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Chapter Fourteen

Assessment of Physical, Chemical, and Tribological Properties of Different Biodiesel Fuels

M. Mofijur¹, M.G. Rasul¹, N.M.S. Hassan¹, H.H. Masjuki², M.A. Kalam², and H.M. Mahmudul³ ¹Central Queensland University, Rockhampton, QLD, Australia ²University of Malaya, Kuala Lumpur, Malaysia ³University Malaysia Pahang, Pahang, Malaysia

Abstract

Fuel properties of biodiesels are influenced by the physical features of the fatty acid composition, such as the degree of unsaturation, the percentage of saturated fatty acid, monounsaturated fatty acid, and polyunsaturated fatty acid. Fuel properties are the key factors in determining the suitability of any fuel as an alternative fuel. In this study, biodiesels from five different feedstocks have been characterized for their physical and chemical properties. Gas chromatography has been carried out to find out the ester composition of these five biodiesels, and correlation between composition and fuel properties of these five biodiesels have been developed. Fuel properties were measured according to standard procedure ASTM D6751 and EN 14214 and estimated based on the previously published correlation. Also, the quality of these biodiesels was assessed and compared with commercially available biodiesels through multivariate data analysis using PROMETHEE-GAIA software. In the last part, wear and friction of selected biodiesel fuels have been studied and compared with diesel fuel. The result shows that the properties of produced biodiesel are within the acceptable limit of ASTM and EN standards. Highly linear correlations were found between the composition and cetane number, iodine value, oxidation stability, and cold flow plugging point with the regression value of 0.9965, 0.9983, 0.7044, and 0.9985, respectively. Overall, this study found that, among the biodiesels studied, the palm biodiesel was the most suitable alternative followed by the macadamia, moringa, and jatropha, and beauty leaf biodiesel.

Keywords

Biodiesel; Calophyllum; Production; PROMETHEE-GAIA; Properties; Renewable energy

14.1. Introduction

Biodiesel is a renewable energy source that offers some benefits including the reduction in greenhouse gas emission and pollutants, increasing energy diversity and economic security [1]. Biodiesel is considered as a promising alternative fuel for transportation sector as it has similar fuel properties with diesel fuel [2]. It also can be blended with diesel fuel at any percentage and can be used for power generation in a diesel engine without the change of existing infrastructure. The source-to-wheel carbon dioxide emission analysis of pure biodiesel fuel shows that it reduces 60% CO emission to the environment compared to conventional fossil fuel [3]. In this context, different countries have set their target and mandate to use biodiesel fuel in the transportation sector. For example, the European Union has a target to use 10% biodiesel and China has a target to use 10.6–12 million biodiesel by 2020. Similarly, the Australian government has also set a target to use 20% biodiesel by the year of 2020 [4]. As a result, worldwide biodiesel production has increased too. According to the BP statistics 2015, 10.3% global biodiesel production increased in 2014 compared to the year of 2004.

Biodiesel consists of long-chain alkyl ester and is produced from vegetable oils, animal fats, or waste cooking oils through transesterification reaction [5,6]. In transesterification reaction, vegetable oils are reacted with alcohol (usually methanol) in the presence of a catalyst (commonly used, KOH and NaOH). Through the reversible reaction, triglycerides are converted into monoglycerides, and glycerin is obtained as a by-product. The transesterification reaction is shown in Fig. 14.1.

One of the outstanding credit of biodiesel compared to other biofuels is that a wide range of biodiesel feedstocks are available around the world [7]. Most of the countries use the source for biodiesel production that is readily available in their country. For example, rapeseed oil is used widely in Europe, whereas soybean oil is used in the United States [3]. Similarly, Malaysia is a top palm oil producer country [8], that is why palm oil is widely used in Malaysia for biodiesel production.

Figure 14.1 The transesterification reaction.

Biodiesel is usually characterized by some physical and chemical properties including the fatty acid compositions. The properties of biodiesel, either physical or chemical properties, vary from source to source, country of origin, production process, reaction time, methanol used, temperature, and speed [9]. For this reason characterization of biodiesel is important before using as an alternative to diesel fuel. To this aim, both United States and the European Union have issued standard specification (namely ASTM D6751 by US and EN 14214 by EU) [10] that should be met by the produced biodiesel before being used in the diesel engines. Recently, in the 2010s, the governments of Australia [11], Malaysia [12], Korea [12], and some other countries also have issued their specification. Biodiesel has some limitations that it is vulnerable to oxidation, and it has poor cold temperature properties which could be tackled by using additives [13].

