Influence of transitions between SI and HCCI combustion on driving cycle fuel consumption

A model for a vehicle equipped with a multimode combustion engine is formulated and calibrated to experiments. A study is performed for the FTP-75 driving cycle about the influence of the mode switch strategy on the engine operation and fuel consumption, using simulation results and driving cycle measurements. It is found that the fuel penalty for mode transitions cancels a significant part of the theoretical benefits of advanced combustion modes. A smoothing strategy, where a mode switch is delayed, is introduced and it is shown that, by computing the optimal wait time, the negative influence of mode transitions on the overall efficiency can be reduced.