Influence of biodiesel blending on physicochemical
Transcription
Influence of biodiesel blending on physicochemical
Energy Conversion and Management 94 (2015) 51–67 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman Influence of biodiesel blending on physicochemical properties and importance of mathematical model for predicting the properties of biodiesel blend M.A. Wakil a,⇑, M.A. Kalam a, H.H. Masjuki a, A.E. Atabani b, I.M. Rizwanul Fattah a a b Center for Energy Sciences, Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia Department of Mechanical Engineering, Faculty of Engineering, Erciyes University, 38039 Kayseri, Turkey a r t i c l e i n f o Article history: Received 24 October 2014 Accepted 16 January 2015 Available online 6 February 2015 Keywords: Biodiesel Edible oil Non-edible oil Blending Physicochemical properties Mathematical modeling a b s t r a c t The growing demand for green world serves as one of the most significant challenges of modernization. Requirements like largest usage of energy for modern society as well as demand for friendly milieu create a deep concern in field of research. Biofuels are placed at the peak of the research arena for their underlying benefits as mentioned by multiple researches. Out of a number of vegetable oils, only a few are used commercially for biodiesel production. Due to various limitations of edible oil, non-edible oils are becoming a profitable choice. Till today, very little percentage of biodiesel is used successfully in engine. The research is still continuing for improving the biodiesel usage level. Recently, it is found that the blended biodiesel from more than one feedstock provides better performance in engine. This paper reviews the physicochemical properties of different biodiesel blends obtained from various feedstocks with a view to properly understand the fuel quality. Moreover, a short description of each feedstock is given along with graphical presentation of important properties for various blend percentages from B0 to B100. Finally, mathematical model is formed for predicting various properties of biodiesel blend with the help of different research data by using polynomial curve fitting method. The results obtained from a number of literature based on this work shows that the heating value of biodiesel is about 11% lower than diesel except coconut (14.5% lower) whereas kinematic viscosity is in the range of 4–5.4 mm2/s. Flash point of all biodiesels are more than 150 °C, except neem and coconut. Cold flow properties of calophyllum, palm, jatropha, moringa are inferior to others. This would help to determine important properties of biodiesel blend for any percentage of biodiesel and to select the proper feedstock for better performance. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The primary catalyst of any country’s socio-economic development is energy. However, through modernization the demand of energy consumption is facing a serious threat due to the gradual declination of fossil fuels. Various sectors for instance, industry, transport, agriculture, domestic sector, etc. require energy from sources like wood, coal, petroleum products, nuclear power, solar, and wind [1]. Currently, more than 80% of energy demand is catered by fossil fuels [2]. The deep concern about fossil fuels is that it’s generation of toxic pollutants links to global warming, climate change and even some impasse diseases [3]. To compete with this critical situation, a good number of research have been ⇑ Corresponding author. Tel.: +60 163269524. E-mail addresses: [email protected] (M.A. Wakil), [email protected] (M.A. Kalam). http://dx.doi.org/10.1016/j.enconman.2015.01.043 0196-8904/Ó 2015 Elsevier Ltd. All rights reserved. conducted to find alternative to fossil fuels for eco-friendly condition. Biodiesel is considered to be a notable option for at least complementing conventional fuels [3]. Its production from renewable sources such as vegetable oils and fats has been widely reviewed [4–10]. It is advantageous over petroleum product because it is safe in handling, biodegradable, non-toxic, has higher combustion efficiency, higher cetane number, contains no sulfur, etc. [1,3,11–14]. In addition, it is advantageous for numerous social benefits like rural revitalization, creation of new jobs and reduced global warming [15]. Among the available sources of biodiesel, edible oils are dominating in several countries as diesel substitute. For instance, canola and soybean are used in USA, palm oil in Malaysia, rapeseed oil in Europe etc. [12,14]. Currently, more than 95% of the world biodiesel comes from edible oil. In the year 2004–2007 the edible oil used for biodiesel production was 6.6 million tons which would attribute 34% of the increase in global consumption of biodiesel and 52 M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 Nomenclature APME CIME COME CME CMME JCME MOME NME POME RBME Aphanamixis polystachya methyl ester Calophyllum inophyllum methyl ester Coconut methyl ester Canola methyl ester Croton megalocarpus methyl ester Jatropha curcas methyl ester Moringa oleifera methyl ester Neem methyl ester Palm methyl ester Rice bran methyl ester also lead to one third of the total projected growth of edible oils between 2005 and 2017 [16]. This large usage of edible oils for biodiesel has caused a serious impact on food supply. It has the ability to lead to starvation especially in developing countries and impose antagonistic effect on environment [13]. The prominent solution is to use second generation feedstocks (non-edible oils) which has higher potential for biodiesel production [13] and can easily eliminate the food vs fuel concern. Another boosting feedstock is algae. Although full scale commercialization from algae has not begun yet, but it is expected to be rich in oil content (oil content in microalgae can exceed 80% of its weight of dry biomass) [3]. The use of vegetable oils started more than a century ago. Apart from the remarkable advantages, biodiesel has couple of difficulties to be used as a replacement of fossil fuels in engine such as high viscosity and density and low volatility and heating value [12]. These difficulties lead to problems in pumping, atomization, gumming, injection fouling, piston ring sticking, etc. [1]. Another serious threat for biodiesel industry is the cost of feedstock which currently accounts for over 70–85% of biodiesel production cost [13,17,18]. One