Energy Conversion and Management 80 (2014) 202–228 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman Review Production and comparison of fuel properties, engine performance, and emission characteristics of biodiesel from various non-edible vegetable oils: A review A.M. Ashraful ⇑, H.H. Masjuki, M.A. Kalam, I.M. Rizwanul Fattah, S. Imtenan, S.A. Shahir, H.M. Mobarak Centre for Energy Sciences, Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia a r t i c l e i n f o Article history: Received 28 October 2013 Accepted 21 January 2014 Available online 13 February 2014 Keywords: Biodiesel Non-edible oils Fuel properties Performance Emission Renewable energy a b s t r a c t Energy demand is increasing dramatically because of the fast industrial development, rising population, expanding urbanization, and economic growth in the world. To fulfill this energy demand, a large amount of fuel is widely used from different fossil resources. Burning of fossil fuels has caused serious detrimental environmental consequences. The application of biodiesel has shown a positive impact in resolving these issues. Edible vegetable oils are one of the potential feedstocks for biodiesel production. However, as the use of edible oils will jeopardize food supplies and biodiversity, non-edible vegetable oils, also known as second-generation feedstocks, are considered potential substitutes of edible food crops for biodiesel production. This paper introduces some species of non-edible vegetables whose oils are potential sources of biodiesel. These species are Pongamia pinnata (karanja), Calophyllum inophyllum (Polanga), Maduca indica (mahua), Hevea brasiliensis (rubber seed), Cotton seed, Simmondsia chinesnsis (Jojoba), Nicotianna tabacum (tobacco), Azadirachta indica (Neem), Linum usitatissimum (Linseed) and Jatropha curcas (Jatropha). Various aspects of non-edible feedstocks, such as biology, distribution, and chemistry, the biodiesel’s physicochemical properties, and its effect on engine performance and emission, are reviewed based on published articles. From the review, fuel properties are found to considerably vary depending on feedstocks. Analysis of the performance results revealed that most of the biodiesel generally give higher brake thermal efficiency and lower brake-specific fuel consumption. Emission results showed that in most cases, NOx emission is increased, and HC, CO, and PM emissions are decreases. It was reported that a diesel engine could be successfully run and could give excellent performance and the study revealed the most effective regulated emissions on the application of karanja, mahua, rubber seed, and tobacco biodiesel and their blends as fuel in a CI engine. Ó 2014 Elsevier Ltd. All rights reserved. Contents 1. 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1. Current energy scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Resources of non-edible vegetable oils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Biology, distribution, and chemistry of the selected non-edible sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1. Karanja . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.2. Polanga . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.3. Mahua . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.4. Rubber seed oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.5. Cotton seed oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.6. Jojoba oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.7. Tobacco oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.8. Neem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ⇑ Corresponding author. Tel.: +60 1 02577943; fax: +60 3 79675317. E-mail address: alam.ashraful31@gmail.com (A.M. Ashraful). http://dx.doi.org/10.1016/j.enconman.2014.01.037 0196-8904/Ó 2014 Elsevier Ltd. All rights reserved. 203 203 205 205 205 205 205 205 205 206 206 206 203 A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 3. 4. 5. 6. 7. 8. 2.1.9. Linseed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.10. Jatropha. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fuel properties of various non-edible biodiesels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Kinematic viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Flash point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4. Cloud point and pour point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5. Cetane number (CN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6. Calorific value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fatty acid composition of various non-edible oils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Engine performance of a diesel engine using non-edible vegetable biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1. Karanja biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2. Polanga biodiesel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3. Mahua biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4. Rubber seed biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5. Cotton seed biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6. Jojoba oil biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7. Tobacco oil biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.8. Neem biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.9. Linseed oil biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.10. Jatropha biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Engine emission performance when non-edible vegetable biodiesel is used in a diesel engine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1. Karanja biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2. Polanga biodiesel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3. Mohua biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4. Rubber seed oil biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5. Cotton seed biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6. Jojoba oil biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7. Tobacco oil biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8. Neem biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.9. Linseed oil biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.10. Jatropha biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion and summary of results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 207 207 207 207 207 207 207 208 208 208 208 210 210 210 213 213 213 214 214 214 216 216 216 216 218 218 220 220 220 225 225 225 225 226 226 1. Introduction Since the industrial revolution, different forms of energy have become essential for human beings to maintain a standard of living and to conserve economic growth. In the past few decades, fossil fuels, mainly petroleum-based liquid fuels, natural gas and coal, have played an important role in fulfilling this energy demand. However, because of their non-renewable nature, these fossil fuels are projected to be exhausted in the near future. This situation has worsened with the rapid increase in energy demand with significant worldwide population growth. Therefore, the demand for clean, reliable, and yet economically feasible renewable energy sources has led researchers to search for new sources. In this context, biodiesel derived from vegetable oil has drawn attention as a potential alternative for diesel fuel for diesel engines. 1.1. Current energy scenario Gobal energy demand is increasing dramatically because of rising population. In 1980, fuel consumption was 6630 million tons of oil equivalents (Mtoe). It almost doubled in 2012 at 12,239 Mtoe, as shown in Table 1 [1]. According to the International Energy Agency estimation, global energy demand is expected to increase by 53% by 2030. Currently, a major part of energy demand (88.6%) is fulfilled by fossil fuels, in which crude oil accounts for 33.7%, coal for 30.5%, and natural gas for 24.4% [2]. Conversely, nuclear energy and hydroelectric energy contribute only small proportions at 4.6% and 6.8%, respectively. Over the past 25 years, total energy supply has increased steadily. However, with the cur- Table 1 World primary energy consumption and percentage of share [1]. Source Petroleum Coal Natural gas Nuclear Hydropower Total 1980 2012 Mtoe Share (%) Mtoe Share (%) 2979.8 1807.9 1296.8 161 384.3 6629.8 44.9 27.3 19.6 2.4 5.8 100 4130.5 3730.1 2987.1 560.4 831.1 12239.2 33.7 30.5 24.4 4.6 6.8 100 rent consumption rates, the reserves of crude oil and natural gas will diminish after approximately 41.8 and 60.3 years, respectively. The total primary fuel consumption was estimated to reach approximately 12,239 Mtoe in 2012; the estimate is 70% higher than that in 1987, as shown in Fig. 1 [1]. Globally, we consume the equivalent of more than 11 billion tons of oil in fossil fuel every year. Crude oil reserves are vanishing at a rate of 4 billion tons a year. If this rate continues, oil deposits will be exhausted by 2052 [3]. However, if increased gas production can fills up the energy gap left by oil, then those reserves will give an additional backup of eight years until 2060. The world has enough coal reserve to a last century, but production is necessary to fill the gap caused by depleting oil and gas reserves. Coal deposits will give us enough energy to last as long as 2088. Moreover, the rate of energy consumption in the world is not steady, as it increases dramatically with the increase in global population and living 204 A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 Fig. 1. World’s primary energy consumption [1]. standards. Therefore, fossil fuel stock will run out in the near future. Fig. 2 shows the global energy reserves for coal, gas, and oil and marks the point at which fossil fuel could run out in the future. Consequently, the world is moving toward an energy crisis, driving the world to look for alternatives [4–6]. Many renewable energy sources have drawn the attention of researchers. Among these sources, biodiesel is the most popular choice. Biodiesel is derived from renewable resources that can be produced by a simple chemical process using edible, non-edible, waste vegetable oils and animal fats. Biodiesel is usable in diesel engines in pure form or by blending it with petroleum diesel. Biodiesel is environment friendly and non-toxic, and it emits lesser pollutants [7–9]. Many potential feedstocks are available for biodiesel production. Currently, more than 95% of biodiesel produced globally is from edible vegetable oil because of its abundant agricultural production [10]. The various types of edible vegetable oils and biodiesel as substitutes for conventional fuels are considered in many countries depending on the climate condition. For instance, palm oil in Southeast Asia, soybean oil in the United States, coconut oil in the Philippines, and rapeseed and sunflower in Europe are being Fig. 2. World’s energy reserves for coal, gas, and oil [3]. produced [4]. Although biodiesel produced from edible vegetable oil has many advantages, it also has disadvantages, such as inferior storage and oxidation stability, high feedstock cost, low heating value and higher NOx emission compared with diesel fuel. Moreover, 60–80% of biodiesel production cost depends on feedstock cost [11,12]. The use of edible oils for biodiesel production may lead to a self-sufficiency problem in vegetable production. The use of non-edible vegetable oils is significant because edible oil is necessary as food. The demand for both food and biofuel has increased rapidly because of population growth. To minimize the reliance on edible vegetable oil feedstocks for biodiesel production, alternative sources, such as non-edible feedstocks, have been sought for biodiesel production. The use of nonedible vegetable oils compared with edible vegetable oils is significant in developing countries because of the tremendous demand for edible vegetable oils as food; these edible vegetables oils are expensive for biodiesel production [13]. Globally, a huge amount of non-edible vegetable oil plants is naturally available [14]. Energy crops such as Jatropha curcas, Maduca indica, Pongamia pinnata, Simmondsia chinesnsis, Linum usitatissimum, Nicotianna tabacum, Calophyllum inophyllum, Hevea brasiliensis, Corton megalocarpus, Carmellia, Simarouba glauca, Desert date, Alagae, Sapindus mukorossi etc. represent second-generation biodiesel feedstocks. Biodiesel production from non-edible feedstock-based oils has been extensively investigated over the past few years. Non-edible vegetable oil is not suitable for human consumption because of the presence of toxic components in these feedstocks. Furthermore, non-edible vegetable oil crops are grown in wastelands, and their cultivation cost is much lower than that of edible vegetable oil crops because intensive care is not required to sustain a reasonably high yield [15]. As wastelands are not suitable for edible crop cultivation, this review focuses on biodiesel produced only from non-edible vegetable oils as alternative fuel. Reviewing the existing reviews on the selection of non-edible oils for possible alternative diesel fuel is