Preliminary Investigation of A Diffusing-Oriented Spray Stratified Combustion System for DI Gasoline Engines

A new diffusing-oriented spray stratified combustion system for direct injection gasoline engines is proposed in this study. A reflector with multi-impingement wall head attached ahead of multi-hole injector nozzle is used in this system as a strategy of breaking up the fuel spray and directing it in a desired direction to form a perfect atomization and stratification of fuel air mixture. A comparatively rich fuel-air mixture is always formed over a wide range of engine operation conditions in the vicinity of spark plug due to the fuel spray oriented by the special surface shape of impingement wall, and the finely atomized fuel spray is formed in the other areas of combustion chamber due to the impacting of fuel spray against the impingement wall. Therefore, it is possible to achieve stable and fast burn of lean fuel air mixture.

The combustion system is preliminary investigated on a single cylinder four-stroke DI gasoline engine which is shifted from a DI diesel engine. The effects of main parameters of the system, such as location and electrode height of spark plug, fuel injection pressure, design of reflector, intake swirl and fuel injection timing, on engine performances are assessed on condition that the engine operates without throttling. Especially, The effects of intake swirl and fuel injection timing on combustion & emission characteristics at middle & light load conditions are investigated in detail. Furthermore, the effects of two types of fuel spray structure oriented by different reflectors on mixture formation and combustion process are discussed too.