Combustion characteristics of a diesel engine

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Combustion characteristics of a diesel engine operating on biodiesel–diesel–ethanol mixtures G R Kannan and R Anand* Department of Mechanical Engineering, National Institute of Technology, Tamilnadu, India The manuscript was received on 24 November 2010 and was accepted after revision for publication on 4 April 2011. DOI: 10.1177/0957650911408209

Abstract: Experimental investigation was carried out to analyse the combustion, performance, and emission characteristics of DI diesel engine using selective biodiesel–diesel–ethanol mixture or diestrol fuels. Eleven diestrol fuels were selected on the basis of good miscibility, calorific value, and clear appearance based on the stability test carried out at different temperatures from 40 C to 10 C. The engine was made to run under varying loads at a constant speed of 1500 r/min. The results revealed that the maximum heat release rate of diestrol fuel was 7.5 per cent lower than that of diesel, while the cylinder gas pressure was nearly close to that of diesel fuel at 100 per cent load condition. A shorter ignition delay of 12.8 CA was observed with diestrol fuel consisting of 30 per cent biodiesel 60 per cent diesel and 10 per cent ethanol, which was 1.9 CA higher than biodiesel and comparable to that of diesel. Maximum brake thermal efficiency of 29.91 per cent was observed for diestrol fuel. While using diestrol and biodiesel, nitric oxide (NO) and smoke emissions were lower than that of diesel at all the load conditions. Keywords:

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waste cooking oil, biodiesel, phase diagram, combustion, performance, emission

INTRODUCTION

Biodiesel has received a very good response worldwide as an alternative fuel to diesel owing to the diminishing dependency on petroleum fuels and rising awareness on environmental protection. Biodiesel is produced by transesterification process which involves a chemical reaction between an alcohol and triglyceride of fatty acid in the presence of a suitable catalyst leading to the formation of fatty acid alkyl esters (biodiesel) and glycerol [1]. From the emission perception, a reduction in UHC, CO, smoke and a slight increase in NO emission is observed while using biodiesel in diesel engine. The increase in NO emissions serves as the major impediment in the usage of biodiesel [2]. The major drawback of biodiesel is its high production cost which is attributed to the high cost of vegetable oil that *Corresponding author: Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli 620 015, Tamilnadu, India. email: [email protected]

accounts for nearly 78 per cent of the biodiesel production [3–10]. Besides, biodiesel has some disadvantages such as higher viscosity, lower volatility, and lower calorific value compared with diesel. This can lead to poor atomization and mixture formation with air which results in slower combustion, lower thermal efficiency and higher emissions [11–16]. Further, biodiesel derived from fats or oils has significantly higher amount of saturated fatty compounds which results in higher cloud point and pour point. Fuel starvation, clog of fuel lines and filters might occur owing to the crystallization of the saturated fatty acid methyl ester components of biodiesel during cold seasons [17]. Thus, these different physical and chemical properties of biodiesel compared to diesel pose technical challenges in operating the diesel engine with biodiesel. The present design and operating parameters of the engine are standardized only for diesel fuel. For all other fuels, either the operation parameters of the engine or fuel composition has to be changed in order to achieve optimum performance and emission characteristics. Proc. IMechE Vol. 0 Part A: J. Power and Energy

