A review on the properties, performance and emission aspects of the third generation biodiesels

Renewable and Sustainable Energy Reviews 82 (2018) 2970–2992

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Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser

A review on the properties, performance and emission aspects of the third generation biodiesels

T

⁎

R. Sakthivela, , K. Rameshb, R. Purnachandrana, P. Mohamed Shameera a b

Department of Mechanical Engineering, Research Scholars, Government College of Technology, Coimbatore 641013, India Department of Mechanical Engineering, Faculty of Engineering, Government College of Technology, Coimbatore 641013, India

A R T I C L E I N F O

A B S T R A C T

Keywords: Biodiesel Waste cooking oil Algae Animal fat Fish oil Emission

In the effect of robust industrialization and rapid augmentation of a number of fleets, there has been a huge rise in the fossil fuel consumption. Tremendous increase in global warming threatens the ecological balance of the earth. Based on the recent sorts of hardship about the fuel, researchers are profoundly pondered over the field of renewability, environmentally friendly and economically doable. In recent decades biodiesel fuel becomes the center of attraction among researchers since it is renewable, bio degradable, non-noxious, eco-friendly and sustainable. This review paper highlights and reviews the properties of prosperous variety of the biodiesel fuels derived from non-edible feedstocks which are termed as third generation biodiesel and its effects on the performance and emissions of the diesel engines. It was observed that the physicochemical properties of the biodiesel differ based on the types of feedstocks and also have a considerable effect on the potential performance of engine and dynamic characteristics of emission level. Also, the usage of biodiesel commonly leads to a reduction in noxious pollutants like carbon monoxide, unburnt hydrocarbon and particulate matter with an obvious increase in fuel consumption and NOx emission. This review provides a prospective strategy for the researchers for enhancing the engine performance and emission characteristics by using the third generation biofuels and its blends with the productive marvelous outcomes.

1. Introduction With the simultaneous expansion of population and industrialization, the diminution of fossil fuel reserves leads to increased petroleum price [1]. The various sectors like transport, industry and agriculture consume the major part of the energy produced by the different sources like coal, petroleum, wood, wind, solar, nuclear [2–4]. On analyzing sector wise fuel oil consumption, transportation sector contributes 64.5% of total world's oil consumption in 2014 and is displayed in Fig. 1. This is nearly 42% hike when compared to 1973 [5]. Since the major prime mover used for the transportation fleets are diesel engines, biofuels gain thriving attention among the researchers a potential substitute for diesel fuels [6,7]. In the environmental aspects, diesel engine emits harmful pollutants like particulate matter, unburnt hydrocarbon, Nitrogen oxides, carbon monoxide and smoke. Among the diverse pollutants, the most noteworthy are oxides of nitrogen and smoke [8–12]. Also, the carbon dioxide accumulation and other green house gases in the atmosphere are responsible for climatic change and other global consequences for life on earth realm [13]. The atmospheric CO2 concentration has been predicted to rise by 80% in the year 2030

above the levels of the year 2007 [14]. The deterioration of fossil fuel reserves and mounting environmental concerns has moved researchers to develop alternate sources for traditional petro based fuels [15–17]. Vegetable oil becomes one of the most important sources of alternatives to fossil fuels due to its economic perspective and emission quality [18–20]. Biodiesel is the mono alkyl ester derived from the fatty acid esters of raw vegetable oil or animal tallow [21,22]. Even though biodiesel possesses enhanced properties than crude vegetable oils, the major setbacks of biodiesel are high viscosity, low volatility, poor spray characteristics, lower energy content, augmented nitrogen oxide (NOx) emission, high cloud point and pour point, when compared to diesel fuel [23]. Many studies have been empirically carried out to resolve all sorts of hardships within the ambit of biodiesel utilization by using various strategies like using various feedstocks, engine modifications and by using fuel additives. 1.1. Indian scenario In a highly populated country like India, the need for petro based products is quite imperative and inevitable to a greater extent as

⁎

Correspondence to: No.5, Deyvanai Nagar, Thiruppalaithurai, Papanasam, Thanjavur dt-614205, India. E-mail addresses: [email protected] (R. Sakthivel), [email protected] (K. Ramesh), [email protected] (R. Purnachandran), [email protected] (P. Mohamed Shameer). http://dx.doi.org/10.1016/j.rser.2017.10.037 Received 12 March 2017; Received in revised form 14 September 2017; Accepted 26 October 2017 Available online 02 November 2017 1364-0321/ © 2017 Elsevier Ltd. All rights reserved.

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Nomenclature BTE BSFC BFCE HC CO CO2

NOx PM ASTM EN D B CRDI

Brake Thermal Efficiency Brake Specific Fuel Consumption Brake Fuel Conversion Efficiency Hydrocarbon Carbon monoxide Carbon dioxide

Oxides of Nitrogen Particulate matter American Society for Testing Materials European Standards Diesel Biodiesel Common Rail Direct Injection

compared to other countries. In India, diesel fuel consumption is five times higher than gasoline [24]. Due to the mass energy insecurity and a huge hike in energy prices, India will face a serious energy shortage within next couple of decade [25]. According to a report by Greenpeace on March 24, 2009, renewable energy can lucratively meet over 35% of power requirement in India by 2030 [26]. In India, Ministry of New and Renewable Energy (MNRE) have prepared the National Policy on biofuels which propose the 20% blending of biofuels to traditional petro based fuels by 2017 [27]. According to British Petroleum's statistical review of world energy 2016, India's oil consumption has increased from 180.8 Million tons to 195.5 Million tons which are 8.1% increase in 2015 when compared to 2014 which is 4.5% of world's total oil consumption. In biofuel production India holds 0.5% of global share and also there was 13.1% lift up in biofuel production in 2015 over 2014. In 2015 India's primary energy consumption was satisfied by coal (407.2 Mtoe) and oil (195.5 Mtoe). The primary energy consumption was increased by 5.1% in 2015. India also shows a drastic amplification in the CO2 level of 5.3% in 2015 which is 6.6% of total share of world's CO2 emission. India became third largest electricity producer in 2013 with 4.8% of global share but the rate of electricity generation in India has increased in 2015 with a global share of 5.4% [28]. Despite the energy generation, India is still facing energy deficit which forces the government to take serious steps towards promoting renewable energy sources which in turn provides energy security. 1.2. Global scenario

Fig. 2. World biofuel production (in million tonnes of oil equivalent).

Global carbon dioxide emissions from the petroleum based fuels and mushroom growth of industries increased to a new height of 35.3 billion tons of CO2 in 2013 [29]. In 2014, the consumption of fossil fuels has been increased by 2.6% and 1.2% higher than that of 2013 for China and United states, whereas the global biofuel increased gradually by 7.4% [30]. In the 8.5% of Brazilian agricultural territory, about 0.9% of the land is entirely devoted to sugarcane cultivation (for ethanol production). In the Sao Paulo state of Brazil, bioethanol contributes

57% of fuels consumed by flex fuel vehicles during 2012 [31]. In the United States and Brazil, soybean is commonly used as feedstocks for biodiesel production whereas palm oil gets a top major source of biodiesel in Malaysia and Indonesia [32,33]. The leading producers of biofuel in the world are the United States, Brazil and Germany whose global share of biofuel production is 41.4%, 23.6% and 4.2% respectively in 2015. While analyzing the world's biofuel production, it can be clearly seen that North America contributes a spectacularly maximum of 42.9% and total Africa contributes a minimum share of 0.1%. From Fig. 2, it can be clearly seen that the global biofuel production raised by 0.9% in 2015. In a global perspective, Ukraine and Venezuela show a radical decline in oil consumption rates of 16.1% and 12.7% in 2015 when compared to 2014. On the other side, Philippines and Slovakia shows a prominent increase of oil consumption rates of 14.3% and 11.3% in 2015. The most important context in the global view is that Organization for Economic Cooperation and Development (OECD) countries contribute 47.5% and Non-OECD countries contribute 52.5% of global oil consumption [28].

1.3. Feedstocks for biodiesel production From the literature survey conducted, there are copious feedstocks reported for the production of biodiesel. The selection of feedstocks depends upon the availability and economic aspects of the concerned country. In countries like USA and Brazil, soybean oil is broadly used for biodiesel production whereas canola oil is main raw material in Canada. Meanwhile, Finland, UK Germany and Italy depend on

Fig. 1. Worldwide oil consumption by sector (in Million Tonnes of Oil Equivalent).

2971

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content i.e. the average lipid content of most species varies up to 70% but under certain enhanced conditions some species can yield up to 90% of dry weight [55]. Irrespective of an algal source, waste cooking oil proves a cost effective and very heterogeneous raw material for biodiesel production [131]. The utilization of waste cooking oil also reduces the burden of sewage treatment and reduction of water contamination. In recent decades, animal fats including beef, poultry, goat, pork emerging as a potential and reliable source for biofuel synthesis. This trend is due to the fact that change in feeding habits of human and the soap factories cannot take up all the fats produced [56]. The unprocessed fish oil produced from discarded fish parts is found to be a stable and cheap source to extract biodiesel. Since the lipid content of red flesh marine fishes is more, it is mostly preferred for raw oil production. Pyrolysis is one of the most recommended processes used to convert biomass into a suitable fuel for particular use. The liquid obtained from pyrolysis process is known as bio-oil or pyrolysis oil which can be used as fuel additive after necessary upgradation. Meanwhile, several studies proved that gas obtained from pyrolysis of biomass can also be used as fuel in IC engines.

rapeseed oil. Similarly, Asian countries like Malaysia, Indonesia with coastal belts have surplus palm and coconut oils which are utilized for biodiesel production. Also, Jatropha and Karanja have been reported to be potential feedstocks in the Indian peninsula. Among them, rapeseed oil, palm oil, castor oil and sun flower oil have been considered earlier for biodiesel production but their adverse effect on food crops have stalled their usage as feedstocks for biodiesel synthesis. Table 1 shows the wide range of vegetable oils which can be used as a potential raw material for biodiesel production. From the table, it can be clearly seen that there are two types of vegetable oils namely edible and non-edible oils. The usage of edible oils has been of great concern because they contend with food materials in a long term. It can also be seen that there are plenty of non-edible oils which poses advantages like liquid nature portability, availability, low sulphur and aromatic content, biodegradability and apparently no negative impact on food crops. As a step ahead, there are some emerging feedstocks like animal fats, micro algae, fish oil, tallow oil etc which can be used to synthesize biodiesel on large scale. 1.3.1. Edible oils (First generation) In the advent of biodiesel era, widespread usage of edible oils is highly noticeable raw materials for biodiesel production. Hence the edible oils derived from feedstocks like soybean, mustard, rice, wheat, coconut, rapeseed, olive, palm, corn etc are categorized as first generation feedstocks of biodiesel synthesis. Although the first generation feedstocks possess advantages like availability of crops and relatively simple conversion process, the major drawback of this feedstock is the threat of limitation in food supply which may lead to increase in food prices as the fuel is derived from food sources. On the whole, the controversial issue arises that is necessary to prefer one, or the other of ‘food vs fuel’ alternatives. On the other hand high cost, a restricted region of cultivation and adaptability to climatic conditions also obstruct the utilization of first generation feedstocks. These setbacks restricted the users to move on to other resources for biodiesel production.

1.4. Objective of the review After performing a wider literature survey in the area of biofuel, it was categorically observed that no review literature discusses the various aspects of third generation biodiesel fuels which is one of the upcoming energy resources. This was the major motivating factor for the authors to come up with this review article and discuss various aspects of the third generation biodiesels. This review paper shines a light on properties, performance and emission parameters of diesel engine powered by biofuels derived from third generation feedstocks. 2. Properties and characteristics of non-edible oils The quality of biodiesel is influenced by enormous factors like the composition of feedstock, method of oil extraction, biodiesel synthesis methodology and refining processes. In order to assess the quality of biodiesel substantial standards were formulated. All biodiesel fuels must meet the specifications of biodiesel prescribed by American Society for Testing and Materials (ASTM 6751), European Standard (EN

1.3.2. Non-edible oils (Second generation) As the results of the tremendous setbacks of first generation feedstocks, researchers started to use a meticulous variety of oils derived from non-edible crops. The fuel derived from these feedstocks are termed as second generation biofuels or advanced biofuels. These oils include Calophyllum inophyllum [132], Jatropha curcus, Mahua indica [133], Karanja, Neem, Rubber seed, Thevettia peruviana, Nagchampa etc. The major advantage of using non-edible is that there will be no necessity to saddle on food crops when compared to first generation oils. Adding to its advantage, the second generation feedstock can be grown on non-agricultural land or marginal land. Meanwhile, the problem arises when it comes to the yield of crops, where yield drops for major second generation crops like Jatropha, Cammelina, Rapeseed and oil palm when they are cultivated in marginal lands. So the farmers are forced to cultivate the second generation crops in agricultural lands which in turn affect the food production and economy of the society. To overcome the socioeconomic problems of second generation biofuels, the researchers focussed on novel feedstocks which are economically viable in a productive manner and easily available to a larger extent.

Table 1 Feedstocks for biodiesel production.

1.3.3. Other sources (Third generation) Regardless of vegetable oils, some other sources like micro algae, waste frying oil, animal fat, fish oil, pyrolysis oil etc constitute third generation source of biofuel [54]. These viable sources of biofuel overcome the difficulties faced by previous generation feedstocks such as availability, economic feasibility, affecting food chain and adaptability to climatic conditions. Microalgae can be a potential feedstock for biodiesel production. Since several algal species have the ability to live in harsh conditions, it is best suited to local environments with low culturing cost. Another major advantage of micro algae is the lipid 2972

Edible oil (1st generation)

Non-edible oil (2nd generation)

Other sources (3rd generation)

Rapeseed oil [34] Palm oil [35]

Calophyllum inophyllum [45,132] Jatropha curcus [46]

Sun flower oil [36] Castor oil [37]

Mahua indica [46,133] Neem [46]

Hazelnut oil [38] Rice bran oil [39] Cotton seed oil [40] Tigernut oil [41] Raddish oil [42] Walnut oil [42] Cashewnut oil [42] Pistachio oil [42] Soyabean oil [43] Mustard oil [44]

Rubber Seed [46] Nicotiana tabacum [46] Aleutites fordii [46] Crambe abyssinica [46] Sapindus mukorossi [46] Cerbera odollam [46] Thevettia peruviana [46] Cerbera odollam [46] Aleutites fordii [46] Nagchampa [42] Karanja [42] Silk cotton tree [42] Tall oil [42] Milk bush [42] Petroleum nut [42] Babassu tree [42] Jojoba [42]

Dunaliella salina algae [47] Chlorella vulgaris algae [47] Botryococcus braunii [47] Waste cooking oil [30,48,131] Animal Tallow oil [49] Chicken fat oil [50] Poultry fat oil [51] Biomass Pyrolysis oil [52] Fish oil [53]

Renewable and Sustainable Energy Reviews 82 (2018) 2970–2992

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and type of feedstock [58–60]. The important physicochemical properties of different third generation biodiesels are summarized in Table 3 and are explained in detail below.

