Bio-Diesel as an Alternative fuel for Compression Ignition Engine: A Review

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Bio-Diesel as an Alternative fuel for Compression Ignition Engine: A Review

Mr. Shidagonda Jabade^1,2, Dr. M. Sakthivel³, Dr. Supriya Chavan⁴

1Research Scholar Department Of Mechanical Engineering Koneru Lakshmaiah Education Foundation, Vijayawada 522502, AP India

2 Asst. Prof. Department Of Mechanical Engineering Sant Gajanan Maharaj College Of Engineering, Mahagaon 416503, MS., India

3 Associate Professor Department Of Mechanical Engineering Koneru Lakshmaiah Education Foundation, Vijayawada 522502, AP, India

4Research associate at Indian Biodiesel Corporation, Baramati, 413102, MS, India

Abstract

Compression ignition (CI) engines are most commonly used in automobile sectors and power generation sector than spark ignition (SI) engines due to its fuel lean operation. The most common fuel source for diesel is petroleum based fossil fuel and it is depleting continuously at very faster rate. Many countries import the fossil fuel due to very low fossil fuel reserves; it directly impacts on economy of the countries. In addition to this, main problem associated with the CI engines are emissions like smoke, oxides of nitrogen (NO_x) and carbon monoxide (CO). Since last many years researchers doing investigations to replace the fossil diesel fuel to several alternative fuels such as alcohols, dimethyl ether and biodiesel. Many number of investigations have been performed by number of researchers to check the suitability of biodiesel as an alternate fuel for CI engine and found that biodiesel is relevant alternative fuel for CI engines, due to characteristics like renewable, biodegradable, oxygen content, free from sulphur, also having certain advantages like low exhaust emissions, low wear and tear of engine, and low consumption of engine oil, hence researchers in all over world getting attention towards biodiesel. This paper presents the review of combustion, performance and exhaust pollutants from CI engine when biodiesel is used as a fuel.

Keywords— Alternative fuels, Biodiesel, Compression ignition engine, Performance, combustion, emission.

1. INTRODUCTION

Diesel engines are commonly used in many sectors like transportation, marine engines, power generation & in agricultural due to their better thermal efficiency, lower fuel consumption. Hence demand for the fossil diesel fuel is increasing rapidly. The main problem associated with the CI engine is particulate matter (PM) emission and oxides of nitrogen (NOx). The reduction of PM and NOX is a difficult task [1] in conventional CI engines. Numbers of researchers have suggested that biodiesel as the replacement completely or can be used partially blended with mineral diesel, because use of biodiesel reduces the exhaust emissions. Biodiesel contains more oxygen, less carbon and sulphur by weight than the mineral diesel [2]. Different countries such as USA, Germany, France, Italy, Brazil, and Indonesia are using biodiesel blended with diesel. The neat palm oil not used as an edible oil in Malaysia it is used as the Palm biodiesel as alternative to diesel [3]. In Europe & USA the rapeseed and soyabean biodiesels are generally used in USA and Europe respectively [4]. These oil seeds can be planted and cultivated in the waste lands available in India. Another benefit of biodiesel is it can be used in IC engine in a similar fashion as mineral oil diesel without any engine geometry modification or with little engine modification.

Biodiesel have certain advantages like intimacy to diesel properties, local availability & renewable in nature, good lubricity, safe to store and lack of difficulty in transportation, low exhaust emissions [5]. However it is having disadvantages like cold flow & low heat content. This deficiency can be eliminated by choosing of proper feedstock material for biodiesel production which is done by the process of transesterification and use of proper catalyst in the transesterification process.The use biodiesel noted that increase in the emission of NOx [6]. Different conclusions were made for increase of NOx, like advancement in injection [7], high temperature of flame [8], change in fuel properties like density, volatility and iodine number [9], and rapid burning due to availability of oxygen [10]. It is also identified that biodiesel is capable to reduce soot emission [11, 12] because of sulphur & aromatic compounds

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are not present [13], and existence of fuel-bonded oxygen [14]. Thus it is important to study performance, combustion and exhaust emissions of biodiesel and embrace as alternative fuel for CI engines.

2. BIODIESEL PRODUCTION & ITS PROPERTIES 2.1 Production of biodiesel

Different methods are used for production of biodiesel from locally available feedstocks vegetable oil both edible

& non-edible, animal fats, algae and waste cooking oil. The oil produced from above different feedstock is having higher viscosity, thus it is essential to decrease the viscosity to use this in an engine, and this can be done by using a chemical reaction known as transesterification. During transesterification triglyceride or fat present in the oil will reacts with alcohol in presence of reaction accelerator known as catalyst alkaline in nature. The reaction of transesterification is shown in following figure 1., Saka and Kusdiana [15].