The selection of biodiesel source is very important as feedstock alone consists of 75% total production cost. The study on the fuel properties is also crucial as the suitability of biodiesel depends on the fatty acid composition and fuel properties. The fatty acid composition also influences many fuel properties. A research work has been done to study the effect of five edible and nonedible biodiesel feedstocks (macadamia, beauty leaf, palm, jatropha, and moringa oils) on the physical and chemical properties. Also, the correlation between composition and fuel properties of biodiesel has been established. Finally, to validate the data and choose the better alternative among them based on 15 criteria (fuel properties), namely kinematic viscosity (KV), dynamivc viscosity (DV), density (D), flash point (FP), calorific value (CV), cetane number (CN), iodine value (IV), saponification value (SV), cloud point (CP), pour point (PP), acid value (AV), oxidation stability (OS), cold filter plugging point (CFPP), polyunsaturated fatty acid (PUFA), and monounsaturated fatty acid (MUFA) using a PROMETHEE-GAIA multicriteria decision analysis software.

14.2. Materials

In this study, five types of fuel, namely palm, jatropha, moringa, macadamia, and beauty leaf oils have been selected. Palm and Jatropha oils were supplied by forest research institute, Malaysia. Macadamia oil was purchased from Coles, whereas moringa and beauty leaf oils were collected from a colleague through personal communication. The detailed properties of crude oils are presented in Table 14.1. All other reagents, methanol, and 150 mm filter paper were available in the chemical laboratory, Central Queensland University (North Rockhampton, Australia).

14.2.1. Biodiesel Production

The viscosity of vegetable oils (as shown in Table 14.1) are 10–15 times higher than fossil diesel fuel. The direct use of higher viscous fuel in the internal combustion engine causes some problems including wear in the injectors, fuel pump, and engine deposition and blocking the fuel system which consequently affect the fuel spray and combustion process inside the cylinder [14]. Therefore, crude oils could be passed through a chemical process called transesterification process to reduce the viscosity. Transesterification process is very popular process among all the other biodiesel conversion process due to simplicity, reliability, low cost, and the fuel quality. One of the problems of this conversion process is the formation of soap with the reaction of higher free fatty acid (FFA) and catalyst [15]. To avoid soap formation, FFA should be reduced through the preesterification process using sulfuric acid [16]. Fig. 14.2 shows the schematic diagram of two-step biodiesel production process.

Table 14.1

Properties of Crude Oils Used in This Study

Properties	Units	Standards	Macadamia Oil	Palm Oil	Jatropha Oil	Moringa Oil	Beauty Leaf Oil
Dynamic viscosity	mPa.s	ASTM D445	35.23	36.30	31.52	38.90	48.73
Kinematic viscosity at 40°C	mm²/s	ASTM D445	39.22	40.40	34.93	43.33	52.13
Density at 15°C	kg/m³	ASTM D4052	898.60	898.4	902.5	897.5	922.2
Flash point	°C	ASTM D93	167.5	165	220	268.5	195.5
Pour point	°C	ASTM D97	8	9	−3	11	8
Cloud point	°C	ASTM D2500	0	8	−2	10	8
Calorific value	MJ/kg	ASTM D240	39.89	39.44	38.66	38.05	38.51
Acid value	mg KOH/g oil	ASTM D664	4	3.47	10.7	8.62	40

In this study, a small-scale laboratory reactor (water jacketed), as shown in Fig. 14.3A, 1 L in size equipped with reflux condenser, thermometer, and water-circulated bath was used to produce biodiesel from vegetable oils. The FFAs of crude moringa, jatropha, and beauty leaf oils were found to be higher (above two), which indicates that esterification is necessary to produce biodiesel from jatropha, moringa, and beauty leaf oils. The rest of the vegetable oils including palm and macadamia oil was processed only through the transesterification process.

Figure 14.2 Schematic diagram of biodiesel production process.

Figure 14.3 (A) Biodiesel reactor, (B) settling, (C) washing, and (D) filtering.

In the esterification process, the molar ratio of methanol to refined beauty leaf, jatropha, and moringa oils were maintained at 12:1 (50% v/v). 1% (v/v) of sulfuric acid (H₂SO₄) was added to the preheated oils at 60°C for 3 h under 600 rpm stirring speed in a glass reactor. On completion of this reaction, the products were poured into a separating funnel to separate the excess alcohol, sulfuric acid, and impurities present in the upper layer. The lower layer was separated and heated at 95°C for 1 h to remove methanol and water from the esterified oil.

In the transesterification process, esterified/preheated oil was reacted with 6:1 M ratio of methanol to oil in the presence of 1% (w/w) of KOH catalyst. The reaction was maintained at 60°C for 2 h at 800 rpm. After completion of the reaction, the mixture was poured into a separation funnel for 14 h to be cooled and settled, and then glycerol was separated from biodiesel (Fig. 14.3B). The upper part of the funnel contained biodiesel, and the lower part contained glycerin along with excess methanol and impurities. The biodiesel was collected, and the glycerin was drawn off. The produced biodiesel was then heated at 65°C to remove remaining methanol. Then the biodiesel was washed using warm distilled water to remove entire impurities (Fig. 14.3C). Finally, the washed biodiesel was heated at 95°C for 1 h to remove water and then dried using Na₂SO_4. Then the biodiesel was filtered through a filter paper (Fig. 14.3D), and the final product was collected and stored for characterization.