14214) etc. These standards set guidelines for testing the biodiesel fuels and prescribes the suitable ranges for various physical and chemical properties of the fuel in order to use it in the engine. Some of the key physicochemical properties of biodiesel are density (kg/m3),cetane number, kinematic viscosity (mm2 /s), flash point (°C), Pour point and cloud point (°C), calorific value (MJ/kg), acid value (mg KOH/g-oil), copper strip corrosion, ash content (%), sulphur content, glycerine (% m/m), oxidation stability [30,32,46,57,134,135]. Table 2 shows the ASTM 6751 and EN 14214 standards of biodiesel along with petroleum diesel fuel standard ASTM D975. The biodiesel fuel obtained from non-edible third generation feedstocks have been reviewed from various aspects. The key properties of biodiesel which influence the engine performance and emission characteristics depend on the chemical composition, fatty acid composition

2.1. Density Density is one of the principal fuel properties used to estimate the quantity of fuel injected by the injection systems to provide proper combustion. The density of the biodiesel fuels depends on several factors like feedstock used, method of biodiesel conversion and methyl ester profile [116]. The fuel density plays a crucial role in injector nozzle design because it affects the engine operation directly. Moreover, this can directly influence the fuel atomization which in turn affects the thermal efficiency of the engine. The density of biodiesel fuels

Table 2 ASTM D6751 and EN 14214 standards for biodiesel fuels and ASTM D 975 for petroleum diesel fuel [30,46,57]. Property specification

Units

Flash point Cloud point Pour Point Cetane number

°C °C °C

Density at 15 °C

Kg/m3

Kinematic viscosity at 40 °C Iodine number

mm2/s g I2/ 100 g mg KOH/ g °C

Acid number Cold filter plugging point Oxidation stability

Diesel ASTM D975

Biodiesel

Test method

ASTM D6751

Limits

EN 14214

Test method

Limits

Test method

Limits

60–80 −15 to −5 −35 to −15 46

ASTM ASTM ASTM ASTM

130 minimum −3 to −12 −15 to −16 47 minimum

EN ISO 3679 – – EN ISO 5165

101 minimum – – 51 minimum 860–900

ASTM D975 ASTM D975 ASTM D975 ASTM D4737 ASTM D1298 ASTM D445 –

D 93 D2500 D97 D613

820–860

ASTM D 1298

880

2.0 to 4.5 –

ASTM D445 –

1.9–6.0 –

EN ISO 3675/ 12185 EN ISO 3104 EN 14111

–

–

ASTM D664

0.5 maximum

EN 14104

0.5 v maximum

−8 25 mg/L maximum

ASTM D6371 –

Maximum +5 –

EN 14214 EN 14112

– 3 h minimum

0.2 maximum

ASTM D 4530

0.050 maximum

EN ISO 10370

0.3 maximum

Class 1 maximum 370 maximum 0.460 mm (max.) (all diesel containing less than 500 ppm – sulphur) –

ASTM D 130 ASTM D 1160 ASTM D6079

No. 3 maximum 360 520 maximum

EN ISO 2160 – –

Class 1 – –

ASTM

EN ISO 3987

0.02 maximum

– EN ISO 12937

– 500 mg/kg 0.8 maximum 0.2 maximum 0.2 maximum 0.02 maximum

3.5–5.0 –

Carbon residue

% m/m

Copper corrosion Distillation temperature Lubricity (HFRR)

°C m

EN 590 ASTM D2274 ASTM D4530 ASTM D130 ASTM D86 IP 450

Sulphated ash content

%mass

–

Ash content . Water and sediment

%mass

100 maximum 0.05 maximum

– ASTM D 2709

Monoglycerides Diglycerides Triglycerides Free glycerine

% mass % mass % mass %mass

ASTM D482 ASTM D2709 – – – –

– – – –

– – – ASTM D 6584

D874 0.002 maximum – 0.005 vol% maximum – – – 0.02 maximum

Total glycerine Phosphorus

%mass %mass

– –

– –

ASTM D6548 ASTM D4951

0.24 0.001 maximum

EN 14105 EN 14105 EN 14106 EN 1405/ 14016 EN 14105 EN 14107

Sulphur (S 10 grade)

ppm

10 maximum

–

–

–

Sulphur (S 15 grade) Sulphur (S 50 grade)

ppm ppm

– 50 maximum

ASTM D5453 –

150 maximum –

– –

– –

Sulphur (S 500 grade)

ppm

500 maximum

ASTM D5453

500 maximum

–

–

Carbon Hydrogen Oxygen BOCLE scuff Conductivity at ambient temperature

wt% wt% wt% g pS/m

ASTM D5453 – ASTM D5453 ASTM D5453 ASTM D975 ASTM D975 – ASTM D975 ASTM D2624

0.25 0.001 maximum –

ASTM ASTM ASTM ASTM –

77 12 11 > 7000 –

– – – – –

– – – – –

Total contamination Boiling point Saponification value

mg/kg °C mg KOH/g

87 13 – 2000–5000 50 m minimum at ambient temp. (all diesel held by a terminal or refinery for sale or distribution) – – –

24 100–615 370 maximum

EN 12662 – –

24 – –

– – –

2973

PS121 PS121 PS121 PS121

ASTM D5452 ASTM-D7398 ASTM D5558 − 95

2974

Mutton fat

Beef tallow

Chicken fat Chicken fat Camelus dromedaries (Camel) fat Fleshing oil Fleshing oil

Chicken fat

Fleshing oil

Chicken fat

Animal fat traps

Animal fat (Cat. 1 and 2) Animal fat

Animal fat

Schizochytrium mangrovei Ankistrodesmus braunii and Nannochloropsis. Animal fats Animal fat

Spirulina platensis

Auxenochorella protothecoides Chlorella protothecoides

Heterotrophic microalgae (sugar plant) Chlorella protothecoides Chlorella vulgaris Melanothamnus afaqhusainii Euglena sanguinea

Spirulina Pond water algae Chlorella variabilis

Algae Diesel

Feed stock of biodiesel

0.875 at 15 °C 0.877 at 15 °C 0.818 0.877 at 15 °C 0.87 at 15 °C 0.883 at 15 °C 0.907 at 15 °C 0.8897 at 15 °C 0.869 0.867 0.871 at 15.6 °C 0.876 0.8767 at 15 °C 0.832 at 15 °C 0.856 at 15 °C

186.3

–

71 – 128

−18 3 –

74 – 158 174.8 168 152–171 –

– – – 11 10 – −5

2.8 6.25 3.39 at 40 °C

4.7 at 40 °C 4.7 at 40 °C

5.98 at 40 °C

4.89 at 40 °C

169

–

3

–

–

5.3 at 40 °C

2

172

–

–

5

−4

–

– –

– – 15

−7 −5 12.7

–

– – −6 15.5

–

−7

– –

–

– –

–

–

7

19.12

−3

–

–

–

– – −1

–

– – –

–

Cloud point °C

–

– –

–

–

3

−6

–

−9

–

–

13

– – −2

–

−18 −16 –

1

Pour point °C

144

–

189

4.98 at 40 °C

4.7

1.99 at 40 °C 4.03 at 40 °C

4.03 at 40 °C

4.25 at 40 °C

4.19 at 40 °C

5.22 at 40 °C

12.4 at 40 °C

–

160

4.354 at 40 °C – –

172

4.545 at 40 °C –

0.868 at 15 °C 0.877 at 15 °C 0.882 at 15 °C 0.8637 at 15 °C 0.880 at 15 °C 0.869 at 40 °C –

115 115 –

– −11 –

4.41 at 40 °C 5.2 at 40 °C 3.67

0.864 0.86 0.87

4.43 at 40 °C

–

–

–

71

Flash point °C

130 – 157

8

Cold filter plugging point (°C)

5.66 at 40 °C – 5.82 at 40 °C – 4.875 at 40 °C –

3.4 at 40 °C

Viscosity (mm2/s)

0.82 at 20 °C 0.86 0.872 0.867 at 15 °C 0.772

Density (g/cm3)

Table 3 Physio-chemical properties of third generation biodiesels.

59

60.36

– 58.8

48 61 58.7

52.3

–

48

53

52.9 65.6

65.70

63.88

–

–

70

–

52.6

65

– – –

75

– – 58.6

45

Cetane number

–

40,230

39,954 39,900

– – 39,520

39,700

39,613

40,173

37,000

– 36,830

36,830

36,730

40,720

–

45,630

–

–

–

39,010 – –

44,000

41,360 40,800 38,780

43,200

–

–

– –

– – –

–

–

–

– 138.1 ppm

– – 0.031 wt%

81.5 ppm

> 990 ppm

23.45

– –

–

67 –

–

–

–

9.37 ppm

Nil

–

–

– –

– – 0.05 wt%

–

–

– 76.14 (% w/w) –

–

–

–

0.42

Nil

–

0.09

8.63 × 10−6 –

0.05

– – –

–

– – –

290

Carbon content % mass

< 0.015

– – –

–

– – Nil

< 10

Sulphur content (mg/kg)

– 11.03 (% w/ w) –

–

–

–

–

–

–

–

–

– – –

–

– – 10.37

13.4

Calorific Oxygen value (kJ/kg) content % of mass

0.65

0.2

0.32 0.28

– 0.25 –

0.43

–

0.22

0.3

1.05 –

–

0.38

–

7.59

0.75

0.29

0.2

0.29

0.374 – 0.75

–

0.45 0.40 –

0.07

Acid Value mg of KOH/ g of sample

126

44.4

61 53.6

– 130 65.3

95.5

52

–

–

–

–

83.02

–

46.12

102

112.2

118

–

–

–

– – –

6

Iodine value ( g I2/100 g)

–

–

– –

– – –

–

–

[81]

[49]

[80] [78]

[60] [56] [79]

[78]

[77]

[56,77,79]

[76]

[74] [75]

[73]

[72]

[137]

[136]

[70,71]

[70]

[70]

[70]

[67] [68] [69]

[66]

[64] [64] [65]

[61–63]

Refs.

(continued on next page)

6 at 110 °C

–

42 –

13.03 at 110 °C –

–

0.05

–

4.52

1.2

6.20

– – –

–

– – –

110

Oxidation stability (hr)

R. Sakthivel et al.

Renewable and Sustainable Energy Reviews 82 (2018) 2970–2992

2975

172 143.5

– –

4.87

186 140 165

– – –

–

– 169

– –

–

– 140 94 – 153 158 134 190 –

12 – – – −3 5

–

6.8 at 40 °C

6.1 at 40 °C 4.6 at 40 °C

4.5 at 40 °C

4.9 at 40 °C

4.603 at 40 °C 1 –

4.83 at 40 °C

4.4 at 40 °C

4.6 at 40 °C

–

–

–

–

–

–

–

–

–

– –

–

–

–

–

– –

–

–

–

−5

4.42 at 40 °C

–

–

170

–

13

–

–

–

– – –

– –

–

1 –

−5 −4 –

–

– –

–

–

Cloud point °C

9

–

4.36 at 40 °C

–

–

4.92 at 40 °C

–

170

–

–

5.16 at 40 °C

–

– – –

– −1

–

– –

−6 −5 –

–

– 0

7

3

Pour point °C

4.027 at 40 °C 8

165

–

6.1 at 30 °C 4.31 at 40 °C

2.72 at 40 °C 6.8 at 40 °C 4.79

160

3.658 at 40 °C –

– – – – 70.6

– – –

– – –

161.50

– – 4.401 at 40 °C 10

–

4.42 at 40 °C

177 30

Flash point °C

Cold filter plugging point (°C)

4.45 at 40 °C – 5.072 at 40 °C –

4.84 at 40 °C

6.86 at 40 °C

Viscosity (mm2/s)

0.890 0.875 at 15 °C 0.876 at 40 °C – 0.880 at 15 °C 0.890 0.870 –

at

at

at

0.887 at 15 °C 0.878 at 15 °C 0.866 at 27 °C Waste cooking oil 0.8835 at 27 °C Waste sunflower oil 0.8875 at 15 °C Waste mixed vegetable oil 0.8789 at 15 °C Waste fried oil – Methyl 0.870 ester Waste cooking oil 0.900 Waste cooking oil 0.871 at 20 °C Waste cooking oil - Methyl 0.8843 at ester 15 °C Waste cooking oil – Ethyl 0.883 at ester 15 °C 4 Waste cooking oil 0.8749 at 15 °C Waste cooking oil 0.878 at 15 °C Waste cooking oil

Waste cooking oil Waste Fried oil Waste cooking oil (Indian restaurant) Waste cooking oil (Chinese restaurant) Waste cooking oil - Methyl ester Waste cooking oil - Ethyl ester Waste cooking oil

Waste cooking oil Waste cooking oil

Waste cooking oil

Chicken fat Mutton fat Waste fat oil Waste cooking oil Waste cooking oil Waste frying palm oil

Animal fat

Fish oil inedible animal tallow

Lard

0.877 15 °C 0.877 15 °C 0.881 0.877 17 °C 0.871 15 °C 0.867 0.856 –

Poultry fat

at

Density (g/cm3)

Feed stock of biodiesel

Table 3 (continued)

51

–

64.2

53.5

54.9

– 51

–

59.7

51.4

58

66

–

–

57.4

41 – 56.7

62 54.1

50.4

54.5 60.4

61 59 –

57.49

47 58.8

–

–

Cetane number

37,500

38,850

–

40,051

39,869

39,600 37,500

39,000

–

–

38,600

38,034

39,480

39,260

–

35,401 39,000 –

37,900 41,200

39767.23

– 38,730

– – –

37,467

40,546 –

36,500

38,580

10.8 (%wt)

–

–

–

–

– 10.8 (%wt)

–

–

–

9.816 (%w/ w) –

10.43 (wt)

10.91 (wt)

–

– – –

– –

–

–

– – –

–

– 0.18

–

–

Calorific Oxygen value (kJ/kg) content % of mass

< 10

1

12.7

4.4

2.3

– < 10

–

–

–

–

0

–

–

7.8 ppm

– – 0.6 ppm

0.001 6.2 ppm

–

–

– – –

–

– –

–

–

Sulphur content (mg/kg)

–

–

–

–

–

– 77.1 (%wt)

0.24 (%m/ m) 0.19 (%m/ m) –

76.26 (% w/w) –

77.38 wt

76.95 wt

0.05

– – 0.05

0.005 –

–

– 0.0004

– – –

–

– 76.77

0.21

–

Carbon content % mass

–

–

0.6

0.36

0.36

– –

–

–

–

–

0.38

0.27

0.55

–

– – –

– –

–

0.48 0.51

0.25 0.65 10.91

–

– –

0.12

0.55

Acid Value mg of KOH/ g of sample

–

–

–

107.11

103.01

– –

–

60

125.21

–

57.3

105.6

97.5

–

– – –

– –

–

– 62

130 126 71.02

81.60

– –

67 – 77

78.8

Iodine value ( g I2/100 g)

–

–

15.9

–

–

– –

–

[48]

[98]

[97]

[97]

[95] [96]

[94]

[93]

[93]

[99] (continued on next page)

14.12

0.43

[92]

[91]

– –

[90]

[90]

[89]

[87] [88] [89]

[85] [86]

[84]

[56] [83]

[56] [56] [138]

[123]

[82] [49]

[81]

[81]

Refs.