solution to alleviate this problem is to use multiple feedstocks of varying percentage. It will not only subside the cost of production but also enhance product quality. Problems of using edible oils can also be moderated by switching these with non-edible oils. It has been proven that biodiesel containing up to B5 will have no notable difference in terms of power and fuel economy when it is compared to diesel [19]. ASTM D7467 suggests blending of 20% biodiesel with diesel. In 2014, the Chevy Cruze Clean Turbo Diesel is directing the engine with rated B20 biodiesel compatibility [20]. Now-a-days research is going on to increase the use of biodiesel blending with diesel. Consequently, biodiesel blending (biodiesel and diesel) bring a new topic in research arena. A number of researches have been undertaken already on biodiesel blending [17,21–27]. Accordingly, it has become easier to have a clear concept of the physicochemical properties of edible and non-edible vegetable oils with varying blending percentages for a better understanding on blend qualities. Survey of existing literature shows that most of the studies focus on pure biodiesel SME SFME CB10 CoB CrB JB CP PP CFPP Sesame methyl ester Sterculia foetida methyl ester Calophyllum biodiesel (10% + Diesel 90%) blend Coconut biodiesel, diesel blend Croton biodiesel, diesel blend Jatropha biodiesel, diesel blend Cloud point Pour point Cold filter plugging point properties rather than properties of blending. Therefore, this review aims firstly at focusing on the physicochemical properties of edible and non-edible biodiesel and their blends with diesel (B0–B100). Secondly, mathematical equation for various biodiesel blends would be produced in order to predict the important properties of blended biodiesel for any percentage of biodiesel. Here, a polynomial curve fitting method is used to generate the equation. It is believed that such kind of studies will assist researchers for further study about optimal usage of biodiesel. 2. Biodiesel feedstocks Feedstock-related cost has been regarded as a primary obstacle as it constitutes roughly around 60–90% of the total biodiesel production cost [28]. Biodiesel can be produced from a wide variety of oils. These include vegetable oils (edible and non-edible oils) [13,29–34], food processing waste (waste cooking oils, animal fat (tallow, lard, yellow grease, chicken fat) [28,35–37]), industrial residues) [38], algae, halophytes (Salicomia bigelovii [39]), sewage sludge [40], etc. Globally, more than 350 oil-bearing crops have been identified as potential biodiesel sources [12,13,29,41]. The regional climate mainly affects the feedstock selection for biodiesel production [13]. Table 1 presents some important oil bearing species [1,2,8,13,14,16,29,42]. A concise description of some edible and non-edible oil plants including their country of origin, oil content and their necessary uses are portrayed in Table 2 with their fatty acid composition in Table 3. The identification of plants and seeds of the selected oil sources are shown in Fig. 1. 3. Characteristics of crude oils and biodiesels Characterization of oil properties is necessary to research about the processing of crude oil to biodiesel and afterwards to diesel engine successfully. The physical and chemical properties of any fuel are significant factors which help to decide whether the oil Table 1 Oil species for biodiesel production. Category Source of oil Edible oil Sunflower, Rapeseed, Rice bran, Soybean, Coconut, Corn, Palm, Olive, Pistachia Palestine, Sesame seed, Peanut, Opium Poppy, Safflower oil, Amaranth, apricot, argan, artichoke, avocado, babassu, bay laurel, beech nut, ben, Borneo tallow nut, carob pod (algaroba), cohune, coriander seed, false flax, grape seed, hemp, kapok seed, lallemantia, lemon seed, macauba fruit (Acrocomia sclerocarpa), meadowfoam seed, mustard, okra seed (hibiscus seed), perilla seed, pequi,(Caryocar brasiliensis seed), pine nut, poppy seed, prune kernel, quinoa, ramtil (Guizotia abyssinica seed or Nigerpea), rice bran, tallow, tea (camellia), thistle (Silybum marianum seed), and wheat germ Jatropha, Karanjaor Pongamia, Neem, Jojoba, Cottonseed, Linseed, Mahua, Deccan hemp, Kusum, Orange, Rubbe rseed, Sea Mango, Karanja or Honge, milk bush, Nagchampa, Rubber seed tree, Tobacco seed oil, Algae, Halophytes and Xylocarpus moluccensis Non-edible oil Waste or recycled oil Animal fats Tallow, Yellow grease, chicken fat and by-products from fish oil, etc. Table 2 Acknowledgement of some edible and non-edible oils. Name of oil Characteristics Country of available Oil Yield of content plant seed Uses Refs. kg/ Kg/ha tree A widespread species found in Indo-China and 30– Species in the family Meliaceae also known as pitraj tree. It is indigenous as evergreen tree mainly growing in the tropical area of western Malaysia. Indonesia, India, Bangladesh, 40% Asia. This deciduous, perennial tree grows to 20–30 m long. Flower etc. clusters occur in leaf axils, less than a foot long. Seeds are greyish brown. Flowering: May–September 25– 40 [43–47] Herbal medicine, potential for biodiesel, The wood is used for construction of ships, vehicles, posts and agricultural tools Calophyllum inophyllum L. Known as penaga laut, non-edible oil seed tree belongs to Clusiaceae Native Australian tree, Found in tropical region 45– family. It enables to tolerate harsh environmental conditions (acidity, of India, Malaysia, Indonesia, Philippines, etc. 70% salinity, and drought), require little maintenance, 1000–4000 mm rainfall is sufficient per year. It is non-invasive, fruits profusely (3000–10,000 seeds tree1 season1). Duration of harvest is two months, Flowering in March–May and fruiting in October–November 25– 4680 50 For burning, timber, medicinal uses, [13,47–50] etc. Croton megalocarpus 40– C. megalocarpus belongs to Euphorbiaceae family. It is a multipurpose The plant id indigenous to East Africa and tree of Mexican and Central American origin with height 15–40 m. It widely found in mountain of Tanzania, Kenya, 45% Uganda, etc. is capable to engender at the altitude of 1200 m and 2450 m respectively. It requires less water footprint and fertilization during cultivation stage 50 Coconut Coconut is member of the family Arecaceae. Found throughout the Indigenous to Indo-pacific origin. Philippines, tropic and sub-tropic area. It is familiar as large palm growing up to Indonesia, India, Thailand, Sri Lanka, Mexico, Brazil etc. 30 m tall with pinnate leaves 4–6 m long. On very fertile land a coconut tree can yield 75 fruits per year but often yield less than 30 mainly due to tough cultural practices. Coconut palms are growing in more than 80 countries of the world with a total production of 61 million tons per year. Coconut trees are very hard to establish in dry climates and cannot grow without frequent irrigation, in drought conditions Jatropha curcas This plant is native to Mexico, Central America, 43– J. curcas belongs to the family Euphorbiaceae. It grows throughout Africa, India, Brazil, Bolivia, Peru, Argentina, and 59% most of the tropics and can survive on poor soil and drought condition. It is reported as wild, semi-arid-climates plant. It flowers in Paraguay March–September and fruiting in April–May and October–November of ellipsoidal green fruits. It produces seeds after 12 months and reaches its maximum yield after 4–5 years. 