Physicochemical fuel properties and tribological behavior of aegle marmelos correa biodiesel

Physicochemical fuel properties and tribological behavior of aegle marmelos correa biodiesel

11

Vinoth Thangarasu, R. Anand Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, India

Nomenclature AMC ASTM B0 B100 CFPP CO2 COF EN FAME FFA FTIR FTP GC HCl IV KOH NMR OSI PAHs STP ULSD WSD

Aegle Marmelos Correa American Standard for Testing Material Diesel AMC Biodiesel Cold Filter Plugging Point Carbon dioxide Coefficient of Friction European Standard Fatty Acid Methyl Ester Free Fatty Acid Fourier Transform – Infrared Spectroscopy Flash Point Temperature Gas chromatography Hydrochloric acid Iodine Value Potassium hydroxide Nuclear Magnetic Resonance Oxidization Stability Index Poly-nuclear Aromatic Hydrocarbons Standard Temperature Pressure Ultra-low Sulfur Diesel Wear Scar Diameter

11.1

Introduction

Production of fossil fuels and consumption of energy are continuously increasing due to a rapid increase in the worldwide population and industrial sectors [1–3]. Currently, fossil fuels contribute about one-third of the world energy supply and play a crucial role in improving human living standards and economies. The International Energy Outlook 2017 reported that world energy consumption was 607 quadrillion kilojoules Advances in Eco-Fuels for a Sustainable Environment. https://doi.org/10.1016/B978-0-08-102728-8.00011-5 © 2019 Elsevier Ltd. All rights reserved.

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in 2015; it is projected to reach 700 quadrillion kilojoules in 2030 [4]. Overdependency and burning of fossil fuels leads to increases in CO2 emissions and global warming [5]. Ever-increasing energy demand, depletion of fossil fuels, and air pollution problems have created the awareness and attention toward ecofriendly and renewable fuels [6]. Recently, biodiesel has gained attention as a promising alternative to fossil fuels to meet future energy demands [7]. Biodiesel is biodegradable and can be directly usable in a diesel engine without any modifications in the form of blending with diesel. Several studies on biodiesel-fueled diesel engines have been performed, showing that they emit fewer toxic emissions than diesel [8]. Right now worldwide, more than 360 feedstocks have been found to produce biodiesel. Nonedible feedstocks had no competition with edible oils and are considered wastes, which gained noteworthy attention due to the low cost, positive energy balance, and environmental impacts compared to food feedstock-based biodiesels [9]. Biodiesel is a mono-alkyl ester produced from triglycerides of plant and animal feedstocks via the alcoholysis process known as transesterification [10]. Transesterification is a conversion process of fatty acids into alcoholic esters in the presence of acid or an alkaline catalyst [11]. The conversion process takes place in three steps in which triglycerides are converted into di, mono, and finally esters with glycerol as a byproduct [12, 13]. Stoichiometrically, three moles of alcohol are required to convert one mole of fatty acid into esters. However, more alcohols are required to forward the reaction because transesterification is a slow and reversible process. Generally, the homogeneous or heterogeneous catalyst is used to accelerate the reaction [14]. Biodiesel physicochemical properties differ from one source to another due to their different fatty acid composition, which affects the fuel properties [15, 16]. Moreover, the biodiesel properties depend on the alcohol used, pretreatment, production, and posttreatment processes. International standards, namely ASTM D6751 and EN14214, have been set up to assess the quality of biodiesel to resolve these issues. This standard specifies the quality requirement and test methods to determine the physicochemical properties of biodiesel and its blends [17]. The key parameters to utilize biodiesel in a diesel engine are acid value, iodine value, saponification value, density, kinematic viscosity, oxidation stability, calorific value, cetane number, and cloud and pour point [10]. The fatty acid composition, the number of double bonds, and the chain length of biodiesel are major influences on the biodiesel properties. The density and kinematic viscosity properties of the biodiesel influence the atomization and vaporization characteristics of the fuel during combustion [18]. Biodiesel with high fatty acid content increases the cetane number and pour point temperature and decreases the kinematic viscosity [19]. Unsaturated fatty acid content of biodiesel improves the cold flow behavior, calorific value, and density [20]. The cetane number of biodiesel is directly correlated with the calorific and density value of the fuel. Biodiesel has a higher cetane number due to its higher oxygen content compared to diesel, which improves engine performance and combustion characteristics [21]. Even though biodiesel has many advantages, the higher unsaturated fatty acid content of biodiesel is the major drawback that decreases the oxidation stability [22]. The poor oxidation stability of biodiesel deposits the gums over the period of storage, which clogs the fuel filter and corrodes and damages the various engine parts [23].

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So the requirement of good fuel is not only to provide energy but also to act as a lubricant between engine parts. Many of the properties of biodiesel influence the tribological behavior when it contacts engine parts at sliding conditions [24]. The excellent lubricity fuel increases the engine life and minimizes the energy consumption by reducing the friction between sliding parts [25, 26]. Numerous studies have proven that biodiesel possesses good lubricity compared to diesel fuel. The lubricity capacity maybe differs with different biodiesel due to its different chemical composition. So, assessing the physicochemical and tribological behavior of biodiesel is important before utilizing it in a conventional diesel engine [15]. The aegle marmelos correa (AMC) tree belongs to the Rutaceae family and Aurantioideae subfamily, and is commonly known as Vilvam (Tamil), bael (Hindi), Matum (Thailand), and Wood apple (English). India, Nepal, and the Andaman Islands are the native countries of the AMC tree, but it is now naturalized and found in Sri Lanka, Thailand, Malaysia, and throughout the South Asian countries [27]. AMC is a slow growing and 10–12 m medium-sized subtropical plant that can be grown at a maximum altitude of 1200 m from sea level. It can adapt and grow in a variety of soils such as sandy, waterlogged, clay, unirrigated, and even in acidic or basic conditions. The matured tree takes 10–11 months to ripen the fruits and produce 400–1000 fruits. The fruits can be harvested once the outer color changes from green to yellowish green [28]. The present study aims to examine the physicochemical and tribological characteristics of AMC biodiesel for the first time. The ultrasonic-assisted extraction method was used to extract crude oil from the AMC seeds. The two-step transesterification process was to convert oil into biodiesel by using potassium hydroxide as a catalyst. The nuclear magnetic resonance technique was used to confirm the ester formation and determine the conversion percentage. The gas chromatography analytical instrument was employed to separate them and identify the chemical composition of AMC methyl ester. Physicochemical properties of biodiesel were determined and detailed as per the ASTM D6751 and EN 14214 standards.

11.2

Materials and methods

11.2.1 Materials The AMC fruits were collected from Coimbatore and Anthiyur, Tamilnadu, India. All other reagents such as acetone, heptane, ethanol 95%, methanol 99.9%, hydrochloric acid (HCl) 37%, diethyl ether 99.9%, potassium hydroxide (KOH) 85%, sodium thiosulfate 99%, potassium iodide 99%, wiji’s iodine solution, and chloroform 99.5% were purchased from the local supplier.