14.2.2. Determination of Fatty Acid Composition

The fatty acid composition was determined using gas chromatography (GC 7890A, Agilent Technologies) equipped with a flame ionization detector. The capillary column was 30 m in length, with a film thickness of 0.25 μm, and with an internal diameter of 0.25 mm. The carrier gas He was supplied at 20 mL/min speed. The temperature was 100°C hold for 0 min and 10°C/min to 250°C hold for 5 min. The injector and detector temperatures were 250°C. The split ratio of injector ratio was 50:1 and the volume were 0.3 μL. In this test, 0.25 g of each sample was diluted with 5 mL n-heptane to analyze the fatty acid composition test.

14.2.3. Fuel Properties

In this study, all the fuel properties were measured according to the ASTM standards. Table 14.2 shows the list of equipment used in this study. CN, IV, SV, degree of unsaturation (DU), and long-chain saturated factor (LCSF) were calculated from the fatty acid profile of all biodiesel using following equations as described by [16–20]:

$CN = 46.3 + (5458 / SV) - (0.225 \cdot IV)$ $CN = 46.3 + (5458 / SV) - (0.225 \cdot IV)$

(14.1)

$SV = \sum (560 \cdot A_{i}) / M_{wi}$ $SV = \sum (560 \cdot A_{i}) / M_{wi}$

(14.2)

Table 14.2

Equipment Used in This Study

Property	Equipment	Standard Method	Accuracy
Kinematic viscosity	NVB classic (Norma Lab, France)	ASTM D445	±0.01 mm²/s
Density	DM40 LiquiPhysics density meter (Mettler Toledo, Switzerland)	ASTM D127	±0.1 kg/m³
Flash point	NPM 440 Pensky-martens flash point tester (Norma Lab, France)	ASTM D93	±0.1°C
Cloud and pour point	NTE 450 cloud and pour point tester (Norma Lab, France)	ASTM D2500	±0.1°C
Higher heating value	IKA C 2000 calorimeter, United Kingdom	ASTM D240	±0.001 MJ/kg
Acid number	Automation titration rondo 20 (Mettler Toledo, Switzerland)	ASTMD664 and EN 14111	±0.001 mg KOH/g
Oxidation stability, 110°C	873 Rancimat (Metrohm, Switzerland)	EN 14112	±0.01 h

$IV = \sum (254 \cdot A_{i} \cdot D) / M_{w i}$ $IV = \sum (254 \cdot A_{i} \cdot D) / M_{w i}$

(14.3)

$LCSF = 0.1 (C 16 : 0, wt %) + 0.5 (C 18 : 0 wt %) + 1 (C 20 : 0 wt %) + 1.5 (C 22 : 0 wt %) + 2.0 (C 24 : 0 wt %)$ $LCSF = 0.1 (C 16 : 0, wt %) + 0.5 (C 18 : 0 wt %) + 1 (C 20 : 0 wt %) + 1.5 (C 22 : 0 wt %) + 2.0 (C 24 : 0 wt %)$

(14.4)

$DU = \sum (Monounsaturated Fatty Acid + 2 Polyunsaturated Fatty Acid)$ $DU = \sum (Monounsaturated Fatty Acid + 2 Polyunsaturated Fatty Acid)$

(14.5)

where A_i is the percentage of each component; D is the number of double bonds; and M_w is the molecular mass of each component.

In this study, a multicriteria decision analysis tool named PROMETHEE-GAIA was used to find out the best fuel that has the suitable chemical composition to ensure the compliance with standard biodiesel properties. The critical parameters of biodiesel fuel properties, such as D, KV, CN, IV, OS, and CFPP, are depended on oil nature. Therefore, data on properties of two more commercial biodiesel were obtained from literature including sunflower biodiesel (SBD) and rapeseed biodiesel (RBD) to validate the data obtained from produced biodiesels. The better alternative fuel among these biodiesels for diesel engine application was selected based on 15 criteria (fuel properties), namely KV, DV, D, FP, CV, CN, IV, SV, CP, PP, AV, OS, CFPP, PUFA, and MUFA using a multicriteria decision analysis software. PROMETHEE-GAIA software was used for multicriteria decision analysis because of their rational decision vector that stretches toward the preferred solution compared to other multicriteria decision software [20]. The name of the biodiesels was set to “action” and fuel properties were set to “criteria.” The preference function was set as minimum (i.e., lower values preferred for good biodiesel) or maximum (i.e., higher values preferred for good biodiesel), and weighting was considered equal for all criteria in this analysis. Table 14.3 shows the variables and preference used in PROMETHEE-GAIA analysis.

