Theoretical Research Of The Combustion And Emission Process For The Direct Injection LPG Engine

LPG (Liquefied Petroleum Gas), compared with gasoline, has lower carbon hydrogen ratio, higher octane number, lower price of per calorific value and lower HC, NOx, soot pollutants emissions. Therefore, LPG becomes an excellent alternative fuel for its good fuel economy and low emission. But currently LPG engine mainly uses a pre-mixing homogeneous ignition method, which leads to poor fuel economy and low emission. DI(Direct Injection)LPG engine can evidently improve the power performance, fuel economy and emissions, especially employing lean-burn direct injection can efficiently improve fuel economy at part load. In this paper the combustion and emission process is simulated based on layered lean mixture. Also, chemical reaction kinetics software CHEMKIN is employed to analyse the emission, which makes the study more accurate. All of the data provides theoretical basis to optimize LPG engine.To make the DI LPG engine model simulate the work process accurately, visualization experiment of spray and cylinder pressure experimental are carried out to validate and demarcate computational model. Compared the experiment and computational data, the computational model is good for the study.Based on the computational model the combustion of the layered lean mixture is simulated, the results are as follows. On part load (2000rpm), through the cylinder pressure, temperature and concentration field data, ignition time is put off, and the emission of NOx and the output of power is bad, while the emission of soot is good. Through the emission results, temperature plays an important role in the formation of NO. In the early time of ignition, much NO is generated. At5°CA ATDC the NO formation rate reaches the peak, and also NO concentration field reaches the peak subsequently. In the early time of ignition, Φ<1around the spark, the concentration of CO and the temperature in cylinder is high which lead to the oxidation of CO, and its concentration decreases. The soot around the spark maintains at a high level in the early time of combustion, because the O2is consumed rapidly. Then O2and soot is fully blended by the whirl and tumble, and the temperature in cylinder increases. The big soot grain is oxidized to small one and the soot concentration decreases gradually. Based on3D CFD calculation, CHEMKIN OD internal engine reactor is used to simulate LPG emission as complementarity. All the work is to make the result more accurate.