Biodiesel Production - Engine Combustion - Lecture Notes, Study notes of Sustainability Management

Download Biodiesel Production - Engine Combustion - Lecture Notes and more Study notes Sustainability Management in PDF only on Docsity! Objectives_template file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture40/40_1.htm[6/15/2012 3:11:13 PM] Module8:Engine Fuels and Their Effects on Emissions Lecture 40:Alternative Fuels (contd.) The Lecture Contains: BIODIESEL Biodiesel Production – Esterification of Oils Properties of Biodiesel Emissions Hydrogen Greenhouse Gas Emissions with Alternative Fuels Questions Objectives_template file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture40/40_2.htm[6/15/2012 3:11:13 PM] Module8:Engine Fuels and Their Effects on Emissions Lecture 40:Alternative Fuels (contd.) BIODIESEL In a 1912 speech, Rudolf Diesel said, "the use of vegetable oils for engine fuels may seem insignificant today, but such oils may become, in the course of time, as important as petroleum and the coal - tar products of the present time". The revival of biodiesel derived from vegetable oils started as a result of agricultural surplus in some European countries and under Kyoto protocol the need of reducing greenhouse gas CO2 emissions. Biodiesel is a renewable fuel that is produced from a variety of edible and non-edible vegetable oils and animal fats. The term “biodiesel” is commonly used for methyl or ethyl esters of the fatty acids in natural oils and fats, which meet the fuel quality requirements of compression-ignition engines. Straight vegetable oils (SVO) are not considered as biodiesel. The straight vegetable oils have a very high viscosity that makes flow of these oils difficult even at room temperatures. Moreover, presence of glycerine in the vegetable oil causes formation of heavy carbon deposits on the injector nozzle holes that results in poor and unacceptable performance and emissions from the engine even within a few hours of operation. Biodiesel Production – Esterification of Oils Biodiesel is produced by reacting vegetable oils or animal fats with an alcohol such as methanol or ethanol in presence of a catalyst to yield mono-alkyl esters. The overall reaction is given in Fig. 8.6. Glycerol is obtained as a by-product. Figure 8.6: Esterification reaction for vegetable oils and fats.’ Properties of Biodiesel A variety of vegetable oils such as soybean, rapeseed, safflower, jatropha-curcas, palm, and cottonseed oils have been used for production of biodiesel. Waste edible oils left after frying/cooking operation etc., have also been converted to biodiesel for study of their performance. The biodiesel are also known as fatty acid methyl esters [FAME]. Recently non-edible oil produced from jatropha- curcas seeds has gained interest in India as this plant can be easily grown on wastelands. The properties of methyl esters of rapeseed and jatropha oils are given in Table 8.18. Objectives_template file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture40/40_4.htm[6/15/2012 3:11:13 PM] Module8:Engine Fuels and Their Effects on Emissions Lecture 40:Alternative Fuels (contd.) Hydrogen Interest in hydrogen as a potential alternative automotive fuel has grown due to need of reducing greenhouse gas, CO2 emissions and to minimize dependence on fossil fuels. Hydrogen can be produced from a variety of fossil and non-fossil sources. Hydrogen is a colourless, odourless and non-toxic gas. It burns with an invisible and smokeless flame. The combustion products of hydrogen consist of water and some nitrogen oxides. The major hurdles in the use of hydrogen as a fuel are lack of production, distribution and storage infrastructure. On board storage of hydrogen is another major challenge. Hydrogen has very low boiling point (– 253º C) and very low volumetric energy density. Volumetric energy density of compressed hydrogen is just one-third of energy density of natural gas. Liquid hydrogen also has a very low volumetric energy density, which is about one-fourth of gasoline. Hydrogen can be stored as compressed gas, as iron, magnesium, titanium or nickel hydride, or in liquefied form. The liquid, hydride and compressed hydrogen storage methods are compared in Table 8.20 for storing 19 litres of gasoline equivalent in energy. Hydrogen storage space required is at least 10 to 12 times higher than for gasoline. Storage and fuel weight for hydrides is 27 times and for compressed H2 is 4 to 5 times of gasoline. Table 8.20 Comparison of Hydrogen Storage Methods Gasoline Liquid H2 Hydride Fe- Ti (1.2%) Compressed H2 (70MPa) Energy (LHV) stored, MJ Fuel mass, kg Tank mass, kg