11.2.2 Oil extraction The fruit has a hard woody outer shell that was broken to extract the pulp and seed. After extraction, the seeds were separated from the pulp by soaking in water for an hour. The cleaned seeds were dried in the sunlight for 24 h and stored in airtight bags.

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Then the seeds were crushed in a household mixer-grinder and sieved to a particle size less than 0.75 mm. Ultrasonic-assisted extraction is one of the oil extraction techniques from the kernel. In this, an ultrasonic sonicator (Lark Innovative Teknowledge, India) with a maximum output power of 900 W Model 650Y was used. The extraction process was carried out with 100 g of seeds that were taken in a beaker and mixed with acetone: heptane (400 mL) solvent at 35% of ultrasonic output power. The operating temperature was maintained to below 40°C using an ice bath to prevent solvent evaporation. After 20 min extraction time, the mixture of solvent-oil was separated from the solid seed powder by gravity filtration. Finally, the solvents were distilled in the rotatory evaporator at 95°C and then crude AMC oil was obtained and stored in an airtight container for further processes.

11.2.3 Biodiesel synthesis The free fatty acid value of oil is the deciding parameter to proceed with one-step or two-step transesterification process. If the acid value of oil is greater than 1.0 mg KOH/g oil, the two-step transesterification process is required for the conversion of oil into biodiesel and to prevent saponification. The AMC crude oil acid value was measured 2.5 mg KOH/g oil, so two-step microwave-assisted transesterification was chosen. The microwave system Cata-R Model (Catalyst System, India) consists of a magnetic stirrer, a temperature control system, and a reflux condenser that allows continuous stirring and constant temperature control.

11.2.3.1 Acid-catalyzed transesterification Acid-catalyzed transesterification was carried out in a two-neck, flat-bottom glass reactor (500 mL) with a sample of 30% of the reactor volume. After the oil temperature reached 60°C, the stoichiometric ratio of methanol (6:1) and 0.5% (wt/wt) of an acid catalyst (HCl) were poured into the glass reactor. The reaction process was carried out for 20 min with a continuous stirring speed of 650 rpm. The products were shifted to a separating funnel after the accomplishment of the process and allowed to form two distinct layers. The top layer contained the excess methanol and acid catalyst and the bottom layer contained esterified oil. The bottom layer was collected and several times washed with warm water to remove impurities and right after, the methanol was recovered by the rotatory evaporator.

11.2.3.2 Base-catalyzed transesterification Base-catalyzed transesterification was performed in the same manner as the acidcatalyzed process except for the catalyst and process conditions. The reaction was carried out with oil, a sodium methoxide catalyst (1% wt/wt), and stoichiometry methanol (1:6) at 60°C for 20 min. After attainment of the process, the products were discharged to a separating funnel to form two dissimilar layers. The top layer consists of biodiesel and excess methanol. The bottom layer consists of glycerol and base

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catalyst. Thereupon, water washing was done to remove glycerol, the catalyst, and other impurities from the biodiesel. Finally, the biodiesel was gently heated in the rotatory evaporator to evaporate water and methanol.

11.2.4 Nuclear magnetic resonance A nuclear magnetic resonance instrument was employed to confirm the methyl ester formation. Proton NMR analysis was performed using a 300 MHz AVANCE II (Bruker Biospin, Switzerland) equipped with a 5 mm BBO probe (Bruker BioSpin, Switzerland). The TMS and chloroform (CDCl3) were used as the internal standard and solvent, respectively. The experiment was carried out at 25°C using the standard pulse sequence library of TopSpin and followed by processing of the data.

11.2.5 Gas chromatography The chemical composition of biodiesel was identified by using gas chromatography with FID, model Trace 1110 (Thermo Scientific). The separation was carried out in a capillary column TR-FAME, which has a 60 m length, 0.22 mm inner diameter, and 0.25 μm of film thickness. Helium was used as the carrier gas, and the flow rate was maintained at 1.5 mL/min. The column temperature was programmed from 120–300°C at the rate of 10°C/min. The temperature of both injector and detector was set at 250°C. The AMC biodiesel sample was mixed with hexane solvent in a ratio of 1:10 and injected.

11.2.6 Fourier transform–Infrared spectroscopy Fourier transform infrared spectroscopy (FTIR) was used to investigate the functional groups of biodiesel. A Bruker tensor 27 FT-IR spectrophotometer (Germany), equipped with an attenuated total reflectance cell that has a ZnSe single crystal, was used to obtain the IR spectra (absorbance mode) in the region of 400–4000 cm
1 with 24 scans.

11.2.7 Determination of physicochemical properties According to ASTM 6751 and EN 14214 standards, the physicochemical properties of diesel, AMC oil, and biodiesel were determined. These properties include acid value, saponification value, iodine value, calorific value, kinematic viscosity, density, cloud point, pour point, flash point, fire point, carbon residue, and oxidative stability.

11.2.7.1 Acid value The acid value of raw oil and biodiesel were measured as per the standard EN 14104 titration method. In this, 50 mL of a mixture of ethanol and diethyl ether was taken in a beaker, and 1 g of sample was dissolved into it. Then, 2–3 drops of phenolphthalein indicator were added to the mixture. Finally, the beaker solution was titrated against

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0.1N of an aqueous solution of potassium hydroxide (KOH). The acid value of the sample was calculated using the following equation: Acid value ¼

MW  N  VKOH Ws

(11.1)

where, MW, molecular weight of KOH, g/mol; VKOH, volume of KOH, mL; N, normality of KOH, mol/mL; WS, Weight of sample, g.

11.2.7.2 Saponification value The saponification value of oil and biodiesel were estimated by the ASTM D1962 titration method. The fat sample of 1 g was taken in the beaker and dissolved in 10 mL of ethanol solvent. Further, 25 mL of ethanolic 0.5 normality of KOH was quantitatively transferred to the fat-solvent mixture and named as a test sample. The same procedure was followed to prepare the blank sample without the fat sample. Then, both the samples were attached to the reflux condenser and heated up to the boiling point of the water for about 30 min. After that, the samples were allowed to attain room temperature. Finally, 2–3 drops of phenolphthalein indicator were added to samples and titrated against 0.5 normality of hydrochloric acid. The saponification was estimated using the following equation. Saponification value ¼

MW  N  ðVBlank
VTest Þ Ws

(11.2)

where MW, Molecular weight of KOH, g/mol; VBlank, volume of HCl for Blank sample, mL; VTest, volume of HCl for the Test sample, mL; N, normality of KOH, mol/mL; WS, weight of sample, g.

11.2.7.3 Iodine value The iodine value of raw oil and biodiesel were determined as per the titration method described by the EN 14111 standard. In a tared beaker, 1 g of fat sample was taken and dissolved in 10 mL of chloroform solvent, which is labeled as “test.” Then, 20 mL of iodine monochloride reagent was thoroughly mixed into it. In the same way, another sample labeled as “blank” was prepared, except the fat sample. Then, both samples were kept in a dark place for incubation about 30 min. After that, 10 mL of potassium iodine solution was added to the sample and the side of the beaker was rinsed with 50 mL of distilled water. The samples were titrated against 0.1 normality of aqueous solution of sodium thiosulfate (Na2S2O3) until the color changed to pale straw. Then, 1 mL of the starch indicator was added to the solution, and the color of the solution changed to purple. The titration process was continued until the solution color changed to colorless. The following formula was used to estimate the iodine value of the fat sample.

