Handbook of plant based biofuels - Chapter 19 potx

The results showed that the thermal efficiency was high in the case of the methyl ester compared to other esters and to diesel fuel.. The methyl ester dominated other esters on the basis

from Mahua Oil and Its Evaluation in an Engine

Sukumar Puhan, Nagarajan Vedaraman,

and Boppana Venkata Ramabrahmam

AbstrAct

Vegetable oils and animal fats can be transesterified to biodiesel with alcohol for use as an alternative to diesel fuel This chapter deals mahua oil, its transfer into dif-ferent esters, their performance and emission characteristics in a four-stroke, direct injection diesel engine The results showed that the thermal efficiency was high in the case of the methyl ester compared to other esters and to diesel fuel The tail-pipe emissions and noise levels were lower in the case of the methyl ester, compared to those of diesel and other esters The methyl ester dominated other esters on the basis

of engine performance and emissions and can be used as an alternative fuel for exist-ing diesel engines

contents

Abstract 267

19.1 Introduction 268

19.1.1 Worldwide Research on Vegetable Oil as Fuel 268

19.1.2 Mahua (Madhuca indica) Oil for Biodiesel Production 268

19.1.3 Transesterification 269

19.2 Properties 269

19.3 Engine Tests 270

19.3.1 Brake Specific Fuel Consumption 271

19.3.2 Specific Energy Consumption 271

19.3.3 Brake Thermal Efficiency 272

19.3.4 Exhaust Gas Temperature 272

19.3.5 Noise Level 273

19.3.6 Oxides of Nitrogen 273

19.3.7 Carbon Monoxide Emission 275

19.3.8 Carbon Dioxide Emission 276

19.3.9 Hydrocarbon Emission 276

19.4 Conclusions 277

References 278

19.1 IntroductIon

Nearly a hundred years ago, Rudolf Diesel tested vegetable oil as fuel for diesel engines In the 1930s and 1940s vegetable oils were used as diesel fuels from time

to time, but usually only in emergency situations Recently, because of the increase

in crude oil prices, dwindling resources of fossil fuel, and environmental concerns, there has been a renewed focus on vegetable oils and animal fats that can be used as biodiesel fuels in existing diesel engines Biodiesel is, in principle, carbon dioxide (CO2) neutral, that is, when plants grow, they absorb CO2, and after they are har-vested, converted into biofuel, and burnt, CO2 is produced Ideally, a closed CO2 circuit arises The use of biodiesel has the potential to reduce the level of pollutants and potential or probable carcinogens

19.1.1 w orldwide r eSearcH on v eGetaBle o il aS f uel

Researchers have investigated the effect of using vegetable oils alone (Barsic and Humke 1981; Frgiel and Varde 1981; Suda 1984; Murayama et al 1984) or their blends with diesel (Ziejewski and Kaufman 1983) in a diesel engine for extended periods of time, and encountered a number of problems Gerhard (1983) reported that the high viscosity and low volatility of pure vegetable oil reduced the fuel atomization and increased the fuel spray penetration Higher spray penetration and polymerization

of the unsaturated fatty acids at higher temperatures are partly responsible for the difficulties experienced with engine deposits and thickening of the lubricating oil Several approaches have been undertaken to improve the physical properties of the vegetable oil, for example, (1) the addition of chemicals (additives) to improve the air-fuel mixture by decreasing the surface tension, (2) preheating to diminish the viscosity for improving the internal formation of the mixture and combustion, and (3) mixing with other fuels, to give a better internal formation of the air-fuel mixture

as a consequence of a lower viscosity of the blends or to initiate better burning by easier burning components These techniques are not suitable for long-term testing (Last and Kruger 1985), hence, the derivatives of vegetable oils in the form of alkyl esters and blends with diesel were more attractive as biodiesel A number of studies have been carried out on the preparation and engine testing of biodiesel from various oils (canola [Spataru and Romig 1995], rapeseed [Staat and Gateau 1995], soybean [Schumacher et al 1996], palm [Kalam and Masjuki 2002], sunflower [Da Silva, Prata, and Teixeira 2003], karanja [Raheman and Phadatare 2004], and neem oil [Nabi, Akhter, and Shahada 2006])