essential. M. Balat [16] reviewed potential alternatives to edible oils for biodiesel production and selected five sources of non-edible vegetable oils. These sources are jatropha, karanja, rice bran oil, microalgae, mahua, and selected waste cooking oil and animal fats. A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 In a review of oil production, vegetable oils, and their methyl ester characterization as alternatives to diesel fuel [7], four nonedible vegetable oils, namely, jatropha, karanja, polanga, and rubber seed oils, were suggested as sources for biodiesel production. Silitonga et al. [17] recently reviewed the general properties of biodiesel blend from edible and inedible feedstocks, such as palm oil, Alurietas mollucana, Jatropha curcas, Sterculiafoetida, Calophyllu inophyllum, Ceiba pentandra, Cerbere manghas, Pangium edule and Hevea brasilinensis, as potential alternatives to diesel fuel. They recommended that these fuel meet the biodiesel standards of US ASTM D 6751 and European EN 14214. Moreover, they found that jatropha and karanja vegetable oils are suitable for used in cold climate conditions compared with other vegetable oils. In a critical review of biodiesels, Balat et al. [18] found that more than 350 oilseed crops have been indentified. They argued that edible oils such as rapeseed, soybean, sunflower, peanut, and safflower are potential alternative sources of diesel fuel for diesel engines. They also recommended other non-edible vegetable oils such as jatropha, tobacco, karanja, rice bran, rubber seed, and mahua. However, only jatropha, karanja, and mahua oils were briefly explained in this review on the progress in biodiesel processing. A recent review discussed the sources of non-edible vegetable oils, as well as their production and characterization, as sustainable petroleum diesel fuel [19] and the performance of non-edible oils as sources of fuel. Moreover, 15 oilseed crops were recommended as sources of biodiesel in India. Non-edible vegetable oils have high potential for biodiesel production. Olivera et al. [15] identified nine vegetable oils and examined their fuel properties and biodiesel production methods. They found that biodiesel production using jatropha, karanja, mahua, and castor oil is commonly used in biodiesel synthesis. Based on the review works considered in this study, several trees that are naturally available can be exploited for the production of sustainable fuel for petrodiesel engine. The raw materials of the biofuel being exploited commercially and scientifically by several researchers are the non-edible oils derived from jatropha, mahua, karanja, rubber seed, linseed, neem, tobacco seed, polanga, cotton seed, castor, jojoba, moringa, poon, desert date, crambe, mango and so forth [6,8,9,20]. The selection of non-edible oils as possible fuel for use in a diesel engine is based on the literature. Some of the non-edible vegetable oils that are promising substitutes for petroleum diesel and the acceptable non-edible biodiesel feedstocks for biodiesel production include karanja, polanga, mahua, rubber seed, cotton seed, Simmondsia chinensis (jojoba), tobacco, neem, linseed, Jatropha carcus, and so on [20–25]. The objective of this paper is to present the various sources of non-edible oils that can replace edible oils and fossil fuels for biodiesel production as well as their fuel properties. This study also compares their physicochemical properties, engine performance, and emission characteristics in a diesel engine through a review and discussion. 2. Resources of non-edible vegetable oils Non-edible oils have several advantages over edible oils. Nonedible oils possess toxic components that make them unsuitable [26]. The use of non-edible oils for biodiesel production solves the food-versus-fuel concern and other issues [27]. Moreover, unproductive lands, degraded forests, cultivators’ fallow lands, irrigation canals, and boundaries of roads and fields can be used for the plantation of non-edible oil crops. Biodiesel development from non-edible oil can become a major poverty alleviation program for the rural poor apart from providing energy security for the masses. This development can upgrade the rural non-farm sector and help in the sustainable biodiesel production. Many researchers have recommended non-edible oils to be a sustainable alternative to 205 edible oils for biodiesel production [6,28–31]. Researchers have identified several non-edible crops that can be used for biodiesel production [28,32]. Fig. 3 shows the various non-edible vegetable oil feedstocks for biodiesel. 2.1. Biology, distribution, and chemistry of the selected non-edible sources 2.1.1. Karanja Karanja is a medium-sized green tree from the legumnosae family. It grows approximately 15–25 m in height. Flowering starts three to four years after plantation, and it matures four to seven years after. Recently, karanja has been recognized as an invaluable source of oil. A single tree is said to yield 9–90 kg of seeds. Several researchers have discovered the large variability of oil content in karanja seed oil. The seed contains approximately 25–40 wt.% oil [16,36–38]. Karanja mainly grows in Southeast Asia and has been successfully introduced in humid tropical regions of the world and part of China, the United States, and Australia [39,40]. Karanja oil mainly contains oleic acid (44.5–71.3%), followed by linoleic (10.8–18.3%) and stearic acids (2.4–8.9%) [41–43]. 2.1.2. Polanga Polanga is a large- or medium-sized green tree that grows in deep soil or on exposed sea sand. It belongs to the Clusiaceae family. The rainfall requirement of polanga seed plantation is 750 mm/ year to 5000 mm/year. The tree has multiple origins, such as Southeast Asia, India, East Africa, and Australia [36,39,44,24,45]. Its growth rate is 1 m in height, and it yields approximately 100 fruits/kg to 200 fruits/kg. Oil yield per unit area is approximately 2000 kg/ha (cite). The seed has a high oil content of 65–75 wt.%. The oil is thick and nutty smelling [5,44,24,45,46], and it contains mainly unsaturated fatty acids, that is, approximately 34.09– 37.57% oleic acid and 26.33–38.26% linoleic acid. Saturated acids, such as stearic (12.95–19.96%) and palmitic (12.01–14.6%) acids, can also be found in this oil [47,48]. 2.1.3. Mahua Mahua is a large-sized evergreen or semi-evergreen tree from the Sapotaceae family. Mahua is a forest-based tree largely produced in India [4,16,49,50]. It is cultivated in warm and humid regions for its oleaginous seeds (producing 20–200 kg of seeds annually per tree, depending on maturity), flowers, and wood. Mahua oil fat (solid at ambient temperature) has been used in skin care and in manufacturing soap or detergents. The mahua tree starts producing seeds 10 years after plantation and continues to do so up to 60 years. Tree growth is approximately 20 m in height, and its seed has an oil content of 35–50 wt.% [16,24,50,51]. Mahua oil contains approximately 41–51% oleic acid. Other fatty acids are also present in the oil, such as stearic (20.0–25.1%), palmitic (16.0– 28.2%), and linoleic acids (8.9–18.3%) [52–54]. 2.1.4. Rubber seed oil Rubber seed oil comes from the Euphorbiaceae family. This tree originates from Brazil. It is a forest-based tree largely produced in Malaysia, India, Thailand, and Indonesia. In the wild, plant height can reach up to 34 m [55]. The tree requires heavy rainfall and non-frost climate condition. Rubber seed contains 50–60 wt.% oil, and its kernel contains 40–50 wt.% of brown oil [4,39,24,56]. Rubber seed oil is high in unsaturated constituents, such as 39.6–40.5% linoleic acid, 17–24.6% oleic acid, and 16.3–26% linolenic acid [55,57]. 2.1.5. Cotton seed oil Cotton seed oil is extracted from the seeds of the cotton plant of various species, mainly Gossypium hirsutum and Gossypium herba- 206 A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 pongamia pinnata (karanja) calophyllum inophyllum (polanga) madhuca indica (mahua) hevea brasiliensis (rubberseed) cotton seed simmondsia chinensis (jojoba) nicotiana tabacum (tobacco) azadirachata indica (neem) Linseed Jatropha Fig. 3. Various non-edible vegetable oil feedstocks for biodiesel [24,33–35]. ceum, which are grown for cotton fiber. Cotton plant grows mainly in China, the United States, and Europe. Crude cotton seed oil contains several types of non-glyceride materials, such as gossypol, phospholipids, sterols, resins, carbohydrates, and related pigments. Cotton seed oil has a density that ranges from 0.917 g/cm3 to 0.933 g/cm3. The seed contains 17–25 wt.% oil. The fatty acid composition of cotton seed oil is mainly linoleic (55.2–55.5%), palmitic (11.67–20.1%), and oleic acids (19.2–23.26%) [58–60]. 2.1.6. Jojoba oil Jojoba is native to the Mojave and Sonoran deserts of California, Arizona, and Mexico. The jojoba tree is from the Simmondsiaceae family. Jojoba has been grown commercially for its oil, a liquid wax ester, extracted from the seed. The plant has been used to combat and prevent desertification in some parts of India. The jojoba tree grows to a height of 1–2 m, and it has a broad and dense crown. The leaves are oval in shape, approximately 2–4 cm long and 1.5–3 cm broad; they are thick, waxy glaucous grayish green [61,62]. The seed contains approximately 40–50 wt.% oil [63] with a fatty acid composition of 43.5–66% oleic acid and 25.2–34.4% linoleic acid [24,63,64]. 2.1.7. Tobacco oil Tobacco belongs to the Solanaceae family, and it is cultivated in several countries worldwide, such as Turkey, Macedonia, North America, South America, India and Russia [37,65,66]. The tree is commonly grown for leaf collection. The physical and chemical properties of tobacco oil are comparable with those of other vegetable oils, and tobacco is considered a new potential feedstock for biodiesel production [66–68]. The seed contains approximately 35–49 wt.% oil with fatty acid composition of 69.49–75.58% of linoleic acid [67,69]. 2.1.8. Neem Neem is a medium-sized evergreen tree from the Meliaceae family. The tree grows 12–18 m in height. The neem tree can grow in all kinds of soil, including saline, clay, dry, shallow, alkaline, and stony soils, and even in highly calcareous soil. Neem grows in several Asian countries, such as Sri Lanka, Pakistan, India, Bangladesh, Japan, Malaysia, Indonesia, and Burma, and in the tropical regions of Australia. Normally, neem thrives in areas with sub-arid to subhumid conditions and with an annual rainfall of 400–1200 mm. It reaches a maximum productivity of 15 years after plantation, with a life span of approximately 150–200 years. Neem seed contains 20–30 wt.% oil, and its kernels contain 40–50% brown oil [24,36,39,70]. Neem oil has high-unsaturated constituents, such as linoleic acid (6–16%) and oleic (25–54%) acid, and saturated oil like stearic acid (9–24%) [71,72]. 2.1.9. Linseed Linseed is an herbaceous annual-type plant that grows in countries such as India, Canada, Argentina, and some parts of Europe. Linseed contains 35–45 wt.% oil and is high in unsaturated constituents, such as linoleic (13.29–14.93%), oleic (20.17–24.05%), and linolenic acids (46.10–51.12%). Other fatty acids found in linseed oil include saturated species such as stearic (5.47–5.63%) and palmitic (5.85–6.21%) acids [73,74]. 207 A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 2.1.10. Jatropha Jatropha is a small tree from the Euphorbiaceae family, and it grows 5–7 m in height [23,28,30,75–77]. Jatropha thrives in arid, semi-arid, and tropical areas with an annual rainfall of 1000–1500 mm. The jatropha plant is native to the United States, Brazil, Bolivia, Argentina, Mexico, Africa, Paraguay, and India [23,28,36,24,78]. The jatropha seed contains 20–60 wt.% oil. Jatropha produces seeds after 12 months of plantation, reaches maximum productivity by 5 years, and can live for 30 years to 50 years [29]. Jatropha oil contains mainly unsaturated constituents, such as linoleic (31.4–43.2%) and oleic acids (34.3–44.7%), and some unsaturated species, such as stearic (7.1–7.4%) and palmitic acids (13.6–15.1%) [79,80]. of fuel has been proved to decrease with the increase in temperature. Kinematic viscosity is determined using the ASTM D445 and EN ISO 3104 test methods [91]. Table 2 shows that some non-edible biodiesels, such as jojoba, neem, and linseed, have high viscosity that ranges from 19.2 mm2/s to 25.4 mm2/s, 20.5 mm2/s to 48.5 mm2/s, and 16.2 mm2/s to 36.6 mm2/s, respectively, which are higher than that of diesel fuel [86–89,92]. However, the viscosity of jatropha, tobacco, and mohua biodiesels ranges from 3.7 mm2/s to 5.8 mm2/s, 3.5 mm2/s to 4.23 mm2/s, and 3.98 mm2/ s to 5.8 mm2/s, respectively, which are close to that of diesel at 2.5–5.7 mm2/s [66,68,93–96]. Therefore, these biodiesels can give better atomization and provide improved combustion than others. 