Physicochemical fuel properties and tribological behavior of aegle marmelos correa biodiesel

Iodine value ¼

MW  N  ðVBlank
VTest Þ  100  10
3 Ws

315

(11.3)

where MW, molecular weight of Na2S2O3, g/mol; VBlank, volume of Na2S2O3 for Blank sample, mL; VTest, volume of Na2S2O3 for the Test sample, mL; N, normality of Na2S2O3, mol/mL; WS, weight of sample, g.

11.2.7.4 Density The density of diesel, oil, and biodiesel was determined as per the ASTM D1298 and IS 1448: Part 32: 1992 standard at 15°C. The empty 60 mL capacity vessel was weighed, and then fuel was poured into the vessel up to the mark and weighed. The fuels were maintained at 15°C by keeping them in the defreezer chamber. The weight of the fuel samples was calculated by subtracting the empty vessel weights from the filled one. The density of the fuel samples can be found using the following equation. Density ¼

Weight of fuel at 15° C Volume of fuel at 15° C

(11.4)

11.2.7.5 Viscosity and calorific value A Brookfield viscometer (DV2TLV) was used to measure the kinematic viscosity of the fuel samples. The experiment was performed at 40°C as per the ASTM D445 standard. The calorific value of the fuel samples was determined as per the ASTM D240 standard. The process was performed in a bomb calorimeter with 1 g of sample taken in the crucible and electrically ignited to burn in the presence of pure oxygen. During the combustion, the heat was released, and a rise in temperature was measured. The dry benzoic acid was used as a test fuel to measure the effective heat capacity of water. The calorific value of the sample was calculated using the following equation. Calorific value ¼
 Water equivalent of calorimeter 2883 Cal=° C  Rise in temperature ð° CÞ Mass of sample ðgÞ (11.5)

11.2.7.6 Cloud and pour point As per the ASTM D2500 standard, the cloud and pour point of diesel, oil, and biodiesel samples were determined using Subzero equipment. This equipment consists of four glass tubes that are 12 cm in high and 3 cm in diameter. These tubes are enclosed by a copper vessel that is kept in a refrigerated chamber. The glass tube is filled with 50 mL of fuel sample and closed with a rubber cork. Then, the filled glass tube is kept

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in a refrigerated chamber and at every 1°C temperature interval, the glass tube was taken out from the copper vessel to check the cloud and pour point. The point at which cloud was formed inside the fuel is called the cloud point temperature. After the identification of the cloud point, the examination was continued until the fuel sample became motionless when tilting the glass tube to a horizontal position for 5 s, which is called the pour point temperature.

11.2.7.7 Flash and fire point The Open Cup Cleveland apparatus was used to measure the flash and fire of diesel, oil, and biodiesel as per the ASTM D93 standard method. The test cup was filled to a specified level with the fuel sample. Then the test cup was electrically heated, and the temperature rise was measured with a thermometer. The flame was introduced at the surface of the fuel at every 1°C temperature rise, using a matchstick. The flash point was recorded as the temperature at which the flash appeared at the fuel surface with the help of an external ignition source. The fire point was noted as the temperature at which fuel vapor catches fire when introducing the ignition source at the fuel surface and continues the fire a minimum of five seconds after removal of the ignition source.

11.2.7.8 Conradson carbon residue A carbon residue apparatus was used to find out the amount of carbon residue of diesel oil and biodiesel fuels. According to the ASTM D4530 method, the measurement was carried out. This method was used to find out the amount of carbon residue present after pyrolysis of the fuel sample. It is envisioned to bring a few ideas of relative coke forming properties. In this experiment, 5 g of a moisture-free fuel sample were taken in the iron crucible of the apparatus. The iron crucible was then placed in the center of the Skidmore crucible of the apparatus. Then, the crucibles were closed with a lid and made an exit to escape the vapors. The electric oven was used to heat the fuel samples. In this, the oven temperature was slowly increased to 500°C with a heating rate of 10° C/min and this temperature was maintained for 15 min to pyrolysize the fuel sample. Nitrogen gas was purged during this pyrolysis process with a flow rate of 600 mL/min. After the pyrolysis of fuel, the oven power supply was shut off, but the nitrogen flow continued until the sample temperature reached 150°C. When the oven temperature reached 150°C, the crucible was taken out from the oven and kept in a desiccator to reduce the sample temperature to 30°C. Finally, the carbon residue was weighed in a precision weighing balance, and the mass percentage of carbon residue was calculated using equation as given below: % carbon residue ¼

A  100 Ws

(11.6)

where A, carbon residue, g; WS, weight of sample, g; tribological behavior of AMC biodiesel. A four-ball tribotester (DUCOM, India) was used to study the friction and wear characteristics of biodiesel and its blends. It is the simplest and most widely used

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instrument in the lubricant industry to develop and test new lubricants. The experiment was carried out in accordance with the ASTM D4172 standard method and details are given in Table 11.1. In this study, the lubricity of pure AMC biodiesel (B100) and diesel (B0) were investigated. The schematic representation of the four-ball wear test is shown in Fig. 11.1. In this, three balls are held together inflexibly in a lower cup, and the fourth one is held in an upper rotating spindle at the top. Table 11.1 Test conditions for four-ball friction and wear test

Test parameters Applied load (kg) Speed (rpm) Fuel temperature (°C) Time (s)

40 1200 35 3600

Ball dimensions Material Composition Diameter (mm) Hardness (HRc)

Chrome alloy steel C: (0.95–1.10)%, Cr: (1.3–1.6)%, Fe: balance 12.7 62

Load

Rotating ball chuck

Rotating ball

Fuel sample

Stationary ball

Fig. 11.1 Schematic representation of four-ball tribotester.

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Four balls and the oil cup were cleaned with acetone solvent and wiped using tissue paper before starting the experiment. Then, approximately 10 mL of test fuel was poured into the oil cup to cover the three balls completely. The test was conducted at a constant speed of 1200 rpm with 70 kg of the load for 3600 s. After accomplishment of the test, three balls were collected and cleaned with solvent to investigate the wear scar diameter and surface morphology of worn surfaces using an optical microscope and scanning electron microscope. The friction torque of the test fuel was measured by a recording device connected to the calibrated arm. The coefficient of friction was calculated using the following equation pffiffiffi T 6 Coefficient of torque ðμÞ ¼ 3Wr

(11.7)

where, T, frictional torque, Nm; W, load applied, N; r, distance from the center of the contact surface of the bottom three balls to the axis of rotation, (3.67 mm); μ, coefficient of friction. The flash temperature parameter (FTP) is a single number used to indicate the critical flash temperature of the test fuel at which the lubricating film gets to break down. The FTP of tested fuel was calculated using the given formula FTP ¼

W d 1:4

(11.8)

where d, mean wear scar diameter of the balls, mm; W, applied load, kg.