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G R Kannan and R Anand

The investigation of Park et al. on the atomization of ethanol biodiesel blends concludes that the addition of ethanol improves the atomization owing to its low kinematic viscosity and surface tension of the ethanol blended fuel [18]. Moreover, ethanolblended biodiesel can provide higher oxygen content in the blended fuel and increase the heat of evaporation. Thus it has the potential to reduce both NO and PM emissions. Further, biodiesel–ethanol blends have improved the cold flow properties [19]. But the addition of ethanol to biodiesel reduces the calorific value and cetane number. In spite of having superior lubricity and environmental friendly characteristics, biodiesel–ethanol blend has lower energy value and cetane number owing to the presence of ethanol. To increase calorific value and cetane number, a small amount of diesel is added with biodiesel–ethanol blends [20]. The calorific value and cetane number of the biodiesel–diesel–ethanol mixture are comparable to those of fossil fuels [21, 22]. Prommes et al. analysed the phase diagram of diesel–biodiesel–ethanol blends at different temperatures and different purities of ethanol. The fuel properties of the selected blends along with performance and emissions in a diesel engine were determined. The result revealed that a blend of 80 per cent diesel, 15 per cent palm oil biodiesel and 5 per cent ethanol was the most acceptable composition because of the good fuel properties and reduction in emission [23]. However, there is a lack of research on the combustion characteristics of engine using biodiesel–diesel–ethanol mixtures. The aim of this paper is to investigate the stability of biodiesel–diesel–ethanol mixture or diestrol fuels and to evaluate the combustion, performance, and emission behaviours of an unmodified diesel engine using selected diestrol fuels. 2

MATERIALS AND METHODS

2.1 Biodiesel preparation In this study, waste cooking oil (WCO) has been selected as an alternative fuel because of its cheap cost. Also it avoids the cost of waste product disposal treatment. FFA content of the WCO was found to be 1.44 per cent, which was within the acceptable limit (0.5–5 per cent) for alkaline esterification [7, 24–27]. Potassium hydroxide (KOH) and sodium hydroxide (NaOH) are the most commonly used alkali catalysts but higher yield has been reported for KOH [27]. Methanol and ethanol are the alcohols employed frequently in the transesterification process; but in this work methanol was preferred owing to its low cost and higher reactivity. [7, 28, 29]. The waste cooking palm oil was obtained from local restaurants near

Dindigul, Tamilnadu, India. A four-necked round bottom glass flask with a capacity of ten litres batch reactor was used for the transesterification process at National Institute of Technology, Trichy. This reactor was equipped with a Liebig condenser, a mechanical stirrer with tachometer, a thermometer pocket with thermocouple and a stopper to remove samples. A constant temperature heating mantle was used to maintain the reaction temperature within 0.1 C. The biodiesel produced was a clear yellow liquid. Diesel was procured from Indian Oil, Trichy and ethanol (99.9 per cent) was procured from the Eswarr scientific company, Chennai. 2.2 Stability test Different proportions of biodiesel, diesel, and ethanol were mixed to a homogeneous mixture in a threeneck round bottom flask using a mechanical stirrer. Each component was varied from 0 to 100 per cent in steps of 10 per cent increments and 36 possible combinations were prepared. The prepared three fuel mixture was named as diestrol. A stability test was carried out for all diestrol fuels which was kept in a glass vial with a stopper for four weeks at different temperatures of 40 C to 10 C to observe the phase behaviour. The phase behaviour of diestrol fuels are indicated using different symbols on the phase diagrams as shown in Fig. 1. All the diestrol fuels were in clear liquid phase at the temperature of 40 C as shown in Fig. 1(a). Eighteen diestrol fuels had miscibility with clarity. Among the highly miscible diestrol fuels, 11 diestrol fuels showed acceptable calorific values. Hence, it could be concluded that the diestrol fuel containing biodiesel (above 30 per cent), diesel (below 70 per cent), and ethanol (below 20 per cent) showed good miscibility with acceptable calorific value. Figure 1(b) shows the effect of temperature on diestrol stability at a temperature of 30 C, which was similar to the phase behaviour of diestrol fuels at 40 C. The diestrol stability at a temperature of 20 C is presented in Fig. 1(c). Among the 36 diestrol fuels, it can be noted that 19 diestrol fuels showed immiscibility. Eleven diestrol fuels with biodiesel (above 30 per cent), diesel (below 70 per cent), and ethanol (below 20 per cent) showed good miscibility with clear liquid appearance. The other six diestrol fuels were in a clear liquid phase with lower calorific value. Figure 1(d) represents the stability of diestrol fuel at a temperature of 10 C. The diestrol fuel with ethanol in the range of 60 to 80 per cent by volume was a clear liquid with proper miscibility such as B10D10E80, B20D10E70, and B20D20E60. The diestrol fuel containing biodiesel (above 30 per cent), diesel (below