3.3. Flash point 3. Fuel properties of various non-edible biodiesels Density, viscosity, flash point, cetane number, cloud and pour point, and calorific value, among others are the most important fuel properties considered in the application of non-edible biodiesels in diesel engines. Many researchers have reported that fuel properties of non-edible biodiesels vary depending on their fatty acid and chemical composition [51,69,81–83]. Therefore, before using non-edible-based biodiesels in diesel engines, measuring the fuel properties of selected biodiesels is necessary. The fuel properties of biodiesels are specified by different standardization organizations; the ASTM D6751 and EN14214 are the most popular standards for biodiesel. Fuel properties of various non-edible biodiesels are shown in Table 2. The following section discusses the fuel properties of the reviewed biodiesels. Flash point is the most important property that must be considered in assessing the overall flammability hazard of a material. At this temperature, vapor stops burning if the source of ignition is removed. Each biodiesel has its own flash point. Many factors affect the change in biodiesel flash point, with residual alcohol content being one of them [97]. Moreover, flash point is influenced by the chemical compositions of the biodiesel, including the number of double bonds, number of carbon atoms, and so on. [98]. The flash point of biodiesel is measured using the ASTM D93 and EN ISO 3697 test methods [85]. Table 2 shows that biodiesel has a higher flash point than diesel fuel. The ASTM D6751 standard recommends a minimum flash point of 130 °C for biodiesel, as clearly illustrated in Table 2. With the exception of neem, linseed, and jojoba, all biodiesels meet the ASTM specification. 3.1. Density 3.4. Cloud point and pour point The molecular weight of biodiesel is one of the factors that contribute in the increase in biodiesel density [84]. Biodiesel density is measured using the ASTM standard D1298 and EN ISO 3675 test method. According to these standards, density should be tested at 15 °C [85]. Table 2 shows that biodiesel density is usually higher than that of ordinary diesel fuel. Neem biodiesel has the highest density ranging from 912 kg/m3 to 965 kg/m3 [86,87], and jojoba biodiesel has the lowest density ranging from 863 kg/m3 to 866 kg/m3 [88,89]. Diesel has a density range of 816–840 kg/m3 [90]. Biodiesel has higher cloud and pour points than conventional diesel fuel [99,100]. Cloud and pour points are measured using the ASTM D2500 and D97 test methods, respectively. Table 2 illustrates that linseed and cotton seed biodiesels have the lowest cloud point of 1.7 °C, whereas jojoba oil has the highest cloud point range of 6–16 °C. On the contrary, cotton seed and linseed biodiesel have the lowest pour point range of 10 °C to 15 °C and 4 °C to 18 °C, respectively, whereas mohua has the highest pour point range of 1–6 °C. 3.5. Cetane number (CN) 3.2. Kinematic viscosity Viscosity is the most important property of fuel that must be considered to maintain engine performance that is close to diesel operation. High viscosity causes poor flow of fuel in the engine combustion chamber during intake stroke and takes a long time to mix with air. Therefore, it results in delayed combustion. Viscosity CN is the most important property of fuel that directly affects its combustion quality. Ignition quality of fuel in a power diesel engine is measured by CN. Higher CN implies shorter ignition delay. The CN of pure diesel fuel is lower than that of biodiesel [39,101]. The CN of biodiesel is higher because of its longer fatty acid carbon chains and the presence of saturation in molecules. CN is based on Table 2 Fuel properties of various non-edible biodiesel. Vegetable oil Density at 40 °C (kg/m3) Viscosity at 40 °C (mm2/s) Flash point (°C) Cloud point (°C) Pour point (°C) Cetane number Calorific value (MJ/kg) Refs. Karanja (Pongamia pinnata L.) Polanga (Calophyllum inophyllum) Mohua (Madhuca indica) Rubber Seed oil (Hevea brasiliensis) Cotton seed Jojoba oil (Simmondsia chinensis) Tobacco oil (Nicotiana tabacum) Neem (Azadirachta) Linseed oil (Linum usitatissimum) Jatropha (Jatropha curcas L.) Diesel 876–890 888.6–910 904–916 860–881 874–911 863–866 860–888.5 912–965 865–950 864–880 816–840 4.37–9.60 4–5.34 3.98–5.8 5.81–5.96 4–4.9 19.2–25.4 3.5–4.23 20.5–48.5 16.2–36.6 3.7–5.8 2.5–5.7 163–187 151–170 127–129 130–140 210–243 61–75 152–165.4 34 108 163–238 50–98 13–15 13.2–14 3–5 4–5 1.7 6–16 – – 1.7 – 10 to 5 3 to 5.1 4.3 1–6 8 10 to 15 6 to 6 12 – 4 to 18 5 20 to 5 52–58 57.3 51–52 37–49 41.2–59.5 63.5 49–51.6 51 28–35 46–55 45–55 36–38 39.25–41.3 39.4–39.91 36.5–41.07 39.5–40.1 42.76–47.38 38.43–39.81 33.7–39.5 37.7–39.8 38.5–42 42–45.9 [38,39,47,108,109] [39,48,110] [39,95,107,96,111] [55,105,112,113] [83,114,115] [61,64,70,88,89] [65,67,68] [72,83,86,87] [73,83,92] [94,116] [6,90,117] 0.045 5.85–6.21 0.3 5.47–5.63 20.17–24.05 13.29–14.93 46.10–51.12 0.2 0.3 35–45 0.2–0.26 16–33 0.24 9–24 25–54 6–16 0.56 1.04 0.3 20–30 – 3–16 – 0.5–6.5 43.5–66 25.2–34.4 0 _ – 40–50 – 3.7–7.9 – 2.4–8.9 44.5–71.3 10.8–18.3 – 2.2–4.1 4.2–5.3 25–40 Tetradecanoic acid Hexadecanoic acid 9-Hexadecanoic acid Octadecenoic acid 9-Octadecenoic acid 9,12-Octadecenoic acid 6,9,12-Octadecenoic acid Eicosanoic acid Docosanoic acid C14H28O2 C16H32O2 C16H30O2 C18H36O2 C18H34O2 C18H32O2 C18H32O2 C20H40O2 C22H44O2 Myristic acid (C14:0) Palmitic acid (C16:0) Palmitoleic acid (C16:1) Stearic acid (C18:0) Oleic acid (C18:1) Linoleic acid (C18:2) a-Linolenic acid (C18:3) Arachidic acid (C20:0) Behenic acid (C22:0) Oil content (wt%) 0.09 12.01–14.6 2.5 12.95–19.96 34.09–37.57 26.33–38.26 0.27–0.3 0.94 – 65–75 – 16–28.2 – 20.0–25.1 41.0–51.0 8.9–18.3 14.74 0.0–3.3 – 35–50 2.2 8.7–10.6 – 8.0–12 17–24.6 39.6–40.5 16.3–26 – – 50–60 0.7 11.67–20.1 – 2.6–3.15 19.2–23.26 55.2–55.5 0.6–6.31 – – 17–25 0.09–0.17 8.46–10.96 0.2 2.64–3.34 11.24–14.54 69.49–75.58 0.69–4.20 0.25 0.12 35–49 Linseed oil Neem Tobacco oil Jojoba oil Cotton seed Rubber seed oil Mohua Polanga Karanja Systemic name Chemical formulae Fatty acid (xx:y) Table 3 Typical fatty acid composition of various non-edible vegetable oils (wt.%) [18,36,38,41,42,55,61,64,71,87,89,52,123–132]. 1.4 13.6–15.1 – 7.1–7.4 34.3–44.7 31.4–43.2 – 0.2–0.3 – 20–60 A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 Jatropha 208 two compounds, namely, hexadecane and heptamethyl nonane. The CN of biodiesel is measured by the ASTM D613 and EN ISO 5165 test methods [85]. Table 2 shows that most biodiesel fuels have higher CN than diesel fuel (45–55), except for rubber seed and linseed biodiesels, which have low CN that is equal to 37–49 and 28–35, respectively [55]. Jatropha, mohua, neem, and tobacco have CN close to that of diesel fuel. Jojoba, karanja, and polanga usually have higher CN than other biodiesels; thus, they are more superior. 3.6. Calorific value Calorific value is the measure of heat energy content of a fuel. Higher calorific value of fuel is desired because it releases higher heat and consequently improves engine performance during combustion [102–104]. Biofuel usually has lower calorific value than diesel fuel because of its higher oxygen content [105–107]. Table 2 shows that the calorific values of jojoba and jatropha are 42.76– 47.38 MJ/kg and 38.5–42 MJ/kg [93,94], respectively, which are close to that of diesel at 42–45.9 MJ/kg. Jojoba biodiesel has the highest calorific value of 47.38 MJ/kg among all reviewed biodiesels; this value is also much higher than that of diesel fuel. Therefore, jojoba gives better engine performance than other biodiesel fuels. 4. Fatty acid composition of various non-edible oils Fatty acid composition, such as the type and percentage, determines the fuel properties of biodiesel. It depends on the fatty acid composition of the parent oil. Non-edible-based biodiesel mainly contains C16 and C18 acids. However, some feedstocks have a significant amount of fatty acids other than C16 and C18 acids [118]. Palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), and linolenic acid (C18:3) are the common fatty acids in vegetable oils [119]. The quality of biodiesel and its fuel properties highly depend on the presence of fatty acid composition in the fuel blend. The presence of monounsaturated fatty acid in a biodiesel blend at low temperature may improve ignition quality, fuel flow properties, and fuel stability [39]. Several researchers have found that biodiesel oxidation stability and fuel flow properties increase with the presence of capric acid [120,121]. However, Sahoo et al. [122] reported that fuel CN, cloud point, and stability increase with the presence of saturated fatty acid alkyl ester in fuel blend. Biodiesel viscosity and freezing point increase with the increase in carbon chain length and decrease with the increase in double bond chain. Table 3 shows the average fatty acid composition of the reviewed non-edible vegetable oils [121]. 5. Engine performance of a diesel engine using non-edible vegetable biodiesel Availability and economic aspects are first considered when selecting biodiesel. The characteristics of engine performance are then considered, indicating the applicability of the biodiesel in engines. Brake power, brake torque, brake thermal efficiency (BTE), and brake specific fuel consumption (BSFC) are the performance indicators. Factors such as air–fuel mixture, fuel injection pressure, fuel spray pattern, and fuel properties affect performance. These parameters are tested against engine load or engine speed in the literature review [42,43,47]. Engine performance characteristics of the reviewed biodiesel are discussed below. 5.1. Karanja biodiesel Karanja gives higher BTE at higher load condition and higher BSFC with the increase in blend ratio [42,95,133]. However, the Table 4 Engine performance results using karanja (Pongamia pinnata L.) biodiesel compared with diesel fuel at different test condition. Engine type 1- Cylinder, 4S, WC, DI, RP: 7.5 kw, CR: 16:1, CI engine 1- Cylinder, 4S, RP: 3.75 kw, D: 553 cm3, CR: 16.5, DI, WC, CI engine 1- Cylinder, 4S, WC, DI, D: 553 cm3, RP: 4.476 kw, CR: 16.5:1, CI engine 4-Cylinder, DI, D: 3298 cm3, CR: 17.5:1, RP: 70 kw, WC, CI engine 1- Cylinder, DI, WC, 4S, CR: 17.5:1, RP: 3.5, CI engine Result Refs. Power/torque BTE BSFC Full/part throttle at different speeds (1200 rpm, 1800 rpm and 2200 rpm) and different blends (20%, 50% and 100%) Constant speed (1500 rpm) and different blends (5%, 10%, 20% and 30%) Slightly reduction in the range of 0.44– 1.93% and 1.2–2.55% using 20% and 40% biodiesel blend at higher speed engine operation – – Increases with increase of blend ratio and decreases with increase engine speeds. For part throttle experiment BSFC decrease with use higher biodiesel blend Slightly Higher (Min 0.313 kg/kw h) as compared to diesel fuel [47] Different blends (10%, 20%, 50%, 75%) and constant speed (1500 rpm) and different load condition Constant speed (1500 rpm), 20% blend and different load condition Different blends (5%, 10%, 15% and 20%) and different load (0%, 20%, 40%, 60%, 80% and 100%), constant speed (1500 rpm) Different loads (10%, 25%, 50%, 75%, 85% and 100%), different blends (20%, 40%, 60%, 80%) and constant speed 3000 rpm Different loads (33.3%, 66.6% and 100%), different blends (20%, 40%, 60% and 80%) and constant speed 1500 rpm Different blends (10%, 25%, 50% and 100%) and constant speed (1200 rpm) – Improve (0–25%) compared with diesel fuel and use without preheating biodiesel blends BTE is higher in all loads condition Improve use preheated lower biodiesel blend up to 50% [42] Decreases with the increases engine load [133] Slightly Improve at lower loads and reduce at higher loads condition as compared to neat petroleum based diesel fuel Increase with increases engine load Slightly increases as all blends compared with neat petro-diesel [43] 0.8–7.4% lower at 20% and 40% blend, and higher with higher percentage of blend ratio [109] Slightly decrease with uses higher percentage of biodiesel bland ratio Increase with up to 40% bland ratio used in diesel engine [135] – Almost unchanged compared with diesel fuel – [136] Constant speed, different loads and blend (B100, B90M10) – Increase 4.2% at high load condition – [137] Constant speed (1500 rpm) and different load condition – Increase significantly at higher load condition Decrease 12% at higher load condition compared with other biodiesel blend, but increase 14.7% compared with diesel fuel [134] At similar performance compared with diesel fuel – Engine power increases on average 6% up to biodiesel blend used 40% and increases with decreases blend ratio – Reduce 5.72% as compared with diesel fuel [41] A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 3-Cylinder, AVL make CI engine, D: 3.44 l, CR: 18.1, WC, RS: 2200 rpm, P: 44.1 kw 2-Cylinder, 4S, petter Kirloskar CI engine, RP: 10HP, RS: 1500 rpm, DI, WC, CR: 16.5:1,RP: 7.5 kw 1-Cylinder,AV-1, 4S, CS, WC, DI, CI engine, RP: 3.67 kw, D: 552.92 cm3, CR:17.5 1- cylinder, 4S, RP: 5.9 kw, CR: 17.5, CI engine 1- Cylinder, 4S, DI, RP: 6 kw, WC, CI engine Test condition Engine codes: S = stock; DI = direct injection; AC = air cooled; WC = water cooled; IC = intercooled; TC = turbocharger; CI = compression ignition; CR = compression ratio; RP: rated power; D: displacement; RS: rated speed; EGR: exhaust gas recirculation. Performance analysis codes: BTE: Brake thermal efficiency; BSFC: Brake specific fuel consumption; BSEC: Brake specific energy consumption. Emission analysis codes: CO: Carbon monoxide; HC: Hydrocarbon; NOx: Nitrogen oxide; BSU: Bosch smoke unit. 209 0.1% Increase with increase of blend ratio Increase with addition additives in the biodiesel fuel blend Slightly increase compared with diesel fuel – 1- Cylinder, 4S, WC, DI, CI engine Most experiments show that BSFC is higher when rubber seed biodiesel is used in a diesel engine. However, higher BTE and brake power were observed with increased percentage of biodiesel in fuel blend and with engine load [106,141]. Table 7 shows the engine performance when rubber seed biodiesel is used in different test conditions. BTE increases at about 1.14–1.33% in a full load condition. The following conclusions can be made from the analysis of the different experimental results: Full/part throttle at different speeds (1200 rpm, 1400 rpm and 2200 rpm) and different blends (20%, 50% and 100%) Different loads (0%, 20%, 40%, 60%, 80% and 100%) and different blends (20%, 40%, 60%, 80% and 100%) Different blends (B10, B20, B30 and B40) and constant speed (1500 rpm) 5.4. Rubber seed biodiesel 3 Cylinder, AVL make CI engine, D: 3.44 l, CR: 18.1, WC, RS: 2200 rpm, P: 44.1 kw 1-Cylinder, 4 S, WC, DI A 20% biodiesel blend gives about 1–32.5% higher BTE at higher engine load condition than any other blend. BTE is reduced with the presence of a higher percentage of biodiesel in the fuel blend. BSFC increases by 4.1% with the increased proportion of biodiesel in the fuel blend. Result Mahua biodiesel gives poor results in terms of engine performance. Most researchers found that it has high BSFC and low BTE [96,107,111,138]. However, some test conditions gave higher thermal efficiency [53,54,139]. Different experimental results using mahua biodiesel in different test conditions are shown in Table 6. The following conclusions can be made by analyzing the different experimental observations: Test condition 5.3. Mahua biodiesel Engine Engine power is slightly reduced when a lower biodiesel fuel blend is used but increases when a medium percentage of biodiesel fuel blend is used. BTE increases with the use of higher biodiesel blend and added additives in the fuel. Lower BSFC is observed when the biodiesel blend has added additives and when the engine is operated at high speed. Table 5 Different experimental engine performance results using polanga (Calophyllum inophyllum) biodiesel compared with diesel fuel. Polanga biodiesel usually gives high power output, high BTE, and low BSFC when used in a diesel engine [44]. However, some researchers obtained the opposite trend [47]. Table 5 presents the engine performance parameters using polanga biodiesel in a diesel engine. The following conclusions can be made by analyzing the results: [48] Increases with increase of blend ratio and decreases with increase engine speeds. For part throttle test BSFC decrease with more than 20%, blend Reduce with using higher biodiesel blend ratio and engine speeds – Slight reduction in power 1.93% using 20% biodiesel blend but improve 0.19–0.88% using 50% biodiesel blend compared with diesel fuel during the entire range of engine operation 5.2. Polanga biodiesel Decreases with added additives in the fuel blend BSFC BTE Engine power increases by about 6% with the presence of higher biodiesel percentage in fuel blend. Higher engine speed and lower biodiesel concentration give higher engine power. BTE increases with higher engine load and decreases when a lower percentage of biodiesel is used in the fuel blend. BSFC decreases about 0.8% with used lower biodiesel blend ratio and higher engine speed. BSFC decreases significantly when pre-heated biodiesel fuel blends are used. [47] Refs. opposite trend was observed by some researchers [47,109]. Srivastava et al. [41] experimented different karanja biodiesel blends using a two-cylinder CI engine. They concluded that pure biodiesel gives lower BTE than diesel fuel, but biodiesel blend gives higher BTE than pure biodiesel. Jindal et al. [134] found that karanja biodiesel blend gives better BTE and BSFC than other biodiesels. Table 4 shows different experimental results of engine performance using karanja biodiesel. The following conclusions were drawn based on the result analysis: [44] A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 Power/torque 210 Table 6 Different experimental engine performance results using mahua (Madhuca indica) biodiesel compared with diesel fuel. Engine type 3-Cylinder, 4S, AC, DI, D: 2826 cm3, CR: 17:1 Result Refs. Power/ torque BTE BSFC Different blends (B20, B40, B60 and B80), different loads (25%, 50%, 75% and 100%) and constant speed (1500 rpm) Different blends (10, 20 and 30%), different loads and constant speed (1500 rpm) Different loads, different blends (B20, B40, B60) and constant speed (1500 rpm) Constant speed (1500 rpm) – Increase 1% with using 20% biodiesel blend and Decrease 10.1% with used 100% biodiesel Increased 0–30% with increased of biodiesel percentage in the fuel blend Increased 32.5% using 20% biodiesel blend compared with diesel fuel 13% Lower than that of diesel fuel Increased min 4.1% with the increased proportion of biodiesel in the blends – [96] Increase with increase in the proportion of biodiesel in the fuel blends and engine loads 20% Higher than the ordinary diesel fuel [111] Constant speed (1500 rpm) – – Increase about 6% and 14% compared with diesel fuel Higher compared to diesel fuel [54] Constant speed (1500 rpm) Gradually increase 26.42%-28.307% for both ester used compared to diesel fuel 1.95% higher than that of diesel fuel Blend (B20), constant speed (1500 rpm), and steady state condition Different loads, different blends (B10, B20, B40, B60, B80) and constant speed (1500 rpm) – 20% biodiesel blend gave higher efficiency than diesel fuel at higher load condition Decrease with increase of blend ratio. Maximum efficiency obtained at use B20 bland – [139] Increase with increase biodiesel blend ratio compare with diesel [138] – _ – – [53] [107] [140] Table 7 Different experimental engine performance results using rubber seed oil (Hevea brasiliensis) biodiesel compared with diesel fuel. Engine type Test condition 1-Cylinder, 4S, DI, RP: 5.5 kw, WC, CI engine, RS: 1500 rpm 1-Cylinder, 4S, DI, RP: 5.5 kw, WC, CI engine, RS: 1500 rpm Different loads, different blends (B20, B40, B60, B80 and B100) and constant speed (1500 rpm) Different loads, different blends (B10, B20, B50, B75 and B100) and constant speed (1500 rpm) 1-Cylinder, 4S, DI, RP: 4.4 kw, CR: 17.5:1, D: 661.5 cm3, RS: 1500 rpm 1-Cylinder, DI, 4S, RP: 5.5 kw, CI engine, WC, RS: 1500 rpm 1-cylinder, AC, CR: 17.5:1, 4S, DI, CI engine, RP: 4.4 kw, RS: 1500 rpm 1-Cylinder, WC, 4S, DI, RS: 1500 rpm, RP: 5.5 kw, CR: 16.5:1 Constant speed (1500 rpm) and different load (25%, 50% 75%, 100%), Duel fueling with hydrogen induction (25%, 50% and 75%) Result Refs. Power/torque BTE BSFC Increase with increase of biodiesel blend ratio Increased with the increased in engine load – Increase with the increase of biodiesel blend ratio compared to diesel fuel 3% Increase using 20% biodiesel blend with increase in engine loads Higher compare with diesel fuel Increased 12% using 100% biodiesel compared with diesel fuel – Constant speed (1500 rpm)and different load condition – Using net RSO and Various diethyl ether with RSO (50 g/h, 100 g/h, 150 g/h, 200 g/h and 250 g/h) and full load condition – Reduce for incomplete combustion compared with diesel fuel 3.4% Lower than that of diesel fuel using net RSO. But improved at using RSO with DEE injection Higher than that of diesel fuel for duel fuel operation – Different loads and constant speed 1500 rpm Less than that of diesel fuel 4.95% Lower than that of diesel fuel at full load condition 34.8% Higher than that of diesel fuel at 70% load condition Increase about 1.33% and 1.14% at full load condition with hydrogen induction using RSOME [141] [106] A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 1-Cylinder, 4S, WC, CR: 18:1, P: 9 kw, CI engine 1-Cylinder, 4S, WC, CI engine, RP: 4 kw 6- Cylinder, 4S, AC, D: 5.9 L, CR: 17.6:1, HP: 158, CI engine 1-Cylinder, 4S, WC, DI, CR: 16.5:1, RP: 3.7 kw, D: 553 cm3 1-Cylinder, 4S, WC, DI, CR: 16.5:1, RP: 3.7 kw, D: 553 cm3 1-Cylinder, 4S, WC, DI, CR: 16.5:1, RP: 3.7 kw, D: 553 cm3 1- Cylinder, 4S, WC, DI, HP: 7, Test condition [113] [142] [143] [144] 211 212 Table 8 Different experimental engine performance results using cotton seed biodiesel compared with diesel fuel. Engine type Test condition Result Refs. BTE BSFC 1-Cylinder, WC, 4S, DI, CR: 19.8:1, RS: 4500 rpm 6-Cylinder, 4S, WC, DI, D: 5958 , CR: 18:1, RP: 177 kw, RS: 2600 rpm 1-Clynder, 4S, DI, WC, CR: 17:1, D: 770 cm3, RP: 8 HP, RS: 2000 rpm 1-Cylinder, 4S, AC, DI, D: 406 cm3, RP: 10 HP, RS: 3600 rpm, CR: 18:1 1-Cylinder, 4S, DI, WC, NA, D: 553 cc, CR: 16.5:1, RP: 4.476 kw, RS: 1800 rpm 6-Cylinder, 4S, DI, WC, TC, D: 5958 cc, CR: 18:1, RP: 177 kw, RS: 2600 rpm 1-Cylinder, 4S, DI, CR: 18:1, NA, RS: 3600 rpm, Constant speed 2000 rpm, Different blends (10% and 20%) medium and high load condition Different speeds (1200 and 1500 rpm), different loads (20%, 40%, 60% and full load) Same compared with diesel fuel all load condition _ Same compared with diesel fuel all load condition Similar compared with neat diesel fuel Higher than that of diesel fuel at medium and higher load condition Little higher than that of diesel fuel with the higher percentage of biodiesel in the blend [114] Full load and different speeds (900–1800 rpm) Reduced about 3% compared with diesel fuel – [115] Different speeds (1250–2500 rpm) and different blends (B5, B20, B50, B75 and B100) Increase at higher engine speed but less then diesel fuel – – SFC of methyl ester has lower compared with raw oil fuel, Higher fuel consumption due to lower energy contain Lower at full load operation and 2000 rpm speed for using 5% and 20% biodiesel blend 1-Cylinder, DI, 4S, AC, CR: 18:1, D: 395 cc, RS: 3600 rpm, RP: 6.25 kw 4-Cylinder, 4S, DI, NA, WC, CR: 16.8:1, RP: 51 kw, RS: 2400 rpm, 1-Cylinder, 4S, AC, DI, CR: 18:1, RP: 6.25 kw, RS: 3600 rpm, 1-Cylinder, 4S, AC, DI, CR: 18:1, RP: 6.25, RS: 3600 rpm Full load and different speeds (2800–1300 rpm) [147] [145] Increase with the increased in engine torque, but decreased due to the maximum torque Same compared with diesel fuel at all load condition Decrease with increase in engine torque [59] Littlie higher than that of neat diesel fuel [148] Decrease compared with diesel fuel at all operating temperature 3–9% Lowers than that of diesel fuel Increase 6.34% at high operating temperature – [149] – 8–10% Higher than that of diesel fuel [150] Full load and different speeds (1200–2400 rpm) Increase with the increased of engine speed Improved slightly both NA and TC operation compared with diesel fuel Slightly higher both NA and TC operation compared with diesel fuel [146] Full load and different speeds (1700, 2000, 2300, 2600 and 3000 rpm) Full load, varied injection pressure and constant speed 2.2–2.3% Increased at full load operating condition 3–6% Decreased than diesel fuel at all injection pressure Increased 6% at B20 and 3.5% at B40 biodiesel _ Increased compared with diesel fuel [151] 3–7% Increased compared with diesel fuel [60] Constant speed 850 rpm and different blends (B10, B20, B30) Different blends (B10, B20), different speeds (1200 rpm and 1500 rpm) and different load condition (20%, 40% and 60%) Different speeds and preheated blend (30°, 60°, 90°, 120 °C) – A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 Power/torque [152] [64] 8.2% and 9.8% lower at engine speed 1200 and 1600 rpm compared with diesel fuel Decreased 8% with EGR and 14% increased without EGR operation Slightly higher compared with diesel fuel with the increase of engine speed Decreased 6% and 13% with EGR and without EGR operation Slightly higher than that of diesel fuel with the increase of engine speed Increased 5% with EGR operation 2-Cylinder, 4S, WC, DI, D: 2266 cc, CR: 16.4:1, RS: 1500 rpm, RP: 26HP 1-Cylinder, 4S, AC, DI, NA, CR: 17:1, RP: 5.775 kw, RS: 1500 rpm Various loads (no load, 1/3, 2/3 and full load), different blends (B20, B40, B60) and different speeds Different speeds (1000–1900 rpm) and full load 1-Cylinder, 4S, AC, DI, CR: 17:1, RP: 5.775 kw, RS: 1500 rpm Different speeds and injection timing of 24 CAD BTDC [61] Slightly increased with increased of biodiesel percentage in fuel blend – Slightly decreased with increased of biodiesel percentage in fuel blend Test condition Engine type Table 9 Engine performance results using jojoba oil based biodiesel at different test condition. Result BSFC Refs. BTE Power/torque A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 213 Engine power increases with the increased percentages of biodiesel in the fuel blend and higher engine speed condition. A 20% biodiesel blend ratio and higher engine speed give higher BTE. Diethyl ether (DEE) injection with rubber seed oil-based biodiesel blend shows high peak pressure and gives high BTE. BSFC increases with increased engine load and higher biodiesel percentages in the fuel blend. 