11.3

Results and discussion

11.3.1 Infrared spectra of AMC biodiesel The fatty acid methyl ester composition of biodiesel was determined using Gas Chromatography (GC) and Fourier Transform Infrared analysis. FTIR method give some advantages over GC like time consumption is less, cheap and sample preparation required not required for determination of Fatty Acid Methyl Ester. In the AMC biodiesel FTIR spectra (Fig. 11.2), the region in the range of 678.55–960 cm
1 represents ]CdH functional groups. Functional groups ]CdH are unsaturated and represent olefinic esters (alkenes) such as methyl oleate and methyl linoleate in biodiesel. The methylene (–(CH2)n-) functional group in biodiesel was represented in spectra by a particular peak at 721.72 cm
1. The presence of the methylene functional group in the biodiesel FTIR spectra indicates a long-chain aliphatic structure was present. In biodiesel, the existence of CdO, CdOdC, and OdCH3 functional groups was represented by an extending peak found in region 1016.44–1361.08 cm
1. Methyl group of CdH existence in biodiesel was confirmed by band region of 1370.23–1450.03 cm
1 and a peak nearer to 1600 was an indication of the C]C functional group present in biodiesel. Carbonyl functional groups C]O

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Fig. 11.2 Infrared spectroscopy spectrum of AMC biodiesel.

were represented by the strongest peak in the FTIR spectra at 1741.67 cm
1. This carbonyl functional group was an indication of methyl ester produced by the conversion of triglycerides. The symmetric and asymmetric CdH alkane existence in biodiesel was represented by peaks at 2854.13 and 2923.70 cm
1, respectively, in the FTIR spectra. They could be methyl (CH3) or methylene groups in the ester chains of the biodiesel. The alkene groups were spotted above the wave number of 3000 cm
1. The OdH group presence in biodiesel indicates a peak at 3500 cm
1.

11.3.2 The fatty acid composition of AMC biodiesel Gas chromatography (GC) is the most commonly adopted technique as the standard method to determine FAME content in biodiesel by regulatory and monitoring agencies in the majority of countries. The composition percentage of fatty acids in Aegle Marmelos Correa Biodiesel was determined using the analytic method GC-MS that combines features of gas chromatography and mass spectrometry. GC-MS results show that Aegle Marmelos Correa Biodiesel contains saturated fatty acids such as behenic acid, arachidic acid, palmitic acid, lignoceric acid, and stearic acid, and unsaturated fatty acids such as linolenic acid, oleic acid, and linoleic acid. AMC biodiesel contains 32.29% saturated fatty acids and the remaining are unsaturated fatty acids. Linoleic acid, oleic acid, and palmitic acid were present in a large percentage, approximately 25% each in AMC biodiesel. The percentage of each fatty acids shown in Fig. 11.3.

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Fig. 11.3 Fatty acid composition of AMC biodiesel.

11.3.3 Physicochemical characterization of AMC oil and biodiesel The determined physicochemical properties of diesel, AMC oil, and AMC biodiesel are listed in Table 11.2.

11.3.3.1 Cetane number The cetane number is the percentage by volume of hexadecane (known as cetane) in a combustible mixture that contains cetane and 1-methylnaphthalene whose ignition properties are similar or match with the fuel that is being tested. The one ignition property that is compared here is engine knock. Cetane (Hexadecane)—C16H34 Alpha-methyl naphthalene—C11H10 Ignition delay in fuel is defined as the approximate period between the start of injection of fuel and the first observed pressure rise during combustion of the fuel, and according to experimental studies, the cetane number is inversely proportional to the fuel’s ignition delay. When the fuel enters the cylinder, it needs to be atomized, then mixed with air. Then its temperature must be raised, and the chemical reaction of combustion takes its time. All these times added is the ignition delay. So the cetane number is a rating that indicates how long the ignition delay of the fuel as compared to that of cetane. The cetane number of AMC biodiesel, Karanja, and Jatropha were found to be 58, 42.9, and 49.5, respectively. The following observations can be made from Fig. 11.4.

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Table 11.2 Physicochemical properties of diesel, AMC oil, and AMC biodiesel AMC biodiesel

EN 14214/ ASTM limit

Properties

Diesel

AMC oil

Density at 15°C (kg/m3) Acid value (mg of KOH/g of oil) Cloud point (°C) Pour point temp (°C) Flash point (°C) Fire point (°C) Viscosity at 40°C (mm2/sec) Calorific value (MJ/kg) Carbon residue (wt.%) Saponification (mg KOH/g of oil) Iodine value (mg of I2/g of oil) Peroxide value (ppm) Fat content g/ 100 gm

824

910

880

875–900

0

5.6

0.2

0.5 max.

0
14

4 0


1
4

NS* NS*

54 62 2.39

325 335 27.92

164 175 3.75

130 min NS 3.5–5

42

39.46

37.5

NS

D 93 D 93 ASTM D445, EN ISO 3104 D240

0.0109

0.03

0.025

0.05max.

D 4530

NS

277

224

NS

D1962

NS

85

56

<120

EN 14111

NS

50

NS

NS

NS

NS

98.96

NS

NS

NS

Fig. 11.4 Transesterification reaction mechanism.

Test methods ASTM 1298, EN ISO 3675 EN 14104, D 664 D 2500 ASTM D 97

322 l

l

l

l

l

l

l

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The cetane number increases as the length of the fatty acid chain increases. The cetane number decreases as unsaturation increases. In the case of Jatropha biodiesel, the degree of unsaturation was found to be 77.2%. For Karanja biodiesel, it was found to be 73.93%. For AMC biodiesel, the degree of saturation was found to be 66.6%. As the double bonds increase in the parent fatty acid ion R, the cetane number decreases. Unsaturated compounds are unstable and more reactive because of the presence of double bonds (pi orbitals overlap, more electron loving). The C]C distorts the symmetry of the hydrocarbons, which makes them more polar. The branched esters obtained from different alcohols such as isopropanol have cetane numbers comparable to the straight-chained methyl fatty acid esters and other alkyl fatty acid esters (Fig. 11.4). The long chain is the sufficient parameter for increasing the cetane number, and the branched moieties are of less interest. In fact, we have to be more focused on finding branched alkyl fatty acid esters because of their improved melting point, which helps us to work more efficiently at low temperatures. The length of the chain of any hydrocarbon is directly related to the boiling point, and the number of branches in any hydrocarbon is directly proportional to the melting point of that particular hydrocarbon. The more methylene groups (CH2) in the fatty acid chain, the higher the cetane number because it makes the compound saturated. In unsaturated fatty acid esters (e.g., linoleic and linolenic acids), the position of double bonds and the carbonyl group plays a role in determining the cetane number. As the double bonds and the carbonyl group are more toward the center of the fatty compound, the cetane number decreased further. The reason is that the attack on the carbonyl group or doubly bonded carbon is enhanced by the two heavy alkyl groups on the sides of the unsaturated carbons. The cetane number was found to increase more with an increase in the degree of saturation of the methyl ester. The degree of saturation for AMC biodiesel is 32.29%. The degree of saturation for Jatropha biodiesel is 28.1%. The degree of saturation for Karanja biodiesel is 26.04%. Hence, an increase in the degree of saturation of Jatropha biodiesel compensates for its very high degree of unsaturation, owing to its higher cetane number compared to Karanja biodiesel. Compared to these two, AMC biodiesel has the highest degree of saturation and the lowest degree of unsaturation, making its cetane number much higher than the other two biodiesels. An increase in chain length implies an increase in the molecular mass of the ester. The molecular mass of the ester can be increased by two ways: by changing the parent fatty acid or by changing the alcohol. The increase in cetane number was more by changing the fatty acid when compared to the increase obtained by changing the alcohol.