0.5– 100– 2.0 8000 Moringa oleifera Native to sub-Himalayan tracts of north-west Moringa oleifera is the most widely cultivated tree species in the India, Africa, Latin America, Pakistan, family of Moringaceae grows throughout most of the tropics. It is drought tolerant and can survive in arid, harsh and infertile land. The Bangladesh, Afghanistan, etc. tree can range from 5 to 10 m in height; sometimes can be even 15 m. The plant starts bearing pods 6–8 months after planting 35– 45% 3000 Neem Neem (Azadirachta indica), a tree of mahogany family Meliaceae. It is Native to Asian countries like India, Pakistan, fast growing evergreen tree and can reach a height of 15–20 m, rarely Bangladesh, etc. to 35–40 m. It is drought tolerant, thrives in area with sub-arid to sub-humid condition with annual rainfall 400–1200 mm and hardly below 400 mm. This is a typical tropical to subtropical tree can tolerate high to high temperature but cannot tolerate temperature below 4 °C. Duration of harvest is 2–3 months. Flowering starts in March–April and fruiting in June–July. The white, hard inner shell of the fruits enclose with one and rarely two or three seeds 30– 39% Palm Palm oil tree belonging to the species namely, Elaeis guineensis. Oil Mostly available in South East Asia (Indonesia, palms are originally from Western Africa, but can flourish wherever Malaysia), Thailand, Brazil, Nigeria, Colombia, heat and rainfall are abundant. It is found to be a tropical perennial Ecuador, Costa Rica Venezuela, etc. 5000– Rejuvenating chemical peels, pain 10,000 relieving and anti-inflammatory drag, biodiesel production, etc. 60% [13,51–53] Coconut oil is used for Skin [1,54] moisturizer, ingredient for soap, etc. 20– 35 Bio-fuels, carbon dioxide sequestration, etc. [13,47,53,55– 57] Moringa leaves uses as sources of food, as forage for livestock, etc. [53,58–60] Toiletries, pest control, cosmetics, Pharmaceuticals, etc. [47,61,62] 4000– Cooking ingredient, confectionery, 5000 cosmetics, body products and cleaning agents (oil) M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 Aphanamixis polystachya [12,63–66] 53 (continued on next page) Originated from Africa and Turkey, Also in India, 57– China, Sudan, Burma, Tunisia, Egypt, Thailand, 63% Mexico, Guatemala, Afghanistan, Pakistan, Bangladesh, etc. Sesame (Sesamum indicum L) is an oil seed herbaceous crop of the Pedaliaceae family primarily found in tropical and subtropical areas. It is very drought-tolerant, in part due to its extensive root system and requires adequate moisture for germination and early growth. It is an annual plant growing 50–100 cm tall with opposite leaves 4–14 cm long. The flowers are yellow, tubular with four-lobed mouth. The flower may vary in color with some being white, blue or purple Sesame Rice bran plant grows well in lowland with humid places. Identifies as unbranched, single stemmed which can grow up to 20–30 m in height. Can be cultivated for 40–50 years. It carries fruits from the fourth year onward. Due to the reduction in fruit production it is right choice to replanting for every 25 years rotation However, rice can be grown practically Rice is the seed of the monocot plants Oryza sativa (Asian rice) or anywhere, even on a steep hill Oryza glaberrima (African rice). Rice is the most important cereal cultivated in the world which fed more than half of the people of the world. Rice bran is a by-product of rice milling process. Due to the presence of active lipase and high free fatty acid, about 60–70% of rice bran oil production is non-edible. Rice cultivation requires ample water 16– 32% 440 kg/ Kg/ha tree Food, nutraceutical, Pharmaceutical industry Refs. Uses Oil Yield of content plant seed Country of available Characteristics Name of oil Table 2 (continued) [68,69] M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 Popular ingredient in Japan, Also uses [1,18,67] as medicine, animal food, cosmetics, shoes cream, etc. 54 is suitable for engine or unsuitable. Researchers have shown that the properties of biodiesel vary significantly due their diverse fatty acid composition which provides an obvious effect on engine performance. Therefore, it is important to characterize biodiesels according to preset standard testing methods [13]. American Standard Test Method (ASTM) and European (EN) standard have formulated the specification for biodiesel as shown in Table 4 [1,2,12,13,87,88]. Table 5 shows some selected properties of crude edible and non-edible oils. It is seen that the heating value of crude oils vary in the range of 38,500–40,000 kJ/kg. The maximum kinematic viscosity was reported for Calophyllum inophyllum (55.478 mm2/s) and rice bran (52.225 mm2/s). Among these feedstocks Moringa oleifera contains highest oxidation stability (41.75 h at 110 °C) while the maximum acid value was in C. inophyllum (41.74 mg KOH/g oil). On the other hand, except coconut (38,300 kJ/kg) the heating value of other edible and non-edible methyl esters are almost above 39,500 kJ/kg as shown in Table 6. Coconut possesses the lowest kinematic viscosity (3.1435 mm2/s). However, according to data found from various researches, all feedstocks indicated in this study have satisfied ASTM limit for viscosity. It is found that Neem and coconut have lower flash point rather than other feedstock. Cetane number varies from 45 to 75. 