Combustion and Emission Characteristics of Biodiesel-diesel-ethanol Fuel Blends

To improve the performance of engines fueled with a high proportion of biomass fuel blends, ethanol was added to medium proportion biodiesel-diesel fuel blends by a volume percentage of 5%, 10%, and 20%, respectively denoted as BD50E5, BD50E10, and BD50E20. The combustion and emission performances of biodiesel-diesel-ethanol fuel blends were investigated on a turbocharged, 6-cylinder, common rail diesel engine at a constant speed of 1 600 rpm and seven engine loads, and the engine performances of the fuel blends were compared to that of diesel fuel. The results show that the fuel injection strategy of the test engine is pilot injection plus main injection at low loads when the brake mean effective pressure (BMEP) is equal to 0.322 MPa. The maximum cylinder pressure and the maximum heat release rates of the biodiesel-diesel-ethanol blends are higher than that of diesel, because a large number of hydroxyl radicals are generated in the low-temperature reaction of the pilot injection stage. With increased engine loads, the fuel injection strategy becomes single-stage injection at 0.805 MPa BEMP. The maximum cylinder pressure and the maximum heat release rate of the biodiesel-diesel-ethanol blends are lower than diesel fuel owing to the lower caloric value of ethanol. Moreover, with the increasing proportion of ethanol, the ignition delay of biodiesel-diesel-ethanol blends is obviously prolonged due to the lower cetane number and higher latent heat of ethanol, and the combustion speed of the fuel blends are distinctly accelerated due to the stronger premixed combustion and the higher oxygen content of ethanol. Therefore, the addition of ethanol is helpful to concentrate the heat release and shorten the combustion duration. In terms of exhaust emissions, compared to diesel fuel, NOx emissions from biodiesel-diesel-ethanol blends of BD50E5, BD50E10, and BD50E20 increased by 10.46%, 12.59%, and 17.52%, respectively; whereas, soot emissions decreased by 37.91%, 45.85%, and 49.25%. CO emissions decreased by 20.24%, 36.43%, and 46.43%, and HC emissions decreased by 12.53%, 4.40%, and 0.76%, respectively. © 2018, Editorial Department of China Journal of Highway and Transport. All right reserved.