Combustion Control Technologies for Direct Injection SI Engine 960600
Novel combustion control technologies for the direct injection SI engine have been developed. By adopting up-right straight intake ports to generate air tumble, an electro-magnetic swirl injector to realize optimized spray dispersion and atomization and a compact piston cavity to maintain charge stratification, it has become possible to achieve super-lean stratified combustion for higher thermal efficiency under partial loads as well as homogeneous combustion to realize higher performance at full loads. At partial loads, fuel is injected into the piston cavity during the later stage of the compression stroke. Any fuel spray impinging on the cavity wall is directed to the spark plug. Tumbling air flow in the cavity also assists the conservation of the rich mixture zone around the spark plug. Stable combustion can be realized under a air fuel ratio exceeding 40. At higher loads, fuel is injected during the early stage of the intake stroke. Since air cooling by the latent heat of vaporization increases volumetric efficiency and reduces the octane number requirement, a high compression ratio of 12 to 1 can be adopted. As a result, engines utilizing these types of control technologies show a 10% increase in improved performance over conventional port injection engines.