Figure 1. Transesterification reaction [15]

A biodiesel blend is prepared by mixing of biodiesel with mineral diesel in suitable proportions. Biodiesel blends are represented as Bxx. Where 'xx' indicates that the percentage of the biodiesel by volume in the blend of the biodiesel and mineral diesel [16]. For example, B20 refers to the blend of 20% of biodiesel and 80% of mineral diesel by volume. The biodiesel production methods from different feedstocks as described by different investigators are given in below section. Singh et al. [17] prepared biodiesel from non-edible feedstocks like mahua and karanja in same ratio on basis of volume. A two step esterification reaction of acid to lower free fatty acid up to certain limit was followed by the transesterification process. This was done to convert oils to fatty acids of methyl esters.

Sulphuric acid (H2SO4) was used as a catalyst to accelerate the esterification reaction. In transesterification process potassium hydroxide (KOH) and Methanol were added as catalysts.

Saka and Kusdiana [15] prepared biodiesel from rapeseed oil by method of transesterification reaction without use of a catalyst. This method is known as the supercritical methanol biomass conversion. In this process the pressure and temperature were high compared to the normal transesterification reaction. Venkanna and Reddy [18]

produced biodiesel through a three steps transesterification method from hone oil, with methanol which consists of the acid esterification, the alkali transesterification and after treatment. H2SO4 and KOH were used as catalyst in acid esterification alkali transesterification respectively. After treatment consist of three times gentle water wash by using distilled water. Li. Et al. [19] produced biodiesel from the vegetable oil of eruca sativa gars (ESG) on lab scale by transesterification process by methanol. Heteropoly acid salt was used as a catalyst for the transesterification of the ESG oil. Ramadhas et al. [20] produced biodiesel from the rubber seed oil by two stage transesterification method with methanol, which followed an alkali esterification using H2SO4 as a catalyst and transesterification with methanol using NaOH as a catalyst. Ghadge and Raheman [21] produced the biodiesel from mahua oil by method of transesterification with methanol; KOH was used as the alkaline catalyst. Firstly, the fatty acid content was found by a standard method and to lower the higher acid value pretreatment method was used.

R. L. Krupakaran et al. [22] prepared biodiesel from Mimusopes elengi oil by transesterification of Mimusopes elengi oil with methyl alcohol at 65^OC temperature in presence of the potassium hydroxide as a catalyst.

To remove water moisture present in mixture it was heated beyond the boiling point of water. Arun S. B. et al. [23]

prepared yellow oleander methyl ester from the yellow oleander (Thevetia peruviana) by transesterification method by using a calcinated calcium oxide (CaO), a heterogeneous catalyst. The advantages of the heterogeneous catalysts over the homogeneous catalysts it can be separated eaisly and purity of final products. M. K. Parida and A. K. Raut [24], prepared biodiesel from non-edible oil seeds of Argemone Mexicana by two step transesterification, due to high acid value. To remove alkaloids and gums, raw Argemone Mexicana oil was treated with methanolic H3PO4 solution

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after this methanol layer is separated from the oil. In transesterification process due to faster reaction methanol was used, refined Argemone oil was mixed with sulphuric acid and methanol in first transesterification and in second step the oil prepared from first step was treated with the sodium hydroxide. R. Sathish Kumar et al. [25], prepared biodiesel from the Manilkara Zapota seed oil (MZO) by alkaline catalyst transesterification method by use of methanol; along with the KOH as a homogeneous catalyst. Ghadge and Raheman [26] prepared Biodiesel from raw mahua oil by method of transesterification with KOH as alkaline catalyst, after this ph value is measured by titrimetry method and esterification of the raw mahua oil with methanol and H2SO4 as a catalyst.

