Simulation And Analysis Of BED Multi - Component Fuel Combustion Process Simulation

With the global growing energy crisis and people’s growing environment-protection awareness, searching for clean and renewable fuel has been the key of diesel engine development. Diesel is the main fuel of large vehicle engine and its alternative fuel has gained more and more concerns. Biodiesel and ethanol, which are the key alternative fuel for diesel, are rarely used independently because of cost, technology and application restriction. Blending any two or three kinds of fuel is the usual way. Physical and chemical properties of biodiesel, ethanol and diesel are different, so learning combustion and spray mechanism of biodiesel-ethanol-diesel (BED) multi-component fuel plays an important role in improving combustion efficiency and reducing pollution of multi-component fuel.Combustion testing of pure diesel, B15E3(Volume fraction of biodiesel is15%and ethanol is3%), B15E5(Volume fraction of biodiesel is15%and ethanol is5%) and B25E5(Volume fraction of biodiesel is25%and ethanol is5%) were conducted. Data of cylinder pressure, rate of heat release and pressure rise are collected. Cylinder pressure and heat release rate variation curve of these four kinds of fuel were analyzed. Engine spray and combustion model was established by AVL-FIRE software, and cylinder spray and combustion appearance of different ratio BED multi-component fuel was analyzed. By combining testing and simulation, variation and developing law of fuel-air equivalence ratio, temperature, velocity, turbulent kinetic energy and emissions (NOx, soot) under different crank angle were studied. Those results of BED were compared with the results of pure diesel to research spray, combustion and emission mechanism of BED multi-component fuel.The result shows:(1) With the increase of biodiesel and ethanol proportion, cylinder peak pressure of BED engine increased and its corresponding crankshaft angle position advanced; On the contrary, crankshaft angle position of peak heat release rate would lag behind. At operating point of2200r/min and200N·m, pressure rise rate of B25E5and pure diesel were greater than B15E3and B15E5, and2200r/min and 200N·m the maximum pressure rise rate of four fuel was not significantly different.(2) With fuel injection, fuel-air equivalence ratio of fuel beam center area was greater; the multi-component of BED has a lower fuel-air equivalence ratio relative to pure diesel fuel, with the accumulation of fuel in the cylinder, and fuel air equivalence ratio of BED multi-component fuel is higher than pure diesel, Fuel-air equivalence ratio of B25E5was the lowest, and B15E3and B15E5were basically identical. After the fuel entering into the cylinder, injection speed was very great. Pure diesel has the highest flow rate, injection speed of B15E5was greater than B15E3, and cylinder speed of B25E5resulted from injection and combustion was the lowest. Local maximum combustion temperature of BED multi-component fuel decreased. Cylinder turbulent kinetic energy of B25E5was greatest, and pure diesel was lowest.(3) For spray penetration distance, spray penetration distance of BED was greater than pure diesel. When the fuel combustion process, fuel air equivalence ratio of BED multi-component fuel is higher than pure diesel, combustion end of the fuel-air equivalence ratio change just the opposite; B15E3and B15E5were closer; pure diesel was the lowest. At operating point of2200r/min and200N·m, Maximum difference of spray penetration distance among these four kinds of fuel was about5mm, and maximum difference at operating point of3200r/min and150N*m was about10mm.(4) NOx was mainly distributed in the burned area, NOx generating rate of BED was faster than pure diesel. In the area of greater fuel density and higher combustion temperature, soot generating rate was always identical. For soot distribution and variation, these four kinds of fuel were basically the same and stabilized by the late. In3200r/min and150N·m, NOx emissions operating point than2200r/min and200N·m working conditions o’clock, soot emissions less than2200r/min and200N·m working conditions.