5.5. Cotton seed biodiesel Cotton seed biodiesel gives poor engine performance results compared with other biodiesel fuels. BSFC is high in most test conditions, along with lower brake power and BTE [115,145], but it gives high thermal efficiency in some specific conditions [59,146]. Table 8 presents the engine performance results using cotton seed biodiesel in different test conditions. The following conclusions can be made by analyzing the different experimental results: Engine power increases by about 2.2–2.3% in a full load operating condition. Engine power decreases with the use of preheated biodiesel blend and higher injection pressure. BTE improves in both naturally aspirated and turbo-charged operations, the increment of which is about 6.34% with fuels at elevated temperature. BTE increases by about 6% with low biodiesel present in the blend and with high engine torque condition. BSFC increases by about 3.7% with increased engine load and high percentage of biodiesel present in the fuel blend. BSFC decreases with the lower percentage of biodiesel present in the fuel blend. 5.6. Jojoba oil biodiesel Jojoba oil-based biodiesel can be considered a good alternative fuel because of its give higher brake power using in diesel engine. Moreover, its thermal efficiency and BSFC decrease at different speeds and in a full load condition [64,152]. However, it gives higher BSFC in some specific conditions [61]. Different engine performance results using jojoba oil-based biodiesel in a diesel engine are shown in Table 9. The following conclusions can be made from the analysis of the different experimental results: Engine power increases by 5% using jojoba oil methyl ester with EGR operation. Engine power slightly decreases when the fuel blend used has a high percentage of biodiesel in the fuel blend. BTE slightly increases in a full load condition and with high engine speed but decreases by 6% with EGR operation. BSFC decreases about 8% when jojoba oil methyl ester is used in EGR operation and with high engine speed. 5.7. Tobacco oil biodiesel Tobacco oil biodiesel has shown excellent results in terms of engine performance, with high brake power and BTE, and low BSFC [66,68,153]. However, it gives high BSFC in some specific conditions [154,155]. Different engine performance results using tobacco oil-based biodiesel in a diesel engine are shown in Table 10. The following outcomes can be concluded by analyzing the results: Engine power increases by about 3.13% with high engine load and low biodiesel percentage in the fuel blend. At high engine speed and low biodiesel percentage, BTE increases by 2.02%. 4-Cylinder, 4S, TC, WC, IDI, CR: 21.5:1, D: 1.753, RP: 55 kw, RS: 2200 rpm 1-Cylinder, 4S, NA, RS: 1500 rpm, RP: 5 HP 1-Cylinder, 4S, NA, DI, RP: 14.7:1, RS: 2500 rpm 1-Cylinder, 4S, DI, WC, RP: 5.2 kw, CR: 17.5:1 Constant speed 1500 rpm, different loads and different blends (B2 and B5) Full load and different speeds (1200, 1400, 1600, 1800, 2000, 2200 and 2400 rpm) Different injection pressures (205, 220, 240 and 260 bar) Increased with the increased of engine speed and full load condition – Lower compared with diesel fuel at lower injection pressure [155] [154] 9.8% Lower that of diesel fuel low biodiesel percentage in the blend Increased slightly compared with diesel fuel at lower engine speed Decreased with increased of break power and lower injection pressure [153] [68] Slightly increased with low load condition 3.13% Higher than that of diesel fuel at higher load and lower blend ratio used in diesel engine – [66] Increased with the increased of engine speed 0.272–0.292% Increased with increased of engine speed and higher load condition 2.02% Higher compared diesel fuel with lower biodiesel percentage in the fuel 1.69% Increased than that of diesel fuel at higher load condition – Increased with the increased of engine speed and higher load condition Different loads (50%, 75% and 100%), different blends (B10, B17.5 and B25) and speed (1500– 3000 rpm) Different loads (50%, 75% and 100%), different blends (B10, B17.5 and B25) 4-Cylinder, 4S, TC, WC, RP: 55 kw, RS: 2200 rpm Result Test condition Engine type Table 10 Engine performance results using tobacco oil based biodiesel at different test condition. Power/torque Refs. BSFC A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 BTE 214 High engine load condition, high injection pressure, and biodiesel percentage affect the BTE of an engine. BSFC slightly decreases because of high brake power and low injection pressure. Engine load and speed also affect specific fuel consumption. 5.8. Neem biodiesel Neem biodiesel generally gives slightly lower BTE and higher BSFC [86,156–158] but gives higher BTE than diesel fuel in some conditions [87,159,160]. Different experimental engine performance results are shown in Table 11. Its low calorific value causes neem biodiesel to give low BTE with high fuel consumption in most cases. The following deductions can be made based on Table 11: BTE significantly increases with increased biodiesel percentage in the fuel blend and engine load. In a part load condition, the BTE of an increases about 63.11% compared with that of diesel fuel. However, it decreases in a full load condition. BSFC decreases by about 8.25% at constant speed in a part load condition but significantly increases in a full load condition. 5.9. Linseed oil biodiesel The use of linseed oil biodiesel in diesel engine gives excellent results, such as high BTE, high power output, and low BSFC. Some experimental results also show its high BSFC and low BTE [73,92,164]. Table 12 shows the engine performance results using linseed oil-based biodiesel in a diesel engine in different conditions. The following conclusions can be made from the analysis of the different experimental findings: Engine power increases with the presence of high engine load and high percentage of biodiesel in the fuel blend. BTE increases because of improved atomization and better mixing process at a high injection pressure. BTE increases by about 10–12% with increased biodiesel concentration in the fuel blend and high engine load condition. BSFC decreases by about 4–6% with high engine load and high biodiesel percentage in the fuel blend. It significantly increases with at a high injection pressure in the engine. 5.10. Jatropha biodiesel Jatropha biodiesel gives high thermal efficiency with high fuel consumption [116,166–168]. Its blends give better brake power than diesel fuel in some cases [47]. It also exhibits low BTE in some conditions [116,169]. Engine performance results in different test conditions are shown in Table 13. The following deductions can be made by analyzing the results in Table 13: A 20% biodiesel blend gives better engine power, which is about 0.09–2.64% higher, than diesel fuel. Engine power decreases with increased biodiesel percentage in the fuel blend. BTE slightly improves (percentage) in medium engine speed and improves by 0.1–6.7% in high engine speed. However, it decreases when a high biodiesel percentage is present in the fuel blend. BSFC increases by 6.8% with increased engine speed and high biodiesel percentage in the fuel blend. Table 11 Engine performance results using neem biodiesel at different test condition. Engine type Test condition Refs. Power/ torque BTE BSFC Constant speed 1500 rpm, duel fueling – 5% lower than that of diesel fuel – [161] Different blends (B5, B10 and B15), different speed (600–1200 rpm) and different BMEP Different loads (4, 8, 12, 16 and 20 kg) and constant speed 1500 rpm Constant speed and different loads (1000–4000 Watt) condition Different BMEP (100, 200, 300, 400, 500, 600 and 650) and constant speed 1500 rpm Constant speed and different BP (0–5 kw) – – [162] – Increased with increased of fuel supply up to 1000 rpm and decreased when engine speed above 1000 rpm Increased with the increased of engine load Decreased with the increased of engine load [87] – Slightly lower at higher loads compared with diesel fuel [156] _ 63.11% higher than that of diesel fuel at part load condition and 11.2% lower at full load condition Lower than that of diesel fuel at all loads condition Slightly higher at low load condition compared with diesel fuel 8.25% Lower at part load and 27.25% higher at full load condition than that of diesel fuel – Different blends (B10, B20, B30, B40 and B50), constant speed and different break power Different blends (B20, B40, B60, B80 and B100), Different BMEP and constant speed 1500 rpm Different blends (B5, B10, B15, B20), different loads and constant speed 1500 rpm Different loads, constant speed 1800 rpm and different blends (B10, B20) – – – – – Decreased with the increased of biodiesel percentage in the blend Increased 7.01% at full load condition and lower biodiesel percentage in the fuel blend Increased with the increased of percentage of biodiesel in the fuel blend at all load condition Decreased with higher biodiesel in the blends compared with diesel fuel Slightly higher for B20 and all biodiesel nearly closed to diesel fuel 27.75% Higher at full load condition and higher biodiesel percentage in the blend – Increased 23.38% and 12.12% of B10 and B20 compared with diesel fuel [163] [157] [158] [159] [160] [86] Table 12 Engine performance results using linseed oil biodiesel at different test condition. Engine type 1-Cylinder, WC, 4S, DI, D: 662 cc, RP: 4 kw, RS: 1500 rpm 1-Cylinder, 4S, AC, DI, RP: 4.4 kw, CR: 17.5:1, RS: 1500 rpm 1-Cylinder, 4S, AC, DI, RP: 4.4 kw, D: 661 cc, CR: 17.5:1, RS: 1500 rpm 1-Cylinder, WC, 4S, Di, RP: 3.5 kw, CR: 17.5:1, RS: 1500 rpm Test condition Different blends (B10, B20, B30 and B50, v/ v), constant speed 1500 rpm and different loads Different loads, constant speed 1500 rpm and different injection pressure (200, 220 and 240 bar) Different loads and constant speed 1500 rpm Different blends (B5, B10, B15 and B20), constant speed 1500 rpm and different loads Result Refs. Power/torque BTE BSFC – Increases with the increase of engine loads and concentration of biodiesel in the fuel blend Lower by used blend B50 compared with others blends [164] – Increases at full load condition are closer to diesel fuel because of improved atomization and better mixing process at higher injection pressures Lower compare with others biodiesel blend at full load condition Higher than that of diesel fuel at all load and higher injection pressure Similar compare with others biodiesel blend [92] Increases 10–12% with the increase of engine power and increasing concentration of biodiesel in the fuel blend Decreased 4–6% with the increase biodiesel percentage in fuel blend [165] – Decreases with increasing biodiesel concentration in the fuel blend A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 1-Cylinder, 4S, DI, WC, RP: 5.2 kw, CR: 17.5:1, RS: 1500 rpm 1-Cylinder, 4S, DI, NA, WC, RP: 9.8 kw, CR: 20:1, RS: 2000 rpm 1-Cylinder, 4S, DI, D: 425 cc, CR: 15.5:1, RP: 7.5HP, RS: 1500 rpm 1-Cylinder, 4S, DI, WC, RS: 1500 rpm, RP: 3.7 kw, CR: 16.5:1 1-Cylinder, 4S, WC, DI, CR: 17.5:1, D: 661 cc, RP: 5.2 kw, RS: 1500 rpm 1-Cylinder, 4S, DI, NA, WC, RP: 5HP, RS: 1500 rpm, CR: 16.5:1 1-Cylinder, AC, DI, CR: 17.5:1, RP: 4.4 kw, RS: 1500 rpm 1-Cylinder, DI, WC, RP: 5.2 kw, RS: 1500 rpm 1-Cylinder, 4S, NA, DI, CR: 16.5:1, RP: 3.5 kw, RS: 1500 rpm 1-Cylinder, 4S, DI, WC, RP: 8 HP, CR: 16.5:1, RS: 1800 rpm Result [73] 215 [171] Higher than that of diesel fuel and increased with the increased of blend ratio Decreased with the increased of percentage of biodiesel in the fuel compared with diesel [94] Higher than that of diesel fuel Lower compared with diesel fuel [166] [169] Increased with the increased of percentage of biodiesel in the fuel Average 9.3% and 6.8% increased for 1500 rpm and 2000 rpm 7% Decreased compared with diesel fuel for B100 0.2–3.5% and 0.1–6.7% increased for 1500 rpm and 2000 rpm Biodiesel is an oxygenated fuel. Therefore, it produces a complete combustion, provides excellent emission properties, and creates less negative environmental effects [82,172]. Different experimental investigations on engine emission characteristics using the reviewed non-edible oil biodiesels are presented. 