The review article by P. Tamilselvan et al. [27] provides comprehensive report on performance, combustion and emissions of biodiesel fuelled plain biodiesel and its blends more than 40 number of biodiesel fuels were studied for engine type, test conditions, effect on different parameters and concluded that high BSFC (Brake Specific Fuel Consumption) and less thermal efficiency than diesel. Biodiesel and the blends biodiesel produce low exhaust emission of HC (Hydrocarbons), CO (Carbon Monoxide) and PM (Particulate Matter) and higher emission of NOx &

CO2 due to more oxygen in fuel and high Cetane number. Biodiesel up to 20% blend may be used as alternate fuel with the little or no engine modification. The flow chart of various steps involved in production of biodiesel along with reactants, different products from vegetable oil is shown in Figure 2. From the work of Sharma et al. [28]

Figure 2. Flow chart for biodiesel production [28]

Efe Şű et al. [35] prepared biodiesels from five vegetable oils (soyabean, canola, corn, sunflower and hazelnut) by transesterification methanol was used as alcohol and KOH as a catalyst; three stage water washing was did for filtering out contaminants from biodiesel. Ahmet Uyumaz [36] used transesterification method to prepare biodiesel from mustard oil; methanol was used as alcohol; reaction temperature was 60^oC methanol mustard oil ratio was 20%. Pankaj Shrivastava et al. [38] prepared biodiesels from two different feedstocks Roselle and Karanja by transesterification method; methanol was used as alcohol, KOH as a catalyst; biodiesel was washed with pure water to remove methanol content. At last biodiesel was heated up to 100^oC for one hour to remove moisture. S. R. Mishra et al. [39] produced oil from Simarouba Glauca by two step transesterification; in first step was acid esterification methanol was used as a alcohol and H2SO4 as an catalyst; in second step of alkaline esterification methanol and KOH was used as catalyst. J. N. Nair et al. [40] produced Neem biodiesel by two step transesterification in first step NaOH was used as catalyst; in second step H2SO4 was used as catalyst in both steps methanol was used as alcohol. L. A.

Raman et al. [41] produced biodiesel from rapeseed oil by transesterification using hexane solvent and alkaline catalyst method; NaOH was used as catalyst and methanol as alcohol.

G. Goga et al. [42] produced oil from rice bran oil by single stage alkaline transesterification process; KOH was used as catalyst and methanol as alcohol. K. Nathagopal et al. [44], have prepared Calophyllum inophyllum methyl ester (CIME) from Calophyllum inophyllum oil by three stage transesterification process; first stage was acid catalyzed Esterification with methanol and concentrated H2SO4 as catalyst; second stage esterification KOH was used as an catalyst; third stage was purification, produced CIME washed withpure (distilled) water followed by heating to remove moisture. Higher alcohol blends were prepared by addition of higher alcohols (n-pentanol and n-octanol) on volume basis. K. A. Abed et al. [45], have prepared biodiesel by transesterification from waste cooking oil (sunflower oil), using methanol and NaOH as catalyst. M. A. Asokan et al. [46], prepared biodiesel from juliflora oil by two step transesterification; in acid transesterification, juliflora oil was mixed with methanol and sulfuric acid (catalyst), followed by alkali transesterification with methanol and NaOH as catalyst. From number of studies it is

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understood that biodiesel may be produced from different feedstocks under different conditions and by using different catalysts. Information related to this is summarized and tabulated in Table 1

Table 1. Production of Biodiesel by different feedstocks with reaction condition

Researcher name Feedstock Alcohol type

Ratio of alcohol to

oil

Catalyst used

Catalyst amount

Reaction condition Saka and Kusdiana [15]

Rapeseed oil Methanol 42:1 NaOH - 350-400^oC at

45 -65 MPa Sharma and Singh [17] Karanja oil,

Mahua oil, mixture of two

Methanol 6:1 8:1

H2SO4, KOH

1 ml

1 wt% 50^oC for 1 h Venkanna and Reddy

[18] Honne oil Methanol 8:1

4:1

H2SO4, KOH

0.5 ml 0.75 – 1.5%

45, 55, 60 and 65^oC Li et al. [19] Eruca sativa

gars oil Methanol 6:1 Hetropoly

acid 0.04m mol 65^oC for 12 h Ramdhas et al. [20] Rubber seed

oil Methanol 6:1

9:1

H2SO4,

NaOH

0.5%

5 gm

40 -50^oC for 2h Ghadge and Raheman

[21] Mahua oil Methanol - H2SO4

KOH

1%

0.7%

60^oC for 30 min.

R. L. Krupakaran et. al.

[22]

Mimusopes

elengi Methanol - KOH - 65^oC for 30

min.

Arun S. B. et al. [23] Yellow

oleander Methanol 5:1 CaO 2.80% Wt 70^oC

M. K. Parida and A. K.

Raut [24]

Argemone

Mexicana Methanol 11:1 H2SO4 - 50^oC for 4 h

R. Sathish Kumar et al.

[25]

Manilkara

Zapota Methanol 6:1 KOH 1 wt% 50^oC, 90 min

Ghadge and Raheman

[26] Mahua oil Methanol 6:1

KOH 0.7 %

w/v

60^oC for 30 min.

