Alexandria Engineering Journal (2015) 54, 1285–1290
H O S T E D BY
Alexandria University
Alexandria Engineering Journal www.elsevier.com/locate/aej www.sciencedirect.com
ORIGINAL ARTICLE
Effect of biodiesel production parameters on viscosity and yield of methyl esters: Jatropha curcas, Elaeis guineensis and Cocos nucifera Godwin Kafui Ayetor a,*, Albert Sunnu b, Joseph Parbey a a b
Koforidua Polytechnic, Faculty of Engineering, Box 981, Koforidua, Ghana Kwame Nkrumah University of Science and Technology, Department of Mechanical Engineering, Kumasi, Ghana
Received 29 August 2014; accepted 29 September 2015 Available online 26 October 2015
KEYWORDS Jatropha curcas; Palm kernel oil; Biodiesel; Coconut oil; Transesterification; Viscosity
Abstract In this study, the effect of H2SO4 on viscosity of methyl esters from Jatropha oil (JCME), palm kernel oil (PKOME) from Elaeis guineensis species, and coconut oil (COME) has been studied. Effect of methanol to oil molar mass ratio on yield of the three feedstocks has also been studied. Methyl ester yield was decreased by esterification process using sulphuric acid anhydrous (H2SO4). Jatropha methyl ester experienced a viscosity reduction of 24% (4.1–3.1 mm2/s) with the addition of 1% sulphuric acid. In this work palm kernel oil (PKOME), coconut oil (COME) and Jatropha oil (JCME) were used as feedstocks for the production of biodiesel to investigate optimum parameters to obtain high yield. For each of the feedstock, the biodiesel yield increased with increase in NaOH concentration. The highest yield was obtained with 1% NaOH concentration for all. The effect of methanol in the range of 4:1–8:1 (molar ratio) was investigated, keeping other process parameters fixed. Optimum ratios of palm kernel oil and coconut oil biodiesels yielded 98% each at methanol: oil molar ratio of 8:1. The physiochemical properties obtained for each methyl showed superior properties compared with those reported in published data. Ó 2015 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Biodiesel produced from vegetable oil has been long known as a viable alternative to petroleum diesel. It is known to be biodegradable, renewable, produce lesser emissions, nontoxic and free from sulphur. Rudolf Diesel (1858–1913), credited * Corresponding author. Tel.: +233 243129514/576414148. E-mail addresses:
[email protected],
[email protected] (G.K. Ayetor). Peer review under responsibility of Faculty of Engineering, Alexandria University.
with the invention of diesel engine originally used peanut oil as fuel. Over 100 other feedstocks have since been discovered for the production of biodiesel. The choice of feedstock adapted by a country depends on availability, cost and whether it is edible or not. Argentina prefers to use soybean oil contrary to china who has a high demand for soybean for preparation of Chinese food [1]. However edible palm oil is preferred in Asian countries since they have surplus in production while rapeseed oil is preferred in Europe. Other countries such as Ghana are struggling to choose their preferred feedstock since there is not enough of any of the oils whether edible or not.