11.3.3.2 Saponification value Saponification is a word that simply means “soap making." Saponification is a chemical reaction involving the hydrolysis of triglycerides (fats) under a basic environment to yield a salt of the corresponding carboxylic acid and free glycerol (Fig. 11.5). This way, the free fatty acid content is determined quantitatively by measuring the amount of alkali that is added to neutralize the fat. Experimentally, this is achieved by mixing a strong caustic soda solution (alkali) with the given amount of fat, where all the fatty acids present in the fat gets converted to soap. Finally, the soap is removed entirely,

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Fig. 11.5 Saponification reaction of triacylglyceride.

and the quantity of remaining fat is determined. The difference obtained is the amount of loss. The saponification value is the amount of potassium hydroxide (in mg) required to neutralize the fatty acids resulting from the complete hydrolysis of 1 g of fat. The saponification value of AMC biodiesel is 224 mg KOH/g. The saponification value of Karanja biodiesel is 180 mg KOH/g. The saponification value of Jatropha biodiesel is 188.98 mg KOH/g. Saponification value indirectly indicates the character of the fatty acids present in the fat. Less acid is liberated on hydrolysis of 1 g of fat if the fat contains long chain fatty acids. It is also indicative of the average molecular mass (or indirectly denotes the chain length) of all the fatty acids present. As the average molecular weight of fatty acids of AMC biodiesel > Jatropha > Karanja (based on their specific gravities), we have this trend in their saponification values. Due to a lesser number of carboxylic functional groups per unit mass of the fat in long chain fatty acids, long chain fatty acids are usually associated with very low saponification values. Weight percentage of long chain fatty acids (C20, C22, and C24) is highest for Karanja. Hence it has the least saponification value whereas the long chain fatty acids (C20, C22, and C24) are the least for AMC biodiesel. Hence it has the highest saponification value. Jatropha lies somewhere in between these two regarding the weight percentage of long chain fatty acids.

11.3.3.3 Iodine value The iodine value is the amount of iodine (in grams) that is consumed by 100 mL/100 grams of a fuel/substance. Iodine numbers directly indicate the level of unsaturation in oils. The double bonds that are a major source of unsaturation react with iodine to form complex compounds. The more C]C bonds present in the fatty acids, the greater the value of the iodine number. The IV of AMC biodiesel is 56 mg I2/g. The IV of Karanja biodiesel is 91 mg I2/g. The IV of Jatropha biodiesel is 100 mg I2/g. This trend is because of the increase in the degree of unsaturation in these biodiesels, respectively. Iodine absorption takes place at unsaturation spots, thus a high IV indicates a high level or magnitude of unsaturation. The iodine value (IV) sometimes does not take into

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account the positions of the double bonds available for oxidation and these values are sometimes misleading. The IV does not always correlate well with oxidative stability. There is an entirely different test for estimating the biodiesel’s stability, and it is known as the oil stability test (OST).

11.3.3.4 Flash and fire point The flashpoint for any volatile material is defined as the lowest temperature at which vapors of the material will ignite when ignited by a source. Similarly, the fire point is defined as the lowest temperature at which vapors of the material will catch fire and continue burning even after the ignition source is removed. The fire point is higher than the flash point because the vapors produced at the flash point are not sufficient enough to ignite the fuel. Flash and fire points depend upon the volatility of the biodiesel. Volatility is the tendency of the substance to vaporize, and it is directly related to the vapor pressure of the biodiesel at that particular temperature. The biodiesel exhibiting higher vapor pressure at a given temperature is said to be more volatile than the one exhibiting lower vapor pressure at the same temperature. Hence the lower the NBP (normal boiling point), the higher the volatility, which is in turn inversely proportional to its flash and fire point. The flash and fire point of AMC biodiesel was found to be 164°C and 175°C, respectively. The flash point of Karanja biodiesel was found to be 97.8°C. The flash point of Jatropha biodiesel was found to be 192°C. The reason for the close flash point values of AMC biodiesel and Jatropha biodiesel is their identical average molecular masses. Also, the length of the fatty acid chains is directly proportional to their boiling points, and branching is directly proportional to their melting points. Weight percentage of long chain fatty acids is greater for Jatropha compared to AMC, even though they have identical average molecular masses. Therefore, the NBP of Jatropha is more compared to AMC, owing to its higher flash and fire points. Karanja biodiesel’s average molecular mass is quite low compared to these two, and hence the NBT is quite low and very volatile. The source temperature will always be higher than either the flash or fire point, and both these parameters are independent of ignition temperature. The flashpoint of fossil diesel is always less than that of biodiesel, and hence it cannot be safely stored.

11.3.3.5 Cold filter plugging point (CFPP) cloud point and pour point It is a challenge to fuel vehicles with biodiesel blends in cold climates because these biodiesels tend to freeze earlier than conventional petroleum diesel. The type of oil from which the biodiesel is made decides this freezing point. These cold-weather characteristics are measured by three factors: cloud point (CP), pour point (PP), and cold filter plugging point (CFPP). The cloud point is the temperature of the fuel at which small solid crystals can be observed as the fuel cools. The cold filter plugging point is the temperature at which a fuel filter clogs due to the crystallized fuel components. The pour point refers to the lowest temperature at which there is absolutely no movement of the fuel components when the container is flipped. The cloud points of AMC