Efe Şű et al. [35] Soyabean, Canola, Corn, Sunflower and Hazelnut

Methanol - KOH - 56^oC for 60

min.

Ahmet Uyumaz [36] Mustard

Oil Methanol - - 0.5% w/v 60^oC for 90

min.

Pankaj Shrivastava et al.

[38] Karanja ,

Roselle Methanol 1:3 KOH 10g

60^oC – 80^oC for 55 – 90

min S. R. Mishra et al. [39] Simarouba

glauca Methanol - KOH - -

J. N. Nair et al. [40] Neem Methanol - NaOH 1 wt% 75^oC

L. A. Raman et al. [41] Rapeseed Methanol - NaOH - -

G. Goga et al. [42]

Rice bran Methanol 10:1 KOH 2.5 ml 50^oC for 120

min S. Ramalingam, S.

Rajendran [43] Annona Methanol - KOH or

NaOH - -

K. Nathagopal et al. [44] Clophyllum

inophyllum Methanol 16:1 H2SO4 1% (w/w) 60^oC for 45 min

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K. A. Abed et al. [45] Waste- cooking oil (Sunflower)

Methanol 6:1 NaOH 1 % by wt. -

M. A. Asokan et al.[46]

Juliflora Methanol - H2SO4 - 60^oC for 60

min

2.2 Biodiesel Properties

The essential properties of biodiesel include viscosity, flash and fire point, calorific value, cetane number, density, cloud point and pour point. Based on the above properties of biodiesel performance, combustion and emission characteristic depends. Number of researchers reported different properties depend on chemical composition and fatty acid present. Thus it is necessary to measure the properties of the biodiesel as per the ASTMD6751 and EN 14214. In India for automotive engine biodiesel IS 15607 standard is followed. Different properties of biodiesels produced from different feedstocks are summarized in Table 2. In general properties of biodiesel fuel are similar to petro- diesel, but viscosity is very important property and it is directly linked with the fuel injection system of engine. If viscosity is higher it affects fluidity which directly influence the atomization of fuel which results in incomplete combustion and carbon deposit on injectors tip [29]. Flash point also affected by the chemical composition of the biodiesel, total carbon atom present [29]. Combustion quality of fuel is depends upon the cetane number, if cetane number is higher it indicates shorter ignition delay. In general biodiesel consists of fatty acid carbon chain, for this reason cetane number of biodiesel is more than diesel. Due to this improves ignition quality [29]. High viscosity of biodiesel affects delay period, atomization of fuel which leading to reduce brake thermal efficiency (BTE) [25]. Higher viscosity of fuel will result in incomplete combustion of fuel due to this increased fuel consumption [25]. Qi et al. [30] recorded that power output and torque were lower than diesel due to high density and low calorific value. Flash point is more than the diesel hence there is not any problem for storage and transportation. Pour point of biodiesel is higher than a diesel this can create a problem in cold weather operation.

Content of sulphur is very small in biodiesel that’s why there is no emission of oxides of sulphur (SOx).

Table 2.Pproperties of diesel and biodiesel produced from different feedstock

Fuels Density (kg/m³)

Kinematic viscosity @ 40^oC (mm²/s))

Cetane number

Heating value (MJ/kg)

Cloud point

(^oC)

Flash point (^oC)

Fire point

(^oC)

Pour point (^oC) Diesel [26,

38,40] 850 2.44 - 2.60 47-51 42- 44.3 - 68 -75 80 -20

Mahua [26,35] 880 - 916 3.98 – 5.72 - 37 – 39.4 - 129 – 208 141 6 Mimusopes

elengi [22] 873 - 49 41.89 - 185 - -

Yellow Oleander

[23] 870 4.5 - 37.56 -4 158 - 5

Argemone

Mexicana [24] 868 5.07 - 41.5 - 130 - -

Manilkara

Zapota [25] 875 4.67 - 37.2 - 234 - -

Palm [36,37] 870 –

878.4 4.5 – 5.11 50 – 62 37.2 –

39.91 14 173 182 8

Soyabean [36,

37, 40] 885-914 4.057 – 39.5 37 – 51.3

37.3 –

39.82 - 69 – 163 - -

Sunflower [36, 37, 40]

868 –

885.6 4.22 – 4.4 46.7 – 51.6

37.5

39.95 - 162 - 183 - -

Rapeseed [31] 872 –

885 4.585 – 11 37.6 - 54.5

37.3 –

39.9 - 177 – 275 - -

Peanut [32] 886.4 5.251 54 39.7 - 193 - -

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Corn [32] 885.8 4.363 55.4 39.87 - 167 - -