6.1. Karanja biodiesel Engine operating condition and biodiesel percentage in the blend significantly affect engine emission characteristics. Although some experimental results show high CO and NOx emissions, others present low CO, HC, and smoke emission [41,42,47]. Table 14 shows the engine emission results using karanja biodiesel in different test conditions. The following conclusions can be made by analyzing the different experimental results: CO emission decreases by approximately 4–46.5% in a high load condition but increases with the presence of a high percentage of biodiesel in the fuel blend. HC emission decreases with a low percentage of biodiesel present in the fuel blend and in a high load condition. PM decreases with increased biodiesel content in the fuel blend. NOx emission increases by 4.15–14.18% with increased biodiesel percentage in the fuel blend. However, it decreases by 4–39% with the presence of low biodiesel percentage in the fuel blend. Smoke level is reduced (20–43%) with a high engine load and high biodiesel concentration in the fuel blend. – – Different blends (B5, B10, B20, B30 and B100) and different loads (20%, 40%, 60%, 80% and 100%) – Different blends (B25, B50, B75 and B100) and constant speed Different speeds (1500 and 2000 rpm) and different load – Only a few researchers conducted experiments using polanga biodiesel in a diesel engine. These researchers found that it gives low-criteria engine emission. Table 15 presents the engine emission results using polanga biodiesel in different operating conditions. Clearly, biodiesel blends greatly affect emission. The following deductions can be made based on the analysis of the different experimental results: Different speeds (1800, 2500 and 3200 rpm) [80] Higher than that of diesel fuel Almost same compared with diesel fuel 6. Engine emission performance when non-edible vegetable biodiesel is used in a diesel engine 6.2. Polanga biodiesel 4-Cylinder, 4S, DI, TC, D: 1609 cc, RP: 84.5 kw, CR: 18.5:1, RS: 3800 rpm 1-Cylinder, 4S, DI, WC, RP: 8 HP, RS: 1500 rpm 1-Cylinder, 4S, WC, DI, D: 815 cc, RP: 8.82 kw, CR: 17:1, RS: 2000 rpm 1-Cylinder, 4S, DI, AC, CR: 18:1, D: 395 cc, RP: 5.59 kw, RS: 3600 rpm 1-Cylinder, 4S, DI, AC, D: 947.8 cc, CR: 17.5:1, RP: 7.4 kw, RS: 1500 rpm Decreased compared with diesel fuel Higher than that of diesel fuel about (20–80%) blends [170] Increase with increased of percentage of biodiesel in the fuel blend, but decreased with higher engine speed Lower compared with diesel fuel when B20 used, for other blends almost same as diesel _ Increased 0.09–2.64% used 20% biodiesel blend with entire range of engine operation – Different speeds (1200, 1800 and 2200 rpm) and different blends (B20, B50 and B100) Different blends (B20, B40, B50, B60, B80 and B100) and different loads (25%, 50% 75% and 100%) Different speeds and full load condition [79] Higher than that of diesel fuel Lower compared with diesel fuel Decreased with increased of percentage of biodiesel in the fuel Different blends (B10, B20, B50 and B100) and different speeds (1000–2400 rpm) 1-Cylinder, 4S, DI, WC, D: 1007 cc, CR: 18.5:1, RS: 2400 rpm 3-Cylinder, 4S, DI, WC, D: 3440 cc, CR: 18:1, RS: 2200 rpm 1-Cylinder, 4S, DI, CR: 16.5:1, RP: 5HP, RS: 1500 rpm BSFC BTE Power/torque Result Test condition Engine type Table 13 Engine performance results using jatropha biodiesel at different test condition. [47] A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 Refs. 216 Higher biodiesel blend ratio gives higher CO emission. HC emission significantly decreases with the presence of high biodiesel percentage in the fuel blend. Polanga biodiesel produces a low reduction of PM at about 9.88–42.06% with increased biodiesel percentage in the fuel blend. NOx emission increases when a fuel blend is used with high biodiesel percentage. However, it decreases by 4% in a high load condition. Smoke level decreases at a maximum of 35% at high biodiesel blend and high engine speed condition. 6.3. Mohua biodiesel Experimental results on engine operation using mohua oilbased biodiesel show that it gives low CO, HC, NOx, and smoke emission [54,95,107,139,140] but produces high NOx emission in some cases [53,96,111]. An emission characteristic of the different experimental results using Mohua biodiesel and its blends is shown in Table 16. The following conclusions are attained by analyzing the different experimental results: CO emission decreases by 0.02–0.16% with the increase in biodiesel concentration in the fuel blend. Table 14 Engine emission results using karanja biodiesel at different condition. Engine Test condition Emission Refs. HC PM Nox Smoke Full throttle at different speeds (1200 rpm, 1400 rpm and 2200 rpm) and different blends (20%, 50% and 100%) Constant speed (1500 rpm) and different blends (5%, 10%, 20% and 30%) Improvement 2.93–5.87% less than that of diesel fuel using 20% 50% and 100% biodiesel blend entire range of engine operation Slightly Increase about 0.03% at increases of blend ratio Reduce range of 4.30– 20.64% with increase of bland ratio Slightly increase with range of 4.15–14.18% with increase of blend ratio Increase 12% compared with diesel fuel Reduction with increase of blend ratio [47] – [41] Different blends (10%, 20%, 50%, 75%) and constant speed (1500 rpm) Increase min 10 g/kw h use without preheating blend – – Reduce with use of net biodiesel and blend – 1-Cylinder, 4S, DI, RP: 6 kw, WC, CI engine Different blends (5%, 10%, 15% and 20%) and different load (0%, 20%, 40%, 60%, 80% and 100%) Approximately 4% decreases with higher load condition Lower at 10% blend and 70% load – Smoke was significantly reduce for all blends [43] 1-Cylinder, 4S, WC, DI, RP: 7.5 kw, CR: 16:1, CI engine Different loads (10%, 25%, 50%, 75%, 85% and 100%), different blends (20%, 40%, 60%, 80%) and constant speed 3000 rpm Different loads (33.3%, 66.6% and 100%), different blends (20%, 40%, 60% and 80%) and constant speed 1500 rpm Different blends (10%, 25%, 50% and 100%) and constant speed (1200 rpm) Constant speed, different loads and blend (B100, B90M10) Reduce 60% at low load condition _ –– Increases 10–25% compared with conventional diesel At 20% blend and 80% load give 4% lower Nox compared to diesel Average 26% reduction as compared to diesel Smoke density almost same compared with diesel fuel Reduce with use of net biodiesel and blend [42] Constant speed (1500 rpm), 20% blend and different load condition Exhibited 11.76% higher HC emission with the increased biodiesel percentage Lower as use of lower blends compared than diesel Reduce with use of net biodiesel and blend Reduce range of 16.43–45.48% with increase of bland ratio – [109] Slightly higher than baseline diesel Reduce 2.85%-12.8% for 20% and 40% biodiesel blends used in diesel engine – – Decrease 28%-39% with 20% and 40% biodiesel blends used Smoke density min 20% decrease and maximum 80% decrease with high engine load – – Increases 15% Nox emission B100 reduce smoke opacity by 43% [136] Slightly higher at low load condition – – Lower at high load (80%) condition [137] Reduce 50% compared with diesel fuel – 48% reduction in NOx compared with diesel fuel Lower (20%) as compared with diesel fuel [134] 3 Cylinder, AVL make CI engine, D: 3.44 l, CR: 18.1, WC, RS: 2200 rpm, P: 44.1 kw 2-Cylinder, 4S, petter Kirloskar CI engine, RP: 10HP, RS: 1500 rpm, DI, WC, CR: 16.5:1, RP: 7.5 kw 1-Cylinder, 4S, CS, WC, DI, CI engine, RP: 3.67 kw, D: 552.92 cm3, CR: 17.5 1-Cylinder, 4S, RP: 5.9 kw, CR: 17.5, CI engine 1-Cylinder, 4S, RP: 3.75 kw, D: 553 cm3, CR: 16.5 DI, WC, CI engine 1-Cylinder, 4S, WC, DI, D: 553 cm3, RP: 4.476 kw, CR: 16.5:1, CI engine 4-Cylinder, DI, D: 3298 cm3, CR: 17.5:1, RP: 70 kw, WC, CI engine 1-Cylinder, DI, WC, 4S, CR: 17.5:1, RP: 3.5, CI engine Constant Speed (1500 rpm) and different load condition Reduce 50% compared with diesel Decrease significantly at higher load condition, maximum 46.5% decrease at full load condition Lower 23% compared with diesel fuel emission [133] [135] A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 CO 217 [48] [47] – – Reduction with increase of blend ratio and engine speeds 35% reduce with B60 biodiesel used as compared to diesel – Increase 14.87–22.5% with increase of blend ratio 4% Reduce for B100 biodiesel used at full load Marginally increase Reduce 9.88–42.06% with increase of bland ratio – Reduce 6.75% with use of higher bland ratio – Smoke PM HC Nox [44] A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 Refs. 218 HC emission dramatically decreases by 35-60% with the increase in biodiesel percentage in the fuel blend and in high engine load condition. NOx emission increases (6–16%) with increased engine load and high biodiesel percentage in the blend. However, it decreases (9–27%) when mohua ethyl ester is used. Smoke level decreases (5–46%) in a full load condition and with high biodiesel percentage present in the fuel blend. 6.4. Rubber seed oil biodiesel Rubber seed biodiesel produces lower emission than diesel fuel [106,113,141]. However, it produces high emissions in some specific conditions [142]. The emission characteristics of rubber seed biodiesel are presented in Table 17. The following deductions can be made by analyzing the findings of the different experiments: CO emission decreases by about 0.13–1.13% with a low biodiesel concentration in the blend and a high load condition. With the DEE additive, high load, and low biodiesel percentage concentration, CO and HC emission is considerably decreased. NOx emission increases by about 13% with a high biodiesel percentage in the blend and a high load condition. Smoke opacity decreases by 37.09% with a low load condition and high biodiesel concentration present in the fuel blend. The volatility and oxygen enrichment provided by DEE are beneficial in improving fuel evaporation and smoke reduction. The presence of oxygen and the better mixing of DEE with air lead to an improved combustion rate. – Slightly improvement 12.96% with higher biodiesel blend ratio – 1-Cylinder, 4S, WC, DI, CI engine Full throttle at different speeds (1200 rpm, 1400 rpm and 2200 rpm) and different blends (20%, 50% and 100%) Different loads (0%, 20%, 40%, 60%, 80% and 100%) and different blends (20%, 40%, 60%, 80% and 100%) Different blends (B10, B20, B30 and B40), Constant speed (1500 rpm) and added additives 3 Cylinder, AVL make CI engine, D: 3.44 l, CR: 18.1, WC, RS: 2200 rpm, P: 44.1 kw 1-Cylinder, 4 S, WC, DI Emission Test condition Engine Table 15 Engine emission results using polanga biodiesel at different condition. CO 6.5. Cotton seed biodiesel Some studies examined the use of cotton seed-based biodiesel in a diesel engine, and the emission results showed low emissions of CO, HC, NOx, and smoke opacity [145,146,173]. However, some conditions also showed high emissions [145,148]. Table 18 presents the different experimental results of emission characteristics using cotton seed biodiesel and its blends. The table also shows that the maximum reduction of cotton seed biodiesel of CO, HC, and smoke emission is 45%, 67%, and 14%, respectively, with NOx decreasing by 25% in some conditions compared with diesel fuel. The following conclusions can be made from the analysis of the different experimental results: CO and NOx emissions decrease with the increase in fuel injection pressure. CO and HC emissions drastically decrease with high BMEP and turbo charging operation. CO emission decreases by about 4–45.66% depending on different conditions. HC emission increases with increased percentage of biodiesel present in the fuel blend. PM emission decreases (24–69%) because of high BMEP. Higher NOx emission is emitted (6–39.5%) because of low engine load condition. However, low emission is produced with a high concentration of biodiesel present in the fuel blend. NOx emission decreases by about 10–25% in a full load condition. NOx emission increases with increased BMEP in the combustion chamber. Low smoke emission is produced because of the low percentage of biodiesel present in the fuel blend. However, it increases in a high load condition. Table 16 Engine emission results using mohua (Madhuca indica) biodiesel at different condition. Engine type 1-Cylinder, 4S, WC, CI engine, RP: 4 kw 6-Cylinder, 4S, AC, D: 5.9 L, CR: 17.6:1, HP: 158, CI engine Different blends (B20, B40, B60 and B80), different loads (25%, 50%, 75% and 100%) and constant speed (1500 rpm) Different blends (10%, 20% and 30%), different loads and constant speed (1500 rpm) Different loads, different blends (B20, B40, B60) and constant speed (1500 rpm) Emission HC PM Nox Smoke Reduce 0.02–0.2% comparison of diesel fuel with the increase of biodiesel concentration in the blends – – – Increased 6% compared with diesel fuel Reduce 5–46% with increase of percentage of biodiesel in the blends [96] – – Higher at lower load compared to diesel fuel – [53] Reduce with increase of blend ratio compared with diesel fuel Reduce 35% compared with diesel 49%-60% lesser compared to diesel fuel. – Increased 11.6% with increase proportion of biodiesel in the blends – [111] – – [107] – [54] Lower than that of diesel – – Reduced 11% compared with diesel Reduced 9% for methyl ester and 27% for Ethyl ester compared to diesel. Lower compared to diesel fuel – _ [140] Higher compared with diesel fuel [139] – 4% Lower than diesel fuel [95] – 16% Increase with increase of concentration of biodiesel in diesel fuel At part load 30% reduction and full load condition there about 15% reduction compared with diesel fuel – Reduce 0.02–0.16% with the increase of biodiesel blends compared with diesel fuel 1-Cylinder, 4S, WC, DI, CR: 16.5:1, RP: 3.7 kw, D: 553 cm3 1-Cylinder, 4S, WC, DI, CR: 16.5:1, RP: 3.7 kw, D: 553 cm3 Constant speed (1500 rpm) Constant speed (1500 rpm) and used MME and MEE Reduce 30% compared with diesel fuel Reduce 67%-79% for both ester