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Multi-mode combustion is an ideal combustion strategy to utilize HCCI for internal combustion engines. It combines HCCI combustion mode for low-middle load and traditional SI mode for high load and high speed. By changing the cam profiles from normal overlap for SI mode to the negative valve overlap (NVO) for HCCI mode, as well as the adjustment of direct injection strategy, the combustion mode transition between SI and HCCI was realized in one engine cycle. By two-step cam switch, the throttle action is separated from the cam action, which ensures the stabilization of mode transition. For validating the feasibility of the stepped switch, the influence of throttle position on HCCI combustion was carefully studied. Based on the research, the combustion mode switch was realized in one engine cycle; the whole switch process including throttle action was realized in 10 cycles. The entire process was smooth, rapid and reliable without any abnormal combustion such as knocking and misfiring.

The effect of direct water injection into the combustion chamber on NOx reduction in an IDI diesel engine was investigated. The temperature distribution in the swirl chamber was analyzed quantitatively with high speed photography and the two color method. Direct water injection into a swirl chamber prior to fuel injection reduced NOx emission significantly over a wide output range without sacrifice of BSFC. Other emissions were almost unchanged or slightly decreased with water injection. Water injection reduced the flame temperature at the center of the swirl chamber, while the mean gas temperature in the cylinder and the rate of heat release changed little.

A 1-Dimensional (1-D) model of fluid dynamic and chemistry kinetics following hot spot auto-ignition has been developed to simulate the process from auto-ignition to pressure wave propagation. The role of wall effect on the physical-chemical interaction process is numerically studied. A pressure wave is generated after hot spot auto-ignition and gradually damped as it propagates. The reflection of the wall forms a reflected pressure wave with twice the amplitude of the incident wave near the wall. The superposition of the reflected and forward pressure waves reinforces the intensity of the initial pressure wave. Wall effect is determined by the distance between the hot spot center and the cylinder wall. Hot spot auto-ignition near the wall easily initiates detonation under high-temperature and high-pressure conditions because pressure wave reflection couples with chemical reactions and propagates in the mixture with high reactivity.