4. Impact of blending on physicochemical properties of biodiesel Though biodiesel satisfy the ASTM and EN limits, it cannot be used alone in diesel engine due to its high kinematic viscosity and density and also lower oxidation stability and heating value. To improve those properties, it is blended with diesel. In this paper we carried out some work to review the variation of physicochemical properties such as kinematic viscosity, calorific value, density, flash point, cloud point, pour point, CFPP, and oxidation stability with the varying blended percentage, B0 (Pure diesel)–B100 (Pure biodiesel). The data were gathered from different resources as in Refs. [18,51,100–115] and depicted in Figs. 2–9, respectively. As biodiesel is completely miscible to diesel, biodiesel and diesel blend was prepared using a beaker glass on a volume basis and the mixture was agitated with a shaker for about 15–30 min at ambient temperature. The effects of blend on the important properties are discussed in the following sections. 4.1. Kinematic viscosity Kinematic viscosity is the measure of resistance to fluid flow over another due to internal friction. It is the most critical property as it affects injection behavior [14]. Viscosity of vegetable oil is typically ten times higher than petroleum based diesel [116]. High viscosity leads to a poorer atomization and vaporization, formation of shoots, etc. [13,14,117]. The data collected from various research articles based on viscosity of many feedstocks at various blend percentages are depicted in Fig. 2. It is seen from figure that at any blend percentage, Calophyllum, Moringa, Neem and Rice bran biodiesel blends show higher viscosity than other feedstocks except that at lower blend percentages (below B30), the viscosity variation are small. For instance, results for B20 show that the average viscosity of each feedstock, APME = 3.657, CIME = 3.482, COME = 3.54, CMME = 3.50, JCME = 3.74, MOME = 3.67, NME = 3.81, POME = 3.54, RBME = 3.50, SME = 3.37 mm2/s respectively. Average value of B100 for each feedstock biodiesel are APME = 4.46, CIME = 5.23, COME = 4.06, CMME = 4.376, JCME = 4.57, MOME = 4.87, NME = 5.4, POME = 4.39, RBME = 4.82, SME = 4.339 mm2/s respectively. Table 3 Fatty acid composition of crude edible and non-edible oils. C8:0 C10:0 C12:0 C14:0 C16:0 C16:1 C17:0 C18:0 C18:1 C18:2 C18:3 C18:4 C20:0 C20:1 C22:0 C22:1 C24:0 C24:1 Aphanamixis polystachya (meliaceae) [13,70] Calophyllum inophyllum L. [13] N/D N/D N/D N/D 23.1 N/D N/D 12.8 21.5 29 13.6 N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D 0.09 14.6, 17.9 2.5 N/D 37.57, 42.7 26.33, 13.7 0.2, 2.1 N/D 0.94 0.72 N/D N/D 2.6 N/D Croton megalocarpus [52] Coconut oil [1,11] N/D N/D N/D 14 N/D 51,48.8 6.5 7.5, 7.8 0.1 0.1 0.1 11.6 5, 4.4 72.7 1, 0.8 3.5, o.4 0 N/D 65.7 N/D N/D 0.9 N/D N/D N/D N/D N/D N/D N/D N/D Jatropha curcas[1,13,16] N/D 0.1 N/D 0.1 18.5, 19.9 1.4, 0.1 19.96, 18.5 3.8 3 0.2, 0.4 N/D N/D N/D N/D N/D N/D N/D N/D 41.6, 32.1, 31.4, 32.8 1.0, 8.1, 0.7 N/D N/D 0.2 N/D N/D N/D 0.2-0.26 N/D N/D N/D N/D N/D N/D 0.1 N/D 1 0.3, 0.8 0.4–0.6, 0.3 0.23 N/D N/D 2.3-15.8, 18.3 10.2, 10.1 35.4,35.6 26.4–35.1 N/D N/D N/D 14.4-24.1 18.1 4.5, 4.4 2.1, 2.2 1.7–2.5 0.2 Palm [1,11,16] Rice bran [3,11,13,73] 13.6-16.2, 18.1 42.8, 42.6 12.5, 17.7 11.7–16.5 2.0, 5.8 N/D N/D N/D 4, 0.907, 5.8 0.8-3.4 7.1 Neem [3,11] 39.1, 40.8, 44.7 72.2, 66.6, 79.4 49.1-61.9, 44.5 40.5 47.5, 40.6 39.2–43.7 0.2, 0.2 N/D 0.7, 0.9 1.4, 2.1 N/D 0.1 Moringa oleifera [70–72] 12.6,15.6, 15.1,14.2 6.5, 7.8, 9.1 0.2 1.1, 1.8 1.1 N/D N/D 0.2, 0.4– 0.6, N/D N/D N/D 0.3 N/D N/D N/D N/D Sesame [1] Stauntonia chinensis [28] Raphanus sativus [74] Annona diversifolia [75] Syagrus coronate [76] Syagrus coronate [77] chufa sedge [78] Citrus reticulate [79] Phoenix dactylifera [80] Idesia polycarpa [81] Calotropis gigantean [82] Baobab (Adansonia digitata L.) [83] Fodder radish (Raphanus sativus L. var oleiferus) [84,85] Citrullus colocynthis [86] N/D N/D N/D N/D 9.0 6 N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D 6.0 6 N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D 42.0 37 N/D N/D 24 N/D N/D N/D N/D N/D N/D N/D 16.0 11 0.1 N/D 13 N/D N/D N/D 13.1 6.87 6.13 16.40 8.0 8 13.1 26.90 17.44 15.06 15.5 20.96 ± 1.2 N/D 0.21 0.05 N/D N/D N/D 2.1 N/D N/D 6.5 0.3 N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D 3.9 1.19 1.68 5.22 4.0 3 2.8 4.62 <0.3 1.18 10.5 20.29 ± 0.2 52.8 79.95 23.87 70.42 12.0 24 61.6 26.75 36.8 5.5 31.1 22.14 ± 0.7 30.2 8.32 13.46 7.97 3.0 5 17.2 37.65 7 70.6 36.3 27.47 ± 1.4 N/D 0.13 10.34 N/D N/D N/D 1.4 3.80 N/D 1.1 0.8 8.84 ± 2.2 N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D 1.72 0.68 N/D N/D N/D 0.7 0.26 N/D N/D 0.6 0.29 ± 0.9 N/D 0.51 8.58 N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D 1.64 N/D N/D N/D 0.2 N/D N/D N/D 0.1 N/D N/D N/D 31.76 N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D 0.2, 0.4– 0.9 N/D N/D 0.61 N/D N/D N/D 0.8 N/D N/D N/D 0.4 N/D N/D N/D N/D N/D 7 N/D N/D 3.6 27.9 7.6 4.6 N/D 2.2 11.2 N/D 33.3 0.6 2.0 N/D N/D N/D 0.7 10.53 0.05 0.14 9.57 14.07 64.65 0.1 N/D 0.12 0.06 0.01 N/D N/D N/D N/D 5.5, 9.7, 7.1 6.0, 5.5,2.7 N/D N/D N/D 1.26 N/D N/D N/D N/D N/D N/D N/D N/D N/D M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 Oil N/D Not detected. 55 56 M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 Fig. 1. Some pictures of edible and non-edible plants and seed. 4.2. Density The air–fuel ratio and energy content of the air fuel mixture largely depend on fuel density within the combustion chamber of diesel engine [14]. In general, density of biodiesel is slightly higher than petro diesel and it is augmented by increasing biodiesel percentage in blends [12,14]. Fig. 3 shows density variations with blend percentage variations. It is found that except Neem biodiesel (having higher density 0.891 g/cc at 40 °C) the density of other feedstocks biodiesel are lower than 0.87 g/cc. Moreover, Rice bran and Sesame biodiesels have the same trend of increasing density (0.849, 0.853, 0.857, and 0.86 at 50%, 60%, 70% and 80% blend percentage). Except Aphanamixis, Calophyllum and Neem, density of other biodiesel varies slightly with the rise of biodiesel percentages in blend. 