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Combustion characteristics of a diesel engine operating on biodiesel–diesel–ethanol mixtures

Fig. 1

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Phase diagram of diestrol fuels 1(a) at 40 C, 1(b) at 30 C, 1(c) at 20 C and, 1(d) at 10 C

70 per cent), and ethanol (below 60 per cent) had miscibility with unclear crystalline liquid appearance. Remaining diestrol fuels had immiscibility with unclear crystalline liquid appearance. This might be attributable to the effect of saturated fatty acid component of biodiesel, which can increase the cloud point of biodiesel. The miscibility and immiscibility of diestrol fuel is mainly attributed to the constituents of diestrol fuel.

At all temperatures biodiesel derived from waste cooking oil was completely miscible with diesel and ethanol separately. However, in diestrol fuel, biodiesel acts as a surface active agent creating micelles with non-polar tails and polar heads. These micelles are attracted to the liquid–liquid interfacial films and act as polar or non-polar solutes based on the direction of biodiesel molecules. In diestrol mixture the biodiesel molecule’s polar head is directed to ethanol Proc. IMechE Vol. 0 Part A: J. Power and Energy



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as 117 C. The flash point of diestrol mainly depends on highly flammable ethanol. Thus, the storage, handling, and transportation of diestrol must be taken care of accordingly in order to avoid an explosion. However, the fuel properties of the selected diestrol mixture were within the range of ASTM specification. Based on the diestrol fuel characterization, the diestrol fuel B30D60E10, B40D50E10, and B30D50E20 were selected for further experimental investigation.

and non-polar tail is directed to diesel. This was the reason for the good miscibility of diestrol fuel. When biodiesel concentration was decreased in diestrol fuel, it led to immiscibility[23]. Fuel properties of the selected diestrol fuels were determined at the Indian Oil Corporation Limited, Trichy, and the details are given in Table 1. It was noticed that the density and kinematic viscosity of the diestrol fuels decreased with an increase in the percentage of ethanol in the diestrol fuel. This was attributable to the lower density and kinematic viscosity of ethanol. It can be noted that diestrol fuel B30D60E10, B40D50E10, and B30D50E20 had the maximum cetane index. Copper strip corrosion showed a value of class 1a (slight tarnish), for all the selected diestrol fuels which was close to light orange colour of the freshly polished strip. The cloud point and pour point of biodiesel decreased when blended with diesel and ethanol because of the low freezing point of ethanol. The pour point of ethanol is very low and it is reported Table 1

2.3 Experimental set-up and measurements The experimental investigation was carried out on a single-cylinder four-stroke DI naturally aspirated diesel engine under different loads ranging from 0 per cent to 100 per cent in steps of 25 per cent along with 10 per cent excess load at a constant speed of 1500 r/min. The engine specifications and measuring range of the emission analyser are given in Table 2. The experimental set-up is shown in Fig. 2. The test engine was directly coupled with a Kirloskar

Fuel properties of biodiesel, diesel, ethanol, and diestrol fuels

Fuel

Density (kg/m3) at 27 C

Kinematic viscosity (cSt)

Flash point ( C)

Cloud point ( C)

Pour point ( C)

Sulphur content (%wt)

Copper strip corrosion 3 hr at 50 C

Cetane index

Calorific value (MJ/kg)

Biodiesel Diesel Ethanol B30D60E10 B40D50E10 B50D40E10 B60D30E10 B70D20E10 B80D10E10 B30D50E20 B40D40E20 B50D30E20 B60D20E20 B70D10E20

866 828 782 826 831 835 841 845 850 821 827 831 837 841

4.55 2.41 1.03 2.44 2.60 2.78 2.83 3.01 3.25 2.14 2.33 2.46 2.51 2.59

170 49 14 18.5 19 18 17.4 16.5 17 15 15.5 15.3 15 15

13 0 7 1 3 5 6 8 9 4 5 5 6 7

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0 0.049 0 0.0114 0.0087 0.0051 0.0010 0.003 0.0044 0.0088 0.0066 0.0018 0.0007 0.0001

1a 1a 1a 1a 1a 1a 1a 1a 1a 1a 1a 1a 1a 1a

66.9 56.7 12 47.31 47.21 47.2 47.18 47.16 47.15 47.25 46.83 46.80 46.81 46.341

38.034 42.111 26.267 39.109 38.747 38.389 38.032 37.683 37.335 37.85 37.493 37.139 36.789 36.442

a

6 117a 3 3 0 3 6 6 6 0 0 3 3

(23).

