Numerical Parametric Study of a Six-Stroke Gasoline Compression Ignition (GCI) Engine Combustion

Numerical investigation of engine performance and emissions of a six-stroke gasoline compression ignition (GCI) engine combustion at low load conditions is presented. In order to identify the effects of additional two strokes of the six-stroke engine cycle on the thermal and chemical conditions of charge mixtures, an in-house multi-dimensional CFD code coupled with high fidelity physical sub-models along with the Chemkin library was employed. The combustion and emissions were calculated using a reduced chemical kinetics mechanism for a 14-component gasoline surrogate fuel. Two power strokes per cycle were achieved using multiple injections during compression strokes.

Parametric variations of injection strategy viz., individual injection timing for both the power strokes and the split ratio that enable the control of combustion phasing of both the power strokes were explored. The computational results suggest that the operability limit of GCI combustion can be effectively expanded by controlling the mixture thermodynamic conditions and achieving optimum mixture stratification. It was uniquely found that the charge mixtures could burn in the mixing-controlled mode during the second power stroke with the injection timing control and result in substantial soot reduction while maintaining high combustion efficiency. Also, the variation of split ratio was found to be effective in controlling the combustion phasing and pressure rise rate for both the power strokes.