Abstract:

The combustion and emission characteristics of methanol/PODE_n mixed fuel under different fuel injection strategies were investigated to improve combustion efficiency and reduce pollutant emissions of a direct injection diesel engine. Based on the Computational Fluid Dynamics (CFD) and simulation analysis software Converge, three-dimensional modeling is carried out for a direct injection diesel engine with a Premixed Compression Combustion Ignition (PCCI) mode. Under the initial low-load conditions of 1 200 r/min engine speed, initial pressure of 100 kPa and initial temperature of 340.6 K were calculated. The results show that in a single injection, the peak pressure and the peak specific exothermic is greatly increased at the early injection time, the fuel utilization ratio is increased, and the main pollutants is significantly reduced; But the reaction rate becomes faster and the emission of pollution increases when the injection time is too early. With the advance of the pre-injection time, the interval between the pre-injection time and the main injection time becomes longer, and the cylinder pressure changes little, the heat release rate curve has 2 peaks, the peak value is slightly reduced, and the injection time (crankshaft angle, CA) is advanced. The mass emission of Soot, NO_x and CO are decreased by 6.89%, 5.41% and 23.31% respectively, compared with each peak value. The pre-injection time and the main injection time of the optimal injection strategy are -27° and -22°.

Key words: injection diesel engines, premixed compression combustion ignition (PCCI), methanol/ Poden dual fuels, injection strategies, combustion and emission characteristics, fuel utilizations