Numerical Parametric Study of a Six-Stroke Gasoline Compression Ignition (6S-GCI) Engine Combustion - Part III

The aim of this paper is to computationally investigate the combustion behavior and energy recovery processes of a six-stroke gasoline compression ignition (6S-GCI) engine that employs a continuously variable valve duration (CVVD) technique, under highly diluted, low-temperature combustion (LTC) conditions. The effects of variation of parameters concerning injection spray targeting (number of fuel injector holes. injector nozzle size and spray included angle) and combustion chamber geometry (piston bowl design) are analyzed using an in-house 3D CFD code coupled with high-fidelity physical sub-models with the Chemkin library in conjunction with a skeletal chemical kinetics mechanism for a 14-component gasoline surrogate fuel. The foundation of this study stems from the authors previous works, regarding the effects of the change in various operating parameters on the overall performance of 6S-GCI engine, which show that both kinetically-controlled mode of combustion (KCM) and mixing-controlled mode of combustion (MCM) can be achieved in the second power stroke (PS2) with low soot emissions. The focal point of this work is to understand the effects of fuel-spray interaction and mixture stratification on in-cylinder mixing prior to ignition, ignition behavior of charge mixtures, and post-combustion/late-cycle mixing processes, and the underlying physics of combustion regime change, which enables to develop the strategy of combustion regime control in the low-load range. The results showcase the likely trends of extending the operability limit of 6S-GCI cycle by governing local composition and thermal stratification of charge mixtures.