Palm Kernel

[32] 876.6 3.248 62.1 38.53 - 131 - -

Waste Fried [32] 884.2 4.869 55 39.68 - 167 - -

Canola [35] 865.4 4.43 48.7 39.98 - 166 - -

Corn [35] 867.4 4.30 47.4 39.97 - 170 - -

Hazelnut [35] 861.9 4.54 52.2 40 - 168 - -

Mustard [36] 880 5.77 50 39.85 - 158 -12

Jatropha [37] 864 5.2 - 40.83 - - - -

Coconut [37] 845.8 3.74 - 43.84 - - - -

Karanja [38] 880 4.86 52.1 38.91 - 168 - -

Roselle [38] 878 4.6 52.2 38.78 - 156 - -

Simarouba

Glauca [39] 865 4.68 52 41.90 - 76 86 -

Rapeseed [41] 874 4.8 54 37.6 - >140 - -

Rice bran [42] 868 4.38 55.32 39.48 1 155 -2

n-Butanol [42] 810 3.64 - 33 - 35 - -45

Annona [43] 872 5.18 52 39.57 - 76 92 -

Calophyllum

inophyllum [44] 868.6 4.7 53 38 - 142 - -

Waste cooking-

oil [45] 892.6 - 63.63 42.83 - 176 - -

Juliflora [46] 875 6.80 49 38 - 128 - -

3. EXPERIMENTAL INVESTIGATIONS ON DIFFERENT BIODIESEL

Experimental investigations include performance, combustion, and exhaust gases emission. In performance parameters like power output, brake thermal efficiency, specific fuel consumption are considered, along with this emission like carbon monoxide (CO), Nitrogen oxides (NOx), particulate matter (PM), Hydrocarbon (HC) and smoke are reviewed. The performance & emission characteristics are mainly depends upon the different properties of fuel used for experimentation such as viscosity, density, cetane number, calorific value, these properties of Biodiesel depends mainly on the feedstock characteristics. The findings from different researchers are described in following section.

R. L. Krupakaran et al. [22], conducted experiment on single cylinder, four stroke, constant speed, air cooled diesel engine fuelled with diesel and different biodiesel blends of Mimusopes elengi methyl esters found that brake thermal efficiency (BTE) at 75% of engine load condition was maximum for the blend 20MEME-80D (20%

Mimusopes elengi methyl ester and 20% diesel) and it is 4.18% higher for standard diesel. BTE decreases as concentration of blend increases. 20MEME-80D shows improved Brake Specific Energy Consumption (BSEC) as compared to other blends; also it shows reduction of CO, HC and smoke emission compared with neat diesel and other blends, but 20MEME-80D shows increased emission of NOx and CO2 than the normal diesel for full load condition. For 20MEME-80D exhaust gas temperature is decreased this was due to high hear release rate as compared to other blends and normal diesel.

Arun S. B. et al. [23] conducted experiment on single cylinder, water cooled, four stroke, constant speed, direct injection diesel engine fuelled with diesel and yellow oleander biodiesel blends and found that BTE was decreased as concentration of biodiesel increases in the blends, BTE values of biodiesel-diesel blends were lower than the neat diesel. For all blends as load increases BSFC decreases this was due to low calorific values of biodiesel blends than diesel. They also found that for all YOME (Yellow Oleander Methyl Ester) blends EGT increases with increase in load than the normal diesel; also recorded that for all YOME blends decrease in the HC & CO emissions. However increased NOx emissions as compared to diesel. M. K. Parida and A. K. Raut [24] investigated performance and emission characteristics on single cylinder, four stroke, direct injection, constant speed, water cooled, diesel engine at part load conditions fuelled with diesel and blends of Argemone Mexicana biodiesel and found that BSFC

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decreases as load and percentage of biodiesel in blend increases, the increse in BSFC was due to higher viscosity and higher density of biodiesel blends, also found that EGT increased with increase in the load, and percentage of blend;

the emission of CO and HC increases with load and decreases with concentration of blend; as increase in load and percentage of biodiesel blends NOx emissions increases as compared to standard diesel.