http://dx.doi.org/10.1016/j.aej.2015.09.011 1110-0168 Ó 2015 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1286 Biodiesel is the only and first commercial scale fuel to have met America’s EPA definition as an advanced biofuel, since it reduces greenhouse gas emissions by more than 50% compared with petroleum diesel. However, in spite of numerous advances in biodiesel production technology no major Original Equipment Manufacturer (OEM) gives warranty for the use of B100 (100% biodiesel). Use of B20 (20% biodiesel blended with 80% petroleum diesel) or below does not void warranties for 90% of the medium and heavy duty truck vehicles. This position of the OEM is because no biodiesel is the same. Even physiochemical properties of biodiesel from the same feedstock may differ depending on the species, mode of oil preparation, water content, type or concentration of catalyst, molar ratio of alcohol and even reaction time. The quality of feedstock is not guaranteed. This is why in order to protect consumers from unwittingly purchasing substandard fuel, OEMs have stated formally that the biodiesel must meet ASTM D-6751 (American society for testing and materials) [2,3] and/or EN14214 (European committee for standardization). Appropriate feedstock selection and production technology is therefore vital for biodiesel production [4]. Feedstock such as coconut oil and palm kernel oil has not been properly investigated for biodiesel production in terms of production technology. Some have studied high physicochemical properties of coconut oil focusing on temperature and pressure neglecting physiochemical properties [5]. Others studied in situ (Trans) esterification of coconut oil using mixtures of methanol and tetrahydrofuran but did not consider yield or catalyst concentration [6]. Catalyst (KOH) concentration and methanol to oil ratio have been investigated for the production of coconut oil but their combined effect on yield has been neglected and base catalysed (Trans) esterification has not been considered [7]. Ethanolysis of coconut oil to produce biodiesel has been done but the effect of methanol, catalyst concentration and their effect on coconut biodiesel yield has not been specified [8]. Though prevalent in West Africa, not much work has also been done on palm kernel oil (B100) as biodiesel [PKOME]. Studies carried out on PKOME considered KOH and not NaOH as base catalyst [9,10]. While characterisation in the literature have not included cetane number and calorific value [10] and neither are the species from which the oil was obtained mentioned, there are many species of palm oil from which palm kernel oil can be produced. These species include Elaeis oleifera commonly called American oil palm, Elaeis guineensis also called the African oil palm and Butia capitata also called Jelly palm usually grown in the Argentina, Brazil and Uruguay. This research investigates the effect of process parameters including methanol:oil ratio, NaOH base catalyst concentration on coconut, palm kernel and Jatropha biodiesel yield. The influence of sulphuric acid (H2SO4) on viscosity is also investigated for the three feedstocks.
2. Materials and methods 2.1. Materials (Trans) esterification of vegetable oil to biodiesel was carried out in a laboratory scale experiment. The materials used include
G.K. Ayetor et al. 1. Flat bottom reaction flask (250 ml) with three necks to contain the oil. 2. Scilogex MS-H-S Magnetic stirrer with hot plate was used. It had two separate regulators for regulating heat and stirring rate respectively. 3. Electronic Beam Balance with 200 g min. and 6000 g max. e = 10 d, d = 1 g was used to take weight of oils before and after (trans) esterification. 4. Reaction ingredients for the (Trans) esterification include 99.8% methanol, NaOH, 98% sulphuric acid. 5. Other instruments used include a. Separating funnel. b. 8000 ml beaker. c. Spatula. d. Filter paper. e. Graduated eye dropper. f. Graduated syringe. g. Pipette.