–

–

–

– – –

– –

–

– 10.1

– – –

–

– –

–

–

Oxidation stability (hr)

R. Sakthivel et al.

Renewable and Sustainable Energy Reviews 82 (2018) 2970–2992

2976

154 156 – 114 – 176 155 149 1623

6

4.318 at 40 °C –

4.0 at 40 °C – 4.451 at 40 °C –

–

–

4.741 at 40 °C – 7.2 at 40 °C –

–

4.03 at 40 °C

0.885 0.860

114 –

4.741 at 40 °C – 4.45 at 40 °C –

55

–

–

–

–

– – – 528 ppm – – – –

168

–

13

–

– –

–

–

−3

4

–

Algae Diesel Spirulina Pond water algae Chlorella variabilis Heterotrophic microalgae (sugar plant) Chlorella protothecoides Chlorella vulgaris Melanothamnus afaqhusainii

9.38

12.3 at 40 °C

1.918 at 40 °C –

5.64 at 40 °C

145

157

–

5.2 at 40 °C

–

–

–

4.25 at 40 °C

161

–

3.83

4.96 at 40 °C

4.85

– −14

– –

–

−2.5

5

–

–

Pour point °C

Water and sediment content (% vol)

0.881 at 15 °C 0.981 at 15 °C 0.980 at 22 °C 0.982

0.885 at 15 °C 0.890 at 15 °C 0.885 0.881 at 15 °C

0.880 0.881 at 15 °C 0.862 at 15 °C 0.83 at 15 °C 0.871

–

–

4.82 at 40 °C

–

110

4.5 at 40 °C

–

Flash point °C

126

Cold filter plugging point (°C)

−13.2

4.57 at 40 °C

Viscosity (mm2/s)

0.871 at 20 °C 0.855 at 25 °C 0.88 at 20 °C 0.87 at 15 °C 0.8876 at 15 °C 0.888 at 15 °C –

Density (g/cm3)

Feed stock of biodiesel

Neem seed pyrolysis oil

Sludge pyrolysis oil

Plastic pyrolysis oil

Miscellaneous Larvae grease (housefly)

Fish oil (Ethyl Ester) Fish oil (Methyl Ester)

Fish oil (Methyl Ester)

Trout oil

Fish oil

Fish oil

Fish oil

Fish oil Fish oil

Waste frying oil Fish oil Fish oil Fish oil

Waste frying oil

Waste cooking oil

Waste cooking oil

Waste cooking oil

Waste fry oil

Feed stock of biodiesel

Table 3 (continued)

–

–

–

–

– –

–

–

–

−5

–

– –

– –

–

3

7

–

–

−12

Cloud point °C

20,800

37,040

38,300

–

40,057 40,546

37,790

37,800

40,100

37,800

39,700

42,241 40,546

40,057 41,400

–

157 – – – – – – –

Boiling point (°C)

–

–

–

52

52.6 52.4

52.5

51.3

–

51

–

– 52

52.6 50.9

–

39,550

–

– 52

39,900

43,210

40,500

–

0.55 (%wt)

0.155 (%wt)

–

– –

–

–

0 (%wt)

–

10 ppm

– –

– –

–

–

–

–

–

–

Sulphur content (mg/kg)

78.71 (% wt) –

87.9 (%wt)

–

– 77.5 (%wt)

76.53 (% wt) 77.3 (% kg/kg) –

–

–

– 80.01 (% wt) – –

–

–

76.53 (% wt) –

–

–

Carbon content % mass

– – – – – – – –

Saponification value (mg KOH/g)

–

10.08 (%wt)

3.3 (%wt)

–

– 10.84 (%wt)

8.1 (%wt)

–

11.13 (%wt)

–

–

10.9% –

– 7.19 (%wt)

–

–

–

10.93 (%wt)

–

–

Calorific Oxygen value (kJ/kg) content % of mass

58.6

52

52.2

Cetane number

–

–

–

–

–

– 185

–

–

–

–

–

– –

– –

96.80

–

–

–

–

–

Iodine value ( g I2/100 g)

–

–

–

–

– –

–

–

–

–

–

– –

– –

–

–

– – – – – – – –

Refs.

[139]

[130]

[129]

[115]

[113] [114]

[112]

[111]

[110]

[109]

[108]

[107] [108]

[105] [106]

[138]

[104]

[103]

[102]

[101]

[100]

Refs.

[61,62,6371] [64] [64] [65] [66] [67] [68] [69] (continued on next page)

4.7 at 110 °C

–

–

–

Oxidation stability (hr)

Peroxide value (meq kg−1)

26

41

0.63

– 0.35

1.32

–

–

–

–

– –

– –

1.31

–

0.37

–

–

–

Acid Value mg of KOH/ g of sample

R. Sakthivel et al.

Renewable and Sustainable Energy Reviews 82 (2018) 2970–2992

Boiling point (°C) – – – 270 – 71.8 – – – – – – – – – – – – – – – – – – – 337.2 – – – – – – – – – – – – – – – – – – – – – – – – – – –

Water and sediment content (% vol) – – – 39 ppm 0.03 – – – – – – – 0.3 – – – 0 326.4 mg/kg – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Feed stock of biodiesel

Euglena sanguinea Auxenochorella protothecoides Chlorella protothecoides Spirulina platensis Schizochytrium mangrovei Ankistrodesmus braunii and Nannochloropsis. Animal fats Animal fat Animal fat Animal fat (Cat. 1 and 2) Animal fat Animal fat traps Chicken fat Fleshing oil Chicken fat Chicken fat Chicken fat Camelus dromedaries (Camel) fat Fleshing oil Fleshing oil Beef tallow Mutton fat Poultry fat Lard Fish oil inedible animal tallow Animal fat Chicken fat Mutton fat Waste fat oil Waste cooking oil Waste cooking oil Waste frying palm oil Waste cooking oil Waste cooking oil Waste cooking oil Waste cooking oil Waste Fried oil Waste cooking oil (Indian restaurant) Waste cooking oil (Chinese restaurant) Waste cooking oil – Methyl ester Waste cooking oil – Ethyl ester Waste cooking oil Waste cooking oil Waste sunflower oil Waste mixed vegetable oil Waste fried oil – Methyl ester Waste cooking oil Waste cooking oil Waste cooking oil – Methyl ester Waste cooking oil – Ethyl ester Waste cooking oil Waste cooking oil Waste cooking oil Waste fry oil

Table 3 (continued)

2977 – – – – – – – – – – – – – – – – – – – – – – – –

– – – – – – – – – – 202.3 – – – – – – – – – 251.23 244.50 204.16

– –

– – –

Saponification value (mg KOH/g)

– – – – – – – – – – – – – – – – – – – – – – – –

56.7 4.2 – – – – – – – – – – – – – – – –

– – – –

– – – – – –

Peroxide value (meq kg−1)

[56] [83] [84] [85] [86] [87] [88] [89] [89] [90] [90] [91] [92] [93] [93] [94] [95] [96] [97] [97] [98] [48] [99] [100] (continued on next page)

[72] [73] [74] [75] [76] [56,77,79] [77] [78] [60] [56] [79] [80] [78] [49] [81] [81] [81] [82] [49] [123] [56] [56] [138]

[70] [70] [70] [70,71] [136] [137]

Refs.

R. Sakthivel et al.

Renewable and Sustainable Energy Reviews 82 (2018) 2970–2992

Renewable and Sustainable Energy Reviews 82 (2018) 2970–2992

is the most critical barrier to its extensive use. ASTM D1298 and EN ISO 3675/12185 test methods give entire gamut of guidelines in measuring the density of biodiesel fuel [30,46,57,58]. From Table 3, it can be clearly seen that density of most of the biodiesel obtained from third generation feedstocks mostly lies in the range of 860 kg/m3 to 900 kg/ m3. Amidst this comparison, biodiesel obtained from waste fleshing oil [77] showed the maxima of 900 kg/m3 of density where as heterotrophic microalgae biodiesel showed a minimal around 772 kg/m3. On the other hand, pyrolysis liquids show high density as compared to methyl ester fuels ranging about 980 kg/m3 [129,130,139,140].

– – – – 224 – – –

[115] [129] [130] [139]

– – – – – – – – – – – – – – – – – – – – – –

[105] [106] [107] [108] [108] [109] [110] [111] [112] [113] [114]

– – – – – – – – – 195.91

[101] [102] [103] [104] [138]

Peroxide value (meq kg−1)

2.2. Kinematic viscosity Viscosity is one of the vital characteristics of a fuel which signifies the ability of fuel to flow. Being resistance to the flow, viscosity plays a major role in spray atomization and spray penetration. Since biodiesel possesses larger chemical structure and molecular mass, the viscosity of biodiesel is 10–15 times higher than conventional fossil fuel [7,58]. Higher viscous fuels cause insufficient fuel atomization which in turn results in reduced thermal efficiency and soot deposits. On the other hand, reduced viscosity leads to finer fuel droplets which make injector easy to pump fuel into the combustion chamber. Transesterification process is predominately used to reduce the viscosity of methyl esters. The kinematic viscosity of biodiesel is measured using ASTM D445 (1.90–6 mm2/s) and EN ISO 3104 (3.5–5 mm2/s). Table 3 depicts the details of the kinematic viscosity of different biodiesels from which it can be noticeably observed that biodiesel derived from Spirulina platensis microalgae showed maximum out of the bound viscosity value of 12.4 mm2/s [70,71] whereas chicken fat methyl ester showed minimal viscosity value of 2.8 mm2/s [60].

Cold filter plugging point (CFPP) is the most important criterion used to evaluate the cold flow operability of a fuel. It is the minimum temperature at which the test fuel will gush through a standard specific filter [117]. The limit of filterability of fuels can be clearly described by CFPP than cloud point (CP), the CFPP value of a test fuel is always lower than that of its CP. The measurement standard for CFPP is ASTM D6371 [58]. From Table 3, it is evident that animal fat methyl ester exhibits lowest CFPP of −18 °C and fleshing oil shows the highest value of CFPP of 11 °C.

– – – –

– – – – – – – – – – –

– – – – –

2.3. Cold filter plugging point

Flash point (FP) is the lowest temperature at which the vapors of the volatile fuel starts ignite when exposed to an ignition source. The conventional petro diesel has a flash point of about 50–65 °C, whereas biodiesel possesses flash point of more than 150 °C.This signifies that biodiesel has better safety aspects in storage and in transit when compared to petro diesel. Generally, straight vegetable oil has a higher flash point than its methyl esters due to its poor volatility. FP is measured by the procedure prescribed in ASTM D93 and EN ISO 3679 [46]. From Table 3, it is found that Spirulina platensis micro algae biodiesel show uppermost FP value of 189 °C [70,71] and biodiesel produced from inedible animal tallow shows least FP of 30 °C [49].

– 1190 mg/kg 4 (wt%) 25.2 (wt%)

– – – – – – – – – – –

2.4. Flash point

– – – – –

Water and sediment content (% vol)

Boiling point (°C)

Saponification value (mg KOH/g)

Refs.

R. Sakthivel et al.

Waste cooking oil Waste cooking oil Waste cooking oil Waste frying oil Waste frying oil Fish oil Fish oil Fish oil Fish oil Fish oil Fish oil Fish oil Fish oil Trout oil Fish oil (Methyl Ester) Fish oil (Ethyl Ester) Fish oil (Methyl Ester) Miscellaneous Larvae grease (housefly) Plastic pyrolysis oil Sludge pyrolysis oil Neem seed pyrolysis oil

Feed stock of biodiesel

Table 3 (continued)

2.5. Cloud point Cloud point (CP) is the lowest possible temperature at which the wax in the fuel is first seen to crystallize and form a cloudy appearance. CP is the most common criterion used to set the low-temperature fuel controls [117]. CP of biodiesels varies extensively with the feedstocks used based on the fatty acid composition. ASTM D2500 procedures are used to measure the cloud point of a biodiesel. Table 3 shows that mutton fat methyl ester showing least value of CP as −4 °C [56] and the 2978

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lines. AN is experimentally determined by ASTM D664 and EN 14104 standards (maximum of 0.5 mg KOH/g). From Table 3, it can be clearly seen that among methyl ester fuels, Auxenochorella protothecoides microalgae biodiesel and beef tallow biodiesel shows the least value of acid value in the order of 0.2 mg KOH/g [49,70]. The maximum value of AN is recorded in the case waste fat oil methyl ester in order of 10.91 mg KOH/g [138]. On the other hand, due to the high acidic nature, pyrolysis oils possess highest acid value [130,139].

highest value are shown by Schizochytrium mangrovei biodiesel in the order of 19.12 °C [136]. 2.6. Pour point Pour point (PP) of a liquid fuel is the minimum temperature at which the fuel loses its flow characteristics. PP is also a crucial parameter in cold flow operation since the fuel is suitable for operation only above the pour point value. Generally, biodiesel possesses higher CP and PP when compared to conventional diesel. ASTM D 97 formulates the procedure to estimate the PP of a biodiesel fuel. From Table 3, it is evident that Spirulina platensis exhibits lowest PP of −18 °C [64] and Camelus dromedaries fat biodiesel shows the highest value of 15.5 °C [79].