Table 2

Engine specifications and measuring ranges of emission analyser

Engine parameter

Specification

AVL DiGas 444 five gas analyser

Engine make

TV1–KIRLOSKAR

Measured quality

Measuring range

Rated brake power Speed Number of cylinder Method of cooling Bore Stroke Type of ignition Compression ratio Fuel injection

5.2 kW 1500 r/min 1 Water cooled 87.5 mm 110 mm CI 17.5:1 Solid/direct injection

Carbon monoxide (CO) Carbon dioxide (CO2) Hydro carbon (HC) Oxygen (O2) Nitric oxide (NO)

0–10% vol 0–20% vol 0–20 000 ppm vol 0–22% vol 0–5000 ppm vol

Fuel injection system

Pump in line nozzle injection system

Measured quality

Measuring range

Injection opening pressure Injector type Injection timing Nozzle hole diameter and number Piston bowl

220 bar Bosch (9430031258E) 23 bTDC 0.3 mm and 3 Hemispherical

Opacity Absorption Engine speed Lubricating oil temperature

0–100% 0–99.99 m 1 400–6000 r/min 0–150 C

AVL 437 Smoke meter(standard)



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Fig. 2

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Schematic diagram of the engine set-up

made electrical alternator (model AG-10) for making power measurements. A duly calibrated standard burette (100 mL volume and 1 mL division) and a digital stop-watch were employed for the fuel flow measurements. Separate fuel tanks were used for supplying the fuel to the test engine. The flowrate of air was measured using an orifice plate. The orifice plate created a pressure drop which varied with the flowrate. This pressure drop was measured by means of an inclined manometer. A damping tank was used for reducing air pulsation. The Bosch fuel injection pump (9410031021) and Bosch fuel injector (9430031258E) was used to inject the fuel into the combustion chamber. An AVL DIGAS 444 five gas analysanalyser was used to measure the concentration of CO, CO2, NO, and O2 present in the exhaust gas. The concentrations of HC and NO were expressed in ppm whereas those of CO, CO2, and O2 were expressed as percentage volume. Smoke was measured in terms of percentage opacity using an AVL 437 smoke meter. The cylinder pressure was measured using a KISTLER quartz (piezo-electric) transducer in conjunction with a KISTLER charge amplifier. The TDC marker (KISTLER model 5015A1000) was placed near the engine flywheel; at the TDC position a small metallic deflector was fitted. The set-up was aligned in such a way that the sensor gives out a square wave output exactly when the piston is at TDC. The cylinder pressure data were recorded as the average of 20 cycles of data with a resolution of 0.5 CA using a data acquisition system.

Exhaust and cooling water inlet, outlet temperatures were measured using K-type thermocouples. The engine was first fuelled with diesel fuel to determine the baseline parameters of the engine at a standard fuel injection timing of 23 bTDC and standard injection pressure of 220 bar and then fuelled with biodiesel and diestrol fuels. In order to calculate the mean values, each test was repeated for three times.

3 RESULTS AND DISCUSSION 3.1 Combustion characteristics

3.1.1 Cylinder gas pressure and cylinder peak gas pressure The variation in cylinder gas pressure for different test fuels at 100 per cent load condition is illustrated in Fig. 3. Cylinder gas pressure depends on the burned fuel fraction during the premixed burning phase or the initial phase of combustion. Cylinder gas pressure characterizes the ability of the fuel to mix well with air and burn. Higher peak pressure and maximum rate of pressure rise corresponds to a large amount of fuel being burned in the premixed combustion stage. The cylinder gas peak pressure of the test fuels with respect to BMEP is plotted in Fig. 4. From Figs 3 and 4, it can be seen that all the diestrol fuel and biodiesel had lower cylinder gas pressure Proc. IMechE Vol. 0 Part A: J. Power and Energy



