Numerical Study On The Combustion Control Strategy Of Gasoline Compression Ignition(GCI) At High Load

An important reason why gasoline compression ignition(GCI)can achieve high thermal efficiency and low emissions is that it can separate the process of fuel injection and combustion by a long delay period.However,for high load condition,this feature easily causes high maximum pressure rise rate(MPRR).Therefore,the expansion of high load has always been a hotspot and difficult point.Many studies have been shown that the optimized of fuel injection strategy can solve the problem of high MPRR to a certain extent.The essence of the change in injection strategy is the change of mixture distribution.Because it is difficult to observe the distribution of mixture in the cylinder at the experimental study,it is necessary to use numerical simulation to study the high load expansion of GCI from the distribution of mixture.Firstly,the effects of the mixture distribution of port/direct fuel injection strategy and in-cylinder two-injection strategy on GCI combustion and emissions were investigated.The results show that the rate of heat release is closely related to the distribution of the mixture in-cylinder at the moment of ignition.For port/direct fuel injection strategy,when the proportion of port premixing increases,the dispersion of the equivalence ratio at the moment of ignition first decreases and then increases.The peak of the heat release rate first rises and then decreases.For in-cylinder two-injection strategy,when the pre-injection timing is delayed,the equivalent ratio rich zone formed by the pre-injection fuel is gradually changed from the combustion chamber pit region to the shrinkage region and the squish flow region.When the combustion chamber pit region and shrinkage region are simultaneously ignited,the rate of heat release is the fastest.Then,the GCI mode is expanded to a larger load by optimizing the combustion boundary conditions.The results show that the indicated mean effective pressure(IMEP)increased from 18.68 bar to 20.36 bar.Soot emissions are reduced from 0.47 g/kW-h to 0.020 g/kW-h.In addition,the impact of the strategy using port fuel injection and pre-injection on the load expansion of GCI was investigated.Compared with the strategy of only port fuel injection or only pre-injection,the IMEP of strategy combined with port fuel injection and pre-injection has improved,but the improvement is small,only increased by 0.21%,0.24%,respectively.The maximum pressure rise rate for all three strategies is below 12 bar/°CA.For the high-load expansion,if a proper proportion of port fuel injection or an earlier pre-injection is used,the pressure rise rate can meet the limit.The load expansion is limited by the cylinder pressure.