2.2. Experimental procedure Acid-catalysed (Trans) esterification requires a much longer time than alkali-catalysed Trans esterification (4). This is why base-catalysed (Trans) esterification is used in this work. A Two-step process was used in the production of coconut oil biodiesel. An alkaline-catalysed esterification using NaOH to convert FFAs in coconut oil to methyl esters to reduce FFA was carried out for an hour. In the second step acidcatalysed Trans esterification was carried out where the pretreated oil was then converted to methyl ester to further reduce FFA and hence the viscosity. Both esterification and (Trans) esterification were conducted in a laboratory-scale experiment. The raw coconut oil (200 g) was preheated for an hour to ensure removal of water as a precaution of the oil probably not being well prepared. The preheating was terminated when visual inspection showed that there were no more bubbles. For all test runs for the variations, temperature was kept constant and stirring was at same speed. Methanol mixed with NaOH was added to the preheated coconut mixture in the flat bottom reaction flask and stirred for an hour. Test runs for NaOH and H2SO4 catalyst concentrations were all done at 0.6, 0.8,1 and 1.2 (w/w). The weight measurement (wt.%) was used instead of (v%) because weight gives a more precise measurement since volume changes once there is evaporation of the liquid. Methanol:oil molar ratio variations were done at 1:4, 1:5, 1:6, 1:7 and 1:8. The mixture was stirred for some time at the same rate and time for all test runs. In the second step H2SO4 was added to the pre-treated mixture and quickly stirred for about an hour. The essence of adding H2SO4 was to further reduce FFA and hence the viscosity of the biodiesel. Wet washing was then carried out with hot distilled water at 60 °C and then dried to obtain the Coconut oil biodiesel. The same procedure was carried for Palm kernel oil and Jatropha oil. Each of the procedure mentioned above was repeated for each variation of base catalyst (NaOH), acid catalyst (H2SO4) and methanol:oil molar ratio. The effect of base catalyst concentration, acid catalyst concentration and methanol: oil molar ratio on biodiesel yield of coconut, Jatropha and Palm kernel oils was studied. Yield of biodiesel obtained was calculated as
Effect of biodiesel production parameters Yield ¼
1287
weight of biodiesel produced 100 intital weight of oil
3. Results and discussion 3.1. Characterisation Palm kernel oil methyl ester (PKOME) was characterised together with petroleum diesel according to the ASTM D6751. Table 1 shows the properties of PKOME obtained in comparison with petroleum diesel and international standards. Compared to published works, these are the best properties of PKOME ever obtained [9,11,12]. Viscosity of PKOME compares very well with petroleum diesel and passes the two major international standards for biodiesel (ASTM D6751 and EN14214). Viscosity is the major reason why transesterification is necessary [13]. The viscosity of crude palm kernel oil measured was 29 mm2/s compared to palm kernel oil biodiesel of 3.7 mm2/s. If fuel viscosity is too high, it may cause too much pump resistance, filter damage, poor combustion, increased exhaust smoke and emissions [14]. In general, higher viscosity leads to poorer fuel atomisation [15]. Viscosity of PKOME is still slightly higher than petroleum diesel and this is reported in the literature that biodiesel has higher viscosity compared to Petroleum diesel due to high fatty acid composition [16,17]. Fatty acid composition determines the degree of saturation and the higher the composition the higher the degree of saturation. Viscosity increases with increasing degree of saturation. Cetane Number (CN), a dimensionless parameter, is a measure of fuel quality and is vital in determining whether a fuel is suitable for use in a compression ignition engine. The best CN obtained for PKOME as a result of the optimisation was 50 compared to petroleum diesel of 49 and met both ASTM and EN standards. The longer the fatty acid carbon chains the more saturated the molecules, the higher the CN [18]. Since biodiesel is largely composed of long-chain hydrocarbon groups (with virtually no branching or aromatic structures) it typically has a higher CN than petroleum diesel. Flow properties such as pour point (PP) and cloud point (CP) are important in determining performance of fuel flow system. Viscosity is known to be influenced strongly by temperature and is inversely proportional. Operating a diesel engine at low temperatures especially in cold climate regions can be difficult because of high viscosities. This is why low temperature properties are necessary to determine feasibility of use in cold countries. The temperature at which cloud