14.2.4. Equipment for Tribological Study

In this study, a four-ball tester was used to evaluate the wear and friction characteristics of biodiesel. Schematic diagram of four-ball tester is shown in Fig. 14.4. The ball used was made from stainless steel, and three balls were stationary, and one ball was rotating in the steel cup. At least 10 mL of tested fuel was poured into the steel cup so that steel cup is filled minimum 3 mm and three stationary balls are fully dipped. The four-ball tester was connected to a computer to obtain the frictional data through Winducom 2008 software. The test was conducted according to the ASTM D2596 and D2783 methods and at a variable load of 40 and 80 kg. The total test run time was 300 s at a constant speed of 1800 rpm. The wear scar diameter (WSD) of tested ball was measured before removing the steel ball from the cup.

Table 14.3

The Variables and Preference Used in PROMETHEE-GAIA Analysis

Variables	Preference for PROMETHEE-GAIA
KV	Min
D	Min
HHV	Max
OS	Max
AV	Min
FP	Max
CP	Min
CFPP	Min
CN	Max
IV	Min
DU	Min
MUFA	Min
PUFA	Min

Figure 14.4 Schematic diagram of four-ball tester.

14.2.5. Determination of the Coefficient of Friction

The coefficient of friction was calculated by the multiplication of the mean friction torque and spring constant. A load cell was used to measure the frictional torque in this experiment. The frictional torque can be expressed as:

$T = \frac{μ \times 3 \times W \times r}{\sqrt{6}}$ $T = \frac{μ \times 3 \times W \times r}{\sqrt{6}}$

(14.6)

$\approx μ = \frac{T \times \sqrt{6}}{3 \times W \times r}$ $\approx μ = \frac{T \times \sqrt{6}}{3 \times W \times r}$

(14.7)

where μ = coefficient of friction; T = frictional torque (kg-mm); W = applied load (N); and r = distance from the center of the contact surface on the lower balls to the axis of rotation.

14.2.6. Determination of Flash Temperature Parameter

The flash temperature parameter (FTP) is a single number that is used to express the critical flash temperature at which a sample will fail under given conditions. The FTP was calculated for both loads. For the conditions used in the four-ball test, the following relationship was used:

$FTP = \frac{W}{d^{1.4}}$ $FTP = \frac{W}{d^{1.4}}$

(14.8)

where W = load (kg) and d = mean wear scar diameter (mm).

14.3. Results and Discussion

14.3.1. Fatty Acid Profile of Biodiesels

A systematic analysis of the fatty acid composition and comparable fuel properties are important to select the best species for biodiesel production. Table 14.4 shows the fatty acid profile of produced biodiesel, namely macadamia biodiesel (MaBD), palm biodiesel (PBD), jatropha biodiesel (JBD), moringa biodiesel (MoBD), and beauty leaf biodiesel (BBD). These fatty acids have a direct impact on the chemical and physical properties of biofuel. All the biodiesel samples contain saturated fatty acid, MUFA, and PUFA. The total saturated fatty acids of MaBD, JBD, PBD, MoBD, and BBD were found to be 15.80%, 22.6%, 44.6%, 18.6%, and 33.4%, respectively, whereas total unsaturated fatty acids of MaBD, JBD, PBD, MoBD, and BBD were found to be 84.20%, 77.4%, 55.4%, 81.4%, and 66.6%, respectively. Oleic acid (18:1) was the predominant fatty acid in all the biodiesel samples (i.e., macadamia (61.3%), jatropha (44.6%), palm (43.4%), moringa (74.1%), and beauty leaf (38.2%)) followed by the palmitoleic acid (C16:1, 16.2%) for MaBD, linoleic acid (C18:2, 31.9%) for JBD, palmitic acid (16:0, 40.3%) for PBD, palmitic acid (16:0, 7.9%) for MoBD, and linoleic acid (C18:2, 27.6%) for BBD. Among all the biodiesel fuels, JBD has the highest DU (109.60), whereas PBD has the lowest DU (67.80). Also, the DU of BBD, MoBD, and MaBD is 94.50, 85.70, and 84.50, respectively. Unlike the DU, JBD has the lowest LCSF (5.26), and BBD has the highest LCSF (11.64).