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Fig. 3

Cylinder gas pressure with crank angle at 100 per cent load condition

100 B30D60E10 B40D50E10 B30D50E20 B100 Diesel

Cylinder gas peak pressure (bar)

80

60

40

20

0 0

1

2

3

4

5

6

7

BMEP (bar)

Fig. 4

Cylinder peak gas pressure of test fuels

and cylinder gas peak pressure than that of diesel fuel. Among the three diestrol fuels, B30D60E10 exhibited maximum cylinder gas pressure of 73.3 bar at 368.5 CA, which is 1.1 per cent higher than that of biodiesel and closer to the value of diesel. This is because of the higher premixed burning rate owing to longer ignition delay period and more combustible mixture being prepared within the ignition delay period [22, 30].

3.1.2 Heat release rate The effect of heat release rate at 100 per cent load condition is illustrated in Fig. 5. All the test fuels experience a rapid premixed or initial phase of combustion followed by a mixed controlled combustion. Owing to the cooling effect caused by fuel vaporization and heat losses from the engine cylinder walls the heat release rate is negative during the ignition delay period. A maximum heat release rate of


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25.7 J/ CA was observed at 370.5 CA with B30D60E10 diestrol fuel, which is 2 per cent higher and 7.5 per cent lower than that of biodiesel and diesel fuel respectively. This is attributable to the increase in ignition delay period of the diestrol fuel which causes increased amount of fuel air mixture to be prepared within the period and raises the heat release rate at high loads.

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3.1.3 Ignition delay The ignition delay of different test fuels is plotted in Fig. 6. Ignition delay period is an essential factor that greatly affects the combustion behaviour of the engine. Ignition delay is the period between the start of fuel injection into the combustion chamber and the start of combustion. It was computed by


Heat release rate (J/degree CA )

25 20 15 10 5 0 -5 32 0

34 0

36 0

38 0

400

420

Cran k angle (degree)

Fig. 5

Heat release rate with crank angles at 100 per cent load condition

20 B30D60E10 B40D50E10 B30D50E20 B100 Diesel 15 Ignition delay (degree CA)


10

5

0 0

1

2

3

4

5

6

7

BMEP (bar)

Fig. 6

Effect of test fuels on ignition delay Proc. IMechE Vol. 0 Part A: J. Power and Energy



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calculating the change in slope of the pressure crank angle diagram, and from the heat-release analysis of the pressure crank angle data [31]. The ignition delay period of the test fuels decreases with increasing engine load condition. At low engine loads, the fuel injection takes place at a lower temperature inside the cylinder which leads to increase in ignition delay. At a higher engine load, high temperature environment inside the cylinder decreases the ignition delay. The ignition delay of diestrol fuel is longer than that of biodiesel and diesel for the entire load range. At 100 per cent load condition, B30D60E10 diestrol fuel showed a shorter ignition delay of 12.8 CA, which is 1.8 CA higher than that of biodiesel and closer to diesel value. Owing to the higher latent heat of evaporation and lower cetane value of ethanol present in diestrol, a low temperature environment is created in the injected fuel and thus extends the period of ignition delay.

diestrol fuel which increases the combustion duration at low load. However, the faster combustion rate in the premixed phase of combustion and shorter controlled combustion reduces the combustion duration at medium and high loads [22]. 3.2 Performance and emission characteristics

3.2.1 Brake thermal efficiency The variation of brake thermal efficiency with respect to load for different fuels is presented in Fig. 8. The thermal efficiency of a diesel engine depends on the compression ratio and the fuel–air ratio. With fixed compression ratio, the thermal efficiency mainly depends only on the fuel–air ratio [32]. A maximum thermal efficiency of 29.91 per cent is obtained for B30D60E10 diestrol fuel, which is 1.1 per cent higher than that of biodiesel and slightly lower than that of diesel. Among all the test fuels, B30D50E20 diestrol fuel has the lowest brake thermal efficiency of 24.32 per cent at 100 per cent load condition. This is owing to the higher latent heat of evaporation and lower heating value of the diestrol fuel [33]. The lower brake thermal efficiency of biodiesel is because of its higher viscosity and lower calorific value. Higher viscosity causes poor fuel atomization during the spray process, increasing the engine deposits, and also requires more energy to pump the fuel which wears fuel pump elements and injectors [34]. The thermal efficiency of all the test fuels increased from 0 bar BMEP to 6.2 bar BMEP. This is because the complete combustion of mixture in spite