used compared with diesel fuel 1-Cylinder, 4S, WC, DI, CR: 16.5:1, RP: 3.7 kw, D: 553 cm3 1- Cylinder, 4S, WC, DI, HP: 7, Constant speed (1500 rpm) 0.34% lower compared with diesel Blend (B20), constant speed (1500 rpm), and steady state condition Constant speed (1500 rpm) and different loads (0%, 25%, 50%, 75% and 100%) –– 1-Cylinder, 4S, AC, DI, CR: 17.5:1, RP: 4.4 kw 3-Cylinder, 4S, AC, DI, D: 2826 cm3, CR: 17:1 Different loads, different blends (B10, B20, B40, B60, B80) and constant speed (1500 rpm) Refs. CO At full load condition CO reduction, about 26% compared with diesel fuel Lower compared to diesel fuel Reduce gradually with increase of load compared with diesel fuel Lower than that of diesel fuel – – A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 1-Cylinder, 4S, WC, CR: 18:1, P: 9 kw, CI engine Test condition [138] 219 220 A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 13% Higher using DEE in biodiesel compared with diesel fuel [144] – Decrease with using DEE operation compared with diesel fuel Lower compared with diesel fuel 1-Cylinder, 4S, DI, RP: 4.4 kw, CR: 17.5:1, D: 661.5 cm3 1-Cylinder, DI, 4S, RP: 5.5 kw, CI engine, WC 1-cylinder, AC, CR: 17.5:1, 4S, DI, CI engine, RP: 4.4 kw, RS: 1500 rpm 1-Cylinder, WC, 4S, DI, RS: 1500 rpm, RP: 5.5 kw, CR: 16.5:1 1-Cylinder, 4S, DI, RP: 5.5 kw, WC, CI engine Constant speed (1500 rpm)and different load condition Various diethyl ether (DEE)(50 g/h, 100 g/h, 150 g/h, 200 g/h and 250 g/h) and full load condition Different loads and constant speed 1500 rpm Decrease with increasing percentage of biodiesel in the fuel and low load condition Reduced at all load condition with the induction of hydrogen for all injected fuel Higher than that of diesel in all operation condition Decrease 26% with using injection of DEE compared with RSO 0.037% lower than compared with diesel fuel – Higher compared with diesel fuel but lower 6.02–20.1% compare to other biodiesel at all load condition [143] [142] Increase 1.01% with hydrogen energy shear Reduced with the induction of hydrogen for all injected fuel – Higher than that of diesel with high load condition Large reduction in smoke opacity about 34.4% using DEE [106] 20% Biodiesel blend gave lower about 17% smoke opacity compared with diesel fuel Reduced smoke level 37.09% at full load condition Increase with the increasing biodiesel blends – [113] [141] Increase with increase of engine load – – 0.13–1.13% Lower compared to diesel fuel Different loads, different blends (B20, B40, B60, B80 and B100) and constant speed (1500 rpm) Different loads, different blends (B10, B20, B50, B75 and B100) and constant speed (1500 rpm) Constant speed (1500 rpm) and different load (25%, 50% 75%, 100%) 1-Cylinder, 4S, DI, RP: 5.5 kw, WC, CI engine HC Emission CO Test condition Engine type Table 17 Engine emission results using rubber seed oil biodiesel at different condition. Nox Smoke Refs. 6.6. Jojoba oil biodiesel Studies have been conducted on the use of jojoba biodiesel in a diesel engine, and jojoba biodiesel has been found to give higher emission than diesel fuel [61,64,152]. Table 19 shows the different experimental results of the emission characteristics of jojoba biodiesel. Jojoba biodiesel produces high CO, HC, and NOx emissions in most cases but produces low CO emission in some specific conditions. The following conclusions can be deduced from the analysis of the different experimental results: CO emission increases (12–14%) with the increase in biodiesel percentage in the fuel blend and with EGR operation. However, it decreases in a high engine speed condition. CO emission decreases dramatically because of high engine speed. HC emission decreases significantly in a low engine speed condition and increases with EGR operation. NOx emission (14–16%) increases with increased engine speed but decreases by about 11–13% when jojoba methyl ester is used without EGR operation. 6.7. Tobacco oil biodiesel Tobacco biodiesel in diesel engine produces better emission performance compared with diesel fuel in most studies. Table 20 shows that blends of tobacco biodiesel reduce CO and increase HC and NOx emissions. However, HC and NOx emissions significantly decrease in some special conditions. The following deductions can be made from the analysis of the different experimental results: With the increase in engine load and biodiesel content in the fuel blend, CO and HC emissions decrease. However, increase with high injection pressure. With a full load and in a high injection pressure condition, NOx increases by about 5–6% but significantly decreases with low content of biodiesel in the fuel blend. Smoke emission slightly decreases with a full load and in high engine speed condition. 6.8. Neem biodiesel Many researchers have used Neem biodiesel in a diesel engine and have found low emission characteristics [156,158–160,162]. Some specific condition show high emissions of CO, HC, NOx, and smoke opacity [157,161]. Table 21 shows the different experimental engine emission results using neem biodiesel in a diesel engine in different conditions. The following conclusions can be made from the analysis of the different experimental results: CO decreases with increased percentage of ethanol content in the fuel blend. However, with higher BMEP and engine load, CO emission increases by about 20–40%. Engine operation with dual mode condition produces high CO emission. HC emission increases by 24–54% with the increase in engine load and decreases by 2.59–5.26% in full load and half load conditions. HC emission is higher with the addition of ethanol in fuel blends in all operating load conditions. NOx emission decreases by 3.2–6.06% in half load and full load conditions. NOx emission decreases by 37% when pure oil is used and by 19% when methyl ester is used in a full load condition. Table 18 Engine emission results using cotton seed biodiesel at different condition. Engine type Test condition Emission Refs. CO HC PM NOx Smoke Constant speed (2000 rpm), different blends (10% and 20%), medium and high load condition Different speeds (1200 and 1500 rpm), different loads (20%, 40%, 60% and full load) Increase compared with neat diesel fuel at medium and high loads Reduced with increasing biodiesel percentage in the blend – Lower as compare with neat diesel fuel in both medium and high loads Slightly increases with higher percentage of biodiesel in the fuel blend Increase compare with neat diesel fuel at medium and high loads – [114] Full load and different speeds (900– 1800 rpm) Increase compared with diesel fuel Slightly increase with using 10% biodiesel in the fuel blend Slightly increase with increase of biodiesel percentage in the fuel blend – – – [115] Different speeds (1250–2500 rpm) and different blends (B5, B20, B50, B75 and B100) Different speeds and different blends (B10, B20, B30) Decrease with increase of biodiesel percentage in the fuel blend Lower than that of diesel fuel – – Decrease at high engine speed condition Higher than that of diesel fuel but lower compare with other biodiesel blends Increase with increase of blend ratio – 10% increases with increase engine torque Reduced 14% at used 10% biodiesel blend [59] Constant speed 1500 rpm, different BMEP and different methyl ester used Average 4–16% reduced at high BMEP Average 45–67% reduced compare with diesel fuel Increases 10–23% at higher BMEP – [174] 6-Cylinder, 4S, DI, WC, TC, D: 5958 cc, CR: 18:1, RP: 177 kw, RS: 2600 rpm Different blends (B10, B20), different speeds (1200 rpm and 1500 rpm) and different load condition (20%, 40% and 60%) Reduced with the increase of percentage of oil in the fuel blend [148] Different speeds and preheated blend at (30°, 60°, 90°, 120 °C) Increase slightly with increase biodiesel percentage in the fuel blend – Slightly increase with higher percentage of biodiesel in the blend 1-Cylinder, 4S, DI, CR: 18:1, RS: 3600 rpm, NA, Slightly increase with higher percentage of biodiesel in the fuel blend Decreases 14.40%-45.66% compare with diesel fuel Reduced 24% compare with neat diesel fuel Reduced 53–69% on average compare with diesel fuel – – – [149] 1-Cylinder, DI, 4S, AC, CR: 18:1, D: 395 cc, RS: 3600 rpm, RP: 6.25 kw 4-Cylinder, 4S, DI, NA, WC, CR: 16.8:1, RP: 51 kw, RS: 2400 rpm, 1-Cylinder, 4S, AC, DI, CR: 18:1, RP: 6.25 kw, RS: 3600 rpm, 1-Cylinder, 4S, AC, DI, CR: 18:1, RP: 6.25, RS: 3600 rpm Full load and different speeds (2800– 1300 rpm) Decrease about 35% compare with diesel fuel – – Increase approximately 11.21%-39.1% as compare with diesel fuel 10–22% decrease compare with diesel fuel – [150] Full load and different speeds (1200– 2400 rpm) Decrease 5% compare with diesel fuel – – Increase 6% compare with diesel fuel – [146] Full load and different speeds (1700, 2000, 2300, 2600 and 3000 rpm) 17–21% decrease for both engine test – – 6.5–7.4% increase for engine test Lower emission compared with diesel fuel [151] Full load, varied injection pressure and constant speed Reduction about 30% compare with diesel fuel – – Reduction 25% compare with diesel fuel – [60] 1-Cylinder, WC, 4S, DI, CR: 19.8:1, RS: 4500 rpm 1-Clynder, 4S, DI, WC, CR: 17:1, D: 770 cm3, RP: 8 HP, RS: 2000 rpm 1-Cylinder, 4S, AC, DI, D: 406 cm3, RP: 10 HP, RS: 3600 rpm, CR: 18:1 1-Cylinder, 4S, DI, WC, NA, D: 553 cc, CR: 16.5:1, RP: 4.476 kw, RS: 1800 rpm 6-Cylinder, 4S, DI, TC, D: 5.9, CR: 17.5:1, RP: 136 kw, RS: 2500 rpm – [147] [145] A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 6-Cylinder, 4S, WC, DI, D: 5958 cm3, CR: 18:1, RP: 177 kw, RS: 2600 rpm, 221 222 Table 19 Engine emission results using jojoba biodiesel at different condition. Engine type Various loads (no load, 1/3, 2/3 and full load), different blends (B20, B40, B60) and different speeds Different speeds (1000–1900 rpm) and full load Different speeds and injection timing of 24 CAD BTDC Emission Refs. CO HC Nox Smoke Increase with the increase of biodiesel percentage in the fuel blend Decrease with increase of engine speed compare with diesel fuel Increase 12% and 14% with EGR and without EGR – Increase with the increase of engine speeds – [61] Higher at low speed condition and EGR operation but at higher engine speed give lower emission than diesel fuel – Increase about 16% and 14% at engine speed 1200 rpm and 1600 rpm but 33% reduction in NOx with EGR operation Decrease about 11% and 13% with EGR and without EGR operation – [152] – [64] Table 20 Engine emission results using tobacco oil biodiesel at different condition. Engine type 4-Cylinder, 4S, TC, WC, RP: 112 kw, RS: 9000 rpm 4-Cylinder, 4S, TC, WC, IDI, CR: 21.5:1, D: 1.753, RP: 55 kw, RS: 2200 rpm 1-Cylinder, 4S, NA, RS: 1500 rpm, RP: 5 HP Test condition Emission Refs. CO HC Nox Smoke Different loads (50%, 75% and 100%), different blends (B10, B17.5 and B25) and speed (1500– 3000 rpm) Different loads (50%, 75% and 100%), different blends (B10, B17.5 and B25) Reduced 100–1600 ppm at medium load condition Decrease at full load condition – Slightly increase at full load – [66] – 5% Increase at full load condition – [68] Constant speed 1500 rpm, different loads and different blends (B2 and B5) Decrease with the increase of biodiesel percentage Decrease with increase of engine speed Increase with the increase of biodiesel percentage in the fuel blend Decrease with increase of engine speed Decrease with increase of biodiesel percentage in the fuel blend 6% Increase compared with diesel fuel – [154] [153] Slightly higher compared with diesel fuel Higher than that of diesel fuel Increase with increase of engine load Reduced slightly at higher engine speed condition – 1-Cylinder, 4S, NA, DI, RP: 14.7:1, RS: 2500 rpm Full load and different speeds (1200, 1400, 1600, 1800, 2000, 2200 and 2400 rpm) 1-Cylinder, 4S, DI, WC, RP: 5.2 kw, CR: 17.5:1 Different injection pressures (205, 220, 240 and 260 bar) [155] A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 1-Cylinder, 4S, AC, DI, CR: 17:1, RP: 5.775 kw, RS: 1500 rpm 2-Cylinder, 4S, WC, DI, D: 2266 cc, CR: 16.4:1, RS: 1500 rpm, RP: 26HP 1-Cylinder, 4S, AC, DI, NA, CR: 17:1, RP: 5.775 kw, RS: 1500 rpm Test condition Table 21 Engine emission results using neem biodiesel at different condition. Engine type 1-Cylinder, 4S, NA, DI, CR: 16.5:1, RP: 3.5 kw, RS: 1500 rpm Emission Refs. CO HC PM Nox Smoke Constant speed 1500 rpm, duel fueling Increase at dual mode operation Increase with the increase of engine load – – Lower as compare with diesel fuel [161] Different blends (B5, B10 and B15), different speed (600–1200 rpm) and different BMEP Constant speed and different loads (1000–4000 watt) condition Reduced compare with diesel fuel – – Increase compare with diesel fuel Reduced compare with diesel fuel [162] Lower compared with diesel fuel Slightly reduced compare with diesel fuel – Lower than that of diesel fuel Slightly reduced all load condition [156] Increase at increase of BMEP – Decrease about 3.22% at part load and 6.06% at full load condition 37% reduction for pure oil and 19% reduction for methyl ester at full load condition Increases with the increase of engine load – [163] Higher than that of diesel fuel [157] Lower at all load compared with diesel fuel Reduced 5.26% at part load and 2.59% at full load condition Increase 54% and 24% for pure oil and methyl ester at full load condition Lower compared with diesel fuel [158] – Reduced 2.59% at full load – Reduced 6.06% at full load Increase with the increase of percentage of biodiesel in the fuel blend and increase engine load 18.39% reduction at full load condition Lower with the higher percentage of ethanol in the fuel blend at high loads condition Higher with the addition of ethanol in the blends at all loads – Increase slightly at full loads condition Different BMEP (100, 200, 300,400,500,600 and 650) and constant speed 1500 rpm Constant speed and different BP (0– 5 kw) Different blends (B10, B20, B30, B40 and B50), constant speed and deferent break power Different blends (B20, B40, B60, B80 and B100), Different BMEP and constant speed 1500 rpm Different blends (B5, B10, B15, B20), different loads and constant speed 1500 rpm Increase 40% for pure oil and 20% for methyl ester at full load – – Decrease at higher engine load with the addition of ethanol in the fuel blends [159] [160] Table 22 Engine emission results using linseed biodiesel at different condition. Engine type Test condition Emission Refs. CO HC NOx Smoke 1-Cylinder, 4S, AC, DI, RP: 4.4 kw, CR: 17.5:1, RS: 1500 rpm 1-Cylinder, 4S, AC, DI, RP: 4.4 kw, D: 661 cc, CR: 17.5:1, RS: 1500 rpm 1-Cylinder, WC, 4S, Di, RP: 3.5 kw, CR: 17.5:1, RS: 1500 rpm Different loads, constant speed 1500 rpm and different injection pressure (200,220 and 240 bar) Different loads and constant speed 1500 rpm Lower than that of diesel fuel at all the injection pressure HC emission decreases with the increase of fuel injection pressure Higher compare with others biodiesel at high load condition Increase with the increase of engine loads Increase by the increase in engine loads but near the diesel fuel Higher than that of others biodiesel Different blends (B5, B10, B15 and B20), constant speed 1500 rpm and different loads Decrease with the increase of load and increase of biodiesel concentration in the fuel blend Increase with the increase of biodiesel concentration in the fuel blend and engine loads Lower emission compare with diesel fuel Higher emission compare with others biodiesel – Slightly increase compare with the diesel fuel A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 1-Cylinder, 4S, DI, WC, RP: 5.2 kw, CR: 17.5:1, RS: 1500 rpm 1-Cylinder, 4S, DI, NA, WC, RP: 9.8 kw, CR: 20:1, RS: 2000 rpm 1-Cylinder, 4S, DI, WC, RS: 1500 rpm, RP: 3.7 kw, CR: 16.5:1 1-Cylinder, 4S, WC, DI, CR: 17.5:1, D: 661 cc, RP: 5.2 kw, RS: 1500 rpm 1-Cylinder, 4S, DI, NA, WC, RP: 5HP, RS: 1500 rpm, CR: 16.5:1, 1-Cylinder, AC, DI, CR: 17.5:1, RP: 4.4 kw, RS: 1500 rpm 1-Cylinder, DI, WC, RP: 5.2 kw, RS: 1500 rpm Test condition [92] [73] [165] 223 224 Table 23 Engine emission results using jatropha biodiesel at different condition. Test condition Emission Refs. CO HC Nox Smoke 1-Cylinder, 4S, DI, WC, D: 1007 cc, CR: 18.5:1, RS: 2400 rpm 3-Cylinder, 4S, DI, WC, D: 3440 cc, CR: 18:1, RS: 2200 rpm 1-Cylinder, 4S, DI, CR: 16.5:1, RP: 5HP, RS: 1500 rpm 4-Cylinder, 4S, DI, TC, D: 1609 cc, RP: 84.5 kw, CR: 18.5:1, RS: 3800 rpm 1-Cylinder, 4S, DI, WC, RP: 8 HP, RS: 1500 rpm Different blends (B10, B20, B50 and B100) and different speeds (1000– 2400 rpm) Different speeds (1200,1800 and 2200 rpm) and different blends (B20, B50 and B100) Different blends (B20, B40, B50, B60, B80 and B100) and different loads (25%, 50% 75% and 100%) Different speeds and full load condition 6.51–12.32% Reduced with the increase of blend ratio 3.29–10.75% Increases compared with diesel fuel Increased 20.54% with 20% biodiesel blend used and 15.65% increased with used 50% biodiesel Lower compared with diesel fuel Reduced compared with diesel fuel at higher percentage of biodiesel blend Reduced with the increase of biodiesel percentage in the fuel blend – [79] Reduced 5.57–35.21% with the increase of percentage of biodiesel in the fuel blend Lower compare with diesel fuel 14.91–27.53% Decreases with the increase of biodiesel percentage in the fuel blend Reduce about 18.19– 32.28% with lower percentage of biodiesel blend used Lower than that of diesel fuel 10–40% Reduced compare with diesel fuel Lower than that of diesel fuel at full load condition 5–10% Reduction with full load condition Reduce compared with diesel fuel [80] Different blends (B25, B50, B75 and B100) and constant speed Higher than that of diesel fuel at high load [169] Different speeds (1500 and 2000 rpm) and different load Lower compare with diesel fuel at pick load condition Increases with the increase of biodiesel percentage in fuel blend and higher than that of diesel fuel Lower with the increase of engine speed Lower than that of diesel fuel 1-Cylinder, 4S, WC, DI, D: 815 cc, RP: 8.82 kw, CR: 17:1, RS: 2000 rpm 1-Cylinder, 4S, DI, AC, CR: 18:1, D: 395 cc, RP: 5.59 kw, RS: 3600 rpm 1-Cylinder, 4S, DI, AC, D: 947.8 cc, CR: 17.5:1, RP: 7.4 kw, RS: 1500 rpm Decreases with the increase of biodiesel percentage in fuel blend Decreases with the increase of engine speed – [166] Different speeds (1800, 2500 and 3200 rpm) Lower than that of diesel fuel Lower than that of diesel fuel Higher than that of diesel fuel Lower compared with diesel fuel [94] Different blends (B5, B10, B20, B30 and B100) and different loads (20%, 40%, 60%, 80% and 100%) Decreases with the increase percentage of biodiesel in the fuel blend Decreases with the increase of biodiesel blend ratio Higher than that of diesel fuel Decreases with the increase of biodiesel concentration in the fuel blend [171] [47] [170] A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 Engine type A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 Smoke opacity decreases by 18.39% with the addition of ethanol in fuel blends and high load condition. However, it increases significantly when a high percentage of biodiesel is present in the blend. 6.9. Linseed oil biodiesel The emission behavior of linseed oil-based biodiesel used in a diesel engine depends on the engine’s operating condition. Emission results using linseed based biodiesel in a diesel engine show low emissions of CO, HC, NOx, and smoke [73,92]. However, it produces a high emission in some specific cases. Table 22 shows the emission characteristics affected by different blend ratios. The following deductions can be made from the analysis of the different experimental results: CO decreases when a high content of biodiesel is present in fuel blends and in a high engine load condition. Linseed biodiesel produces higher HC emission when higher biodiesel content is present in the fuel blends and in a higher load condition. HC emission dramatically decreases with the increase in fuel injection pressure. NOx emission generally increases when used high biodiesel percentage in the fuel blned. Smoke level decreases but NOx emission increases with increased fuel injection pressure. 6.10. Jatropha biodiesel Low emissions of CO, HC, NOx, and smoke opacity were observed when jatropha biodiesel was used [47,94,166,169]. However, engine emission decreases significantly in some specific conditions [47,94,169]. Table 23 shows the different experimental engine emission results. Specifically, emissions of CO, HC, and smoke opacity decrease, with NOx emission decreasing in most cases. As jatropha biodiesel lowers the heating value, NOx emission significantly decreases. The following deductions can be made from the analysis of the different experimental results: CO and HC emissions increase because of high engine load with EGR operation and gradually decrease because of a high percentage of biodiesel concentration present in fuel blends. CO emission decreases by 5.57–35.21% and HC emission decreases by 14.91–32.28% because of high biodiesel content in fuel blends. NOx emission decreases with EGR operation but increases with increased engine load and biodiesel content in fuel blends. NOx emission increases by 3.29–10.75% in some specific conditions. However, it reduces in a full load condition. Smoke opacity increases in a high engine load condition but decreases with the increase in biodiesel concentration in fuel blends. 7. Recommendations Driven by energy security and other environmental concerns, research on biodiesel is rapidly growing around the globe. Apparently, the demand for biodiesel will significantly increase in the future. Although edible oils are available as feedstock sources for biodiesel production, they may not be sustainable sources. Therefore, reliable, economical, and sustainable feedstocks for biodiesel production must be sought. As mentioned in previous sections, there are many potential non-edible sources of oil that can compete with edible oils, considering that most non-edible oil-growing plants can be cultivated in non-arable lands. Therefore, wasteland 225 can be used for oil–crop cultivation for biodiesel production to minimize the use of limited arable lands for growing edible oil crops for biodiesel production. When all these factors are considered, non-edible oils may definitely overrun edible oils as biodiesel feedstocks. However, feedstocks for biodiesel should have a diversified oil source depending on geographical location. The use of edible oils as fuels instead of food will certainly affect the price of the former. Considering all factors, non-edible vegetable feedstocks have more advantages than edible vegetable feedstocks. Fertile agricultural land should be maintained for planting edible oil crops, while wastelands should be maintained for cultivating non-edible vegetable crops that have simple ecological requirements. Developed countries should maximize the utilization of limited land areas. Variegated resources for biofuel feedstocks will ensure that the quality of obtained biodiesel is suitable for that particular region. Therefore, non-edible vegetable oil feedstocks can ensure sustainable alternative fuel in the future. 8. Conclusion and summary of results Biodiesel has attracted much research because of its economic and environmental benefits as well as its renewable origin. Biodiesel produced from non-edible oil resources can defy the use of edible oil for biodiesel production. Therefore, its demand is growing steadily, and researchers are looking for possible newer sources of non-edible oil. This review concludes that non-edible oil is a promising source that can sustain biodiesel growth. Fuel properties vary depending on feedstock and the biodiesel conversion process. Most reviewed biodiesel fuels have excellent kinematic viscosity, except jojoba, neem, and linseed biodiesel. However, the viscosity ranges of jatropha, tobacco, and mohua biodiesels are close to that of diesel fuel. Rubber seed, jojoba, tobacco, and jatropha biodiesels are better than others in terms of density. Except for jojoba, neem, and linseed oil biodiesels, other biodiesels meet the specified flash point limit. Karanja, polanga, cotton seed, jojoba, and jatropha oil biodiesels are excellent in terms of CN. Jojoba and jatropha biodiesel have better calorific value than other biodiesels. Palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid are the common fatty acids in vegetable oils. Biodiesel quality and fuel properties are highly dependent on the presence of fatty acid composition in the fuel blend. Several researchers found that the presence of monounsaturated fatty acid in biodiesel blend at low temperature could improve ignition quality, fuel flow properties, and fuel stability. Moreover, biodiesel CN, cloud point, and stability increase with the presence of saturated fatty acid alkyl ester in the fuel blend. Several studies were carried out to determine power output, BSFC, and BTE of an engine operating with non-edible oil-based biodiesel. In most cases, cotton seed and jatropha biodiesels gave higher BSFC but had better thermal efficiency than other biodiesels. Their brake power and torque were closer to those of diesel fuel because of their calorific value. Karanja, rubber seed, jojoba, and tobacco biodiesels had higher BTE and power and lower BSFC than other biodiesels. Moreover, the low percentage of biodiesel blends (<20%) caused high brake power and reduced fuel consumption because of complete combustion. Therefore, biodiesels with high calorific value and low viscosity are more suitable for the improvement of engine performance. Biodiesel is an oxygenated fuel that leads to complete combustion. Based on several experimental results, the use of karanja, mohua, rubber seed, and tobacco biodiesel in CI engine can reduce CO, HC, and smoke emission with an increase in NOx emission. The low HC emission in most cases is usually caused by advanced injection timing and proper combustion in the combustion chamber. More- 226 A.M. Ashraful et al. / Energy Conversion and Management 80 (2014) 202–228 over, higher oxygen contains and higher CN, which is favored to lower emission. However, some authors found a significant reduction of NOx emission. 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