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biodiesel, Karanja biodiesel, and Jatropha biodiesel are found to be
1°C, 4°C, and
6°C, respectively. The pour points of AMC biodiesel, Karanja biodiesel, and Jatropha biodiesel are found to be
4°C,
2°C, and
7°C, respectively. Fuel will be gelled entirely and stop working once the temperature goes below the pour point temperature. However, the fuel might still work if the temperature goes below the cloud point. However, when the fuel’s temperature reaches the cloud point temperature, necessary steps must be taken to prevent the fuel from getting clogged in the filters. This can be achieved by adding some antigel additives and also blending the biodiesel with petroleum diesel so that the cloud and pour points are reduced further. The greater the percentage of petroleum diesel in the biodiesel-diesel, the lesser the value of the cloud and pour points of the blend. The antigel additives recommended for biodiesels are different from the ones that are recommended for diesel. Cold weather performance of biodiesel can be improved further by adding heaters all over the fuel passage, such as fuel lines and fuel tanks, etc. Even insulating every part that comes under contact with heaters and fuels will improve the efficiency of heaters to a great extent. The cloud and pour points of the biodiesels were found to increase with increasing weight percentage of saturated long-chain methyl esters (Long chain increases boiling point whereas branched chain increases are melting point. Hence, long chain criteria are inversely proportional to melting point and thus cloud and pour points). As discussed earlier, the weight percentage of long-chain saturated methyl esters/saturated fatty acids decrease in this order: Jatropha, AMC, and Karanja biodiesel. Hence, it can be concluded that their corresponding cloud and pour points also decrease in the same order. "Winterization" is a counterprocess for decreasing cloud and pour points even further by removing saturated methyl esters. This removal is achieved by cooling the biodiesel to the crystallization point and filtering out the high melting components. A significant part of saturated methyl esters is removed during the winterization process, which results in the high yield loss of saturated fatty acid esters; hence, the winterization process is not an efficient method to solve the cold climate problem. Moreover, this process alters a lot of physical and chemical properties. Using branched-chain alcohol instead of methanol during the transesterification process can significantly reduce the cloud and pour points of biodiesel, but this process also has its limitations. It is not feasible to complete the reaction with isopropyl alcohol as it takes too much time to complete the reaction and is also expensive. Another way by which the cold flow properties of biodiesels can be improved is by blending them with another biodiesel having a lower cloud and pour point compared to the primary biodiesel. In our case, Jatropha biodiesel’s cold flow characteristics can be improved by blending it with either AMC biodiesel or Karanja biodiesel.

11.3.3.6 Acid number The acid number indicates the FFA content of transesterified biodiesel. Free fatty acids are those acids that are not present as triglycerides (fats) in the biodiesel. In the saponification reaction, the triglycerides hydrolyze to yield fatty acids that react with the alkali to form soap whereas the free fatty acids directly react with the base while conducting the experiments to find out the acid value. The weight of free fatty

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acids (FFA) present in the biodiesel divided by the entire weight of biodiesel gives the FFA percentage. AV ¼ 1:99 FFA%

(11.9)

The acid values of AMC biodiesel, Karanja biodiesel, and Jatropha biodiesel are found to be 0.2, 0.42, and 0.074, respectively. Saponification value reflects the amount of fat present in the biodiesel or the number of fatty acids present in triglycerides, whereas the acid value denotes the percentage of free fatty acids (FFA) that are not linked with any other molecules (triglycerides or methyl esters) and remain free as acids in biodiesel. In general, acid values are inversely proportional to saponification values because when a number of fatty acids are present in the biodiesel as triglycerides, the greater the saponification value; therefore, the number of free fatty acids present is low, thus giving a lower acid value. Hence, it can be observe that Karanja biodiesel has the highest acid value (almost close to the max limit of ASTM standards), followed by AMC biodiesel and Jatropha biodiesel.

11.3.3.7 Viscosity Fuel viscosity plays a vital role in determining the combustion characteristics of any fuel. For achieving high thermal efficiency, the direct injection of the fuel into the combustion chamber through the nozzle and fuel spray pattern should be perfect and effective, and viscosity has a crucial role to play in this. When the viscosity of fuel is too low, it leads to internal pump leakage, which can bring down the system pressure to an unacceptable level that will ultimately affect the fuel’s spray atomization and ignition characteristics. At low load conditions where the speed of operation becomes low, viscosity becomes more critical. The viscosities of AMC biodiesel, Karanja biodiesel, and Jatropha biodiesel are found to be 3.6, 5.60, and 4.84 centistokes, respectively. The viscosity of biodiesel is always higher than petroleum diesel, often by a factor of two; the viscosity increases as the percentage of biodiesel increases. At low ambient temperatures and cold start engine conditions, viscosity effects become more critical and significant. As the chain length of the fatty acid in the parent oil increases or the alcohol group involved in the transesterification process is heavier, viscosity increases. The weight percentage of long chain fatty acids (C20, C22, and C24) is highest for Karanja. Hence it has the highest viscosity value whereas the long chain fatty acids (C20, C22, and C24) are least for AMC biodiesel. Hence it has the least viscosity value. Jatropha lies somewhere in between these two regarding the weight percentage of long chain fatty acids.

11.3.3.8 Lubricity Lubricity is the measure of the reduction in friction and/or wear by a lubricant. Lubricity is determined by the amount of wear caused to a surface by a wear-producing object for a given set of conditions and time. For two fluids with identical viscosities,

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the one that produces a smaller wear scar is said to have more lubricity. That is why lubricity is also known as the antiwear property of a substance. The lubricity of biodiesel fuel is important in fuel injection pumps (rotary and distributor). The parts in continuous motion are lubricated by the fuel itself and not by the engine oil. Even the injectors are to some extent fuel lubricated. The lubricity indicates the amount of wear and tear that occurs between two components in contact with each other when entirely covered with the biodiesel. High lubricity biodiesel will ensure a longer component life and reduced scarring. Similarly, low lubricity biodiesel may cause high scarring, and it is undesirable. Lubricity has no direct relation whatsoever with a viscosity of biodiesel. The factors present in the biodiesel that affects lubricity are discussed below. l

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Lubricity increases with chain length. As the hydrocarbon part is long, it does not compete with the oxygen moieties during the hydrogen bonding. Lubricity increases with unsaturation (double bonds) but the lubricity-enhancing effect of this is more than the former. Therefore, the lubricity characteristics of different biodiesels are increased in the order of Jatropha, Karanja, and AMC. Shorter chain lengths have very low molecular interactions, and the low-temperature stability of the lubricant film makes it a poor lubricant. The triglycerides of various fatty acids have more lubricity than their corresponding esters. Some small remains of triglycerides can increase the lubricity in biodiesel. Hence, higher saponification values mean improved lubricating properties. The saponification value of AMC biodiesel is found to be higher than the Jatropha biodiesel. Karanja biodiesel has the least saponification value among them. Carboxylic acid moieties have the highest lubricity followed by aldehydes, then alcohols, esters, and ketones. The aldehyde or carbonyl group present in esters is solely responsible for the lubricating properties. Ethers exhibit poor lubricating properties. FFA content in biodiesels is more responsible for lubricity properties. FFA content is directly related to acid value, and hence the FFA value of AMC biodiesel is higher than Karanja and lower than Jatropha. Sterically unhindered electron groups in doubly bonded carbon provide more lubrication. The double bonds at the center of the chain have poor lubricating properties compared to the ones at the end of the chain due to the formation of stable pi complexes such as organometallic complexes. The better lubricating properties of these moieties over others is that the ionic interactions between the metal parts and lubricating molecules due to hydrogen bonding and Van der Waal interactions within the lubricating molecules. With some fatty acids, even physisorption and chemisorption was observed. Fatty acid esters have lower lubricity because of the unavailability of free OH or COOH groups to form hydrogen bonding with the metal substrate for ionic interactions. Byproduct glycerol increases the lubricity to a very high value because of three OH groups.

