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Stratified-charge DISI engines have been launched in the market by Mitsubishi, Toyota, and Nissan. This paper discusses the current production stratified-charge DISI systems and some alternative systems, including the system using air-forced fuel injection and a proposed system that uses a swirl flow in the piston bowl with a special shape to separate the fuel-rich mixture layer from the wall surface. New DISI concepts are proposed to overcome some drawbacks of current bowl-in-piston type stratified-charge DISI systems. Charge stratification can be realized by using a soft spray with proper spray penetration, droplet size, and cone angle, as shown by CFD simulation results. The drawbacks of fuel wall wetting, soot limited load with charge stratification, large surface to volume ratio, etc., of the bowl-in-piston type system can be minimized.

A single-cylinder OKP (optimized kinetic process) engine, which uses homogeneous-charge compression-ignition (HCCI) technology, was tested, following a previous study, to evaluate the combustion system robustness and to improve the engine performance near the boundaries of the HCCI operating regime at light loads, high loads and high speed. To evaluate the robustness of HCCI combustion control, gasoline fuels with different RON were used, and the engine was tested at different coolant temperatures. It was demonstrated that the proposed HCCI control approaches could control the OKP engine system to operate robustly using different fuels and at different coolant temperatures. The effects of fuel injection timing and residual gas fraction on HCCI combustion and emissions, especially CO emissions and combustion efficiency, were tested at light loads; and the mechanisms were analyzed.