2.11. Iodine value The Iodine number (IN) is a mass of iodine absorbed in the double bond positions of the 100 g of sample fuel. IN is the measure of the degree of unsaturation of the test fuel and hence their potential to oxidize when exposed to air. Since IV does not take into account the positions of the double bonds available for oxidation, it did not correlate well with oxidative stability. On the other hand, it was observed that IV is closely related to viscosity, cetane number and CFPP of biodiesel [46]. Even though there are no specifications given for IV in ASTM D6751, EN 14111 has set a peak IV of 120 g I2/100 g [46]. According to Table 3, the highest IV is 185 g I2/100 g for Fish oil methyl ester [114] and the least IV is 44.4 g I2/100 g for beef tallow biodiesel [49].

2.7. Cetane number Cetane number (CN) is one of the most significant properties of biodiesel which directly influence the ignition delay period. Ignition delay is the period between the fuel injection into the combustion chamber and the start of ignition. Higher CN indicates the ability of the fuel to auto ignite shortly after being injected into the combustion chamber [58,118]. Lower CN results in knocking, increased exhaust emissions of the engine and excessive deposits in the engine due to incomplete combustion [46]. It is worth to note that CN of biodiesel increases with chain length and degree of saturation of fatty acids. Due to higher oxygen content, biodiesel has higher CN which results in elevated combustion efficiency. The CN of biodiesel fuel is specified by ASTM D613 (47 minimum) and EN ISO 5165 (51 minimum) [46,118]. From Table 3, it can be seen that Heterotrophic microalgae (sugar plant) biodiesel hold CN of 75 [66] which is the maximum value and waste cooking oil biodiesel have CN of 41 which is the least value [87].

2.12. Oxidation stability Oxidation stability of biodiesel fuel is one of the major indicators for the degree of oxidation and reactivity with air. Oxidation stability of biodiesel primarily depends upon the number of bis-allylic sites in the unsaturated compound. The primary oxidation is initiated by the radical formation at bis-allylic sites which forms peroxides. The secondary oxidation produces volatile organic compounds, ketones and aldehydes by destroying methyl ester which finally polymerizes to form waste sludge that will damage engine fuel injection system [121]. It is evident that higher the degree of unsaturation in the carbon chain, poorer the stability of biodiesel [58,119]. The EN14112 prescribes minimum induction period of 3 h for biodiesel whereas no specific standards are prescribed in ASTM D6751. From Table 3, waste cooking oil biodiesel shows highest induction period of 15.9 h [98] whereas poor oxidation stability was observed in Schizochytrium mangrovei oil biodiesel with induction period in the order of 0.05 h [136].

2.8. Calorific value Calorific value (CV) or heating value of the fuel is precisely defined as the amount of energy released by the combustion of a unit value of fuels. Therefore higher CV is a desirable factor for an internal combustion engine. CV of the biodiesel fuel is lower than that of conventional diesel fuel. Even though the calorific value is not specified in ASTM D6751 and EN 14214 standards, it has been prescribed in EN 14213 (biodiesel for the heating purpose) with a minimum value of 35 MJ/kg [46,120]. Table 3 clearly shows that Spirulina platensis micro algae biodiesel shows highest CV of 45.63 MJ/kg [70,71] and waste cooking oil biodiesel show lowest CV of 35.401 MJ/kg [87].

2.13. Water and sediment content Water and sediment contents present in the biodiesel portrays the cleanliness of biodiesel fuel. It can be present either as suspended water droplets or as dissolved form. The presence of water content in biodiesel reduces the calorific value of fuel and corrodes components of engine fuel system. Meanwhile, the sediments may contain rust and dirt particles which may cause clogging in fuel lines. On the other side, high water content induces hydrolysis reaction which converts biodiesel to free fatty acids. ASTM D2709 and EN ISO 12937 standards provide guidelines to measure the water and sediment contents in biodiesel fuel. From Table 3, it is evident that Camelus dromedaries (Camel) fat methyl ester showed zero water and sediment content [79] whereas many studies discussed water content alone [80,129,130,139].

2.9. Sulphur content Nowadays emission regulations strictly restrict the amount of sulphur in the fuel due to the threat of acid rain caused by the sulphur oxide emission. Sulphur content in a fuel directly influences the magnitude of sulphur oxides emissions during the combustion of fuel. It has been observed that the biodiesel synthesized from vegetable oils have very low levels of sulphur content [46].Table 3 shows the amount of sulphur content in the biodiesel produced from various feedstocks. From the table, it is evident that fish oils show considerably less sulphur content than other biodiesels whereas animal fat derived biodiesel shows a high range of sulphur content.

2.14. Boiling point (BP) The normal boiling point of a typical substance is the temperature at which vapor pressure of the substance equals the atmospheric pressure. The normal boiling point can also act a measure of the overall volatility of the substance. In general, higher the BP of a substance, its overall volatility will be low whereas lower BP imparts high volatility in the substance. On the other hand, BP also depends on the nature of bonding between molecules in the substance. Even though most of the research

2.10. Acid number Acid number (AN) is the direct measure of free fatty acids (FFAs) in the fuel sample and is expressed in mg KOH/g. The higher amount of free fatty acid leads to an elevated acid value which in turn causes rigorous corrosion in the fuel supply lines of an engine [58]. AN can also be viewed as an indication of the level of lubrication in the fuel 2979

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2.16. Peroxide value (PV)

paper reviewed does not hold information about BP of the biodiesel fuel, some studies reported BP of biodiesel fuels. ASTM-D7398 standard underlines the test procedure for evaluating the boiling range of biodiesel fuel by Gas chromatography. Minimum BP was observed for microalgae derived biodiesel which is in the range of 71.8 °C [137] and maximum BP of 337.2 °C was observed for animal fat biodiesel [123].

Determination of peroxide values helps in measuring the existence of oxidative moieties in the biodiesel sample. Generally, the oxidative moieties in biodiesel are found as hydro peroxides which are formed when the fatty acid methyl esters react with oxygen present in the air. The formation of hydroperoxides is considered as the first step in the oxidative degradation pathway of methyl esters. ASTM D3703-13 highlights the methodology to determine the peroxide value of diesel fuels. In the wide literature survey conducted, it was found that chicken fat methyl ester and fleshing oil possess PV of 56.7 meq kg−1 and 4.2 meq kg−1 respectively.

2.15. Saponification value (SV) The saponification value signifies the sum of saponifiable units per unit weight of oil. A relatively high SV indicates the presence of a larger proportion of low molecular weight fatty acid chain. SV provides a direct measure of the average molecular weight of the biodiesel fuel and it is expressed in milligrams of KOH required to saponify 1 g of fat. Also, a high saponification value of raw oil indicates the presence of high fatty acid percentage which may lead to soap formation during transesterification reaction. Saponification value can be measured as per guidelines provided by ASTM D5558-95 standard with a range from 0 to 370 mg KOH/g. From Table 3, highest SV was found in chicken fat methyl ester with a value of 251.23 mg KOH/g [56] whereas least value obtained was 195.91 mg KOH/g for waste frying oil biodiesel [138].

3. Performance and emission characteristics The performance and emission parameters of a diesel engine mainly depends on the physicochemical properties of the fuel used which in turn depends on the characteristics of feedstocks such as saturation, types of double bond (trans or cis), length of carbon chain action the other hand the performance characteristics also directly affected by the operating variables such as injection pressure, compression ratio,

Table 4 Engine specifications. S.No

Ref. No

Engine model

Number of cylinder

Power kW

Speed rpm

Bore mm

Stroke mm

Compression ratio

Displacement cm3

Cooling system

1. 2.

[67] [65]

1 6

5.2 134.22

1500 2500

NM NM

NM NM

NM NM

661 5900

Water Water

3.

[76]

1

3.7

1500

95.3

85.5

18:01

630

Air

4.

[78,97]

6

136

2400

104

114.9

16.4:1

6000

Water

5. 6. 7. 8. 9. 10. 11. 12. 13.

[83] [86] [87] [88] [91] [92] [93] [94] [95]

4 6 1 1 1 4 1 1 1

38.8 118 3.7 3.78 5.2 75 5.4 3.78 4.4

4250 2500 1500 1500 1500 3600 2200 1500 1500

80.26 102 80 80 87.5 92 86 80 87.5

88.9 120 110 110 110 93.8 68 110 110

21.47:1 17.9:1 5:1–22:1 16.5:1 17.5:1 18.5:1 18:01 16.5:1 17.5:1

1800 5880 NM NM NM NM 6000 NM NM

Water NM Water Water Water Water Air Water Air

14. 15. 16. 17.

[96] [48] [99] [100]

4 1 4 4

88 NM 88 12

1800 NM 1800 1800

112 100 112 82.55

110 125 110 92.08

19:01 17.4:1 19:01 19:01

4334 980 4334 NM

Water NM Water Air

18. 19. 20. 21. 22.

[101] [102] [106] [107] [108]

4 6 4 3 1

18 162 NM 20 7.457

1500 2000 NM 1500 3600

85 102 NM 100 NM

100 120 NM 120 NM

17:01 17.3:1 NM 17:01 18:01

2400 5900 3856 2826 406

Water Water Water Air Air

23. 24.

[109,126] [110]

1 6

3.7 280

1500 1800

80 127

110 140

16.5:1 18:01

553 10,640

Water NM

25.

[111]

1

2.2

3000

69.85

57.15

17:01

219

Water

26.

[112,113]

1

4.4

1500

87.5

110

17.5:1

661

Air

27.

[114]

1

10

2000

80

70

18:01

406

Air

28. 29.

[122] [123]

1 4

NM 103

NM 4000

NM NM

NM NM

NM 18:01

NM 2000

Air NM

30. 31.

[124] [125]

4 4

85 NM

3700 NM

94 102

95 120

17.5:1 NM

2636 3922

Water NM

32.

[127]

Kirloskar TV1 BS III Direct Injection four stroke turbocharged diesel engine Lister Petter – TS 1 direct injection diesel engine Ford Cargo direct injection type Indirect injection type Cummins B5.9-160 Direct injection diesel engine Kirloskar (India) TV1- KIRLOSKAR Euro IV direct injection type Antor-6LD400 Kirloskar (India) Single cylinder agricultural diesel engine Isuzu 4HF1 Direct injection diesel engine Isuzu 4HF1 Onan DJC type indirect injected diesel engine generator NWK22 Cummins ISBe220 31 Direct injection diesel engine Kirloskar engine Rainbow-186 direct injection diesel engine Kirloskar AV-1 diesel engine Scania DC1102 direct injection heavy duty diesel engine Lister Petter AA1 indirect injection diesel engine Kirloskar, TAF1 make direct injection diesel engine Rainbow-186 direct injection diesel engine Direct Injection Diesel engine 2.0 TDI Volkswagen direct injection diesel engine ADCR CRDI engine MWM D229/4 direct injection type RUGGERINI 191

2

13

3600

85

75

19:01

851

Air

2980

Constant speed Variable injection timing (20°, 23° & 26°) ETC test cycle

1-Cylinder, 4 stroke, AC, DI, CI engine

UDC/NEDC (5 std. operating conditions: 15, 30, 50, 70 & 100 km/h) –

4-Cylinder, 4 stroke, DI, CI, 2.0 TDI Volkswagen engine, CR: 18, RP:103 kW at 4000 rpm 1-Cylinder, 4 stroke, AC, DI, CI, Lister Petter - TS 1 series engine, RP: 3.7 kW at 1500 rpm 6-Cylinder, 4 stroke, DI, CI, 6 l, Ford Cargo engine, CR: 16.4:1, RP:136 kW at 2400 rpm 6-Cylinder, 4 stroke, DI, CI, 6 l, Ford Cargo engine, CR: 16.4:1, RP:136 kW at 2400 rpm 4-Cylinder, 4 stroke, WC, DI, CI, ADCR engine, RP:85 kW at 3700 rpm 1-Cylinder, 4 stroke, WC, DI, CI, Lister Petter AA1 engine, CR: 17:1, RP:2.2 kW

2981

B100

Animal fat residue

Waste fried oil

Waste cooking oil

Waste cooking oil

Waste cooking oil

Constant speed (1500 rpm) Variable load (0.5–4 kW)

Variable speed Constant load

Constant speed (2200 rpm) Variable load

Constant speed Variable load

Constant speed Variable load (0–25 kW)

4-Cylinder, 4 stroke, DI, CI engine, MWM D229/4 model

Waste cooking oil

Waste cooking oil

Constant load Variable CR (18–22)

↓ approx. 0.32 kg/kWh for 20° BTDC at 3.3 kW ↑ 9.79 g/kWh

↑ 0.2 kg/kWh at 2 kg load

–

↓ 0.12 kW

–

B75

B100

B10

B100

B100

B40

↑ 0.07 kg/kWh (min. BSFC)

↑ 100 g/kWh for 2400 rpm & 25% load ↓ approx. 5 g/kWh

↑ 0.076 kg/kWh

–

↓ 0.05 kW for CR 21

–

↓ 8 kW at 3600 rpm & 100% load –

–

–

–

B5, B10, B20 & B30

↑ 60 g/kWh at economical speed ↑ avg. 0.385%, 1.06%, 1.71% & 3.42% ↓ 0.055 kg/kWh for CR 21

–

↑ max. 1.3%, 2.7%, 4.5% & 5%

↑ avg. 3.2%, 8.5% & −13.8% ↑ avg. 0.45%, 1.04%, 1.1% & 1.47%

–

↑ 50 g/kWh at 150 Nm ↑ 30 g/kWh at 600 Nm

–

↑ 48 g/kWh at 150 Nm ↑ 25 g/kWh at 600 Nm

–

–

–

↑ avg. 50 g/kWh

–

↑ 0.1 kg/kWh at 18 kg load

BSFC

BP

Performance

B100

B10, B20, B40 & B50

Trout oil

Waste frying palm oil Waste cooking oil

B25, B50 & B75

Swine lard

B100

B50

Animal fat

Waste fleshing oil

B100

B100

B100

Microalga – (Chlorella variabilis) Microalgae

Waste chicken fat

B20

Blend percentage

Algae

Feed stock of biodiesel

4-Cylinder, 4 stroke, WC, DI, CI, CR: 21.47:1, RP:38.8 kW at 4250 rpm Cummins B5.9-160, DI engine, CR: 17.9:1, RP: 118 kW at 2500 rpm 4-Cylinder, 4 stroke, WC, VCR, DI, CI engine, CR: 5:1–22:1 (variable), RP:3.7 kW 1-Cylinder, 4 stroke, DI, CI, Kirloskar engine, CR: 16.5:1, RP: 3.78 kW at 1500 rpm 4-Cylinder, 4 stroke, turbocharged, DI, CI engine, CR: 18.5:1, RP:75 kW at 3600 rpm 1-Cylinder, 4 stroke, DI, CI, Antor/ 6LD400 engine, CR: 18:1, RP:5.4 kW at 3000 rpm 1-Cylinder, 4 stroke, AC, DI, CI engine, CR: 17.5:1, RP:4.4 kW

Constant speed (1400 rpm) Variable load (150, 300,450 and 600 Nm) Constant speed (1400 rpm) Variable load (150, 300,450 and 600 Nm) Two speed (1500 & 3000 rpm) Variable load (50, 100 & 150 Nm) Performance: Variable speed (900–2700 rpm) Constant load Emission: Constant speed Variable load Variable speed (1000–3000 rpm) Constant load US-HDD transient cycle

Constant speed (1500 rpm) Variable load (0–18 kg in steps of 2 kg)

1-Cylinder, 4 stroke, WC, DI, CI, Kirloskar TV1 model engine, RP: 5.2 kW at 1500 rpm

6-Cylinder, 4 stroke, WC, DI, CI engine, RP: 180 hp at 2500 rpm

Test condition

Engine type

Table 5 Performance analysis of biodiesel fuelled engine.

