡ s 0/ ¡ 2:51.9h0 ¡ w0/: (5)

In Equation (5), c0, h0, o0y , s 0, and w0 represent the elemental composition of fuels,

and the values for diesel fuel and ethanol have been given in Table 2. Lower heatingvalues for any given fuel mixture can be calculated from

Hu;mix D S .xi½iHu;i/

S .xi½i/D

xDiesel½DieselHu;Diesel C xethanol ½ethanol Hu;ethanol

xDiesel½Diesel C xethanol ½ethanol: (6)

The details of this computation can be seen in Bilgin (2000).

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434 A. Bilgin et al.

Table 2Properties of fuels

Fuel Diesel fuel Ethanol

Chemical formula C14:342H24:75 C2H5OHMolecular weight 197.2098 46.069Composition, weight [%] c0 D 0:8735 c0 D 0:5214

h0 D 0:1265 h0 D 0:1313o0

y D 0:3473Density [kg/m3] 837 788Lower heating value [kJ/kg] 42651.15 27423.79Stoichiometric A/F ratio [kg A/kg F] 14.36 8.98Octane no. (RCM)/2 – 110Auto-ignition temp. [° C] 254 423Vaporization latent heat [kJ/kg] 375 840Boiling point [° C] 210–235 78

Results and Discussion

Because 2, 4, and 6% ethanol have been added to a speci� ed diesel fuel on a volume basis,the real fraction values obtained from Equation (4) are a little different from the addedpercentages. The real percentages and symbols for fuel blends are shown in Table 3.

Variations of Engine Characteristics for Various Blends and Compression Ratios

Variations of brake torque and brake power for various blends and compression ratiosare given in Figures 1 and 2, respectively. At the lower compression ratio (" D 19),brake torque and power characteristics of the engine increase almost all engine speedscompared to neat diesel fuel for the DE2 and DE4 mixtures. At the compression ratios of21 and 23, the improvements in the power output and brake torque have been obtainedonly for the DE4 mixture. Variations in brake torque are considerable, while variationsin brake power are slight. The favorable increase in the brake torque has been obtainedat medium speeds (1200 ÷ 1300 rpm).

The relationships between brake thermal ef� ciency, ´e, and engine speed and brakespeci� c fuel consumption, be , and engine speed for different blends and compressionratios are shown in Figures 3 and 4, respectively. The � gures show that the characteristic

Table 3Percentages and symbols for diesel-ethanol blends

Added ethanolpercentage Real fractions Symbols

2% 98.04% diesel C 1.96% ethanol DE24% 96.15% diesel C 3.85% ethanol DE46% 94.34% diesel C 5.66% ethanol DE6

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Diesel-Ethanol Blends 435

Figure 1. Variation of brake torque for different ethanol percentages and compression ratios.

trends of brake thermal ef� ciency and brake speci� c fuel consumption for diesel andethanol-diesel blends are almost similar in nature for the compression ratios of 21 and23, while differing slightly for the compression ratio of 19. The maximum brake thermalef� ciency values are about 31.25 and 31.50% for 4% ethanol-diesel blends at compressionratios of 21 and 23, respectively. Brake speci� c fuel consumption also decreased to aminimum for the same blends and compression ratios.

Variation Ratios of Engine Performance with Compression Ratio for DE4 Blend

Variation ratios of engine characteristics as a function of compression ratios at mediumspeed (1200 rpm) and high speed (1500 rpm) for the DE4 blend are presented in

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436 A. Bilgin et al.

Figure 2. Variation of brake power for different ethanol percentages and compression ratios.

Figures 5a and b, respectively. In these � gures, variation ratios of brake torque andother characteristics were calculated in a similar way, for example, as follows:

1Md

Md100[%] D

Md;DE4 ¡ Md;D

Md;D100; (7)

where Md;DE4 is brake torque for the DE4 blend and Md;D is brake torque for the neatdiesel fuel. It can be seen from this � gure that the maximum gain in brake thermalef� ciency and the maximum decrease in brake speci� c fuel consumption were obtainedfor the compression ratio of 21, both at lower and higher speeds. For this compressionratio, the increase ratio of brake thermal ef� ciency becomes over 3.5% at 1200 rpm,

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Diesel-Ethanol Blends 437

Figure 3. Variation of brake thermal ef� ciency for different ethanol percentages and compres-sion ratios.

while reaching 4.5% at 1500 rpm, and, similarly, the decrease ratios of brake speci� cfuel consumption become about 2.5 and 3% for the 1200 rpm and 1500 rpm, respectively.

The increasing ratios of the brake power and brake torque become 2 or < 2% forall compression ratios at medium and high speeds.

Conclusions

The general results obtained from the experiments can be summarized as follows:

² The addition of 4% ethanol to diesel fuel increases the brake thermal ef� ciency,brake torque, and brake power, while decreasing brake speci� c fuel consumption.

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438 A. Bilgin et al.

Figure 4. Variation of brake speci� c fuel consumption for different ethanol percentages andcompression ratios.

² Increase ratios in brake power and brake torque become over 1.5%, while theincrease ratio in brake thermal ef� ciency becomes over 3.5% and the decreaseratio in brake speci� c fuel consumption becomes over 2.5% for the compressionratio of 21.

² In spite of the heating value of ethanol being lower than that for diesel fuel, in-creases in power, torque, and ef� ciency and a decrease in speci� c fuel consumptioncan be explained by the possible improvement in the combustion process. As isknown, the self-ignition temperature of the diesel fuel is less than the ethanol(Table 2). Thus in the injected spray of the blends, the diesel fuel could initi-

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Diesel-Ethanol Blends 439

Figure 5. Variation ratios of engine performance characteristics with compression ratios at1200 rpm and 1500 rpm for the DE4 blend.

ate ignition. Since the boiling point of the ethanol is less than that for dieselfuel, ethanol will evaporate before diesel fuel, and after the � rst ignition of dieselfuel, ethanol could assist the development of the combustion process through theunburned blend spray. Besides, because of the lower evaporation latent heat ofthe ethanol, combustion temperature will decrease and accordingly decreases indissociation reactions would be expected.

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