19.1.2 m aHua (madhuca indica ) oil for B iodieSel P roduction

Mahua (M indica) seed oil can be used for biodiesel manufacture Its potential is

about 4,40,000 tonnes and only 10,000 tonnes are currently tapped and used, mainly

by the soap industry (Roma Rao, Nanda, and Kalpana Sastry 2003) M indica is

a large deciduous tree with a short trunk, spreading branches, and large rounded crown The flower is used as a vegetable and as a source of alcohol The cake from the oil seeds is used as a fertilizer Cattle eat the leaves, flowers, and fruits The flow-ering season extends from February to April The mature fruit falls to the ground

in May to July in the north and August to September in south India The yield of the plant depends on the climatic conditions and varies from 5 to 200 kg/plant per season, depending on the size and age of the plant The mahua tree starts producing seeds after 10 years and continues up to 60 years The kernel constitutes about 70%

of the seed and contains 50% oil The fats and oils are primarily water insoluble, hydrophobic substances made up of one mole of the glycerol and three moles of the fatty acids and are commonly referred to as the triglycerides The fatty acids vary in the carbon chain length and in the number of unsaturated bonds (double bonds) The mahua oil contains approximately 47% saturated fatty acids and 53% unsaturated fatty acids Palmitic, stearic, and oleic acids are the major constituents

19.1.3 t ranSeSterification

The mahua oil was used to prepare mahua oil methyl ester (MOME), mahua oil ethyl ester (MOEE), and mahua oil butyl ester (MOBE) Then their physical proper-ties were determined and performance tested on a direct injection diesel engine to determine the engine performance and exhaust emissions in comparison with No 2 diesel fuel

Good quality (≤1% free fatty acid and ≤0.5% moisture content) mahua oil (5 l) was taken in a glass reactor fitted with a stirrer, external heater, and condenser for the transesterification processes The oil was heated to 50ºC in the glass reactor and NaOH dissolved in alcohol was added The contents were heated to the required temperature (between 60 and 110ºC) The reflux condenser condensed the evapo-rated alcohol back into the reactor The stirring helped to achieve uniformity of the reactants and helped the reaction go faster Methanol, ethanol, and butanol (20, 30, and 40 vol.% of oil, respectively) were used for the study The reaction temperature was fixed in the range between 60 and 110oC at the boiling temperature of the cor-responding alcohol and the reaction duration was fixed at 2 h under the reflux condi-tion After this, the reaction was stopped and the product was allowed to settle in two layers The upper layer consisted of the ester and alcohol and was separated from the bottom layer (glycerin) The upper layer was distilled to remove and recover the excess alcohol and the esters were washed with hot water to remove traces of the glycerin and alkali Finally, the product was dried for 1 h in a hot air oven at 105°C and analyzed for the fuel properties as per the standard test methods and subse-quently taken for the engine test

19.2 propertIes

Table 19.1 gives a summary of the fuel properties, such as the cetane number, higher heating values, viscosity, specific gravity, flash point, pour point, sulfur content, and moisture content of different mahua oil esters and the No 2 diesel fuel The cetane number for butyl ester was higher compared to other esters and the diesel The heat-ing value increased with increase in the chain length of the fatty acid ester and decreased with increase in the number of double bonds The increase in the heat content resulted from the increase in the number of carbons and hydrogen, as well

as increase in the ratio of these elements relative to oxygen A decrease in the heat

content was the result of fewer hydrogen atoms (i.e., higher unsaturation) in the mol-ecule The viscosity of a liquid fuel is an important parameter because the fluid has

to flow through pipelines, injector nozzles, orifices, and for the atomization of the fuel in the cylinder Proper operation of an engine depends on the accepted viscos-ity range of the liquid fuel The viscosviscos-ity of the mahua oil was quite high (38 cSt) and reduced to approximately one-eighth to one-tenth of the value after the transes-terification The viscosity of all three alkyl esters was within the acceptable range prescribed by the ASTM standards The fuel consumption was significantly affected

by the specific gravity of the fuel If the specific gravity is more, the fuel is more concentrated and more fuel is likely to deliver on the mass basis, which leads to a higher fuel consumption The MOAE has specific gravity within the range specified

by ASTM standards The flash point measures the tendency of the sample to form

a flammable mixture with air under controlled conditions This is the property that must be considered in assessing the overall flammability hazard of a material The flash point of the MOAE was significantly higher than that of diesel fuel and thus would be quite safe for use in transportation compared to diesel The cloud point for the MOAE was closer to that of diesel fuel