14.3.2. Analysis of Fuel Properties of Biodiesel Samples

Characterization of biodiesel is needed to check the quality of the fuels as every fuel must meet the quality standard before being considered as an automobile fuel [21]. Therefore, the produced biodiesel from any source must meet the recognized worldwide standards to be used as IC engine fuel. Currently, global biodiesel standards are ASTM D6751 and EN14212 [22,23]. Some other countries also have identified their standards [11,14,24]. The properties of biodiesel fuel are varied from feedstock to feedstock, and it also depends on the quality, origin of the source, and biodiesel production techniques [25]. Therefore, to evaluate the impact of a fatty acid profile on the quality of fuel, the physical and chemical properties were calculated and measured. Table 14.5 shows the summary of fuel properties compared with commercial biodiesel.

Table 14.4

Fatty Acid Compositions of Biodiesel Fuels

Fatty Acids	Molecular Weight	Structure	MaBD (Wt%) [18]	JBD (Wt%)	PBD (Wt%)	MoBD (Wt%)	BBD (Wt%)
Lauric	200	12:0	0.100.6	0.1	0	0	0
Myristic acid	228	14:0	0.6	0.1	0	0.1	0
Palmitic	256	16:0	7.9	14.6	40.3	7.9	14.9
Palmitoleic	254	16.1	16.2	0.6	0	1.7	0.2
Stearic	284	18:0	3.2	7.6	4.1	5.5	17.2
Oleic	282	18:1	61.3	44.6	43.4	74.1	38.2
Linoleic	280	18:2	2.1	31.9	12.2	4.1	27.6
Linolenic	278	18:3	0.1	0.3	–	0.2	0.3
Arachidic	312	20:0	2.7	0.3	–	2.3	0.9
Eicosenoic	310	20:1	2.6	–	–	1.3	0.3
Behenic	340	22:0	0.9	–	–	2.8	0.3
Erucic	338	22:1	0.3	–	–	–	0
Lignoceric	368	24:0	0.4	–	–	–	0.1
Total saturated fatty acid			15.80	22.6	44.6	18.6	33.4
Total monounsaturated fatty acid			80.40	45.2	43.4	77.1	38.7
Total polyunsaturated fatty acid			2.20	32.2	12	4.3	27.9
Others			1.6	0	0	0	0
Degree of unsaturation (DU)			84.50	109.60	67.80	85.70	94.50
Long-chain saturated factor (LCSF)			7.24	5.26	6	10.04	11.64

14.3.2.1. Density

Density is an important property of any fuel, which affects the engine performance characteristics directly. Density influences the fuel atomization efficiency and combustion characteristics [26,27]. Density also leads to engine oil sludge problems. In this study, an Anton Paar automatic viscometer (SVM 3000) was used to measure the density (kg/cm³) of the fuel according to ASTM D7042. The standard range of the density of biodiesel fuel is 3.5–5 in EN and Australia, respectively, but there is no specification according to US standards. The densities of MaBD, PBD, JBD, MoBD, and BBD were found to be 859.2, 858.9, 865.7, 869.6, and 868.7 kg/m³, respectively. All the values are within the limit of EN14214 and Australian standards.

Table 14.5

Properties of Produced Biodiesel Compared With Other Commercial Biodiesel

Properties	Unit	MaBD [18]	PBD	JBD	MoBD	BBD	SBD^a	RBD^a	ASTM D6751	EN 14214	Australian Standards
Kinematic viscosity at 40°C	mm²/s	4.46	4.63	4.73	5.05	5.68	4.2	4.4	1.9–6	3.5–5	3.5–5
Density at 15°C	kg/m³	859.2	858.9	865.7	869.6	868.7	880	877	–	860–900	860–900
Higher heating value	MJ/kg	38.21	40.91	39.82	40.05	39.38	41.26	41.55	–	–	–
Oxidation stability	h	3.35	5.16	3.02	4.45	3.58	1.88	3.09	3 min	6 min	–
Acid value	mg KOH/g	0.07	0.05	0.05	0.05	0.34	0.15	0.16	0.5 max	0.5 max	0.8
Flash point	°C	178.5	182.5	184.5	180.5	141.5	177	176	130 min	120 min	120 min
Pour point	°C	0	11	3	19	7	–	–	Report	Report	Report
Cloud point	°C	8	10	3	19	7	–	–	Report	Report	Report
CFPP	°C	8	11	10	18	8	−3	−10	Report	Report	Report
Cetane number	–	56	59	51	56	54	44.90	61.08	47 min	51 min	51 min
Iodine number	–	77.50	61	99	77.50	86	119.47	109	–	–	–
Saponification value		199	206	202	199	201	214	139	–	–	–

14.3.2.2. Flash Point

FP is the safety measure of fuel for storage. It is the point at which fuels are flammable [28]. According to the Australian standards and EN14214 standards, the minimum FP temperature for biodiesel should be 120°C whereas it should be 130°C according to US standards. To measure the FP value of the fuel according to the ASTM D93 method, an HFP 380 Pensky-Martens FP analyzer was used. Table 14.5 shows the FP temperature of different biodiesel fuel. All the biodiesel have a higher FP than diesel fuel which indicates that biodiesel is safer to transport and store [14,29–33]. Among all the biodiesels, JBD has the maximum FP (184.5°C), and BBD has the minimum FP temperature (141.5°C). All the values are within the specified limits.