Hence, we can conclude that the lubricity of biodiesels is influenced by so many factors. Each factor has its trends, and thus the lubricity of different biodiesels can be compared qualitatively for conclusions. In this case, Karanja biodiesel has good lubricity property over the other biodiesels, because it has a higher degree of unsaturation and FFA content. Saponification values have low influence on lubricity compared to FFA content because the lubricity characteristics of carboxylic acids are

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much higher than the corresponding triglycerides. An important point to note is that the lubricity of a substance is not a direct materialistic property and cannot be measured like other properties. Tests performed will evaluate the lubricant’s performance for only a specific system, and it varies for other systems.

11.3.3.9 Carbon residue Carbon residue, regardless whether it arises from biodiesel or petroleum ultralow sulfur diesel (ULSD), can cause engine damage and degradation. It can cause fuel injector fouling and cylinder scoring within an engine, leading to a decreased performance or engine failure. Although biodiesel is known to leave fewer deposits than ULSD, they are a widely recognized problem when burning any carbon-based fuel in an internal combustion engine. Two main types of deposition mechanisms (for diesel and can be thought analogous to biodiesel) are recognized: decomposition of hydrocarbons to elemental carbon and hydrogen and polymerization of hydrocarbon species into poly-nuclear aromatic hydrocarbons (PAHs) that grow into carbonaceous deposits. One major factor determining whether the hydrocarbons are decomposed or polymerized is the presence or absence of a metal catalyst. If a metal catalyst is present, hydrocarbons are typically decomposed into carbon residue, but in the absence of a catalyst (or thermal deposition), polymerization into carbon residue is the dominating mechanism. The liquid phase thermal autoxidation at low temperature (<350°C) and gas phase pyrolysis at high temperature (>450°C) are the two main regions in the thermal stability of jet fuels. Autoxidation causes a stage of hydroperoxide formation, and the resulting deposits tend to have large amounts of oxygen and settle out as spheres because they are insoluble with the bulk fuel. Pyrolysis mechanics are less understood, but are believed to form aromatic deposits through the following steps: Normal alkanes ! Alkenes ! Cycloalkanes=Cycloalkenes ! Alkylbenzenes ! PAHs ! Deposits Vegetable oil used as a fuel without transesterification into biodiesel will lead to more carbon deposits as the saturation level decreases in it. The more unsaturation in biodiesel, the greater the number of carbon deposits formed than a saturated fuel. The percentage of carbon reside in AMC, Karanja, and Jatropha are 0.025%, 0.07%, and 0.21%, respectively. In the case of Jatropha biodiesel, the degree of unsaturation was found to be 77.2%. For Karanja biodiesel, it was found to be 73.93%. For AMC biodiesel, the degree of saturation was found to be 66.6%. Even the kinematic viscosity of Jatropha biodiesel is less than that of Karanja; the carbon residue follows the reverse order. This shows that the degree of saturation is the overriding factor of carbon formation and more important than the viscosity of the fuel. Overall, carbon deposition from biodiesel is much lower compared to that of petroleum diesel, potentially due to the lack of aromatics in biodiesel making the formation of large aromatic residue structures difficult.

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As a fuel ages and oxidizes, some of the fuel will polymerize into heavier, more viscous compounds and some will split into lighter, volatile molecules that may depend on storage conditions and escape the bulk fluid. More viscous fuel will leave more carbon residue, but that is not the only factor responsible. If the fuel is oxidized in a sealed container, these lighter compounds may not be able to escape, and the overall viscosity of the fuel mixture will remain largely unchanged. In this case, viscosity changes should have less of an effect on carbon residue, and degree of unsaturation will have a dominating effect. Another main effect that oxidation could have on carbon residue is the break down of double bonds in the fuel for the creation of hydroperoxides. If these double bonds are eliminated in the reaction, a fuel could become more saturated. If the degree of saturation in the fuel increases during oxidation, then carbon residue can be expected to decrease as the fuel oxidizes. Any increase in viscosity will likely be overshadowed by an increase in saturation. Increase in saturation during oxidation is only possible when there is more unsaturation initially.

11.3.3.10 Oxidation stability In general, the unsaturated components are particularly unstable and are subjected to deterioration on oxidation, which is always undesirable as it leads to fuel darkening, reduced induction periods, and formation of complex polymers. Storage of biodiesel and long use of it in an engine will lead to aging of the biodiesel, forming hydroperoxides initially, then subsequently giving rise to acids, aldehydes, and polymers. Ultimately, the acidity increases as a result of oxidation products which leads to the formation of corrosion and rusting on the metal surface. The formation of insoluble substances makes the blockage in nozzle, filter and increases the viscosity in the form of oil thickening. The role of antioxidants is to increase the induction period or the period for which the biodiesel can be safely stored before any undesirable oxidation products appear. However, this response of biodiesel to any antioxidant additive to achieve an increase in induction period and ultimately oxidation stability depends on both fuel composition and the type of antioxidant additive. Hence complete research of antioxidants and their concentration is important to obtain the best results for a fuel blend and also a cost-effective solution. Biodiesel contains a mixture of long chain fatty acids, both saturated and unsaturated. Saturated fatty acids undergo very minimal oxidation because they are more stable and nonreactive. Hence unsaturation indicates oxidative instability in biodiesels.

Mechanism of oxidation The first step involves the formation of carbon-based free radicals by removing a hydrogen from a carbon atom. The subsequent reaction, in the presence of oxygen, is extremely fast to form peroxy radicals and this reaction is so fast that it does not allow other alternatives for the carbon-based free radical to react. Although the peroxy free radical is not even close to being as reactive as the carbon free radical, it is sufficiently reactive to form another carbon-based free radical by abstracting free

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hydrogen from carbon and thus forming hydroperoxide (ROOH). The cycle keeps propagating when the new free carbon radical reacts with oxygen. Finally, in the termination step, the free radicals react with each other. The ROOH concentration remains very low for some initial period of oxidation, but only up to sometime. This period is called the induction period and is determined by the conditions under which the biodiesel/fatty acid is stressed as well as its oxidation stability. The ROOH level rapidly increases (after the induction period), indicating the commencement of oxidation. The ROOH induction period can significantly influence other important properties of biodiesel. In this peroxidation mechanism, the easily abstracted hydrogens are usually the ones that are bonded to allylic carbons in the long chain fatty acid, and nonallylic carbon hydrogens do not participate in this mechanism. The resonance stabilized rearrangement of the pi electron system is one major reason for this observation. Hydrogens from carbons allylic to two other carbon atoms simultaneously (bisallylic carbon atoms) are extremely susceptible to abstraction. This is because the rearrangement of the mechanism is highly resonance stabilized. These products that are formed in the initial stages of oxidation are known as primary oxidation products. Oxidation instability of any fatty acid ester is directly related to the number of allylic and bis-allylic carbon atoms present. Once the hydroperoxides are formed, they decompose to form aliphatic alcohols, aldehydes, carboxylic acids, and esters. These are known as secondary products of oxidation. Increased acidity is primarily due to oxidation of biodiesel where shorter chain fatty acids are formed.

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Metals such as Ni, Sn, Fe, Cu, and brass can significantly decrease the Oxidization Stability Index (OSI) of biodiesels. Long chain fatty acids, regardless of whether saturated or unsaturated, have a significant influence on the OSI of their corresponding biodiesel. The free acids were found to be far more unstable than their corresponding methyl ester. The trend for increased stability for long unsaturated chain fatty acids was found to be linolenic < linoleic < oleic.