4.3. Calorific value In general, biodiesel has lower calorific value than diesel because of its higher oxygen content [12–14]. Among the data presented in Fig. 4, it is found that only Aphanamixis (Pitraj) and Coconut biodiesel contain significantly lower calorific value (38,080 and 37,722 kJ/kg on an average) where the calorific value of other biodiesels are nearly 40,000 kJ/kg. The heating value of blended biodiesel is higher than biodiesel and slightly lower than diesel. The heating value decreases marginally with the increasing percentages of biodiesel in blend. With the rise of blend percentage (for example, B20–B30–B40, etc.), calorific value decrease to about 250–400 kJ/kg except coconut biodiesel blend which decrease quite higher (about 700 kJ/kg). Up to B60, Palm, Rice bran and Sesame biodiesels have shown considerable heating value above 42,000 kJ/kg. This value is 7% lower than petro diesel where pure biodiesel has normally 12% lower calorific value than diesel. 4.4. Flash point Flash point is a measure of flammability of fuels which is inversely proportional to volatility [12–14]. The biofuels specification for flash point is meant to protect against contamination for highly volatile matters. In general, biodiesel has higher flash point than petro-diesel. The average flash point of pure biodiesel is almost double than that of diesel. There is an increasing trend of flash 57 M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 Manchurian apricot (Prunus mandshurica Skv.) Xylocarpus moluccensis Siberian apricot (Prunus sibirica L.) Baobab (Adansonia digitata L.) Fig. 1 (continued) Table 4 U.S. and European specification for biodiesel. Property Kinematic viscosity at 40 °C (mm2/s) Density at 15 °C (kg/m3) Calorific value (MJ/kg) Flash point °C Pour point (°C) Cloud point (°C) Cold filter plugging point (CFPP) (°C) Cetane number Oxidation stability at 110 °C (h) Acid value (mg KOH/g) Free glycerin (wt% max) Total glycerin (wt% max) Carbon residue (wt% max) Copper strip corrosion (3 h at 50 °C) Iodine value (g/l2/100 g) max. Water and sediments (vol%, max) Total sulfur (ppm), max Phosphorous (ppm), max U.S. (ASTM D6751-08) Europe (EN 14214) Test methods Limit Test methods Limit D 445 D 1298 – D 93 D 97 D 2500 ASTM D 613 D 675 D 664 D 6584 D 6584 D 4530 D130 – D 2709 D 5453 D 4951 1.9-6.0 880 – 93 15 to 16 3 to 12 Max + 5 47 min 3 min 0.5 max 0.02 0.24 0.05 No. 3 (max.) – 0.05 15b 10 EN ISO 3104 EN ISO 3675/12185 EN14214 EN ISO 3679 – – EN 14214 EN ISO 5165 EN 14112 EN 14104 EN 14105 EN 14105 EN 10370 EN 2160 EN 14111 EN 12937g EN 20846 EN 14107 3.5-5.0 860-900 35 101 min. – – – 51 min 6 min 0.5 max 0.02 0.25 0.30e No. 1 120 0.05 10 4 58 M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 Table 5 Properties of crude edible and non-edible oils. Properties Aphanamixis polystachya [89] Calophyllum [2] Coconut [2] Croton [2] Jatropha [2] Moringa [2] Palm [2] Rice bran [90] Sesame [90] Neem [91] 1 Heating value (kJ/kg) 38729 38,511 37,806 39,331 38,961 39,762 39,867 39,548 39,386 2 Kinematic viscosity (mm2/s) at 40 °C Kinematic viscosity (mm2/s) at 100 °C Viscosity Index (VI) Density (kg/m3) at 40 °C Flash point (°C) CFPP (°C) Cloud point (°C) Pour point (°C) Refractory Index Oxidation stability (h at 110 °C) Acid value (mg KOH/ g oil) Transmission (%T) Copper strip corrosion 3 h at 50 °C Absorbance (Abs) MIU (wt%) [95] FFA (wt%) [95] 35.093 55.478 27.64 29.844 48.095 43.468 41.932 52.225 34.087 32,000– 40,000[92] 35.83 7.2547 9.5608 5.9404 7.2891 9.1039 9.0256 8.496 10.393 7.6364 – 177.9 0.9164 165.4 0.9249 168.5 0.9089 224.2 0.9100 174.1 0.9054 195.2 0.8971 185.0 0.8998 192.8 0.9069 202.9 0.9066 – 0.9200 – – 5 4 1.4789 0.09 236.5 26 8 8 1.4784 0.23 264.5 22 17 19 1.4545 6.93 235.0 10 – – 1.4741 0.14 258.5 21 9 ± 1[1] 4 ± 1[1] 1.4652 0.32 263.5 18 10 11 1.4661 41.75 254.5 23 23[93] 12[93] 1.4642 0.08 300.50 0 0 1.4718 4.40 280.0 44 3 4 1.4709 9.795 100 11[92] 19 10 – 12.4 [92] 26.7 41.74 11.6[3] 14.47[86] 32.64 [3] 91.2 1a 18.5[95] 7.40[93] 63.2 1a 13.56 34.7 1a 8.62 2.90[3] 69.2 1a 1.314 61.6 – 12.07 3.343[94] 87.5 1a 87.10 1a 78.4 – – – 0.209 – – 0.46 – – 0.16 0.30 0.21 0.199 0.03 0.54 0.06 2.74 0.05 0.106 – – 2.16 2.14 – – – – 0.04 2.74 0.07(Lauric acid) 2.7 2.0 31.4 7.3 1.0 7.3 4.0 0.9 0[b][68] – 1990 47.6 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Sulfur (ppm) [95] Phosphorous (ppm) [95] 0.058 – 1.68[93] – – 61.8 1a 0.209 0.16 1.17(Palmitic acid) 3.5 322.9 point for biodiesel blends as portrayed in Fig. 5. Calophyllum and coconut biodiesel have shown considerably lower flash point (122 and 139 °C on average) than other biodiesels (APME = 170, CMME = 178, JCME = 166, MOME = 163, NME > 150 [118], POME = 160, RBME = 185, SME = 186 °C on average). It is seen from data that the variation of flash point basically occurs within the range of 3–8 °C with the increase of blend B20. This trend is found up to B60, but the variation is increased about 15–30 °C when biodiesel percentage increase above 60% in blend. 1 °C). Jatropha and croton show a moderate variation of 0–3 °C and 3 to 0 °C, respectively. Jatropha and Palm biodiesel have the same trend of CFPP (Fig. 8). Coconut and Croton were found to have decreasing trends of CFPP (5 to 4 °C), (5 to 6 °C) while Aphanamixis, Calophyllum, Jatropha and Palm biodiesel have increasing trend with the increase of biodiesel blends. The minimum CFPP was found at 90% biodiesel blend for Croton which is 6 °C and for Coconut at 90% and 100% blend (4 °C). Moreover, pure Moringa and Sesame biodiesel show 2 °C and 3 °C respectively. 4.5. Cloud point (CP), pour point (PP), and cold filter plugging point (CFPP) 4.6. Oxidation stability These properties are considered to be cold flow properties as they establish the limit for the use of fuels under cold weather conditions [2,13,14,119,120]. The cloud point is the lowest temperature at which smallest observable cluster of wax crystal first appears [120]. Pour point is the lowest temperature at which the wax becomes semisolid and loses its flow characteristics. Cold filter plugging point is an estimation of lowest temperature at which fuel will provide a trouble free flow in certain fuel systems [13,120]. In general, biodiesel has higher CP and PP than diesel. The CP and PP of biodiesel feedstock largely depends on fatty acid composition [12,13]. The freezing point of biodiesel increases with the increase of carbon atoms in carbon chain and decrease with double bonds [29,121]. It is found from Fig. 6 that Moringa and Palm have rising trend of cloud point while Croton gives the reverse trend. Maximum cloud point is noted on Moringa (19 °C) and it varies from 8 to 19 °C for the blends. The minimum cloud point is observed on croton (4 °C). The minimum pour point was observed for Coconut at 20% biodiesel blend (15 °C) and it increases with blend percentages as shown in Fig. 7. While the highest pour