Effects of fuel compensation in transitional cycles on the smoothness of combustion mode switching in a diesel engine

Because indicated mean effective pressure (IMEP) fluctuation often occurs in diesel homogeneous charge compression ignition (HCCI) engines during the conventional compression-ignition (CI) combustion mode and HCCI combustion mode switching process, in this paper, the effects of a fuel injection compensation strategy on the smoothness in the CI-HCCI combustion mode switching process at equal load were studied. The fuel compensation in one transitional cycle, two transitional cycles and three transitional cycles were discussed, and the return maps of the IMEP variation were analyzed. The results showed that the fuel increase of the first transitional cycle can enhance the combustion of this cycle and prevent the IMEP from decreasing. More transitional cycles with decreased fuel compensation ratio can improve the smoothness of the IMEP. However, the magnitude of the decreasing trend of the IMEP fluctuation ratio decreases and the fuel control strategy becomes complicated as the number of transitional cycles increases. The fuel injection compensation strategy for the diesel engine is optimized when two transitional cycles and fuel ratios of 1.07 for the first cycle and 1.03 for the second cycle are used, and the fluctuation of the IMEP decreased by 68% compared to the direct combustion mode switching process.