14.3.2.3. Viscosity

Viscosity affects the fuel drop size, the jet penetration, quality of atomization, spray characteristics, and the combustion quality [18]. Very high or low viscosity of fuel affects the engine. For example, if the viscosity is very low, then it will not provide enough lubrication which will increase wear and leakage. Higher viscous fuel will form a larger droplet during injection which affects combustion quality thus leading to higher exhaust emission [15]. An Anton Paar automatic viscometer (SVM 3000) was used to measure the viscosity (mm²/s) of the fuel according to ASTM D445. The standard range of KV of biodiesel fuel is 1.9–6 in the United States and 3.5–5 in EN and Australia. Table 14.5 shows the KV of all biodiesel fuel. BBD has a highest KV (5.68 mm²/s) followed by the moringa (5.05 mm²/s), jatropha (4.73 mm²/s), palm (4.63 mm²/s), and macadamia (4.46 mm²/s) biodiesels, respectively. All the KV values are within the US, EN, and Australian standards.

14.3.2.4. Cold Flow Properties

Cold flow properties indicate the low-temperature operation ability of any fuel and reflect their cold weather [34]. The CP is defined as the temperature of a liquid specimen when the smallest observable cluster of wax crystals first appears upon cooling under prescribed conditions [35]. The CFPP is defined as the temperature at which the test filter starts to plug due to fuel components that begin to gel. This causes major operability problems. The cold-temperature properties of biodiesel should be reported according to the Australian, European, and US standards although the limits are not specified. An automatic NTE 450 (Norma Lab, France) CP tester and an automatic NTE 450 (Norma Lab, France) CFPP tester were used to measure the CP and CFPP of all biodiesel fuel samples according to the ASTM D2500 and ASTM D6371 methods, respectively. Table 14.5 shows the cold weather performance of different biodiesel fuels used in this study. The CP and CFPP of MaBD, PBD, JBD, MoBD, and BBD were found to be 8°C and 8°C, 10°C and 11°C, 3°C and 10°C, 19°C and 18°C, and 7°C and 8°C, respectively.

14.3.2.5. Cetane Number

It is a dimensionless number that describes the ignition quality of fuel under a fixed condition [36]. This is one of the parameters that is considered for selection of the biodiesel. Fuels having higher CN play a role to start engine rapidly and make smooth combustion in the engine [13,37]. But, fuel with lower CN affects the combustion characteristics thus emitting higher HC and PM emissions. Australian and European biodiesel standards limit the CN to a minimum value of 51 whereas ASTM standard limits it to a minimum value of 47. Table 14.5 indicates that PBD has good ignition quality followed by the moringa (56), macadamia (56), beauty leaf (54), and jatropha (51) biodiesels. Though the fatty acid composition of both macadamia and moringa is different, they have same ignition quality. The reason of highest CN of PBD could be attributed to the higher saturated fatty acid composition and biodiesel. The lowest CN of JBD may be due to the contents of higher linoleic acid. However, all the results are within the specified limits and meet the standard specification.

14.3.2.6. Higher Heating Value

The heat of combustion or the CV of a fuel blend is another very important property to determine its suitability as an alternative to diesel fuel [38]. The higher heating value of a fuel mixture influences the power output of an engine directly. In this study, the heating value of all the fuel samples was determined using IKA C 2000 calorimeter. The higher heating value (HVV) of the fuel sample used in this study is shown in Table 14.5. PBD has the highest heating value (40.91 MJ/kg) followed by the MoBD (40.05 MJ/kg), JBD (39.82 MJ/kg), BBD (39.38 MJ/kg), and MaBD (38.21 MJ/kg) respectively. The HHVs of all the fuel samples are close to each other and do not have much variation. There is no specified limit on HHV in all US, EN, and Australian standards.

14.3.2.7. Oxidation Stability

Biodiesel produced from vegetable oils is considered more vulnerable to oxidation at high temperature and contact of air, because of bearing the double bond molecules in the FFA [39]. Biodiesels show less oxidative stability compared with petroleum diesel due to their different chemical composition, and this is one of the major issues that limit the widespread use of biodiesel as a fuel in automobile engines [40]. According to the US and EN standards, the OS period should be minimum 3 and 6 h, respectively. Australia also has set the standard that is same as the EN standards (minimum 6 h). The biodiesel and its blend stability were measured by induction period. OS of samples was evaluated with commercial appliance Rancimat 743 applying accelerated oxidation test (Rancimat test) specified in EN 14112. All the biodiesel listed in Table 14.5 meet the US standards but fail to meet the EN and Australian standards. The OS values of MaBD, PBD, JBD, MoBD, and BBD were found to be 3.35, 5.16, 3.02, 4.45, and 3.58 h, respectively.