R. Sathish Kumar et al. [25] conducted experiment to investigate combustion, performance and emission characteristics of an unmodified single cylinder, four stroke, water cooled, constant speed diesel engine fuelled with diesel and Manilkara Zapota methyl ester & its blends, the combustion analysis reported that the highest cylinder pressure was recorded for blends B50( 50% MZME + 50% Diesel) and B25 (25% MZME + 75 % Diesel) than diesel at complete load condition, this was because of the higher oxygen content in biodiesel blends. However, as percent of biodiesel in blend increases, decreases the cylinder pressure and energy release rate, because of high viscosity of blends, more oxygen content results in improper mixing. More heat is released by B50 and B25 blends compared to diesel.

In the performance analysis reported that higher brake thermal efficiency (BTE) was found for B25 and B50 blends than diesel, for B50 maximum BTE was found which was 17% more than diesel. However, as percentage of biodiesel in the blend increases decreases the BTE due to low calorific value of biodiesel blends. Increase in the blends of biodiesel up to 50% shown that decrease in the BSFC (Brake Specific Fuel Consumption) beyond which BSFC increases in comparison to diesel. Reduction in emission of CO was noted for all biodiesel blends as compared to diesel; all blends produce more CO2 and NOx emissions than diesel at low loads, and all loads respectively; B25 and B50 produce lower UBHC (Un Burnt Hydro Carbon) at low and medium as compared with pure diesel. Rakopoulos et al. [31] performed experiment on a four stroke, direct injection (DI), Ricardo/ Cussons 'Hydra' Diesel engine by five different methyl esters viz. cotton seed oil, sunflower oil, soyabean oil, , rapeseed oil and palm oil is blended with petro-diesel in proportion of 10% and 20% blend, it was seen that CO, NOx emission was slightly reduced with use of biodiesel blend in comparison to that of the neat diesel fuel. However, for hydrocarbon (HC) emission observed there is not considerable variation compared to plain diesel. But for smoke density was considerably lowered with use of biodiesels obtained from various feedstocks compared to that noted with neat diesel fuel. The maximum smoke reduction is observed for cotton seed oil Biodiesel B20 blend among the five biodiesels.

Lin et al. [32] performed experiment on a water cooled, four stroke, single cylinder, DICI (Direct injection Compression Ignition) Engine by eight biodiesels prepared from eight different oils soybean, peanut, corn, sunflower, palm, waste fried oil, rapeseed, and palm kernel, methanol is used as alcohol during transesterification, after experimentation found that the exhaust gas temperature was slightly less for biodiesels than the diesel. They reported the reason behind this is low energy content of biodiesels reduces total heat release during combustion process and therefore exhaust gas temperature reduced, also noted that NOx emission was increased for biodiesel as compared to diesel this was due to high temperature and pressure during combustion. The minimum NOx emission found for Palm kernel biodiesel (5.58%) and maximum NOx emission found for rapeseed biodiesel (25.97%). Also found that reduced smoke emission than that of normal diesel, this was due to extra oxygen content and uniform air fuel mixture. Saleh [33] performed experimentation on water cooled, four stroke, two cylinder diesel engine fuelled with jojoba oil methyl ester as a fuel noticed that increase in the carbon monoxide (CO) emission compared to that of diesel this is due to the high viscosity of biodiesel resulting improper mixing of air-fuel mixture. Also observed that with decrease in engine speed and as increase of biodiesel mass fraction the NOx emission increased. He also used exhaust gas recirculation technique and noticed that 50% reduction in NOx emission. Also found that higher hydrocarbon (HC) emission and it was due to the increase in the quantity of fuel per stroke which results in to improper mixing of fuel.

M. K. Parida and A. K. Raut [34] investigated combustion analysis for fixed load, and fixed compression ratio on single cylinder, four stroke, DI, constant speed, water cooled CI engine at part load conditions fuelled with diesel and blends of Argemone Mexicana biodiesel it was found that for low percentage of biodiesel in blend heat release rate increases this was due to oxygen present in the biodiesel, whereas for as percentage of biodiesel in blends increases heat release rate decreases; due to high oxygen content in biodiesel as compared to diesel, mass fraction burnt is slightly high for all blends. Efe Şű et al. [35] investigated performance characteristics of five different

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biodiesels prepared from five different oils hazelnut, corn, Soybean, canola and sunflower oil on two cylinder, four stroke, direct injection, diesel engine and results were compared with each other, and with the normal diesel, engine was tested for seven speeds, brake power decreases as engine speed increases for all biodiesels, this was due to high viscosity of biodiesels is, low calorific value of biodiesel; also noted that increase in thermal efficiency for B100 (100% biodiesel) despite increase in specific fuel consumption. HOME (Hazelnut Oil Methyl Ester) was having high CN (Cetane Number) and density was low among all biodiesel blends and found B20 HOME was shown better performance among all biodiesel blends.