↓ 2 MJ/kWh at lower load ↑ 2 MJ/kWh at peak load –

–

–

–

–

–

–

–

–

–

–

–

↑ 5 MJ/kWh at 2 kg load ↑ 1 MJ/kWh at 18 kg load –

–

–

BSEC

–

↓ max. 4%

[125]

[95]

[93]

[92]

[88]

[87]

[86]

[83]

[111]

[124]

[78]

[78]

[76]

[123]

[67]

[65]

[122]

(continued on next page)

↓ 0.8 and 1.2% for B5 and B10 biodiesel blends

↑ 1.8% at 2400 rpm & 100% load for B100.

↓ 4% for B100 when compared to diesel

↑ 5.4% for B40 at CR 21

–

–

↑ max. of 1.5% for B50

↑ all blends

–

–

–

↓ 3% at min load ↑ slightly at max load

–

↓ 5% at 18 kg load

↓ 2% at 2 kg load

↑ 1.67%

↓ 5% for 20° BTDC at 4.3 kW

BTE

Ref.

R. Sakthivel et al.

Renewable and Sustainable Energy Reviews 82 (2018) 2970–2992

2982

1-Cylinder, 4 stroke, AC, DI, CI engine, CR: 17.5:1, RP: 4.4 kW at 1500 rpm 1-Cylinder, 4 stroke, AC, DI, CI engine, CR: 18:1, RP: 10 kW at 2000 rpm

1-Cylinder, 4 stroke, AC, DI, CI engine, CR: 17.5:1, RP: 4.4 kW at 1500 rpm

Constant speed Variable load Variable speed (1000–2500 rpm) Constant load

Variable load

Variable speed (1000–2500 rpm) Constant load Constant speed (1500 rpm) Variable load Propulsion mode (variable speed & load) Generator mode (constant speed & variable load) Constant speed

1-Cylinder, 4 stroke, AC, DI, CI engine, CR: 18:1, RP: 10 HP 1-Cylinder, 4 stroke, WC, DI, CI engine, CR: 16.5:1 6-Cylinder, 4 stroke, CI engine, CR: 18:1, RP: 280 kW

B100 B25

Fish oil Fish oil

B100

B100

Fish oil

Fish oil

B100

B100

Waste anchovy fish oil Fish oil

B20

B100

Marine fish oil

Fish oil

B100

Waste mustard oil

Constant speed Variable load

B100

Waste fry oil

3-Cylinder, 4 stroke, AC, DI, CI engine, CR: 17:1, RP:32.5 kW

B20

Waste cooking oil

B100

Waste cooking oil

6-Cylinder, 4 stroke, WC, DI, CI engine, CR: 17:1, RP:18 kW at 1500 rpm 6-Cylinder, 4 cycle, AC, IDI, CI engine, CR: 19:1, RP:12 kW 1-Cylinder, 4 stroke, WC, CI engine, CR: 16.5:1, RP:3.7 kW at 1500 rpm 4-Cylinder, 4 stroke, DI, CI engin

ME_B100 & EE_B100

Waste frying oil

Variable speed (1100, 1400 & 1700 rpm) Constant load (600 Nm) Constant speed (1800 rpm) Variable load (28, 84, 140, 196 & 224 N m) Constant speed (1500 rpm) Variable load (2, 3.3 & 4.6 kW) Constant speed (1800 rpm) Variable load (1, 3.6 & 9 kW) Constant speed Variable load (2, 4, 6 & 8 N) Variable speed (800–2000 rpm) Constant torque (98 N-m)

6-Cylinder, 4 stroke, turbocharged, WC, DI, CI, 6 l, Ford Cargo engine, CR: 16.4:1, RP:136 kW at 2400 rpm 4-Cylinder, WC, DI, CI engine, CR: 19:1, RP: 88 kW at 3200 rpm

Blend percentage

Feed stock of biodiesel

Test condition

Engine type

Table 5 (continued)

↑ avg. 14.17% ↑ avg. 11.44% ↑ avg. 50 g/kWh

↑ 75 g/kWh at 4.6 kW ↑ avg. 8.64% ↑ 0.0015 kg/kWh at 2 N ↑ 0.001 kg/kWh at 8 N ↑ approx. 25 g/kWh for 800 rpm ↑ approx. 40 g/kWh for 2000 rpm ↑ slightly

↑ avg. 8.32%

–

–

– – ↑ slightly at 8 N

↓ avg. 7.06%

↑ approx. 15 g/kWh at 2500 rpm

↓ slightly

–

–

–

210 kW at 75% of load

–

↑ 8% at no load ↑ approx. 13% at peak load ↑ 9% at 75% load

–

–

–

BSFC

BP

Performance

–

↓ 5% at 2500 rpm

[114]

[113]

↓ 3.6% at peak load

↓ avg. 12.4%

[112]

–

–

↑ approx. 5000 kJ/kWh at low load ↑ approx. 2500 kJ/kWh at peak load –

[110]

↓ slightly

[109]

[108]

[107]

↓ 0.96% at peak load

↓ avg. 7.39%

[106]

[126]

[100]

[101]

[99]

[97]

↓ 2% at 2 N ↓ 6% at 8 N –

↑ avg. 1.89%

↓ 2% at 4.6 kW

↓avg. 2%

–

BTE

–

↑ approx. 3000 kJ/kWh at 5 kW ↑ approx. 2000 kJ/kWh at 20 kW BP –

–

–

–

–

↑ slightly

BSEC

Ref.

R. Sakthivel et al.

Renewable and Sustainable Energy Reviews 82 (2018) 2970–2992

2983

↑ slightly ↓ 1% at 2500 rpm

↓ avg. 5.2% ↑ approx. 10 ppm

–

↓ approx. 0.25% at 1000 rpm ↓ approx. 0.75% at 2500 rpm ↓ 0.1% at no load ↓ 0.25% at peak load ↓ max. 2% for low and medium loads –

↓ slightly – ↓ 30% at 2 N ↓ 43% at 8 N –

slightly avg. 1.68% 20% at 2 N 8% at 8 N approx. 100 ppm for 800 rpm approx. 50 ppm for 2000 rpm approx. 25 ppm at 0 kW BP approx. 50 ppm at 20 kW BP approx. 120 ppm at 1000 rpm approx. 50 ppm at 2500 rpm slightly at no load 200 ppm at peak load max. 6% for low and medium loads ↑ avg. 5 g/kWh

↑ ↓ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑

↑ avg. 13.3% ↑ avg. 2.08% ↑ avg. 0.92% –

6.5% 11.32% 10.80% 1 g/kWh

↑ ↑ ↑ ↑

avg. avg. avg. avg.

–

↑ slightly

– ↓ 2% for 3600 rpm & 100% load

↑ slightly for CR 22

↑ avg. 46.1% ↓ avg. 22.30% ↓ avg 28.84% ↑ approx. 3 g/kWh at lower load Similar at peak load ↓ slightly ↑ avg. 33.28% ↓ 75% at 2 N ↓ 70.58% at 8 N ↓ approx. 80 ppm for 800 rpm ↓ approx. 60 ppm for 2000 rpm ↓ approx. 0.035% vol. at 0 kW BP ↓ approx. 0.075% vol. at 20 kW BP ↓ approx. 0.6% at 1000 rpm ↓ approx. 1% at 2500 rpm ↓ approx. 50 ppm at no load ↓ approx. 65 ppm at peak load ↓ 24–56% (propulsion mode) ↓ 18–29% (generator mode) ↓ approx. 8 g/kWh for low load & peak load ↓ approx. 4 g/kWh for mid load ↓ avg. 33.7% ↓ avg. 16.24%

↓ 11.8% for low & mid loads ↓ 51% for peak loads ↓ avg. 31%

↓ avg. 0.13, 0.14, 0.17 & 0.26 (g/ kWh) ↓ 0.1% for CR 20 ↑ slightly for CR 21 ↓ avg. 45% ↑ approx. 40% for 3600 rpm & 100% load

↑ avg. 1, 3, 7 & 9 (g/kWh)

↑ avg. 18.33%

↑

↑ ↑ ↑ ↑ ↓

↓ 0.3% for all speeds

↓ 1% at 1000 rpm ↑ slightly at 3000 rpm

↓ avg. 19%, 25% & 30% at 3000 rpm ↓ slightly for all blends at max. load

↓ 12% ↓ 21% ↓ avg. 27%, 38% & 37% at 1500 rpm

↑ 2.5% ↑ 1.1% ↑ avg. 0.3%, 18% & 13.5% at 1500 rpm ↓ avg. 1%, 3% & 6% at 3000 rpm –

Slightly at 3000 rpm 40 ppm for B20 70 ppm for B40 approx. 10 ppm at 1000 rpm at mid speeds approx. 20 ppm at 3000 rpm avg. 0.05, 0.09, 0.09 & 0.15 (g/ kWh) slightly for CR 21 100 ppm for CR 22 avg. 10% slightly for 1200 rpm 100 ppm for 3600 rpm (at 100% load) 8.7%

↓ 0.215 g/kWh ↓ 0.005% vol. for all loads – ↓ slightly at low loads

– – – –

↑ ↑ ↑ ↑ ↓ ↑ ↑

–

–

↑ 40 ppm for 20° BTDC at 100% load ↑ 2.57 g/kWh ↓ 50 ppm at 18 kg load ↑ 14 ppm ↑ approx. 140 ppm at min load ↓ approx. 70 ppm at max load ↑ 16% ↑ 15.2% ↑ 22% at 1500 rpm

CO

CO2

NOX

Emission

Table 6 Emission analysis of biodiesel fuelled engine.

– –

– – –

↑ avg. 39% ↓ avg. 10%

↓ approx. 0.5 g/kWh for low load ↓ approx. 0.2 g/kWh for peak load ↓ avg. 26.2% ↓ avg. 19.81%

– –

↓ 64 mg/m3 at peak load

–

–

–

↓ avg. 5% –

– – –

–

– – – –

– –

↑ approx. 10% for lower & mid loads ↓approx. 15% for peak load – –

–

–

↓ avg. 47% –

↓ avg. 0.012, 0.018, 0.017 & 0.017 (g/kWh) –

–

–

– – –

– – – ↓ 200 ng/s at low loads

–

Particulate matter

↓ avg. 16%

10 ppm at 4.6 kW avg. 78.84% 33% at 2 N slightly at 8 N

23.5% for B50 avg. 29.36% avg. 38.29% slightly for all loads

1% for B10 5% for B40 10% at 1000–1500 rpm 35% for 2000–3000 rpm

↓ 7% for peak load

– –

–

–

↓ ↓ ↑ ↑

– – –

↓ slightly (approx. 5%) for all BTDC at 100% load – ↓ approx. 5% at 18 kg load – –

Smoke

approx. 7.5 ppm at 0 kW BP approx. 27 ppm at 20 kW BP approx. 75 ppm at 1000 rpm approx. 50 ppm at 2500 rpm 30 ppm at no load 100 ppm at peak load max. 70%

↓ ↓ ↓ ↓ ↓ ↓ ↓

↑ ↑ ↑ ↓ –

↑ ↓ ↓ ↓

↓ slightly for low & mid loads ↓ 29% for peak load ↓ avg. 57%

– ↓ for all speeds at 50% load and 100% load

↓ avg. 0.093, 0.177, 0.248 & 0.321 (g/kWh) ↑ approx. 10 g/kWh for CR 21

↓ 6 ppm at 1000 rpm ↓ slightly at 3000 rpm

↓ 45% at 3000 rpm ↓ approx. 45% overall

↑ 9.2% ↓ 2.3% ↓ 72% at 1500 rpm

↓ 0.03 g/kWh ↓ approx. 2% for all loads – ↓ Avg. of 150 ppm

↓ 5 ppm for all BTDC at 100% load

HC

[113] [114]

[112]

[110]

[109]

[108]

[107]

[106]

[101] [100] [126]

[99]

[125] [97]

[95]

[93]

[88] [92]

[87]

[86]

[83]

[111]

[78] [78] [124]

[65] [67] [123] [76]

[122]

Refs.