19.3 engIne tests

The performance and emissions of the MOAE were studied in the diesel engine in comparison with the No 2 diesel fuel The engine used for the study was a single-cylinder, four-stroke, constant-speed, vertical, water-cooled, direct injection (DI), 3.68 kW diesel engine The engine was coupled to a swinging field separating excited type DC generator and loaded by electrical resistance The exhaust gas temperature was measured by an iron-constantan thermocouple The oxides of nitrogen (NOx), carbon monoxide (CO), carbon dioxide (CO2), and hydrocarbon (HC) were measured

by the MRU emission monitoring systems DELTA 1600-L and MRU OPTRANS

1600 The fuel consumption was measured by a U-tube manometer The engine was started in neat diesel fuel and warmed up The warm-up periods ended when the

tAble 19.1

properties of mahua esters in comparison with no 2 diesel and Astm standards

Astmd6751 fAme

Higher heating value MJ/Kg 45 39.276 40.528 41.607 –

Kinematic viscosity (cSt) 2.4 4.2 5.4 4.7 1.9–6.0 Specific gravity 0.82 0.865 0.875 0.854 0.87–0.90

Pour point (ºC) -10–-15 -3–-5 0–-1 -3–-1

Sulphur content – 0.02% 0.04% 0.03% 0.05

Moisture content – 0.01% 0.01% 0.01% ≤0.05%

cooling water temperature was stabilized Then the fuel consumption, exhaust gas temperature, and different exhaust emissions were measured The procedure was repeated for MOME, MOEE, and MOBE

19.3.1 B raKe S Pecific f uel c onSumPtion

The brake specific fuel consumption (BSFC) is the mass of fuel required to develop unit brake power It can be seen from Figure 19.1 that the BSFC was higher for all the ester-based fuels compared to diesel This was due to the higher specific grav-ity and lower heating value of the MOAE compared to the No 2 diesel The methyl ester showed better BSFC compared to the others The BSFC values were 0.299, 0.319, 0.342, and 0.324 kg/kW-h correspondingly for the diesel, MOME, MOEE, and MOBE at full load

19.3.2 S Pecific e nerGy c onSumPtion

Figure 19.2 shows a comparison of the specific energy consumption (SEC) between the different esters and the No 2 diesel The reason for taking SEC into account

is that comparison of thermal efficiency for different fuel becomes easier As the thermal efficiency depends on two variables, specific fuel consumption and heating value, the comparison will be difficult unless we know the individual contribution

of the variables The product of specific fuel consumption and heating value is

0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

BMEP (bar)

Diesel MOME MOEE MOBE

fIgure 19.1 Variation of brake specific fuel consumption with brake mean effective pressure.

called specific energy consumption, which does not relate to any unit The values for the diesel, MOME, MOEE, and MOBE were 3.784, 3.525, 3.779, and 3.744, respectively, at full load SEC was less for the MOME compared to other two esters

19.3.3 B raKe t Hermal e fficiency

Figure 19.3 shows a comparison of the brake thermal efficiency (BTE) between the different esters and No 2 diesel The BTE is purely dependent on the engine design, type of fuel used, and the area of use The vegetable oil-based fuel contains oxy-gen ranges of 10 to 12% and combustion is better in the case of the MOAE com-pared to the diesel The bonded oxygen helps the fuel to burn efficiently inside the combustion chamber, thereby releasing more heat Again, the heat release does not only depend on the oxygen content but also the heating value of the fuel Since the vegetable oil-based fuels have 10 to 12% less heating value compared to diesel fuel, the oxygen content and heating value of the fuel are together responsible for the ther-mal efficiency The data showed that the therther-mal efficiency for the methyl ester was high compared to those of the diesel and other esters at the full load

19.3.4 e xHauSt G aS t emPerature

Figure 19.4 shows a comparison of the exhaust gas temperature (EGT) between the MOAE and diesel In the diesel engine, there are four stages in the combustion

pro-0

1 2 3 4 5 6 7 8 9

BMEP (bar)

Diesel MOME MOEE MOBE

fIgure 19.2 Variation of specific energy consumption with brake mean effective pressure.