point was found for Moringa 19 °C, sesame biodiesel has a little variation in pour point (0– Oxidation stability is a prominent parameter that assesses the fuels quality. Oxidation stability of biodiesel is generally influenced by some factors such as presence of air, heat, traces of metal, peroxides, light and fatty acid composition [12]. The presence of double bonds in biodiesel results in a high level of reactivity with oxygen, especially when placed in direct contact with air, sunlight or water [122–124] which afterwards affects engine adversely. From Fig. 9, it is clear that with the rise of blend percentages the oxidation stability is waning. Moringa biodiesel has the best stability (26.2 h at 110 °C) than other feedstocks at B100 and 88.84 h, 71.27 h and 64.25 h for B40, B60 and B80 respectively, the reverse results were found for Calophyllum biodiesel (0.09 h at 110 °C). On the other hand, Coconut biodiesel also has a good oxidation stability (113.06, 85.88, 64.54, 56.55, 41.05, 32.08, 23.23, 5.12) for B20, B30, B50, B60, B70, B80, B90, B100 respectively. On the other hand, Croton, Sesame and Rice bran biodiesel give moderate stability. 5. Mathematical modeling for predicting the important properties of biodiesel and its blend The prediction of important physical and chemical properties of biodiesel and its blends (weather with diesel or biodiesel) is a very 59 M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 important factor in the design of fuel spray, atomization and combustion and emission system for diesel engines. It is also a highly demanding parameter because research is going on with various feedstocks for biodiesel production. These equations would help to predict the property at any percentages of biodiesel in biodiesel–diesel blend. Recently, several studies have been conducted to examine the physical and chemical properties of biodiesel–diesel blends. The following paragraph will summarize the most important works done in this aspect. Saxena et al. [14] reviewed various methods for the prediction of important thermophysical properties such as cetane number, kinematic viscosity, density, higher heating value, flash point, cloud point pour point, cold filter plugging point and vapor pressure for various biodiesel feedstocks. Sivaramakrishnan and Ravikumar [125] developed an equation to calculate cetane number of various vegetable oils and their biodiesel from their viscosity, density, flash point and higher calorific value. They concluded that this equation gives an accuracy of 90%. Atabani et al. [2] discussed the concept of biodiesel–biodiesel blending to improve the properties of some feedstocks. For instance, blending of Sterculia feotida methyl ester (SFME) and coconut methyl ester (CoME) improves the viscosity of (SFME) from 6.3717 mm2/s to 5.3349 mm2/s (3:1), 4.4912 mm2/s (1:1) and 3.879 mm2/s (1:3) respectively. Similar work was conducted on the effect of biodiesel–biodiesel blending on cloud point, pour point and cold filter plugging point. The properties at different biodiesel–biodiesel blends percentages were estimated using the polynomial curve fitting method. This paper concludes that blending of edible and non-edible biodiesel feedstocks could be considered as an approach to improve the properties of the final product. Moser [17] indicated that the fuel properties of Soybean methyl ester were improved by blending with Canola, Palm and Sunflower methyl esters to satisfy the IV (<120) and OSI (>6 h) specifications contained within EN 14214. The CFPP of Palm methyl ester was improved by up to 15 °C through blending with Canola methyl ester. Statistically significant relationships were elucidated Table 6 Properties of edible and non-edible methyl esters. 1 2 3 4 5 6 7 8 Properties Aphanamixis polystachya [89] Calophyllum [2] Coconut [2] Croton [2] Jatropha [2] Moringa [2] Palm [2] Rice bran [90] Sesame [90] Neem [91] Heating value (kJ/kg) Kinematic viscosity (mm2/s) at 40 °C Kinematic viscosity (mm2/s) at 100 °C Viscosity Index (VI) Density (kg/m3) at 40 °C Flash point (°C) CFPP (°C) Cloud point (°C) 39,960 4.7177 39,513 5.5377 38,300 3.1435 39,786 4.0707 39,738 4.9476 40,115 5.0735 40,009 4.6889 39,957 5.3657 39,996 4.3989 39,810 3.70 1.8239 1.998 1.3116 1.6781 1.8557 1.9108 1.7921 1.9609 1.7236 – 220.7 0.8735 183.2 0.8776 230.8 0.8605 276.3 0.8704 194.6 0.8742 206.7 0.8597 203.6 0.8591 187 0.8681 229.0 0.8848 – 0.8680 188.5 5 8 162.5 11 12 118.5 1 1 164.0 4 3 186.5 10 10 176.0 18 21 214.5 12 13 174.50 0 208.5 1 1, 6[68] 19 67.07[71] 15 52[1] 3 73.6[13] 1, 14[68] 50.48[68] 76, 120[92] 11[96] 9[92], 14.4[96] 2[92] 48–53[92] 1.4494 1.4468 1.4541 – – 9 10 Pour point (°C) Cetane no. 8 – 13 57.3[13] 4 59[1] 2 46.6[52] 11 Refractory Index at 25 (°C) Oxidation stability (h at 110 °C) Acid value (mg KOH/g) [96] Free glycerin (%mass) [96] Total glycerin (%mass) [96] Sulfur (ppm) [96] Carbon residue [96] – 1.4574 1.4357 1.4569 10 55.4[97], 57.1[13] 1.4513 0.16 6.12 8.01 0.71 4.84 12.64 23.56 1.61 1.14 7.1 0.448 0.30 0.106 0.156 0.185 0.046 0.586 0.3[67] 0.649[96] – – 0.025 0.16[94], 0.2[98] 0.019[51] 0.006 0.001 0.003 0.001 – 0.02[92] – – 0.065 0.22[51] 0.10 0.067 0.068 0.083 – – – 4.11 – 0.94 0.01 – – 3.84 0.026 9.9 0.033 1.81 0.01 6.0 0.047 0.0[68] 0.6214[68] 0.158[96], 0.26[92] 473.8[96] 0.105[96] 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Properties Stauntonia chinensis [28] Raphanus sativus [74] Annona diversifolia [75] Manchurian apricot [99] Siberian apricot [99] Heating value (kJ/kg) Kinematic viscosity (mm2/s) at 40 °C Kinematic viscosity (mm2/s) at 100 °C Viscosity Index (VI) Density (kg/m3) at 40 °C Flash point (°C) CFPP (°C) Cloud point (°C) Pour point (°C) Cetane no. Refractory Index at 25 (°C) Oxidation stability (h at 110 °C) Acid value (mg KOH/g) Free glycerin (%mass) Total glycerin (%mass) Sulfur (ppm) Carbon residue N/D 4.48 N/D N/D N/D N/D 36.3 4.451 N/D N/D 4.32 N/D N/D 4.34 N/D N/D N/D 167 -9 N/D N/D 52.1 N/D 2 0.12 0.003 0.14 5 (mg/kg) 0.05 N/D N/D N/D 6 N/D N/D N/D N/D N/D 0.082 0.000 0.108 0.79 (mg/kg) N/D N/D N/D N/D N/D 0 -9 44.7 N/D N/D 0.5 N/D N/D N/D N/D N/D N/D 180 -15 N/D N/D 49.7 N/D 2.9 N/D 0.015 0.16 4.5 (mg/kg) N/D N/D N/D 175 -14 N/D N/D 49.2 N/D 2.7 N/D 0.017 0.14 4.7 (mg/kg) N/D 60 M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 Fig. 2. Kinematic viscosity at 40 °C (mm2/s). Fig. 3. Density at 40 °C. Fig. 4. Calorific value. between oxidation stability and iodine value, oxidation