Effect of Flow and Gasoline Stratification on Combustion in a 4-Valve SI Engine

In a 4-valve SI engine, various levels of gasoline stratification and bulk flows were achieved by modifying the intake configuration and injection mode. Mean flow and turbulence were evaluated with Laser Doppler Velocimetry. Planar Laser Induced Fluorescence on a gasoline doped with a tracer was used to characterise the equivalence ratio field while the pressure traces were simultaneously acquired. Very positive effects of the elevation of tumble levels on combustion speed were observed. The possibility of stratifying the mixture was assessed. An excellent correlation was observed between local equivalence ratio, and early heat release and total burn duration. With highly stratified gasoline distributions, an improvement of combustion behaviour was obtained when ignition was in the richer region. By combining high tumble level and strong gasoline stratification, it was possible to improve remarkably initiation and propagation speeds while reducing cyclic variations, especially in the case of lean or very lean combustion.