Three-dimensional Simulation Research On Combustion Process Of Natural Gas Engine Ignited By Pilot Diesel

With the increasingly serious energy crisis and environmental problems, traditional fossil fuel engine has already can not meet the requirement of the development. Therefore, it is particularly important to research and develop alternative fuel engine. In recent years, with the continuous development of alternative fuel engine, natural gas engine has become the research focus due to its own advantages. But it is difficult to be ignited in lean burn condition and the traditional ignition way of high energy can not meet the requirement well due to its complicated structure and high cost. By contrast, diesel ignition natural gas engine has become the research hot spot because of its simple structure and higher ignition reliability.At present, the research on diesel ignition natural gas engine mainly concentrated in power performance, economy performance and emission performance. However, the study of combustion process is less, especially to the ignition process. Actually, the combustion process are deeply affected by the amount of pilot diesel, the injection timing of pilot diesel, the injection duration of pilot diesel, the nozzle size, the position of fuel injector and the concentration of natural gas air mixture, which then affects the engine performance. Firstly, in order to investigate the influence of the amount of pilot diesel, the injection timing of pilot diesel, the injection duration of pilot diesel and the concentration of natural gas air mixture to the combustion process of natural gas engine ignited by pilot diesel, a 3D geometric combustion chamber of engine have been built by CATIA and a 3D simulation model of natural gas engine ignited by pilot diesel have been built by AVL-FIRE. At the same time, in order to do some preliminary investigation of the natural gas ignition process, a way named “subtraction” have been used to pyrolysis coupling of diesel and natural gas, which means the total “diesel plus natural gas” combustion characteristic parameters are needed to minus the separate pilot diesel combustion characteristic parameters in a same condition.In this paper, the simulation results show that: with the increase of the amount of pilot diesel, the peak pressure, the peak temperature and the peak heat release rate increase by about 27%, 3% and 5% respectively, the diesel and natural gas hybrid combustion phenomenon are more obvious, the fluctuations of combustion heat release are small, the ignition process are more stable; With the delay of the injection timing of pilot diesel, the peak pressure and the peak temperature decrease by about 23% and 3.17% respectively, the diesel and natural gas hybrid combustion phenomenon are enhanced, the ignition process are more stable; With the extension of the injection duration of pilot diesel, the peak pressure and the peak temperature decrease by about 25% and 2.87% respectively, the fluctuations of combustion heat release of diesel and natural gas are big, the hybrid combustion phenomenon are weakened, the ignition process are not stable; With the decrease of the concentration of natural gas mixture, the peak pressure, the peak temperature and the peak heat release rate decrease by about 28%, 14% and 56% respectively. The sensitivity of the ignition process to the concentration of natural gas air mixture is low in the condition of the injection parameters of pilot diesel are fixed and the natural gas can be ignited by the pilot diesel.The research achievements of this paper can provide some help to the study of combustion mechanism of natural gas engine ignited by pilot diesel and develop high performance dual-fuel engine.