Total Fuel System mass, kg Volume, l 600 14 6.5 20.5 19 600 5 19 24 178 600 5 550 555 190 600 5 85 90 227 Combustion characteristics of hydrogen and its impact on emissions are given below; Hydrogen octane rating is 106 RON making it more suitable for spark-ignited engines. The laminar flame speed of hydrogen is 3 m/s, about 10 times that of gasoline and methane. Hydrogen has very wide flammability limits ranging from 5 to 75% by volume (f = 0.07 to 9), which may lead to pre-ignition and backfiring problems. Its adiabatic flame temperature is higher by about 110º C compared to gasoline. If inducted along with intake air, the volume of hydrogen is nearly 30% of the stoichiometric mixture decreasing maximum engine power. Hydrogen on combustion produces water and there are no emissions of carbon containing pollutants such as HC, CO and CO2 and air toxics. Trace amounts of HC, CO and CO2 however, may be emitted as a result of combustion of lubricating oil leaking into engine cylinder. NOx is the only pollutant of concern from hydrogen engines. Very low NOx emissions can be obtained with extremely lean engine operation (f < 0.05) and/or injection of water into intake manifold or exhaust gas recirculation which in this case consists primarily of water vapours. Objectives_template file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture40/40_4.htm[6/15/2012 3:11:13 PM] NOx emissions of 0.013 g/km have been obtained which are about 1/10th of the US Tier 2 regulations. Hydrogen fuelled engines produces almost no CO2 and its global warming potential is insignificant. Hydrogen fuelled IC engines however are not considered a long term option when compared to fuel cell. Hydrogen fuel-cell vehicles are expected to have more commercial potential in the long run. Though it is believed that significant production volumes for customers will not be available until the 2017-2020 time frame. Objectives_template file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture40/40_5.htm[6/15/2012 3:11:13 PM] Module8:Engine Fuels and Their Effects on Emissions Lecture 40:Alternative Fuels (contd.) Greenhouse Gas Emissions with Alternative Fuels Fossil fuels currently supply about 80% of all primary energy and are expected to remain fundamental to global energy supply for at least the next 20 to 30 years. . Presently, it is estimated that power generation accounts for about 40% and surface transport contributes nearly 20% of global CO2 emissions. The Kyoto Protocol signed in December 1997 commits the industrialized countries to legally binding reductions in emissions of greenhouse gases by 2008-2012. Strategy to achieve reduction in CO2 emissions from transport sector involves essentially the following: Reduction in fuel consumption of vehicles. Increased use of low carbon alternative fuels and bio fuels. European Union countries have introduced CO2 emission regulations for the automobiles. A voluntary target of 140 g/km average CO2 emissions for new car sales to be met in 2008 was set that had to be relaxed. By the year 2012, a goal of 130 g/km of CO2 to be achieved by engine and vehicle technology, and further reduction to 120g/km by use of renewable fuels has been set by European Union. When comparing different fuel and power plant alternatives, life cycle CO2 equivalent GHG emissions are to be considered. It should account for CO2 and other GHG emissions generated during production, transportation and use in the vehicles. Lifecycle CO2 emissions for liquid petroleum fuels, LPG, natural gas and biodiesel for heavy vehicle application are compared in Fig 8.8. The CO2 emissions yielded during fuel production and during fuel utilization stage in engines are shown separately. Among the alternative fuels, natural gas having lower carbon content in the fuel molecule has advantage over gasoline and diesel fuels as far as CO2 emissions are concerned. From natural gas vehicles, the greenhouse effect of the fugitive methane emissions as a result of leakage from the transportation and distribution systems is also to be accounted for as methane is nearly 20 times more potent than CO2 in causing global warming. LPG lies in between the natural gas and liquid petroleum fuels. The bio fuels such as ethanol and biodiesel have much lower lifecycle CO2 emissions as the carbon dioxide produced on their combustion would be the same that has been fixed from atmosphere during growth of the agriculture crops. These fuels do contribute to net CO2 emissions resulting from manufacture of fertilizers and other ingredients used for crops and, during processing of these fuels and making them suitable for use in the engines.