14.3.3. Effect of Fatty Acid Composition on Fuel Properties

From the previous section, it has been clear that biodiesel properties from a different source are not same. The fatty acid composition has a significant influence on the properties of biodiesel fuel [34]. The following section discusses the effect of fatty acid composition on the main fuel properties.

CN is associated with the unsaturated fatty acid composition of the biodiesel. Fig. 14.5 shows the correlation between the DU and CN. It is clear that cetane decreases with increasing DU, and it linearly fits with DU with the R² value of 0.9965. The following equation has been developed to predict the CN:

Cetane Number = −0.1927 × Degree of Unsaturation + 72.242, R² = 0.9965

As discussed in the previous section that iodine number is the value that indicates the double bond in biodiesel, therefore, it's also related to the DU of biodiesel. The correlation between the DU and the IV is shown in Fig. 14.6. It is seen that IV increases with the DU that indicates higher the unsaturation in the fuel will have higher IV. IV linearly fits with the DU with an R² value of 0.9983. The following equation has been developed to predict the iodine number:

Iodine Number = 0.9076 × Degree of Unsaturation − 0.0527, R² = 0.9983

Biodiesel is very likely to be oxidized unless an antioxidant is used. OS is highly related to the unsaturated fatty acid [41]. Fig. 14.7 shows the correlation between DU and OS. It is seen that OS has a linear relationship with DU with a higher R² value of 0.9587. The OS value decreases with the DU. The level of unsaturation of most of the biodiesel fuel is high, therefore OS is poor. The following equation has been developed to predict the OS:

Oxidation Stability = −0.0541 × DU + 8.9285, R² = 0.7044

Figure 14.5 Correlation between degree of unsaturation and cetane number.

Figure 14.6 Correlation between degree of unsaturation and iodine value.

Figure 14.7 Correlation between degree of unsaturation and oxidation stability.

CFPP is an important parameter that indicates the low-temperature application capability of biodiesel which mainly depends on the LCSF. The impact of the unsaturated fatty acid composition is negligible in this case. Therefore, Fig. 14.8 shows the correlation between CFPP and LCSF. It is seen that CFPP increases with the LCSF, and correlation between them are linear with a high R² value of 0.9985. The following equation has been developed to predict the CFPP of biodiesel fuel:

CFPP = 3.1028 × Long Chain Saturated Factor − 16.109, R² = 0.9985

14.3.4. Validation of Biodiesel Properties

Analysis of fuel properties and correlation analysis described in the previous section indicate that properties of all the biodiesel fuel are not same. Different biodiesels have different properties, chemical composition, the DU, and LCSF. For example, MaBD has higher unsaturated fatty acid whereas PBD has higher saturated fatty acid composition. Therefore, it is necessary to assess and compare the biodiesel properties with the commercial biodiesel. In this study, a multicriteria decision software PROMETHEE-GAIA was used to evaluate and validate the data that stretches toward the preferred solution.

Figure 14.8 Correlation between long-chain saturated fatty acid and CFPP.

In GAIA plane, the different biodiesel fuels are far away from each other, which means that biodiesels from different sources have different properties. The criteria that lie near to (±45 degrees) are correlated while the criteria that lie in opposite direction (135–225 degrees) are anticorrelated. Also, those lying in the orthogonal direction have no or minimal influence [42]. An axis represents each criterion. The direction and length of the criteria indicate their impact on the decision vector. For example, FP in Fig. 14.9 has little effect on decision vector. The choice of decision vector represents the best fuel, and the furthest criteria toward the selection vector are the most ideal [11]. In Fig. 14.9, it is seen that PBD was the farthest position from the center in the decision vector plane, thus it gave the highest ranking. The positions of macadamia and moringa are closer in the GAIA plane, which indicates that their properties are closer to each other. Although the positions of JBD and BBD are far away from the decision vector, they are positioned closer to each other which also indicates that their properties are also similar.

Table 14.6 shows the PROMETHEE II complete ranking result (phi value). The phi value is the net flow score that could be either positive or negative depending on the angular distance from the decision vector and distance from the center [43]. It is evident from Fig. 14.9 that based on all of the measured data, the highest ranked biodiesel source is palm oil and the lowest ranked source is beauty leaf oil. Among the produced biodiesels, the best biodiesel feedstocks are palm, macadamia, and moringa oils. The phi values of macadamia, rapeseed, and moringa are closer (Fig. 14.9), which indicate that their criteria values are closer to each other. The result of this analysis shows the ability to compare produced biodiesel with commercial RBD.

