Study On The Effect Of Biodiesel Molecular Structure On Injection Characteristic And Engine Performance

With the extensive use of fossil fuel, the energy shortage and environmental pollution problems are caused all over the world. In order to resolve the contradiction, green energy, clean energy, efficient energy and renewable energy are wide application. Decrease emissions from internal combustion engines have been the key issue in energy and environmental fields. The applications of biodiesel in diesel engines have become increasing important. The molecular structure of fatty acid methyl esters in biodiesel, such as carbon chain length, number of double bonds, degree of saturation, affects the cetane number, viscosity, low temperature fluid and oxidation stability and other fuel properties. The injection, combustion and emission characteristics of a diesel engine are also affected. Based on the characteristics of microscopic molecular structure of biodiesel, this paper studies the injection process, the combustion and emissions characteristics of diesel engine fueled with different biodiesels.The AVL-HYDSIM software is utilized to build the model of high pressure, common rail injection system. The injection process of fossil diesel, methyl laurate(C12:0), methyl stearate(C18:0), methyl oleate(C18:1M), ethyl oleate(C18:1E) are investigated. The effects of molecular structures of biodiesel, including the carbon chain length, number of double bonds and the degree of saturation. The results show that the calculated results coincide with the test results. The injection rate curves of methyl laurate and methyl stearate are similar, and the injections of two fuels start nearly same. The end of injection delays, the peak injection rate, injection quantity and injection energy per cycle increase. The injection quantity and energy per cycle of methyl laurate with short carbon chain are lower than methyl stearate with a long carbon chain. For methyl stearate, methyl oleate and ethyl oleate, the injection curves are similar, the start and the end of injection advance, especially the end of injection. The peak injection rate, injection quantity decreases first and then increases. The injection energy decrease.On the basis of the injection characteristics, the model of the six-cylinder turbocharged diesel engine is established using the AVL-BOOST software. Combustion and performance of diesel engine fueled with methyl laurate, methyl stearate, methyl oleate, and ethyl oleate are investigated. The results show that when carbon chain length increase from 12 to 18, the peak cylinder pressure increase and its phase advance, the cylinder temperature curve advances. But cylinder pressure of two fuels is less than that of petroleum diesel. The maximum amplitudes of pressure rise rate for methyl laurate and methyl stearate is similar; it is smaller than that of petroleum diesel. The cylinder temperature of petroleum diesel, methyl laurate and methyl stearate increase, and the difference becomes obvious with the change of crank angle. Compared with methyl laurate, the combustion duration of methyl stearate becomes longer, the exhaust temperature and fuel consumption increase, the exhaust pressure and NO_x emissions decrease. Compared to the petroleum diesel, NO_x emissions of methyl laurate are higher, and those of methyl stearate are slightly lower. Compared to the methyl oleate with a double bond, the cylinder pressure curve of methyl stearate without double bond advances, the peak values are similar. The peak pressure of ethyl oleate is lower, and its phase advance. The maximum amplitudes of pressure rise rate for three fuels are similar. The temperature decrease, the differences of three fuels become remarkable with the change of crank angle. Combustion duration of three fuels shortens, and post combustion decrease, the exhaust temperature and fuel consumption decrease, and exhaust pressure increases. NO_x emissions of methyl oleate are the highest, then methyl stearate, and those of ethyl oleate are the lowest.The rapeseed biodiesel RME with long carbon chain length and high unsaturation degree, palm biodiesel PME with short chain length and low unsaturation degree, and soybean biodiesel SME are blended with petroleum diesel, respectively. The combustion, NO_x emissions and performance characteristics(exhaust temperature, fuel consumption) of a diesel engine are investigated; the effects of blend ratio, operational conditions and types of biodiesel are also investigated. The results are compared to those of petroleum diesel. The results show that, with increase of blend ratio of RME, the peak cylinder pressure decreases, and its phase advances. Peak temperature decreases slightly, and the maximum amplitude of pressure rise rate decrease. The fuel consumption, exhaust temperature and NO_x emissions increase. SME or PME are blended with petroleum diesel, the effects are smilar. For three biodiesel-diesel blends, the peak pressure and the maximum amplitude of petroleum diesel, RME40, SME40 and PME40 decrease. The peak temperature of petroleum diesel, PME40, RME40 and SME40 decreases. Compared to the petroleum diesel, fuel consumption and exhaust temperature increase when biodiesel(RME, SME or PME) are blended with diesel. The change rate of fuel consumption and exhaust temperature of SME added is highest, and then PME and RME added. NO_x emissions increase when RME, SME or PME are blended with petroleum diesel. The change rate of PME added is the highest, then RME and SME.