A NUMERICAL SIMULATION OF FUEL PREMIXING FOR PCCI COMBUSTION BY DIRECT INJECTION

摘要

Diesel engine has some advantages that thermal efficiency is high and control response is fast. On the other hand, more paniculate matter (PM) and nitrogen oxide (NOx) are contained in the exhaust gas of diesel engine. Premixed charge compression ignition (PCCI) combustion is proposed to reduce the PM and NOx. In the lean range of equivalent ratio, unburned fuel is left and in the rich range, PM and soot are generated. For the practical use of PCCI combustion, mixing fuel and air well is important under the low equivalent ratio of injection. In this study, the mixing characteristics of fuel and air in a cylinder were numerically evaluated. A numerical simulation was performed with general-purpose simulator. The fuel has been injected into the vertical direction of cylinder and injection angle has been defined as 0 degree. In order to express the collusion, impingement on the wall model, that defines behavior of a droplet impinged on the wall with the Weber number of a droplet, was applied. By the injection timing, standard deviation of local equivalent ratio at Top Dead Center (TDC) was plotted. In this study, Frequency of mixing in each cell statistically was observed to evaluate the fuel-air mixing degree. The authors have taken notice of the condition which can be reduced the amount of scatter in the distribution of local equivalent ratio.