cess: ignition delay, premix combustion or uncontrolled combustion, controlled com-bustion, and afterburning If the afterburning phase is more or the engine misfires

or the injection time is not proper, then there is every possibility for higher EGT On the other hand, if the combustion process is perfect, then also the EGT is likely to

be high As the thermal efficiency was higher in the case of the methyl ester of the mahua oil, the combustion process was supposed to be more complete and this could

be one reason for a higher EGT

19.3.5 n oiSe l evel

Figure 19.5 shows the variation of the noise level with load for different fuels The noise is the indication of the sound that is created during the running of an engine The result showed that at 100% load of the engine, the noise level for all the esters was low compared to diesel and the lowest noise level observed was

123 dB in the case of methyl ester compared to 169 dB for the No 2 diesel at the same load condition

19.3.6 o xideS of n itroGen

Figure 19.6 shows a comparison of the NOX emission between the different esters and the diesel The oxides of nitrogen are formed inside a diesel engine due to high flame

0 5 10 15 20 25 30

0

BMEP (bar)

Diesel MOME MOEE MOBE

7 6 5 4 3 2 1

fIgure 19.3 Variation of brake thermal efficiency with brake mean effective pressure.

0 1.77 3.11 4.89 6.22 50

100 150 200 250 300 350 400 450 500

BMEP (bar)

Diesel MOME MOEE MOBE

fIgure 19.4 Variation of exhaust gas temperature with brake mean effective pressure.

0

0 1.77 3.11 4.89 6.22 20

40 60 80 100 120 140 160 180

BMEP (bar)

Diesel MOME MOEE MOBE

fIgure 19.5 Variation of noise with brake mean effective pressure.

temperature, peak pressure inside the cylinder, nitrogen content of the parent fuel, and the residence time of the fuel inside the cylinder All these factors affect NOX emission greatly As the cetane number of the ester-based fuel is high compared to diesel, the residence time may be less in the case of ester-based fuel In addition, the oxygen content of the fuel enhances the ignition quality, thereby reducing delay for esters Hence, the MOAE is likely to produce lower heat release at the premix com-bustion phase, and this would lower the peak comcom-bustion temperature and reduce the

NOX emissions In addition, other parameters such as iodine value, chemical bond-ing, and structure may contribute to a lower combustion temperature

19.3.7 c arBon m onoxide e miSSion

Figure 19.7 shows a comparison of CO emission between the different esters and the diesel CO emission depends on the combustion efficiency and carbon content of the fuel This shows how efficiently the fuel is burnt inside the engine cylinder The fuel, during combustion, undergoes a series of oxidation and reduction reactions The car-bon content of the fuel is oxidized with the oxygen available in the air to CO and sub-sequently to CO2 No fuel will give 100% combustion efficiency, so the carbon that

is not converted to CO2 will come out as CO in the exhaust The test results showed that for all the esters, the CO emission was lower than that of diesel and the methyl ester gave the lowest CO emission level compared to the other two esters (0.07% for the methyl ester; 0.34 % for the diesel at full load)

0 100 200 300 400 500 600 700 800 900 1000

BMEP (bar)

Diesel MOME MOEE MOBE

7 6 5 3

2 1

fIgure 19.6 Variation of NOx with brake mean effective pressure.

19.3.8 c arBon d ioxide e miSSion

Figure 19.8 shows a comparison of the CO2 emissions between the different esters and the No 2 diesel Carbon dioxide emission is likely to be more for fuel with better combustion quality The better the combustion, the more carbon as carbon dioxide

is present in the exhaust Actually, all the carbon present in the fuel cannot be con-verted to carbon dioxide As the esters contained oxygen in the chemical structure, the combustion was better than with No 2 diesel Hence, the carbon dioxide emis-sion in the exhaust was more than that observed for the diesel

19.3.9 H ydrocarBon e miSSion

Figure 19.9 shows a comparison of the HC emission between the different esters and the diesel The hydrocarbon present in the fuel is burnt inside the engine cylinder

in the presence of air The amount of HC that is not taking part in the combustion reaction is likely to come out as unburnt hydrocarbon As explained earlier, due to several reasons, combustion is not 100% perfect Hence, the HC emission is likely

to occur in the exhaust system In the case of ester-based fuels, the oxygen present

in the structure helps in better combustion and hence HC emission is less than that

of diesel The results showed that the HC value for the No 2 diesel was 89 ppm, whereas it was 35, 45, and 50 ppm for methyl, ethyl, and butyl esters, respectively,

at full load

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

BMEP (bar)

ol.) Diesel

MOME MOEE MOBE

7 6 5 3

2 1

fIgure 19.7 Variation of CO with brake mean effective pressure.