Effects of pre-injection strategy on combustion performance of methanol/diesel dual fuel engine at low load

In this paper, the effect of pre-injection timing on the combustion and emission performance of methanol/diesel high premixed charge compression ignition (HPCCI) combustion mode at low load was studied by three-dimensional numerical simulation. The simulation is carried out under the conditions of 1900 r/min and 25% load, and the pre-injection diesel mass remains constant and the pre-injection timing is changed under the conditions of 50% and 60% methanol ratio respectively. The results show that with the delay of pre-injection timing, the evaporation of pre-injected fuel in cylinder becomes faster, the low temperature reaction is enhanced, and the peak value of heat release rate is higher. In addition, the distribution of pre-injected diesel in cylinder and the position of impact wall are the important factors affecting the combustion and emission performance in cylinder, and when the injection timing is -35 °CA ATDC, the combustion and emission characteristics of the engine are optimal. Finally, by comparing with the traditional RCCI combustion mode, the enhancement ability of HPCCI combustion mode on methanol combustion efficiency under low load is verified and analyzed.