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oxygenated additive along with waste cooking oil biodiesel in a six cylinder turbocharged diesel engine equipped with common rail injection system. Highest BTE was recorded for pure biodiesel which possesses oxygen content of 10.93%. It was also noted that adding triacetin to biodiesel deteriorates BTE values due to the higher viscosity, lower calorific value and elevated density of triacetin additive [102]. The combustion characteristics of a diesel engine fuelled with waste cooking oil biodiesel-pentanol (BP) blends were analyzed under various loading conditions by Zhu et al. It was inferred that pentanol addition improves BTE due to the augmented oxygen content in fuel which enhances combustion resulting in higher positive work. Also it is worth to note that 20% and 30% pentanol addition to biodiesel deteriorates BTE at 0.65 MPa which is attributed to a longer combustion period [99]. Isik et al. reported that addition of 10% n-butanol and 10% waste cooking oil biodiesel to neat diesel showed highest BTE when compared to biodiesel 20% blends due to the reduced viscosity of butanol blend [101]. Sanli et al. synthesized methyl and ethyl esters from waste frying oil and tested it in DI-Diesel engine. It was inferred that both ester fuels showed superior BTE when compared to petro diesel where as peak BTE was recorded by the ethyl ester blends which is 1.98% higher than methyl ester blend [97]. The combustion of swine lard methyl esters in a four stroke turbocharged common rail fuel injection (CRDI) diesel engine was observed by Mikulski et al. In performance wise analysis 25% biodiesel (B25) shows very least marginal variation (mean value of 1.6%) of brake fuel conversion efficiency (BFCE) values when compared to neat diesel. On the other hand, B50 shows 4.8% and B75 shows 7.8% lower BFCE values when compared to mineral diesel. It was also observed that the BFCE values showed largest variations in peak loads where as it was uniform at smaller engine loads for all fuel blends. The jump down in BFCE values on increasing biodiesel percentage was explained by the heating values of fuel blends [124]. Awad et al. conducted engine tests on biodiesel developed from animal fat residue (AFR) in a single cylinder DI diesel engine at 1500 rpm. The experimental results showed that AFR biodiesel samples showed subtle increase in BTE at higher loads whereas decreasing trend was observed at higher loads when compared with diesel fuel. This phenomena was attributed to the earlier SOC (start of combustion) of AFR biodiesel at lower loads which prolongs the combustion duration and the shorter combustion duration at higher loading conditions [128]. Gnanasekaran predicted the performance of compression ignition (CI) engine at various injection timings (21°,24°,27° before TDC) fuelled with biodiesel produced from fish oil using Fuzzy Inference System (FIS). From experimental runs, it had been observed that, for 21° bTDC, the BTE for pure biodiesel (B100) varies from 15.4% to 29.6% at low load to full load respectively. Similarly at 24°bTDC variations about 14.5–29.6% was observed and at 27°bTDC variations about 15–29.6% was observed for B100. It was clearly inferred that BTE of B20 and B40 was close to diesel whereas B60,B80 and B100 shows decreased BTE when compared to diesel fuel. The main reason reported for this decreased trend in BTE was shorter ignition delay [53]. Behçet et al. studied the performance of commercial diesel engine fuelled with fish oil methyl ester and cooking oil methyl ester. The results showed that thermal efficiency attains its peak at an engine speed of 2000 rpm whereas there was a meagre decline in thermal efficiency after this speed range. It was also inferred that fish oil biodiesel blend showed better thermal efficiency than cooking oil biodiesel blend whereas neat diesel showed superior efficiency at all speed conditions. Lower heating value, higher viscosity and density of biodiesel blends were said to be the reasons for the performance declination of biodiesel blends [114]. Sakthivel et al. investigated the feasibility of using fish oil biodiesel in a diesel engine under variable loading conditions. The results showed that the mean BTE of B20 blend was 22.15% which was in range with neat diesel fuel. When compared with neat diesel, the mean value of BTE of B40, B60, B80 and B100 are less than by about 1.8%, 6.4%, 11.3% and 12.4% respectively. The shorter ignition delay with increase in blend ratio causes earlier SOC than for diesel which increases

ignition delay, air-fuel ratio, turbulence of air inside combustion chamber and other factors. Mostly the biodiesel blended with conventional diesel fuel can be used in the compression ignition (CI) engine without any engine modification and the effect of biofuel addition can be analyzed by determining the performance characteristics like brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), brake specific energy consumption (BSEC) and emission generation. The various diesel engines used by researchers are listed in Table 4. In the following sections a detailed review had been carried out on the parameters such as brake thermal efficiency, brake specific fuel consumption along with exhaust emissions like hydrocarbon (HC),carbon monoxide (CO),carbon dioxide (CO2),oxides of nitrogen (NOx),particulate matter (PM) and smoke of various third generation biodiesel fuelled engines. The variations in the performance and emission indicators are listed precisely in Table 5 and Table 6 respectively. 3.1. Brake thermal efficiency (BTE) Brake thermal efficiency is defined as the ratio of brake power obtained in the crankshaft to the fuel power supplied to the engine. Satputaley et al. extracted oil from Chlorella protothecoides micro algae and converted it to methyl ester using transesterification process. Engine testing had been carried out in four stroke direct injection (DI) diesel engine fuelled with micro algae oil and micro algal methyl ester. Maximum reduction of 5.6% and 3.09% BTE on 5.15 kW brake power was observed for microalgal oil and its methyl ester respectively. The reduction in BTE was attributed to poor fuel atomization of the test fuels due to their high viscosity compared to diesel fuel [67]. Jayaprabakar et al. carried out an experiment on single cylinder direct injection diesel engine using Gracelariaverrucossa and rice bran biodiesel blends by varying injection timings under steady speed. Rice bran methyl ester showed superior BTE than algal methyl ester due to its elevated calorific value. BTE increases slightly for all test fuels when the injection timing was advanced from 23° BTDC to 26°BTDC [122]. Singh et al. studied over the European Transient Cycle (ETC) of a heavy duty diesel engine fuelled with Chlorella variabilis biodiesel and Jatropha curcus biodiesel. It was observed that BTE of the engine was worst in urban driving conditions whereas rural mode showed highest BTE for all the test fuels. The highest BTE was obtained in the rural mode for Chlorella variabilis biodiesel fuel and lowest was recorded in the urban mode for petro diesel fuel [65]. Atmanli investigated the effects of higher order alcohols blends with biodiesel derived from waste oil in the engine performance and emission characteristics. From the test runs, it was observed that pure biodiesel had higher BTE of 1.89% than diesel fuel but 50% addition of diesel to biodiesel (D50B50) slightly reduces the BTE by 0.24%. It was also reported that addition of higher alcohols increases BTE considerably. Among the test fuels, 20% butanol blend showed superior BTE which was 5.58% higher than that of the D50B50 blend. On the other hand, 20% pentanol addition increased BTE to 4.94% higher than D50B50 blend. This increased trend of BTE with the addition of higher alcohols is attributed to the presence of high oxygen content of alcohols with enhances combustion and reduces heat loss when compared to diesel [100]. A novel method for biodiesel preparation from waste mustard oil using infrared radiated reactor was proposed by Pradhan et al. Decreasing trend in BTE was observed when 10% biodiesel blend had been used. An average of 7.78% reduction in BTE was recorded at a load of 8 N and the same extent was found for 20% biodiesel blend [126]. de Paulo et al. evaluated the performance characteristics of a diesel power generator operated with waste frying oil based biodiesel blends. BTE values increases from 5% biodiesel blend (B5) to 20% biodiesel blend (B20) where as BTE reduces from B20 to pure biodiesel (B100). From the results, it had been concluded that B5 showed least BTE and B20 blend exhibited highest BTE.A possible reason for this trend in BTE is attributed to the reduced atomization of fuel due to its high viscosity and density [127]. An investigation had been carried out by Zare et al. by adding triacetin as an 2984

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oxygenates elevated BSFC values [102]. The addition of pentanol with waste cooking oil biodiesel and using it in a diesel engine increased the BSFC values at low and high engine loads [99]. Isik et al. found that waste cooking oil biodiesel blend B20 exhibited highest BSFC values when compared all test fuels used in a direct injection diesel engine where as butanol to B20 blend reduced BSFC values. The trend was attributed to the enhanced oxygen content of biodiesel fuel and lowtemperature combustion behaviour of butanol blended fuel [101]. Sanli et al. stated that methyl and ethyl esters of waste cooking oil showed higher BSFC than petro diesel on an average of 14.17% and 11.44%. When adding 20% diesel to methyl and ethyl esters, the BSFC lowered to an average of 3.71% and 4.22%. This trend was attributed to the lower heating value of methyl ester blend (15.7% less) and ethyl ester blend (13.1% less) than petro diesel [97]. Mikulski et al. analyzed the performance characteristics of a turbocharged diesel engine fuelled with swine lard methyl ester and its blends. The authors concluded that addition of methyl ester augmented the BSFC values on an average of 13.8%, 8.5% and 3.2% for the blends B75, B50 and B25 respectively. It is worth to note that fuel conversion efficiency of B25, B50 and B75 were lower than diesel by an average of 1.6%, 4.8% and 7.8% respectively. These drops of fuel conversion efficiency and BSFC proportional to augmentation of methyl esters was explained by lower heating values and reduced ignition delay of the blends [124]. Alptekin et al. studied the effects of using bioethanol with animal fat biodiesel-diesel blends in a water cooled direct injection diesel engine. As the bioethanol content in animal fat biodiesel mixture increased, the BSFC results showed an elevation with respect to load. The lower heating of the test fuels was recorded as the reason for the elevation of BSFC values [78]. Gnanasekaran stated that BSFC of four stroke DI diesel engine amplified linearly with the percentage of fish oil biodiesel in the fuel blend [53]. Behçet et al. studied the effects of fish oil methyl ester and cooking oil methyl ester in the performance characteristics of a Rainbow-186 diesel engine. The authors reported that BSFC of both methyl ester fuels were higher than commercial diesel fuel. On comparing the ester fuels, fish oil biodiesel showed less fuel consumption than that of chicken fat biodiesel [114]. Buyukkaya et al. found that the BSFC of trout oil methyl ester and its blends were higher than that of standard diesel fuel. Average values of BSFC was found to be 1.47%, 1.1%, 1.04% and 0.45% for B50, B40, B20 and B10 biodiesel blends as compared to diesel fuel. Lower calorific values of the ester fuels stated as the main reason for the augmented fuel consumption rate [111]. Ioannis Kalargaris et al. utilized plastic pyrolysis oil as an alternative fuel and tested engine performance. The authors found that lower heating value of plastic oil leads to higher BSFC values for all blending ratios [129]. Hossain et al. analyzed the performance parameters of a diesel engine fuelled with de-inking sludge pyrolysis oil-waste cooking oil biodiesel blends. It was found that lower heating value of pyrolysis oil elevated BSFC values in order of 14–18% and 4–8% higher than that of neat diesel and cooking oil biodiesel [130]. With the addition to the above results, most of the researchers claimed that BSFC of the engine increased when it has been fuelled with biodiesel and its blends irrespective of the working conditions [83,86,88,92,95,106–110,123]. Meanwhile, very few researchers reported that BSFC decreased with the addition of the biodiesel blends [87,93].

compression work along with heat loss and thus decreases the efficiency of engine [113]. Buyukkaya et al. prepared biodiesel from trout oil and used as fuel in a single cylinder indirect injection diesel engine to analyze its performance characteristics. Maximum value of BTE was observed for B50 blend which was 4.05% higher than that of neat diesel while the BTE of B10 blend was closer to diesel at low speed ranges. With increasing biodiesel fraction in blend, the BTE was observed to rise which is due to the complete combustion and lubricity of biodiesel fuel [111]. The usage of plastic pyrolysis oil with diesel fuel deteriorated the BTE of engine due to the presence of high amount aromatic compound which requires more energy to break the bonds [129]. On the other hand De-inking sludge pyrolysis oil along with waste cooking oil biodiesel improved BTE at low load conditions whereas it deteriorated full load efficiencies about 3–6% when compared to respective biodiesel [130]. Apart from the above results many researchers reported that BTE for all biodiesel fuel blend decreases when compared to the neat diesel fuel. This major reasons for this diminishing behaviour are endorsed to lower heating value, high density, high viscosity of fuel blends which causes poor atomization, early start of combustion [88,93,95,107–109,112]. On the other hand few research shows an increasing trend towards BTE stating the biodiesel fuel possess higher heating value and negligible viscosity at high injection pressure [87,92]. 3.2. Brake specific fuel consumption (BSFC) Brake Specific Fuel Consumption (BSFC) is defined as the ratio of total fuel consumption to the brake power generated by the engine. It is one of the major parameters to evaluate the effects of fuels on engine performance characteristics [97]. When the engine is fuelled with microalgal oil and microalgal oil methyl ester, Satputaley et al. observed that BSFC for both the test fuels were high when compared to diesel at all loading conditions. It was reported that the increasing trend in BSFC values was due to the lower heating value of test fuel results in consumption of more fuel to produce the constant power output [67]. Gracelariaverrucossa biodiesel blends showed less fuel consumption than rice bran methyl ester blends at all injection timings in the experimental work carried out by Jayaprabakar et al. The decreased fuel consumption rate was attributed to the higher heating value of the algal biodiesel when compared to the rice bran biodiesel [122]. Chlorella variabilis and Jatropha biodiesel showed a hike in BSFC of 4% and 11% compared to diesel in European Transient Cycle (ETC) test. It was also concluded that rural mode of operation showed minimum BSFC when compared to urban and motorway modes for all test fuels taken into consideration. Among the test fuels Singh et al. reported that Chlorella variabilis biodiesel showed about 6% lower BSFC than Jatropha biodiesel [65]. Atmanli inferred that addition of butanol and pentanol to waste oil biodiesel blend reduced BSFC by 0.89% and 0.95% as compared to 50% biodiesel blend. On the other hand, propanol addition increased BSFC by 5.28% which was attributed to the diminished calorific value of propanol blend [100]. Pradhan et al. tested waste mustard oil biodiesel in Kirloskar AV-1 single cylinder diesel engine and found that biodiesel blends B10 and B20 exhibited elevated BSFC at all loading conditions. Meanwhile, engine consumed less fuel at high loads when it was fuelled with pure biodiesel [126]. While analyzing the fuel consumption of diesel power generator fuelled with waste frying oil biodiesel blends, de Paulo et al. found that increasing the biodiesel concentration in the test fuel decreases the fuel consumption. In the complete test run, B5 blend was found to possess highest fuel consumption rating (3.10 kg/h) where as B20 showed the lowest value of 2.64 kg/h. Also, the same trend was reported by the authors for BSFC of diesel powered generator [127]. The higher oxygen content of biodiesel fuels increased the BSFC of the engine which was due to the lower calorific value of the oxygenated fuel. In the performance test conducted by Zare et al., it was reported that neat diesel with 0% oxygen content recorded lowest BSFC whereas addition of biodiesel and

3.3. Hydrocarbon (HC) Hydrocarbon emissions are the notable results of incomplete combustion of fuel molecules inside the combustion chamber. Engine operating conditions, combustion chamber design, fuel structure are the major parameters that influence the HC emissions [97]. Satputaley et al. reported that higher cetane number of microalgal oil and its methyl ester reduces HC emission by 4% compared to diesel at all loading conditions [67]. Reduction in HC emission was observed by Jayaprabakar et al. by employing biodiesel derived from rice bran and Gracelariaverrucossa algae. It was also explained that biodiesel fuels 2985