Table 1
wax crystals first appear in the oil when it is cooled is termed cloud point. This is usually visible to the naked eye. The cloud point obtained for PKOME (6 °C) compares very well with petroleum diesel (2 °C) though there are no specified limits prescribed for both ASTM and EN standards. Pour point obtained for both PKOME and petroleum diesel was the same at 1 °C. This implies that the lowest temperature at which both palm kernel oil biodiesel (obtained in this work) and petroleum diesel can be poured is the same. Calorific value and also lower/upper heating values can be used to distinguish among different fuels their likelihood to produce more or less power or torque per the same volume. It compares the energy content per litre for the various fuels under consideration. At 44 MJ/kg palm kernel oil biodiesel is close to petroleum diesel (46 MJ/kg) and meets the standards. Compared to Petroleum diesel, biodiesel has been generally reported to have lesser Heating value [19]. This is because for biodiesel, carbon and hydrogen are the sources of thermal energy while oxygen is ballast. Petroleum diesel fuel is made up of a mixture of various hydrocarbon molecules and contains little oxygen (less than 0.3%), while biodiesel contains significant amount of oxygen (9%). Hence due to its high oxygen content, biodiesel has lower Heating values than petroleum diesel [20], except combustion efficiency of biodiesel will be higher, due to the higher oxygen content. This presupposes that the stoichiometric air/fuel ratio of biodiesel will be lower than that of diesel because lesser air will be required to burn biodiesel compared to conventional diesel [21]. This is why some level of modification is required in a diesel engine for optimum operation of biodiesel. It is also for this same reason that many have reported higher NOx emissions for biodiesel fuelled engines [22–25]. Acid value is a measure of auto-oxidation, storage stability or mental contamination [26]. The acid value for PKOME is higher than petroleum diesel but falls within the required limits. However, it is an indication that PKOME is more unstable compared with petroleum diesel. The results show the Density of PKOME (878 kg/m3) exceeds that of petroleum diesel (839 kg/m3) but well within the standards. It has been generally reported that biodiesel has a higher density than petroleum diesel. This is why biodiesel is considered already ‘chemically advanced’ in terms of injection timing [27]. Implying for the same engine it will take a shorter time for biodiesel compared to petroleum diesel to travel from injection pump to the injector. The high density hence compensates for the lower calorific or heating value. It can be also be seen from the Table 1, that coconut oil biodiesel possesses the lowest kinematic viscosity compared with diesel and falls well within the required standards. Kinematic
Physiochemical properties obtained for JCME, PKOME and COME.
Properties
PKOME
COME
Petroleum diesel
ASTM D6751
EN 14214
Kinematic Viscosity @ 40 °C (mm2/s) Cetane number Pour point (°C) Cloud point (°C) Flash point (°C) High calorific value (MJ/kg) Acid value (mol%) Density (kg/m3)
3.7 50 1 6 170 44 3.4 878
2.4 55 -5 2 122 42 2 894
2.6 49 1 2 90 46 0.17 839
1.9–6 47 min 15 to 6 – 93 min – 0.5 max 880
3.5–5 51 min – – 120 min 35 0.5 max 860–900
1288 Table 2
G.K. Ayetor et al. Viscosity of PKOME for varying concentrations of H2SO4.
H2SO4 (wt.%)
0 0.6 0.7 0.8 0.9 1
Viscosity of experimental runs (mm2/s) Run 1
Run 2
Run 3
5.7 5.1 4.8 4.5 4.1 3.7
5.8 5.0 4.8 4.6 4.2 3.6
5.7 5.1 4.8 4.6 4.2 3.7
