Gasoline compression ignition (GCI) combustion of pump-grade gasoline fuel under high compression ratio diesel engine

Abstract

In this paper, gasoline compression ignition (GCI) combustion was investigated under a high compression ratio (CR = 22:1) system that was developed for a high-efficiency heavy-duty diesel engine platform. The experiment includes Single-Cylinder Engine (SCE) testing of two combustion systems with distinctively different piston designs: wave and stepped-lip. Validated Computational Fluid Dynamics (CFD) simulations provide insights on the in-cylinder phenomenon under GCI combustion. While early spray/flame and ignition characteristics were driven mainly by nozzle configuration in each combustion system, flame-wall and flame-flame interaction during the late-cycle combustion process were strongly affected by the piston's wall-flow-guided feature. The wave piston is unique with a recirculation flow, also known as radial mixing zone (RMZ). RMZ results from in-cylinder flow interactions of adjacent flames, which play a crucial part in enhancing late-cycle soot oxidation.Meanwhile, the stepped-lip piston splits flame jet (at the time of impingement) upward and downward to head and bowl, respectively. Overall, the stepped-lip piston showed lower heat loss due to reduced spray penetration. In contrast, wave piston demonstrated superior end-cycle mixing, reducing soot emissions. Both systems provided similar indicated thermal efficiency (ITE). Comparison between diesel and GCI shows that GCI can reach diesel-like efficiency while maintaining low soot emissions. However, there is a remaining challenge in GCI combustion with higher carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions than diesel combustion.