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engine, it depends on the geometry of combustion chamber and fuel injection system. While testing B25 blend of fish oil biodiesel and cooking oil biodiesel, Behçet et al. observed that the corresponding biodiesel mixtures exhibited lower HC emissions about 19.81% as compared to diesel fuel [114]. Buyukkaya et al. found that trout oil biodiesel lowered HC emission approximately by 45% depending on loading conditions. Higher cetane number and increased gas temperature were noted as the reasons for HC reduction [111]. Most of the research findings apart from the above results clearly describes that HC emission declined while using biodiesel fuel at all operating conditions [76,83,86,92,93,95,107–110,112,113,124]. On the other hand, very few researchers claimed that HC increased with biodiesel addition at particular operating condition [87,100,125].

enhanced the combustion process at all injection timings and produced less HC when compared to diesel [122]. Singh et al. inferred that addition of biodiesel fuels significantly declines the HC emissions of a diesel engine. Jatropha biodiesel and microalgal biodiesel derived from Chlorella variabilis trim down HC emissions by 40% and 33% respectively compared to petro diesel fuel. This diminishing trend was attributed to higher cetane number and enhanced oxygen content of biodiesel fuels. Jatropha biodiesel showed reduced HC emission at all modes in ETC [65]. Atmanli et al. observed the effects of longer chain alcohols in emission characteristics of a diesel engine fuelled with waste oil biodiesel. It was found that pure biodiesel showed an average of 78.84% higher HC emission at all loads except 9 kW as compared to diesel. The addition of 20% butanol and pentanol to biodiesel blends decreased HC by 17.37% and 17.5% respectively. Meanwhile, propanol addition augmented HC emission by 34.47% as compared to 50% biodiesel blend [100]. Waste mustard oil biodiesel enhanced combustion and considerably reduced the HC emission. Especially B10 blend showed least HC emission when compared to all other fuel blends taken for testing by Pradhan et al. [126]. HC emission mainly depends on the oxygen content and cetane rating of the test fuels. Waste cooking biodiesel with highest cetane number and 11% oxygen content showed lowest HC emission where as neat diesel with no oxygen content showed the highest HC emission. Zare et al. also reported that addition of triacetin additive increased HC emission due to its lowest cetane rating which in turn increased ignition delay [102]. Zhu et al. proved that lower cetane rating of pentanol-waste cooking oil biodiesel blends provides additional time for vaporization of fuel which leads to a wide lean outer flame zone and these reasons contributed to hike in HC emissions of the diesel engine [99]. While using butanol additive to waste cooking oil biodiesel in direct injection diesel engine Isik et al. observed that there was an extended blow out region at far ends of the combustion chamber in which the unburnt fuel molecules accumulated and thus HC emission was increased. On the other hand, usage of biodiesel blend B20 reduced HC which is due to the enriched oxygen content of fuel [101]. Sanli et al. observed that at a peak speed of 1700 rpm of turbocharged ford cargo engine, HC emissions were 39.5 ppm, 25.2 ppm and 20.8 ppm for diesel, methyl ester biodiesel and ethyl ester biodiesel respectively. At high engine speeds, the lessened combustion duration contributes to more HC emission. On an average methyl ester and ethyl ester of waste cooking, oil biodiesel exhibited 29.36% and 38.29% less HC emission as compared to diesel fuel. Neat diesel addition to the methyl and ethyl ester reduced HC by 21.47% and 26.30% when compared to pure diesel fuel. Since combustion duration of ester fuels was relatively higher, more time was available to oxidize the fuel particles which reduced HC emission at exhaust [97]. Mikulski et al. found that increasing the percentage of swine lard methyl ester in fuel reduced HC emission. At the engine speed of 3000 rpm the corresponding reduction in HC values for B25, B50 and B75 blends were 25%, 56% and 54% as compared to neat diesel fuel. This tendency of HC emission was explained by the lower calorific value of biodiesel mixtures, lower self-ignition delay and higher oxygen content of the biodiesel components [124]. Alptekin et al. stated that fleshing oil biodiesel and its B20 blend reduced HC emission by 2.3% and 21.5% as compared to petro diesel. Meanwhile, chicken fat biodiesel showed an increase in HC about 9.2% and its B20 blend reduced HC by about 14.1% as compared to diesel fuel. It is worth to note that authors concluded that increasing bioethanol concentration had no impact on HC emission [78]. Gnanasekaran revealed that HC emission of the Kirloskar four stroke diesel engine was higher at 25% load irrespective of injection timings and fuel blends. At the injection timings 21°, 24°, 27° before TDC, fish oil biodiesel showed highest HC emission in the order of 0.20, 0.22 and 0.25 g/kWh where as pure diesel showed the elevation of 0.3, 0.32 and 0.33 g/kWh. Poor fuel distribution, excess air and low temperature at low loading conditions were the reasons stated by the author for the augmentation of HC emission [53]. Even though HC emissions are not directly related to speed and load rating of the

3.4. Carbon monoxide (CO) Carbon monoxide is the product of intermediate combustion of fuels which is produced by factors like lack of oxidants, ineffective mixing of air and fuel, insufficient time for post oxidation etc [93,97]. Reduced CO emission was observed by Satputaley et al. when algal oil and algal methyl ester was fuelled in a diesel engine under variable loading conditions. The prime reasons for lower emissions were said to be the enhanced oxygen content in the test fuel which converts CO to CO2 [67]. The enhanced oxygen content of about 10.37–12.25% and higher CN of biodiesel fuels improves combustion process which in turn reduces CO emission of algal and Jatropha biodiesel fuels. When compared to petro diesel, Jatropha and algal biodiesel reduce CO emissions by 32% and 27% respectively. In ETC, both biodiesel fuels showed lowest CO emission in a rural mode where engine load was lowest [65]. Usage of waste cooking oil biodiesel in an indirect injection diesel engine resulted in 33.28% increase in CO emission as compared to diesel fuel. Higher order alcohols addition to the biodiesel considerably increased CO emission at an average of 39.95%, 38.83% and 12.6% for propanol, butanol and pentanol. Pentanol addition improves higher local oxygen concentration in the cylinder which lowers CO formation when compared to other alcohol blends [100]. Pradhan et al. observed that using pure waste mustard oil biodiesel depreciated CO emission by 75% at low loads and 70.58% at high loads [126]. While using 5% waste frying oil biodiesel in a diesel power generator, CO emission shoots up whereas increasing the biodiesel fraction reduced emission rate [127]. Zare et al. used triacetin as an oxygenated additive along with waste cooking oil biodiesel in a diesel engine and reported that indicated specific CO emission increased at quarter load due to the high air fuel ratio and lean combustion of the fuel mixture. The authors also noted that at all other loading conditions exhibited lower CO emissions than petro diesel [102]. Zhu et al. fuelled diesel engine with waste cooking oil biodiesel-pentanol blends and observed that addition of oxygenated additive increases CO emission considerably. The reason of CO elevation was same as that of HC emission [99]. The higher oxygen content of butanol-waste cooking oil biodiesel blend eliminated fuel rich zones in the combustion chamber and thus reduced CO emission of a direct injection diesel engine [101]. Sanli et al. revealed that ethyl ester biodiesel emitted 28.84% and methyl ester biodiesel emitted 22.30% less CO when compared to petro based diesel fuel. While comparing the ester fuels, the ethyl ester of waste cooking oil showed superior characteristics by emitting 8% reduced CO emission as compared to methyl ester fuel. Higher air-fuel ratios and heating value of ethyl ester blend were stated as the reason for this variation in CO emission [97]. Mikulski et al. observed the highest CO reduction (47%) for the biodiesel blend B75 at 1500 rpm and lowest (16%) for B25 blend at 3000 rpm. At an engine speed of 1500, an average reduction in CO of 37%, 38% and 27% were found for B75, B50 and B25 blends respectively. For 3000 rpm engine speed, the average reductions of CO were found to be 30%,25% and 19% for B75, B50 and B25 respectively. Reduction of CO while using bio components was explained by the presence of oxygen, higher viscosity, density and mixture quality [124]. 2986

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emission of 2.08% higher than petro diesel where as ethyl showed only 1.86% hike. Also, the addition of 20% diesel to the ester blends increased CO2 emission by 0.64% and 0.92% for methyl and ethyl esters respectively. Higher CO2 emission of biodiesel fuels is attributed to higher oxygen and carbon contents of the test fuels when compared to the neat diesel [97]. Mikulski et al. analyzed the variations in CO2 emissions of a turbo charged 4 stroke CRDI diesel engine fuelled with swine lard biodiesel blends. At an engine load of 100 Nm and speed of 1500 rpm, authors observed a sharp fall in the CO2 emission of 6%, 3% and 2% for B75, B50 and B25 blends respectively. When the load was increased to 150 Nm, the average difference of emission was found to be 0.3% for all fuels. Meanwhile, for the speed of 3000 rpm, CO2 emission reduced by 6%, 3% and 1% for biodiesel mixtures B75, B50 and B25 respectively. Maximum reduction of 4% for B75 was found at an engine speed of 3000 rpm and 150 Nm load [124]. Alptekin et al. revealed that revealed that fleshing oil biodiesel, chicken fat biodiesel and their corresponding B20 blends showed augmented CO2 emission of 1.1%, 2.52%, 0.9% and 0.1% on an average when compared to neat diesel fuel. On the other hand, bioethanol addition had a negative impact on CO2 emission which showed decrement of 5.8% and 7.1% for B20 blend of both biodiesel fuel taken into consideration. This decrement was attributed to the poor C/H ratio of bioethanol [78]. Gnanasekaran predicted the CO2 emission of a Kirloskar engine using Fuzzy Interference System and observed the pure fish oil biodiesel showed highest CO2 emission at all injection timings as compared to its B20 blend. Mean CO2 emission for B100 varied as 0.46,0.42 and 0.39 g/ kWh for the injection timing of 21°,24°,27° before TDC respectively. Meanwhile, B20 blend of fish oil biodiesel showed diminished emission levels of 0.42, 0.38 and 0.34 g/kWh for the same corresponding injection timings. This elevation in emission levels was attributed to the higher oxygen content of the methyl esters which enhances the combustion efficiency [53]. Usage of biodiesel fuels maintains the closed carbon cycle which does not raise the CO2 levels in the atmosphere. Behçet et al. found that B25 of fish oil biodiesel showed lowest CO2 emission whereas diesel fuel showed the highest levels of emission. Also, maximum CO2 emission levels for all fuel blends were observed at an engine speed of 2000 rpm, after which the magnitude of emission deteriorates. At engine speeds there prevailed suitable conditions for combustion which produced higher CO2 emission [114]. Kalargaris et al. stated that plastic pyrolysis oil possesses C:H ratio of 10.34 which is higher than that of diesel (C: H = 6.47). Therefore the exhaust CO2 emission increased when using plastic oil in the fuel mixture [129]. Hossain et al. reported that CO2 emissions were similar for cooking oil biodiesel and its blend with de-inking sludge pyrolysis oil but higher by 4% than petro diesel fuel [130]. Mixed opinion has been recorded in the case of CO2 when the engine is fuelled with biodiesel blends. Some authors reported that CO2 levels elevated at exhaust [83,86,87,93,113,125] whereas few authors stated that emission levels decreased with addition of biodiesel [92,108–110].

In peak loading conditions, on compared with petro diesel, Alptekin et al. observed that fleshing oil biodiesel and chicken fat biodiesel showed 21% and 12% lower CO emission. Meanwhile, B20 of both biodiesel showed decrement of CO emission about 10% and 11% compared to neat diesel. Also with the addition of bioethanol concentration in biodiesel mixture, CO emission decreased slightly at higher loads due to the enhanced oxygen content of the bioethanol [78]. Gnanasekaran analyzed the effects of injection timings on CO emission when fuelled with fish oil biodiesel. The average emission was found to be lower at 21° bTDC for all test fuels. For fish oil biodiesel the amplification at 24°bTDC was found to be 21–34% whereas there was 18–25% hike at 27°bTDC when compared to the injection timing of 21° bTDC. This trend in CO was attributed to high heat release of the biodiesel fuels [53]. Behçet et al. found that CO emission of the Rainbow186 diesel engine was higher at low loads for all test fuels whereas at high speeds above 175 rpm there was a decline in CO magnitude about 16.54% for biodiesel fuels. The diminishing in the magnitude of emission was reported due to the higher oxygen content of biodiesel fuel mixtures [114]. Buyukkaya et al. reported that with increasing trout oil biodiesel percentage, CO emission levels drop as compared to diesel. The authors also noted that B50 showed CO reduction about 9% for low load and 17.2% for full load conditions. This trend was attributed to the prominent oxygen content of biodiesel and high C/H ratio of biodiesel fuel [111]. Due to the low cetane number of plastic pyrolysis oil, Ioannis Kalargaris et al. found that there was an increase in CO emission at all loading conditions which indicates the severe deterioration in combustion. But at peak engine loads the increase in CO was marginal for all the ratio of blending [129]. Due to the lack of oxygen content and lower carbon to oxygen ratio, de-inking sludge pyrolysis oil showed increased values of CO in exhaust. At higher loads the emission rates were higher than that of fossil diesel [130]. Many researchers reported that magnitude of CO levels in exhaust got reduced when the fuel contains fraction of biodiesel in it under all operating conditions [76,83,86–88,93,95,106–110,112,113,126]. Meanwhile very few research outcome stated that CO values showing upward trend with biodiesel addition [92,125] apart from above discussion. 3.5. Carbon dioxide (CO2) Carbon dioxide is one of the major green house gases whose formation is an indication of completeness of combustion and efficiency of combustion [87,124]. The tradeoff behaviour of CO and CO2 was observed by Piasy Pradhan et al. such that linear increase in CO2 was observed with respect to loading for all test fuels which represents uniformity in combustion [126]. de Paulo et al. reported that there was an elevation in CO2 emission with augmenting biodiesel fraction in the test fuel. B75 showed the highest value of CO2 emission compared to all test fuels [127]. Zare et al. experimentally investigated the emission characteristics of a diesel engine fuelled with waste cooking oil biodiesel and triacetin additive. The authors found that CO2 concentrations increase by increasing oxygen ratio, load and by decreasing engine speed. Pure waste cooking oil biodiesel with triacetin showed diminished CO2 emission by 2.5% as compared to diesel fuel [102]. The existence of sufficient oxygen in the combustion chamber and elevated post combustion temperature enhances the CO2 levels in engine exhaust which is a good sign of burning. Isik et al. conducted emission test on a 4 cylinder direct injection diesel power generator engine fuelled with waste cooking oil biodiesel-butanol blends. The authors observed a drop in combustion temperature while adding butanol additive which in turn caused in complete combustion of fuel and thus lowered CO2 emission [101]. Sanli et al. studied the variations in emission characteristics of methyl and ethyl esters of waste cooking oil biodiesel in a diesel engine. CO2 emissions showed decreasing trend from 10.16% to 9.1% and 10.06–9.14% for methyl ester and ethyl ester biodiesel fuels respectively when the engine speed was increased from 110 rpm to 1700 rpm. On comparing ester fuels, methyl ester showed predominate