Figure 14.9 GAIA plot for biodiesel fuel and decision vector.

14.3.5. Study of Tribological Characteristics

Lubricity of an engine fuel is an imperative parameter to determine the engine life. Fuel with higher lubricity extends the engine life. It also reduces the energy consumption by reducing the friction between the moving parts. It has been reported that biodiesel exhibits better lubricity than diesel fuel, and due to this behavior, biodiesel can be used as an additive to improve the lubricity of conventional fossil fuel. According to the PROMETHEE-GAIA study in the last section, it was found that PBD is the best alternative fuel among these five biodiesels. In this section, the tribological behavior of only PBD has been studied and compared with diesel fuel.

Table 14.6

Corresponding Ranking and Phi Values of Biodiesel Fuels

Ranking	Biodiesel Samples	Phi Value
1	PBD	0.3667
2	MaBD	0.1667
3	RBD	0.1000
4	MoBD	0.0167
5	JBD	−0.1000
6	BBD	−0.1833
7	SBD	−0.3667

14.3.5.1. Friction Behavior

Frictions are highly dependent on load and temperature. Initially, the friction between metal contact surfaces is not stable which is known as a run period. After a few seconds, the condition becomes stable which is called steady-state condition [44]. In this study, coefficient of friction was calculated at both run time and steady-state conditions by changing load. Fig. 14.10 shows the coefficient of friction of both fuels at both (run time and steady-state) conditions and both (40 and 80 kg) loads. In the run period condition (Fig. 14.10A and B), diesel showed higher COF than PBD fuel. During the run period, maximum COF for PBD fuel was found to be 0.15 at 1.5 s and 0.49 at 2 s, whereas for diesel it was found to be 0.39 at 4 s and 0.52 at 3.8 s for 40 and 80 kg load conditions, respectively. The biodiesel showed better friction performance than diesel fuel due to the presence of ester molecules that are more efficient in protecting scuffing behavior [45]. In the steady-state condition, diesel fuel also shows higher COF than PBD for both 40 and 80 kg loads as presented in Fig. 14.10C and D. The COF for PBD was found to be 0.08 at 200 s for 40 kg load, and it remains almost same up to 209 s. In contrast, COF for PBD varied over the time for 80 kg load condition. In both (run-in and steady-state conditions), highest COF was found for diesel fuel in both loads.

14.3.5.2. Wear Scar Diameter and Flash Temperature Parameter

The effect of load on wear scar diameter of PBD and diesel fuel is shown in Fig. 14.11A. It is seen that the diameter is increased with the load for both fuels which could be attributed to the variation of contact surface pressure. In all load condition, PBD showed 15.5% and 54% lower WSD than diesel fuel at 40 and 80 kg load, respectively. This may be due to the presence of trace element (removal of the metallic soap film generated at high load) in biodiesel that helps to improve the lubricity of biodiesel fuel [46].

FTP is an important parameter that also indicates the lubricity of fuel samples. Higher FTP value of sample is the indication of better lubricity performance, and lower FTP value is the inverse indication of lubricity [47]. The FTP of diesel and PBD is shown in Fig. 14.11B. It is seen that FTP decreases with load, and it has the inverse character of WSD. PBD has higher FTP than diesel fuel in both loads. The maximum FTP was found for PBD at 40 kg load condition.

14.4. Conclusions

In this study, biodiesel was produced from five sources obtained locally or internationally to assess their relevant physical and chemical properties. Moreover, the properties were correlated with the composition of biodiesel, providing linear best-fit curves that will help researchers or designers in simulation work. Summary of the findings of this study are:

Figure 14.10 The coefficient of friction (COF) in (A) run-in-period at 40 kg load, (B) run-in-period at 80 kg load, (C) steady-state condition at 40 kg load, and (D) steady-state condition at 80 kg load.

Figure 14.11 (A) Variation of WSD with loads and (B) variation of FTP with loads.

• The fuel properties of all five biodiesels are within the specified limit of ASTM D6751 and EN 14211 standards.

• A good agreement between the composition and fuel properties of biodiesels was observed. The DU was found to correlate linearly with the CN, IV, and OS. A high statistical correlation (R² = 0.9985) was also established between the long-chain saturated fatty acid and CFPP.

• The multicriteria decision analysis using PROMETHEE-GAIA software indicated that PBD could be a better alternative for diesel engine application compared much with other commercial biodiesel.

• The tribological study shows that PBD has better wear and friction performance than diesel fuel.

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Table of Contents for Chapter Fourteen. Assessment of Physical, Chemical, and Tribological Properties of Different Biodiesel Fuels

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