Ahmet Uyumaz [36] have conducted experiments on single cylinder, four stroke, air cooled, naturally aspired, direct injection CI engine fuelled with diesel and blends of the mustard oil methyl ester (M10, M20, M30) found that for M10 (10% mustard oil biodiesel + 90% Diesel) BSFC increased with 4.8% and ITE were decreased by 6.8% compared to diesel, CO and smoke emissions was decreased for all biodiesel blends, for M30 blend carbon monoxide and smoke decreased by 50.47% and for M10 smoke is decreased by 32.9% as compared with diesel at a full load. However, NOx emission is increased with increase in biodiesel concentration in blends, for M30 NOx was increased by 22.1% compared to diesel.Yogendra Rathore et al. [37] conducted experiment on single cylinder, four stroke, VCR diesel engine with constant Compression ratio and constant speed fueled with biodiesel blends of Jatropha oil and coconut oil they noted that for all blends of both biodiesels BSFC decreases with increase in load;

also found that brake thermal efficiency (BTE) increases as load increases for diesel and all biodiesel blends of both fuels, B20 blend of Jatropha biodiesel shows BSFC close to diesel, at 80% load for B20 blend BTE value for diesel, Jatropha and Coconut was 33.15%, 31.54% and 29.75% respectively. Pankaj Shrivastava et al. [38] have conducted experiment on four stroke, single-cylinder, water cooled diesel engine by using Roselle, Karanja biodiesel and its blends, brake thermal efficiency (BTE) for 10% and 20% blends were high as compared to 100% biodiesel; BTE for KB20 (blend with 20% karanja biodiesel) was higher by 1.5% compared to neat diesel, BSFC reduced as engine load increased, BSFC increased with increasing biodiesel percentage in blends, EGT and indicated thermal efficiency were decreased, volumetric efficiency increased for biodiesel and biodiesel blends compared with diesel; reduced smoke emission for LA100 (pure Roselle biodiesel) by 15.78% than diesel; CO2 emissions were high for biodiesel and blends compared with diesel; NOx emissions were decreased for LA10, KB10, LA20, KB20, LA100and KB100;

NOx emissions increased as engine load increased. S. R. Mishra et al. [39] performed number of tests on single- cylinder, four stroke, constant speed, water cooled, DICI (Direct Injection Compression Ignition) engine with simarouba biodiesel (B100) & its blends (B10 and B20 10% and 20% by volume respectively) and diesel, noted that for full load for B20 blend EGT (Exhaust Gas Temperature) and BSFC (Brake Specific Fuel Consumption) was increased by 3.82%; 3.51% and BTE (Brake Thermal Efficiency) was decreased 3.14% respectively as compared with diesel; CO and HC emission were decreased while NOx and CO2 emission were increased compared with diesel.

J. N. Nair et al. [40] have performed experiments on single-cylinder, 4-stroke, constant speed, water cooled, diesel engine with varying blends of Neem biodiesel and diesel. Noted that for B20 & B30 blends of biodiesel BSFC was increased than B10 and diesel for all loads; for all blends (B10, B20, B30) BTE was increased than diesel; CO, HC and NOx emissions were reduced as compared to diesel; highest reduction of CO, NOx and HC emission were noted for B10 blend 26%, 21.87% and 17% respectively; smoke emission was increased for all blends compared with the diesel; B20 and B30 blends emitted more smoke by 21% compared with diesel. L. A. Raman et al. [41]

have conducted experimentation on single cylinder, 4-stroke, water cooled, constant speed (1500), DICI (Direct Injection Compression Ignition) engine with rapeseed oil biodiesel, biodiesel blends & diesel. For full load BTE of engine was decreased for biodiesel & its blends than diesel; BSEC (Brake Specific Energy Consumption) and EGT for biodiesel & its blends was increased than diesel; Heat release rate and cylinder pressure decreased for biodiesel &

its blends compared to diesel. HC and CO emissions was decreased for biodiesel & its blends compared to diesel at maximum load; for B100 42.1% and 35.4% decreased emission of HC and CO was recorded at full load compared to diesel. Biodiesel & its blends emitted fewer amounts of Oxides of nitrogen and smoke compared to diesel.

G. Goga et al. [42], have performed experimentation on single cylinder, air cooled, four stroke, constant speed diesel engine with two blends of Rice bran oil biodiesel (B10 and B20) and two blends with biodiesel prepared from rice bran oil and n-butanol (B10-nBu10 and B20-nBu20) and diesel. BSFC was higher for biodiesel blends as compared to diesel; BSFC was increased with increase in volume of biodiesel and n-butanol in the blends.