viscosity of coconut oil dropped from 27 mm2/s to 2.4 mm2/s after transesterification. The kinematic viscosity of COME was found to be lower than petroleum diesel (2.6 mm2/s). Cetane number of 55 was obtained for COME and that of petroleum diesel was 49. Since a shorter ignition delay (ID) corresponds to a higher CN and vice versa it implies this COME will ignite at a lower temperature than petroleum diesel. A fuel with higher cetane number will ignite at lower temperatures and have a very short ignition delay. If the period between the injection and the start of the ignition takes too long (low CN) a strong diesel knock could occur leading to misfiring. If a CN is too high, combustion can occur before the fuel and air are properly mixed, resulting in incomplete combustion and smoke. Cetane number obtained for COME fell well within the standards and was much better than petroleum diesel. Pour point of COME (5 °C) measured is better than petroleum diesel (1 °C). Calorific value of petroleum diesel is better than coconut oil biodiesel as expected due to excess oxygen which is ballast in biodiesel. Density of the biodiesel was higher than petroleum diesel which is convenient since the higher speed will make up for the low calorific value. 3.2. Effect of sulphuric acid (H2SO4) on viscosity Effect of sulphuric acid on viscosity of PKOME and COME was investigated as described in the experimental procedure. For this experiments three runs of the same experiment were conducted for both feedstocks and the average found is displayed in the Table 2. Kinematic Viscosity is a measure of resistance to flow of a liquid due to internal friction of one part of a fluid moving over another. If viscosity is too high it may lead to pump damage and filter clogging, poor combustion and increased emissions [15,28]. Neither low nor high viscosity is considered favourable in a diesel engine. Some injection pumps can experience excessive
Table 3
5.7 5.1 4.8 4.6 4.2 3.7
wear and power loss due to injector or pump leakage if viscosity is too low. The results show the higher the sulphuric acid the more favourable the result as the Kinematic viscosity of PKOME was reduced from 5.7 mm2/s to 3.7 mm2/s. The effect was even more profound with coconut oil methyl ester as addition of 1% H2SO4 reduced the viscosity from 3.9 mm2/s to 2.4 mm2/s (about 40% reduction). The viscosity reduced steadily as the sulphuric acid concentration was increased (Table 3). Jatropha methyl ester experienced a viscosity reduction of 24% (4.1–3.1 mm2/s) with the addition of 1% sulphuric acid (Table 4). The favourable effect of sulphuric acid on the viscosity may be due to the fact that the acid further acts as a drying agent drying any remaining water and dissolving any remaining free fatty acid. 3.3. Effect of methanol to oil ratio on yield Ideally, one mole of biodiesel requires 3 mol of alcohol in transesterification. However, due to the reversible nature of the reaction, excess alcohol is usually used in transesterification in order to shift the reaction to the product side [29]. The effect of methanol in the range of 4:1–8:1 (molar ratio) was investigated, keeping other process parameters fixed. The reaction temperature was kept constant at 65 ± 1 °C, and reaction was performed for 1 h. The reaction was performed with constant concentrations of NaOH. Analyses of the three oils (JCME, PKOME and COME) revealed that, increase in methanol/oil ratio produces a corresponding increase in the yield till the optimum yield is achieved (Fig. 1). This is because higher mass ratio of reactant increases the contact between the methanol and oil molecules so the methyl ester concentration increases with increasing mass ratio of methanol to oil. The optimum methanol:oil molar ratio for biodiesel production from Jatropha curcas methyl ester is 6:1. But it seems
Viscosity of COME for varying concentrations of H2SO4.
H2SO4 (wt.%) 0 0.6 0.7 0.8 0.9 1
Average viscosity (mm2/s)
Viscosity of experimental runs (mm2/s)
Average viscosity (mm2/s)
Run 1
Run 2
Run 3
3.9 3.6 3.3 2.9 2.6 2.4
3.8 3.4 3.2 2.8 2.6 2.4
3.9 3.8 3.2 2.9 2.7 2.4
3.9 3.6 3.2 2.9 2.6 2.4
Effect of biodiesel production parameters Table 4
1289
Viscosity of JCME for varying concentrations of H2SO4. Viscosity of Experimental Runs (mm2/s)
H2SO4 (wt.%)
0 0.6 0.7 0.8 0.9 1
Average viscosity (mm2/s)
Run 1
Run 2
Run 3
4.1 4.1 3.9 3.7 3.4 3.1
4.1 4.0 3.8 3.7 3.3 3.1
4.2 4.0 3.8 3.6 3.4 3.2
4.1 4.0 3.8 3.7 3.4 3.1
100 100
Biodieseil yield (%)
96 94 PKOME
92
JCME
90
COME
94 92
PKOME
90
JCME COME
88 86 0.6
0.7
0.8
0.9
1
NaOH catalyst concentraon 4:01
5:01
6:01
7:01
8:01
Methanol:Oil (Molar rao)
Figure 1
96
84
88 86
Biodiesel yield (%)
98
98
Figure 2
Effect of catalyst variation on biodiesel yield.
Effect of alcohol:oil molar ratio on biodiesel yield.