In AMC biodiesel, the percentage of the oleic acid is 26.69, the percentage of the linoleic acid is 24.48, and the percentage of the linolenic acid is 15.43%. In Jatropha biodiesel, the percentage of the oleic acid is 40, the percentage of the linoleic acid is 36.9, and the percentage of the linolenic acid is 0.2%. In Karanja biodiesel, the percentage of the oleic acid is 51.59, the percentage of the linoleic acid is 16.64, and the percentage of the linolenic acid is 5.7. Hence the oxidation stability of AMC biodiesel was found to be poor when compared to Jatropha and Karanja. l

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The oxidation stability of the methyl esters will depend on the alcohol group used in the transesterification process. On exposure to light, the oxidation stability of biodiesels can be decreased. This process is called photo-oxidation, and in this mechanism, the diatomic oxygen attacks the vinylic carbon directly. The energy required to proceed with this unfeasible reaction is provided by the photons. Antioxidants are substances that inhibit oxidation process. There are two types of antioxidants, namely chain breakers and hydro-peroxide decomposers, among which chain breaker antioxidants are more common. Also, there are two types of antioxidants available: synthetic

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antioxidants and natural antioxidants. Fatty oils derived from plants contain natural antioxidants such as tocopherols.

The content of tocopherol (all isomers) is different for different oil sources. Naturally occurring levels of tocopherols are directly optimized for their antioxidant capability. More artificial addition of tocopherol has either no beneficial effect or may even become harmful to the oil or biodiesel. Tocopherols may be completely lost, partially lost, or completely retained, depending on the biodiesel processing conditions. Sometimes after the transesterification process of biodiesel, all the tocopherols that were initially present in the parent oil might be removed.

11.3.3.11 Calorific value Calorific value is the amount of energy released or produced when 1 kg of fuel burns or any other substance is burnt in the presence of oxygen and the products of combustion are cooled to STP. Its SI unit is kJ/kg. Basically 1 mole of hydrogen, which is 1 g, will yield some 30 calories of heat, whereas 1 mol of carbon, which is 12 g, yields some 96 calories. So hydrogen will yield 30 calories per gram while carbon produces only about 8 calories per gram. The calorific values of AMC, Karanja, and Jatropha are found to be 37.5 (MJ/kg), 36.57 (MJ/kg), and 38.5 (MJ/kg), respectively. All the biodiesels contain mixtures of various hydrocarbons (acids, esters), long chained or short chained, but Jatropha biodiesel contains much hydrogen owing to the percentages of various fatty acid constituents. It is followed by AMC and Karanja. Hence, hydrogen is the overriding factor in determining the combustion characteristics of the fuel. Hence Jatropha biodiesel has far more energy-rich hydrogen compared to AMC and Karanja biodiesel.

11.3.4 Tribological analysis Fig. 11.6 shows that in the first few seconds of the experiment, the coefficient of friction (COF) was unsteady for the fuel due to the initial friction between the bottom three stationary balls and the top rotating ball. After a few seconds, the contact surface between the rotating and stationary balls gets smoothed, which leads to reaching the COF becoming a steady state. The experiment was conducted for 3600 s at 1200 rpm in which the first 5 s were found to be run in period (Fig. 11.7). Diesel (B0) has the highest run in the period compared to biodiesel (B100). Moreover, COF of diesel was suddenly rose in the first 5 s and as well as it has longer period of the unsteady state compared to B100. B100 takes a short period to reach the steady state due to its high smoothing capability. The steady-state COF for the last 1000 s of diesel was 13% higher than the biodiesel. The good lubricity of biodiesel is because of its hydrophilic and hydrophobic nature. The ester functional group present in the biodiesel easily gets absorbed on the surface of the metal, which forms a lubricating film on the metal surface. There is another type of interaction between metal and fuel that mainly depends on the chain length and unsaturation percentage. The lubricity of biodiesel is increasing with an increase in chain length.

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Fig. 11.6 Friction coefficient behavior of diesel and biodiesel with respect to time in run in period.

Fig. 11.7 Friction coefficient behavior of diesel and biodiesel with respect to time in steady state condition.

Flash temperature parameter (FTP) and wear scar diameter of fuel are inversely related. The WSD and FTP of biodiesel are approximately 23% less and 30% higher than diesel, respectively. The high FTP value of biodiesel indicates that the lubricating film formed between balls remains stable up to a very high temperature. The very large value of WSD of diesel indicates the adverse wear on the metal. The biodiesel has a lower WSD value due to its high amount of oxygen content, which reduces the friction and improves the lubricity between the top and bottom metal balls.

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(D)

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(F)

Fig. 11.8 SEM micro images of worn surfaces of steel ball.

The scanning electron microscopy image (Fig. 11.8) shows the morphology of the worn surfaces of the balls used in this experiment. The surface of the steel balls used for diesel fuel was severely deformed compared to pure biodiesel. The metal parts of the bottom balls were extruded in one direction from the surfaces when the top rotating ball was in contact with the bottom one. The surface deformation of the bottom balls was caused by the shearing effect of the mating surface balls. The COF of diesel and biodiesel were increased with an increase in temperature due to the heat generated by the rotation of the top ball over the bottom balls. Because of this, the extruded metal parts on the surfaces get welded, which leads to increases in the wear on the surfaces.

11.4

Conclusions

In the present study, crude AMC oil was converted to AMC methyl ester by a two-step transesterification process. The physicochemical properties of the AMC biodiesel met the international standards, such as ASTM D6571 and EN14214. The density and viscosity of AMC biodiesel were significantly reduced after transesterification of AMC oil, which is also comparable to diesel fuel. Diesel exhibits a high unsteady COF with longer duration compared to biodiesel. The ester group is present in the biodiesel, which offers more protection against the shearing of metals than diesel. Biodiesel (B100) has the lowest WSD comparable to that of diesel. Commercial diesel has poor

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lubricating properties due to the removal of some sulfur compounds to meet the strict emission norms. FTP and WSD are inversely related, and biodiesel fuel has the highest FTP and lowest WSD compared to diesel due to good lubricating capability and a high amount of oxygen content.

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Scope for future study

Aegle Marmelos Correa biodiesel has poorer oxidation stability than Jatropha and Karanja biodiesel, so more research could be done to improve its oxidation stability by adding a suitable antioxidant. AMC biodiesel has high percentages of unsaturated methyl ester, so there is a chance for corrosion on engine components. Hence, the corrosion behavior of AMC biodiesel on different types of metal should be studied to understand its corrosive behavior. Thermal characteristics of AMC biodiesel can be studied using thermogravimetric analysis to understand the ignition quality of biodiesel.

Acknowledgments The authors would like to acknowledge the Department of Science and Technology, India, for the financial support under the Young Scientist Scheme. The authors would also like to thank the Director and Head Department of Mechanical, National Institute of Technology, Tiruchirappalli, for providing the experimental facility, valuable help, and support.

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