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B10 blend of rice bran oil biodiesel was having higher BTE as compare to other biodiesel blends and diesel. CO and smoke emission were decreased for rice bran biodiesel blends, and it was further decreased for blends with n-butanol as compared with diesel. HC emission was decreased for rice bran biodiesel blends; for n-butanol blends HC emission was increased compared to diesel. NOx emission was lowered for n-butanol blends and increased for rice bran biodiesel blends was as compared to diesel.S. Ramalingam, S. Rajendran [43], performed experiment on single cylinder, four stroke, water cooled, constant speed, CI engine with Annona methyl ester blends (A20, A40, A60, A80 and A100) and diesel. Noted that, highest BTE was observed for A20 blend among all blends; BSFC decreased with increasing BP for all blends, among all blends A20 was having low BSFC; increase in EGT was observed for all blends than diesel for all loading conditions; HC emission was decreased for all blends at all loading conditions than diesel; CO and smoke emission was increased for all blends compared with diesel except A20; NOx emission was increased for all blends compared to diesel at all loading conditions. Heat release rate and cylinder pressure was high for A20 among all blends and it is lower than diesel.

K. Nanthagopal et al. [44], have conducted experiment on single cylinder, air cooled, four stroke, DICI engine fueled with blends prepared from two higher alcohols (n-pentanol and n-octanol) in concentration 10%, 20% and 30% and CIME. Addition of higher alcohols in biodiesel BTE improved and BSFC was decreased compared with pure CIME for all loads; in cylinder pressure and heat release rate were increased for high alcohol blends compared with pure CIME , it was due to addition of higher alcohols in biodiesel; NOx emission was decreased for higher alcohol addition, CO, smoke and HC emissions were increased for alcohol biodiesel blends compared with plain CIME. K.

A. Abed et al. [45], performed experiment using waste cooking-oil biodiesel and its blends on single cylinder, four stroke, constant speed, air cooled, DICI engine. BSFC was increased and thermal efficiency was decreased for all blends of biodiesel as distinguished to diesel. EGT was higher for biodiesel blends as distinguishaed to diesel.

Emissions concern for all biodiesel blends CO, smoke and HC emissions were decreased; however, CO2 & NOx emissions were increased as compared with biodiesel. M. A. Asokan et al.[46] conducted experiment on four stroke, water cooled, single cylinder, constant speed, diesel engine fuelled with juliflora biodiesel and its blends and diesel.

Noted that for maximum load BSFC for B20 blend was 0.271 kg/kWh, which was approximately close to diesel (0.26 kg/kWh). BTE for B100 was nearly equal to diesel fuel; EGT was decreased for biodiesel and its blends as compared to diesel, for B40 blend EGT was nearer to diesel. CO & HC emissions were decreased as compared to diesel; for pure juliflora diesel NOx emission was increased than diesel; smoke emission for pure diesel was more as compared to pure biodiesel.

4. CONCLUSION

This paper gives literature review on performance, combustion and emission characteristics of diesel (compression ignition) engine fuelled with pure biodiesel and its blends as a alternative fuel for diesel engines. More than 30 numbers of biodiesel fuels are reviewed in simple tabulated form for their important properties like viscosity, cetane number, calorific value, flash point, etc. Also, more than 18 numbers of different biodiesels were studied for biodiesel preparation; 20 numbers of biodiesels, and their blends were studied for their performance, combustion and emissions. Biodiesel is renewable, non-toxic, environment friendly, safe to store; biodiesel can be derived from vegetable oils, animal tallow can be used in CI, engines with minor or no modifications. Biodiesel emits lower HC, CO and PM, however CO2 emission was higher but it was considered as neutral because while growing oil bearing seeds tree it absorbs CO2 from environment thus balancing CO2 emissions. After study of different investigations following conclusions are drawn.

1. Lower calorific value produces low HRR, Higher BSFC and lower BTE compared with diesel.

2. The pollutant emissions CO, HC and PM / smoke were lesser for biodiesel and its blends. However, NOx and CO2 emissions are higher than compared to diesel.

3. Up to 20% biodiesel blends can be used as fuel with no or very minor modification.

Some drawbacks of biodiesel compared to diesel; high viscosity, low calorific value, higher BSFC, higher NOx emission, high density. Biodiesel production on large scale basis is not feasible; cost of biodiesel production can be decreased by implementing proper use of by products; improvement in technology for biodiesel production.

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