4. Conclusion that after the optimum yield was reached the yield began to decline for JCME. This implies that when excess alcohol is used beyond a certain limit in transesterification, the polarity of the reaction mixture is increased, thus increasing the solubility of glycerol back into the ester phase and promoting the reverse reaction between glycerol and ester or glycerides thereby reducing the ester yield. Optimum ratios of palm kernel oil and coconut oil biodiesels yielded 98% each at methanol:oil molar ratio of 8:1. Therefore depending on the type of feedstock and perhaps even the quality (mode of preparation), the optimum methanol:oil molar ratios differ. 3.4. Effect of base catalyst concentration on yield Selecting a catalyst for (Trans) esterification is very important in determining the outcome of biodiesel production process but this is dependent on the type and quality of feedstock. In this work, base catalysed transesterification was conducted with a 6:1 M ratio of methanol to oil at 500C for 2 h. NaOH catalysed (Trans) esterification of Jatropha curcas Oil, Palm kernel Oil and Coconut oil was investigated by varying NaOH concentrations as shown in Fig. 2. The molar ratios varied are 0.6, 0.7, 0.8, 0.9 and 1. For each of the feedstock, the biodiesel yield increased with increase in catalyst concentration. The highest yield was obtained with 1% catalyst concentration for all. At 1% NaOH concentration a yield of 98%, 96% and 95% was obtained for PKOME, JCME and COME respectively at 6:1 methanol:oil ratio. This shows that the optimum conditions for NaOH catalysed (Trans) esterification required more catalyst.
In this work palm kernel oil, coconut oil and Jatropha curcas oil were used as feedstocks for the production of biodiesel to investigate optimum parameters to obtain high yield and best quality of biodiesel. A Two-step process was used in the biodiesel production using NaOH. In the second step sulphuric acid was added in portions (0.6%, 0.7%, 0.8%, 0.9% and 1%) to investigate its effect on viscosity. The base-catalyst was varied, and alcohol:oil molar ratio was also varied to obtain optimum parameters for each feedstock. For each of the feedstock, the biodiesel yield increased with increase in catalyst concentration. The highest yield was obtained with 1% catalyst concentration for all. At 1% NaOH concentration a yield of 98%, 96% and 95% was obtained for PKOME, JCME and COME respectively at 6:1 methanol:oil ratio. This shows that the optimum conditions for NaOH catalysed (Trans) esterification required more catalyst. The results show the higher the sulphuric acid concentration the more favourable the result as the Kinematic viscosity of PKOME was reduced from 5.7 mm2/s to 3.7 mm2/s. The effect was even more profound with coconut oil methyl ester as addition of 1% H2SO4 reduced the viscosity from 3.9 mm2/s to 2.4 mm2/s (about 40% reduction). Jatropha methyl ester experienced a viscosity reduction of 24% (4.1–3.1 mm2/s) with the addition of 1% sulphuric acid. The favourable effect of sulphuric acid on the viscosity is due to the fact that the acid further acts as a drying agent drying any remaining water and dissolving any remaining free fatty acid. The effect of methanol in the range of 4:1–8:1 (molar ratio) was investigated, keeping other process parameters fixed. Analyses of the three oils revealed that, increase in methanol/oil ratio produces a corresponding increase in the yield till the optimum yield is achieved. This
1290 is because higher mass ratio of reactant increases the contact between the methanol and oil molecules so the methyl ester concentration increases with increasing mass ratio of methanol to oil. Optimum alcohol:oil molar ratio of JCME obtained was 6:1, after which the yield began to decline. Implying that when excess alcohol is used beyond a certain limit in transesterification, the polarity of the reaction mixture is increased, thus increasing the solubility of glycerol back into the ester phase and promoting the reverse reaction between glycerol and ester thereby reducing the ester yield. Optimum ratios of palm kernel oil and coconut oil biodiesels yielded 98% each at methanol:oil molar ratio of 8:1. Therefore depending on the type of feedstock and perhaps even the quality (mode of preparation), the optimum methanol:oil molar ratios differ. Besides, all the properties of these three produced biodiesel fulfilled the ASTM 6751 and EN 14214 biodiesel standards.
G.K. Ayetor et al.
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