stability and saturated fatty acid methyl ester (Sunflower methyl ester) content, oxidation stability and CFPP, CFPP and iodine value, and CFPP and Sunflower methyl ester content. However, the only practically significant relationship was that of CFPP vs. Sunflower methyl ester content when Sunflower methyl ester content was greater than 12 wt%. Oghenejoboh and Umukoro [126] indicated that blending of biodiesel from some feedstocks such as palm, palm kernel, Jatropha and rubber oils with diesel has resulted in an increase in the calorific value, decrease in density, cloud point, pour point, kinematic viscosity and flash point of biodiesel. The same work was done by Krishna [127] to improve the cold flow properties of biodiesel. Sivaramakrishnan and Ravikumar [128] developed an equation to predict the higher heating value of biodiesel based on its kinematic viscosity, flash point and density with 0.949 accuracy. A review on the physical and chemical properties and the fatty acid composition of 26 biodiesel feedstocks (including of 22 edible and non-edible oils and four animal fats) was conducted by M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 61 Fig. 5. Flash point. Fig. 6. Cloud point. Fig. 7. Pour point. Giakoumis [129]. The author derived an excellent correlation between iodine number and the degree of unsaturation. Besides, a small statistical correlation (R2 > 0.60) was also established for cetane number, density, pour point, carbon content, number of carbon atoms, stoichiometric air–fuel ratio and T90 distillate temperature. Kalayasiri et al. [130] developed 2 empirical equations to predict the saponification number and iodine value of biodiesel based on its fatty acid composition. SN ¼ X 560 Ai MW i ð1Þ IV ¼ X 254 D Ai MW i ð2Þ where SN the saponification number, Ai the percentage of each component, D the number of double bond, MWi the molecular mass of each component and IV the iodine value. Krisnangkura [131] illustrated a simple method to estimate the cetane number of biodiesel which is based on their saponification and iodine numbers. The range of the calculated values covers all the cetane numbers of vegetable oil methyl esters determined experimentally. When it was applied to individual fatty acid methyl 62 M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 Fig. 8. Cold filter plugging point (CFPP). Fig. 9. Oxidation stability (h at 110 °C). Table 7 Mathematical equation for predicting properties for various biodiesel blends. Biodiesel blends Property Biodiesel-diesel blending APME + Diesel Kinematic viscosity Density at 40 °C Flash point Calorific value CFPP Cloud point Pour point CIME + Diesel Kinematic viscosity Density at 40 °C Flash point Calorific value CFPP Cloud point Pour point COME + Diesel Kinematic viscosity Density at 40 °C Flash point Calorific value CFPP Cloud point Pour point CMME + Diesel Kinematic viscosity Density at 40 °C Flash point Calorific value CFPP Cloud point Pour point JME + Diesel Kinematic viscosity Density at 40 °C at 40 °C at 40 °C at 40 °C at 40 °C at 40 °C Mathematical equation R2 Variable Ref. y = 6E05x2 + 0.0169x + 3.3722 y = 2E07x2 + 0.0005x + 0.8298 y = 0.0137x2 0.6219x + 89.225 y = 0.2778x2 41.011x + 45,223 y = 0.0004x2 + 0.0566x 5.3142 y = 9E05x2 + 0.1131x 4.3545 y = 0.0008x2 + 0.1681x 4.4431 y = 7E05x2 + 0.0141x + 3.191 y = 2E07x2 + 0.0004x + 0.8348 y = 0.0048x2 + 0.0445x + 69.912 y = 0.0869x2 69.155x + 45,336 y = 0.0017x2 0.167x + 7.3147 y = 0.0007x2 0.0629x + 8.3846 y = 0.0003x2 + 0.1194x 0.1888 y = 2E05x2 + 0.0045x + 3.3625 y = 9E08x2 + 0.0003x + 0.8351 y = 0.008x2 0.1823x + 73.239 y = 0.008x2 74.066x + 45,292 y = 0.0017x2 + 0.0494x + 6.1818 y = 0.001x2 + 0.0153x + 7.5524 y = 0.0031x2 0.3092x 2.007 y = 4E05x2 + 0.0044x + 3.3503 y = 1E08x2 + 0.0004x + 0.8271 y = 0.0118x2 0.2759x + 79.312 y = 0.0362x2 61.61x + 45,377 y = 0.0018x2 + 0.0532x + 6.1469 y = 0.0009x2 0.0374x + 7.0699 y = 0.002x2 + 0.1696x 1.3706 y = 5E05x2 + 0.0059x + 3.4774 y = 2E07x2 + 0.0004x + 0.8274 0.9947 1 0.9683 0.9898 0.9161 0.978 0.9893 0.9989 0.9998 0.9948 0.9989 0.5621 0.8207 0.9606 0.9075 0.9994 0.9655 0.9994 0.9536 0.9083 0.4009 0.919 0.9997 0.9293 0.9968 0.8972 0.9609 0.7637 0.8463 0.9997 x is the dependent variable; x biodiesel% [113] 63 M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 Table 7 (continued) Biodiesel blends Property Flash point Calorific value CFPP Cloud point Pour point Kinematic viscosity Density at 40 °C Flash point Calorific value CFPP Cloud point Pour point Kinematic viscosity Density at 40 °C Flash point Calorific value CFPP Cloud point Pour point Kinematic viscosity Density at 40 °C Flash point Calorific value CFPP Cloud point Pour point Kinematic viscosity Density at 40 °C Flash point Calorific value CFPP Cloud point Pour point Kinematic viscosity Density at 40 °C Flash point Calorific value CFPP Cloud point Pour point Kinematic viscosity Density at 40 °C Flash point Calorific value MOME + Diesel NME + Diesel POME + Diesel RBME + Diesel SME + Diesel CIME + Diesel R2 Mathematical equation 2 at 40 °C at 40 °C at 40 °C at 40 °C at 40 °C at 40 °C Biodiesel-biodiesel blending SFME-POME Kinematic viscosity at 40 °C SFME-COME POME-CME Cloud point JCME-CME CIME-CME POME-CME Pour point JCME-CME CIME-CME POME-CME Cold filter plugging point JCME-CME CIME-CME Variable y = 0.0085x + 0.081x + 74.015 y = 0.176x2 68.831x + 45,205 y = 0.0007x2 + 0.0719x + 4.6853 y = 0.0008x2 0.09x + 6.7238 y = 0.0004x2 + 0.013x 1.0594 y = 3E05x2 + 0.0192x + 3.2815 y = 1E07x2 + 0.0003x + 0.8272 y = 0.0075x2 + 0.0604x + 74.8 y = 0.0444x2 56.284x + 45,223 y = 0.0006x2 0.1293x + 4.3843 y = 8E05x2 + 0.1146x + 6.6224 y = 0.0013x2 + 0.316x + 0.042 y = 0.0002x2 + 0.0423x + 2.9568 y = 6E07x2 + 0.0005x + 0.8374 N/D y = 0.5887x2 118.16x + 46,138 N/D N/D N/D y = 7E05x2 + 0.0042x + 3.3741 y = 1E07x2 + 0.0002x + 0.8351 y = 0.0098x2 0.2335x + 77.701 y = 0.1495x2 62.708x + 45,106 y = 0.0022x2 0.1529x + 6.007 y = 0.0023x2 0.1882x + 8.7622 y = 0.0006x2 + 0.0578x 1.3692 y = 4E05x2 + 0.0237x + 3.0904 y = 7E08x2 + 0.0004x + 0.8319 y = 0.0165x2 0.6966x + 80.524 y = 0.1462x2 63.082x + 45,358 y = 0.0007x2 0.0947x + 4.4311 N/D N/D y = 2E05x2 + 0.0102x + 3.1682 y = 3E08x2 + 0.0003x + 0.8319 y = 0.0168x2 0.7353x + 81.618 y = 0.0635x2 59.489x + 45,381 y = 0.0007x2 0.0049x + 4.2296 y = 0.0008x2 + 0.0137x + 5.2554 y = 0.0018x2 + 0.145x 0.2907 y = 0.1664x + 2.8361 y = 3.9209x + 825.46 y = 0.6678 x2 1.0049x + 71.355 y = 0.5934x + 45.848 0.9808 0.9869 0.9709 