3.6. Oxides of nitrogen (NOx) Nitrogen oxides are the most toxic pollutants from engines formed due to high flame temperature, reaction time and oxygen content of fuel [95]. A decreasing trend in NOx was observed by Satputaley et al. with the use of algal oil and its methyl ester at all loading condition. The maximum decrease of 38 ppm and 21 ppm at 5.15 kW brake power was observed for micro algal oil and its methyl ester respectively [67]. Jayaprabakar et al. reported that advancing injection timing enhances the NOx formation for Gracelariaverrucossa and rice bran biodiesel and retarding injection timing significantly reduces the NOx formation. But still, the NOx values of biodiesel fuels were higher than diesel fuel at all conditions [122]. Lower Iodine number and oxygen content of Chlorella variabilis biodiesel diminish NOx value 17% lower than Jatropha biodiesel at standard testing conditions. In ETC analysis, algal biodiesel showed least NOx emissions under all driving conditions. Also, algal 2987

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with reference to B20 blends at lower engine loads. This trend was attributed to the cooling effect and latent heat of vaporization of ethanol [78]. Gnanasekaran found that B20 blend of fish oil biodiesel exhibited lowest NOx rating due to its lower calorific value and higher viscosity which reduced pre mixed combustion and lowered peak temperature [53]. Behçet et al. reported that NOx emission of fish oil and cooking oil methyl ester fuels were higher than that of diesel fuel in all conditions. It was also noted that NOx readings increased up to the engine speed of 2000 rpm after which a drop in NOx observed by the authors which was attributed to the insufficient combustion duration. While comparing both ester fuels, it was concluded that animal fat based biodiesel produced less NOx as compared to vegetable oil based biodiesel fuels [114]. As the fish oil content increased in the test fuels Buyukkaya et al. observed 10–30% increase in NOx across the loading range. Increased oxygen content of biodiesel elevated the gas temperature during combustion which promoted NOx evolution at high levels [111]. Kalargaris et al. found that NOx emissions of the diesel engine were higher as the percentage of plastic pyrolysis oil increased in the fuel mixture. This increasing trend was attributed to the longer ignition delay of the pyro oil fuel blends which results in accumulation of high fractions of fuel in premixed combustion phase [129]. Hossain et al. reported that the presence of water content in de-inking sludge pyrolysis oil-waste cooking oil biodiesel blend reduced the combustion temperature which in turn curbs the NOx emission at exhaust [130]. As the above mentioned results strongly correlate NOx with combustion temperature,most of the research outcome states that biodiesel addition increases NOx emission [86–88,93,95,106–108,110,112,125] whereas some research proves that NOx emission showed variable behaviour based on the operating conditions [76,83,92]. But very few peculiar results have been noted which agrees with the reduction in NOx with biodiesel addition [67,113].

biodiesel showed superior NOx reduction in urban mode which is 2.61% and 1.17% lower than rural mode and motorway mode respectively [65]. Atmanli reported that waste cooking oil biodiesel and its 50% blend reduced NOx emission in a naturally aspirated indirect injection diesel engine by 1.68% and 9.74% as compared to conventional petro diesel. This decrement in NOx was attributed to lower cetane number of test fuels and ignition delay which forces hot gases to stay in the cylinder at high temperature to form less NOx. It was also found that addition of longer chain alcohols reduced NOx emissions within the range of 27.44%, 19.27% and 15.05% for pentanol, butanol and propanol as compared to 50% biodiesel blend. The reason for this trend was found to be the lower cetane rating of alcohols [100]. Pradhan et al. studied the emission characteristics of diesel engine fuelled with waste mustard oil biodiesel. It was found that pure biodiesel showed maximum NOx emission compared to other test fuels. Among the biodiesel blends, authors suggested B10 as environmentally benign fuel because of its least NOx emission values ranges from 100 to 200 ppm [126]. de Paulo et al. reported that usage of waste frying oil biodiesel in a diesel power generator reduced NOx and NO emissions between B5 and B50 blending ratios whereas, after 50% addition of biodiesel, there was an increasing trend of NOx observed [127]. Zare et al. found that NOx emission highly depends upon oxygen ratio, engine load and speed. Pure waste cooking oil biodiesel and its additive blends showed dominating NOx values except at 75% loading. The highest variation observed at full loading conditions in which NOx of oxygenated fuel blends is 19–31% higher than that of neat diesel fuel. This increased trend of NOx was attributed to the enhanced oxygen content of biodiesel fuels which on complete mixing at pre mixed combustion phase leads to higher in-cylinder temperature [102]. Zhu observed that 10% and 20% addition of pentanol to waste cooking oil biodiesel reduces NOx emission where as 30% addition increased the magnitude of NOx when tested in a naturally aspirated direct injection four cylinder diesel engine. The variations in emission characteristics were attributed to lower cetane number, oxygen content and elevated latent heat of vaporization of test fuels [99]. NOx production when using a biodiesel fuel can be retarded by curbing the combustion temperature. Isik et al. stated that using B20 blend of waste cooking oil biodiesel in a diesel engine leads to more NOx emission and it was due to the fact that biodiesel possessed more oxygen content. The authors used butanol additive to reduce NOx and got succeeded in their attempt because of the reduction in cylinder temperature. It is worth to note that authors also reported that iodine number and cetane number of the biodiesel contributes to higher NOx emission of biodiesel fuel [101]. Sanli et al. observed that NOx emission of a turbocharged Ford engine increased up to the speed was increased to 1400 rpm where after that NOx values diminished. The ester fuels and their blends showed elevated NOx at all loading conditions as compared to diesel fuel. On an average of 11.32%, 10.8%, 3.13% and 3.03% increase in NOx emission were observed for methyl ester, ethyl ester and their corresponding 20% diesel blending respectively. This increased trend in NOx was attributed to the higher oxygen content of test fuels from high air fuel ratios, viscosity, density, iodine number and lower cetane rating of test fuels [97]. While using swine lard methyl esters in a turbocharged diesel engine Maciej Mikulski et al. found that NOx emission increased with respect to loading conditions for all test fuel blends. For B50 blends, an increase of NOx emissions by 12.5%, 5.6% and 15% was observed at 1500 rpm under 150 Nm, 100 Nm and 50 Nm respectively. For the same conditions, an increase of 22%, 10% and 12% was observed for the B75 blend. This upward trend in NOx was attributed to elevated combustion pressure and the temperature inside combustion chamber [124]. Alptekin et al. showed that NOx emission of chicken fat biodiesel and fleshing oil biodiesel were 16% and 15.2% higher than that of petro diesel on an average. Enriched oxygen content, early start of fuel injection and higher cylinder pressures of the biodiesel fuel usage were the reason quoted by authors for the elevated levels of NOx in the exhaust. The results also proved that bioethanol addition lessened the NOx emission

3.7. Smoke and Particulate matter (PM) Smoke and PM emissions are the sign of inefficient combustion where as PM emission has three components namely Sulphates, heavy hydrocarbon absorbed or condensed on soot [86]. Due to the oxygenated nature of the algal oil and its methyl ester smoke opacity of the engine got reduced at all loads [67]. The decrease in smoke opacity was observed when advancing the injection timing of a diesel engine fuelled with Gracelariaverrucossa and rice bran methyl ester. This gradually declining pattern was observed due to the oxygen content of fuel which enhances the combustion process [122]. Singh et al. observed that algal biodiesel and Jatropha biodiesel in a DI-diesel engine reduces PM emissions by 23% and 50% respectively when compared to petro diesel. It was attributed to the enhanced oxygen content of biodiesel fuel which enhances the combustion process and also due to the negligible sulphur content of test fuels [65]. Zare et al. reported that diffusion flame combustion, oxygen ratio and engine load are the major parameters that govern the magnitude of PM emission in a CI engine. Neat diesel with zero oxygen content exhibited peak PM emission where as lowest emission was recorded by the highly oxygenated (14.23%) triacetin blended biodiesel fuel. Since the oxygenated fuels help the soot oxidation process and trim down the local fuel rich zone within spray cone, the PM formation was reduced during combustion process [102]. Zhu et al. showed that pentanol addition to biodiesel fuel considerably reduced PM at medium and high loads due to the enriched oxygen content of the biodiesel blend. Also, the adequate time for airfuel mixing in the case of oxygenated fuel leads to a diminution of primary soot particle formation. On the other hand addition of pentanol produces free radicals like OH, H, O which encourages oxidation and suppresses soot precursor formation [99]. Cheung et al. investigated the particulate mass emissions of a 4 cylinder direct injection diesel engine fuelled with waste cooking oil biodiesel and its blends. It was found that oxygen content of biodiesel reduced soot precursors even at high loading conditions thereby reduced PM emissions [96]. Mikulski et al. 2988

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performance and emission evaluation of algal fuels and biomass pyrolysis fuels. Moreover, research should be focussed on the modern combustion strategies like homogeneous charged compression ignition and low-temperature combustion in diesel engine fuelled with biodiesel and its blends. As far as literature reviewed, it is concluded that there is a wide research opportunity in the engine analysis of third generation biofuels.

observed the highest reduction of opacity on an average of 76% and 73% at an engine speed of 1500 pm and 3000 rpm respectively for B75 blend [124]. Gnanasekaran stated that magnitude of smoke depends on the availability of oxygen, combustion quality and made of mixture formation. It was also found that smoke increased by 2–8% at 21°bTDC and decreased by 4–8% at 27°bTDC as compared to 24°bTDC for pure fish oil biodiesel. This lessening in smoke with respect to the advancing of injection timing was attributed to the dominance of premixed combustion phase [53]. Behçet et al. found that smoke opacity levels were found high for diesel fuel and it decreased for biodiesel fuels. Fish oil and cooking oil methyl esters showed a drop in the smoke opacity of 15.36% and 7.81% on an average as compared to diesel fuel. This decrement was attributed to the enrichment of oxygen in biodiesel fuel which compensated the oxygen deficiency in fuel rich zones [114]. While fuelling diesel engine with trout oil biodiesel in concentrations of B50, B40, B20 and B10 Buyukkaya et al. observed a reduction in smoke levels by 60.5%, 29%, 17.3% and 6.2% respectively. Complete fuel oxidation at fuel rich zones in the combustion chamber for biodiesel fuel lead to the reduction of smoke levels at exhaust [111]. Regardless of the above results, some authors have reported elevated smoke readings with biodiesel addition [83,113] but most of the other research results strongly state that smoke and particulate matter in engine exhaust reduced with biodiesel addition to the test fuels [76,83,86,88,93,106,108,112,113].

5. Conclusion In general, biodiesel is an environmental friendly biodegradable alternative fuel that can be used directly in the engine without any major engine modification. By the process of depletion of the floral resources in recent decades, third generation biofuels grab the attention of the world energy community. An in-depth analysis of the fuel properties and its impact on the engine characteristics has been discussed. Biofuels derived from various feedstocks showed promising variations in its physicochemical properties due to its fatty acid compositions. This variation in properties affects the engine performance and emission characteristics considerably. Neat biodiesel and its blends in various proportions reduced unwanted toxic emissions like HC, CO and smoke where as it augmented the emissions like CO2 and NOx. In performance point of view biodiesel still, stands on the negative side by reducing thermal efficiency and increasing the fuel consumption rates. Furthermore, attention should be given to the operating conditions and design parameters of the engine to revert the setbacks of the biodiesel fuels. The ultimate verdict can be given to the third generation biodiesel side is that utilization of biodiesel proves economically feasible solution in the current circumstances, it also conserves the environment and it saves floral lives which are the nature's gift to mankind.

4. Summary of the review and scope for further research Biodiesel production from sources other than flora grabs the attention of the researchers in recent decades. Especially the fuel derived from garbage leads to the sustainable economic development of the community. Therefore research in recent days is focused on the biofuels properties, performance and emission aspects. In order to make a better clarity in the existing scenario of the so called third generation biofuels the following general summary can be drawn: Biodiesel derived from the third generation feedstocks possess physicochemical properties close to the reference diesel fuel which has been measured by standards like EN and ASTM. Very few biofuels deviate from the prescribed range specified from the biodiesel standards, however, these fuels will not significantly deteriorate the engine performance and emission. A detailed review of the important physicochemical properties of the third generation biofuels has been discussed which can give a brief outline of the fuel quality and feasibility to use in a diesel engine. The use of biodiesel fuel in engine widely reduce the thermal efficiency of the engine due to the lower heating value of the biodiesel and its viscosity which limits its proportion to be blended with diesel. Also, another performance parameter which is severely affected by utilizing biodiesel is brake specific fuel consumption. Most of the conclusions from experimental trials implicate that biodiesel usage increases the fuel consumption due to its viscous nature and oxygen content. It is commonly accepted that biodiesel utilization reduces the toxic CO and HC emissions at engine exhaust. Due to the enriched oxygen content and elevated combustion temperature CO gets converted to CO2 whereas the HC particles get oxidized completely. On the other hand, the same reasons lead to the elevated NOx emissions in the biodiesel fuelled engine which is widely concluded by most of the researchers. Other reasons attributed to the NOx elevation are higher cetane number, iodine number of the biodiesel fuels. Due to the complete oxidation of soot precursors and elimination of local fuel rich zones, reduces smoke and PM emission in the biodiesel fuelled engine. Contradictorily very few researchers claimed inverse trending of the above said exhaust emission. Overall, blends of the third generation biodiesel with diesel proved a technically feasible source of alternative fuel for diesel engines. Even though a number of researches have been carried out in various third generation sources, very few researches have been carried out in

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