3.1.4 Combustion duration The variation in combustion duration of different test fuel is given in Fig. 7. The crank angle value corresponding to 5 per cent and 95 per cent of the mass burnt has been considered as the combustion duration. The combustion duration increases with increasing load as more fuel is injected at higher loads. Higher combustion duration of diestrol fuels was noted at low load. At medium and high load condition, combustion duration of diestrol fuels is shorter when compared with biodiesel and slightly higher than that for diesel fuel. This is owing to the longer ignition delay period of 60

B30D60E10 B40D50E10 B30D50E20 B100 Diesel

Combustion duration (degree CA)

50

40

30

20

10

0 0

1

2

3

4

5

6

BMEP (bar)

Fig. 7

Combustion duration of different test fuels


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Fig. 8

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Variation of brake thermal efficiency with BMEP for test fuels

of the mixture becoming progressively rich. The thermal efficiency of test fuels decreased from 6.2 bar BMEP to 6.9 bar BMEP. This is owing to insufficient air available for complete combustion at highest load condition as the mixture becomes too rich for it to burn completely [31].

3.2.2 NO emission The effect of diestrol fuel on NO emission at different load condition is shown in Fig. 9. The NO emission of diestrol fuels and biodiesel was lower than diesel fuel for entire load condition. At 100 per cent load condition, the maximum NO emission with B30D60E10 diestrol fuel is 508 ppm whereas with biodiesel and diesel it is found to be 485 ppm and 578 ppm respectively. The higher latent heat of vaporization and lower calorific value of ethanol in the diestrol causes lower combustion temperature which results in lower NO emissions [35]. The lower NO emission of biodiesel is due its lower iodine number [36, 37]. The iodine number is a parameter that has often been used by the vegetable oil industry to determine the degree of unsaturation or the number of double bonds present in the mixture of fatty acid [38, 39]. The Iodine number of the waste cooking oil based biodiesel was found to be 57.3; the lower iodine value ensured the presence of the more saturated fatty acids in biodiesel [40]. The lower NO emission of biodiesel compared to diesel fuel was similar to the other research findings [40–42].

3.2.3 Smoke emission Figure 10 shows the variation of smoke emission at different engine loads. The smoke emission of test fuels increase with increasing engine load. This is because of injection of more fuel into the engine cylinder which increases the smoke formation at maximum load condition [43].The smoke emission for all the diestrol fuels and biodiesel is lower than that of diesel. Maximum smoke emission is found to be 48.9 per cent for B30D60E10 diestrol fuel, which is 3.3 per cent higher and 3.9 per cent lower than that of biodiesel and diesel respectively. The lower smoke emission of biodiesel was mainly owing to the higher oxygen content, lower carbon to hydrogen ratio and the absence of aromatics in biodiesel [44]. 4 CONCLUSIONS In this study, the stability of diestrol fuel mixture, engine combustion, performance, and emission characteristics of DI diesel engine with biodiesel and diestrol fuels was investigated. Based on experimental investigation, the following conclusions can be drawn. 1. Among B30D60E10, B40D50E10, and B30D50E20 diestrol fuels, B30D60E10 showed highest calorific value and cetane index of 39.1 MJ/kg and 47.3 respectively. 2. Longer combustion duration was noted for all the diestrol fuels at low load whereas slight reduction Proc. IMechE Vol. 0 Part A: J. Power and Energy



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Fig. 9

Variation of NO emission with BMEP for test fuels


Smoke opacity (%)

80

60

40

20

0 0

1

2

3

4

5

6

7

8

BMEP (bar)