0.2857 0.8353 0.9919 0.9994 0.9464 0.9901 0.9361 0.9606 0.9869 0.9559 0.9993 y = 0.5159x2 1.1195 + 6.3599 y = 0.9533 x2 4.1182x + 6.3457 y = 3.4286x2 20.629x + 13.429 y = 1.1429x2 12.857x + 10.457 y = 3.4286x2 12.171x + 12.171 y = 2.2857x2 20.114x + 14.114 y = 13.714x2 6.2857x + 10.286 y = 13.714x2 8.6857x + 13.286 y = 6.8571x2 15.543x + 11.943 y = 6.8571x2 14.743x + 10.543 y = 5.7143x2 16.286x + 11.486 0.9908 0.9981 0.9704 0.979 0.9867 0.9784 0.9785 0.9972 0.9843 0.9639 0.9918 Ref. 0.994 0.8893 0.998 0.9305 0.9696 0.8763 0.7907 0.9076 0.9599 0.9999 0.9521 0.9849 0.932 0.9983 0.9999 0.9438 0.9989 0.9854 0.7033 0.6526 0.9978 0.9998 0.9965 0.9994 [101] x POME% x COME% x CME% [2] N/D Not determined. esters from C8 to C24, a straight line parallel to that of Klopfenstein was obtained. The developed equation was as follows: CN ¼ 46:3 þ 5458 ð0:225 IVÞ SN ð3Þ where CN the cetane number, SN the saponification number, and IV the iodine value. Ramírez-Verduzco et al. [132] attempted to develop 4 empirical correlations that can be used estimate the cetane number, kinematic viscosity, density and higher heating value of biodiesels based on their molecular weight and degree of unsaturation. The estimated values were found to be in a good agreement with the experimental values and an average absolute deviation (AAD) of 5.95%, 2.57%, 0.11% and 0.21% for the cetane number, kinematic viscosity, density, and higher heating value were found. Those derived equations were as follows: ;i ¼ 7:8 þ 0:302 M i 20 N ð4Þ lnðni Þ ¼ 12:503 þ 2:496 lnðMi Þ 0:178 N ð5Þ 4:9 0:0118 N Mi ð6Þ Pi ¼ 0:8463 þ di ¼ 46:19 1794 0:21 N Mi ð7Þ 64 M.A. Wakil et al. / Energy Conversion and Management 94 (2015) 51–67 Table 8 Mathematical equation for predicting properties for various biodiesel feedstocks. Biodiesel blends CMME CIME COME POME MOME CMME CIME COME POME MOME Various biodiesel Feedstocks R2 Ref. FP = 183.95 (KV) + 1221.6 (KV) + 2099.5 FP = 0.4884 (KV)2 + 5.1448 (KV) + 47.913 FP = 33.934 (KV)2 + 188.35 (KV) + 325.3 FP = 74.797 (KV)2 + 517.44 (KV) + 968.12 FP = 13.79 (KV)2 + 73.438 (KV) + 164.68 CV = 2410.4 (KV)2 + 10, 323 (KV) + 37.233 CV = 560.27 (KV)2 7392.4 (KV) + 63. 326 CV = 33.934 (KV)2 188.35 (KV) + 325.3 1413.7 (KV)2 + 15, 028 (KV) + 79.180 3063.7 (KV) + 55. 367 0.9534 0.9887 0.9933 0.9569 0.9724 0.9891 0.9975 0.9933 0.996 0.9912 [113] Higher heating value (HHV) vs. Kinematic viscosity (KV) Kinematic viscosity (KV) vs. Density (DN) Kinematic viscosity (KV) vs. Flash point (FP) Higher heating value (HHV) vs. Density (DN) Higher heating value (HHV) vs. Flash point (FP) Density (DN) vs Kinematic viscosity (KV) Flash point (FP) vs. Kinematic viscosity (KV) Density (DN) vs. Flash point (FP) Density (DN) vs. Calorific value (CV) HHV = 0.4625 (KV) + 39.450 KV = –16.155 (DN) + 930.78 KV = 22.981 (FP) + 346.79 HHV = –0.0259 (DN) + 63.776 HHV = 0.021 (FP) + 32.12 DN = 15.77 (KV) + 929.59 FP = 12.36 (KV) + 176.3 FP = 1.46 (DN) 1099.9 CV = 0.0207 (DN) + 23.28 0.9677 0.9902 0.9819 0.7982 0.9530 0.9724 0.964 0.91 0.9568 [134] Higher heating value (HHV) vs. Kinematic viscosity (KV), Density (DN), Flash point (FP) HHV = 0.4527 (KV) 0.0008 (DN) 0.0003 (FP) + 40.3667 0.949 [128] Property Flash point (FP) vs. kinematic viscosity (KV) Calorific value (CV) vs. kinematic viscosity (KV) Mathematical equation 2 [135] N/D Not determined. where ;i the cetane number of the ith FAME, Mi the molecular weight of the ith FAME, N the number of double bonds in a given FAME, ni the kinematic viscosity at 40 °C of the ith FAME in mm2/ s, Pi the density at 20 °C of the ith FAME in g/cm3 and di the higher heating value of the ith FAME in MJ/kg. Talebi et al. [133] developed a new software package (the BiodieselAnalyzerÓ) that can predict 16 different properties of biodiesel based on the fatty acid methyl ester profile of the oil feedstock used in making it. The polynomial curve fitting method has been used in several studies [2,101,113,134,135] to predict the properties of biodiesel–diesel blends. Mathematically, a polynomial of order k in X is expressed in the form of: Based on the review work that is conducted in this paper, for future work it can be recommended to investigate the optimization of biodiesel blends (both biodiesel–diesel and biodiesel–biodiesel) as different biodiesel feedstocks possess some superior qualities as well as some inferior qualities. Moreover, in depth instrumental analysis for instance, effect of temperature, reaction time and catalyst type on biodiesel yield can help researchers to select more potential candidate for biodiesel to be used commercially. Y ¼ Co þ C1X þ C2X2 þ þ CkXk Acknowledgements where X is the variable as a function of available data and Y is the predicted value. Table 7 shows some examples of the generated equations for various biodiesel blends. Table 8 shows some mathematical equations for predicting properties of various biodiesel feedstock. 6. Conclusion In recent time, the research on biodiesel is reaching to the peak because it is found as a good complementary substitute to diesel than other sources. A number of research have been conducted on biodiesel from different feedstock’s by various researchers and some are still ongoing for a considerable level of usage. Accordingly, this study highlighted the physicochemical properties under various biodiesel–diesel blend. For clear understanding, a short description on feedstock has been also carried out. A polynomial curve fitting method is used to generate mathematical equation for different biodiesel–diesel blend in order to predict the properties of any percentage of biodiesel in the blend. This would help the researchers to optimize the blend percentage which is necessary to meet the impending scarcity of petro-diesel. The other profitable advantage would be the proper selection of combined feedstock to improve the performance of engine relative to diesel without any or little modification. This is necessary as there is the challenge of using single feedstock as biodiesel for better performance along with some demerits of edible feedstock. 7. Recommendation The authors would like to thank the Ministry of Higher Education and University of Malaya, Malaysia for the financial assistance through High Impact Research Grant titled: Development of alternative and renewable energy carrier (DAREC) with Grant Number UM.C/HIR/MOHE/ENG/60. References [1] Kumar N, Varun Chauhan SR. 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