Co-optimization of operating parameters, fuel composition, and piston bowl geometry of gasoline compression ignition (GCI) engine at high loads

Focusing on the gasoline compression ignition (GCI) combustion mode, the operating parameters, fuel composition, and piston bowl geometry were collaboratively optimized at high loads to improve engine performance. A meliorative genetic algorithm coupled with a three-dimensional computational fluid dynamics (CFD) program was adopted as the optimization tool. The optimal GCI combustion strategy is summarized based on the optimization results, and the key parameters affecting engine performance at high loads are further analyzed. The results show that the employment of the open-type piston bowl, high-reactivity fuel, and late start of injection (SOI) is desirable for GCI engines at high loads. Under this strategy, fuel burns in multiple stages, which can reduce the heat release rate and advance the combustion phase. The width of the piston bowl is the geometric parameter with the most notable impact on GCI combustion. Due to the weaker turbulent kinetic energy and the smaller surface area, the larger piston bowl width is conducive to diminishing the heat transfer losses of the engine and promoting the oxidation of unburned hydrocarbon (HC) emissions. Relative to the optimal case, the strategy with the open-type piston bowl, high-reactivity fuel, and early SOI can reduce fuel consumption but results in a higher in-cylinder pressure rise rate and increased ringing intensity (RI). On the contrary, the re-entrant type piston bowl, low-reactivity fuel, and late SOI can significantly reduce the pressure rise rate and RI while deteriorating thermal efficiency.

Automated summary

Focusing on gasoline compression ignition (GCI) combustion, this study optimized operating parameters, fuel composition, and piston bowl geometry to improve engine performance under high loads by using a meliorative genetic algorithm and 3D computational fluid dynamics (CFD) program. The optimal GCI combustion strategy involves utilizing an open-type piston bowl, high-reactivity fuel, and late start of injection (SOI) to achieve multiple-stage combustion, reducing heat release rate and advancing combustion phase. The width of the piston bowl is the most significant geometric parameter impacting GCI combustion, affecting turbulent kinetic energy, surface area, heat transfer losses, and hydrocarbon emissions. Alternative strategies with re-entrant type piston bowl, low-reactivity fuel, and late SOI can reduce pressure rise rate and ringing intensity (RI), but at the expense of thermal efficiency.