Fig. 10

Smoke emission for diestrol, biodiesel, and diesel fuel

in combustion duration was observed at medium and high load conditions when compared to biodiesel and diesel. Among all the tested diestrol fuel, B30D60E10 fuel had the shortest combustion duration of 43 CA. 3. Compared to all the tested fuel, longer ignition delay period of 14.7 CA was observed for B30D50E20 which was 3.7 CA higher than that of

biodiesel. At higher engine loads, the cylinder gas pressure, cylinder gas peak pressure, and heat release rate of B30D60E10 were higher than that of biodiesel and other diestrol fuels. 4. The brake thermal efficiency of B30D60E10 was slightly lower than that of diesel and higher than that of biodiesel, B40D50E10 and B30D50E20 diestrol fuels at 100 per cent load condition.



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5. The NO and smoke emission decreased with the use of B30D60E10 diestrol fuel compared to diesel. 6. Based on the acceptable stability, fuel properties and improvement in engine characteristics, it can be concluded that diestrol fuel consisting of 30 per cent biodiesel, 60 per cent diesel and 10 per cent ethanol (B30D60E10) was the most suitable alternative fuel for DI diesel engine without any engine modification. FUNDING This research received no specific grant from any funding agency in the public, commercial, or notfor-profit sectors. ß Authors 2011 REFERENCES 1 Shashikant Vilas, G. and Hifjur, R. Process optimization for biodiesel production from mahua (Madhua indica) oil using response surface methodology. Bioresource Technol., 2006, 97, 379–384. 2 Lauperta, M., Armas, O., and Jose, R. F. Effect of biodiesel fuels on diesel engine emissions. Progress in Energy and Combust. Sci., 2008, 34(2), 198–223. 3 Bautista, L. F., Vicente, G., Rodriguez, R., and Pacheco, M. Optimisation of FAME production from waste cooking oil for bio diesel use. Biomass and Bioenergy, 2009, 33, 862–872. 4 Gui, M. M., Lee, K. T., and Bhatia, S. Feasibility of edible oil vs. non-edible oil vs. waste edible oil as biodiesel feedstock. Energy, 2008, 33, 1646–1653. 5 Zlatica, J. P. The production of biodiesel from waste frying oils: a comparison of different purification steps. Fuel, 2008, 87, 3522–3528. 6 Leung, D. Y. C. and Guo, Y. Transeterification of neat and used frying oil: optimization for biodiesel production. Fuel Processing Technol., 2006, 87, 883–890. 7 Ma, F. and Hanna, M. A. Biodiesel production: A review. Bioresource Technol, 1999, 70, 1–15. 8 Zhang, Y., Dube, M. A., McLean, D. D., and Kates, M. Biodiesel production from waste cooking oil: 2. Economic assessment and sensitivity analysis. Bioresource Technol., 2003, 90, 229–240. 9 Demirbas, A. Biodiesel production via non-catalytic SCF method and biodiesel fuel characteristics. Energy Conversion and Mgmt, 2006, 47, 2271–2282. 10 Demirbas, A. Economic and environmental impacts of the liquid biofuels. Energy Edu. Sci. Technol., 2008, 22, 37–58. 11 Narayana Reddy, J. and Ramesh, A. Parametric studies for improving the performance of a Jatropha oil-fuelled compression ignition engine. Renewable Energy, 2006, 31, 1994–2016. 12 Knothe, G. Dependence of biodiesel fuel properties on the structure of fatty acid alkyl esters. Fuel Processing Technol., 2005, 86, 1059–1070.

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APPENDIX Notation B100 B30D50E20 B30D60E10 B40D50E10 BMEP CA DI FFA NO ppm TDC WCO


biodiesel 30 per cent biodiesel, 50 per cent diesel and 10 per cent ethanol 30 per cent biodiesel, 60 per cent diesel and 10 per cent ethanol 40 per cent biodiesel, 50 per cent diesel and 10 per cent ethanol brake mean effective pressure (bar) crank angle direct injection free fatty acid nitric oxide (ppm) parts per million top dead center waste cooking oil