Measurements of drop size distribution in a spray and mixture distribution in a direct injection SI engine

摘要

The air-fuel mixing process in the combustion chamber has a dominant effect on the subsequent processes of ignition, flame propagation and pollutant formation on DI-SI engine. The spray structure and characteristics are important to control the mixture formation. The in-cylinder airflow and combustion chamber shape also greatly influence the evaporation of the fuel spray and control the distributions of liquid and vapor fuel in the combustion chamber. The relationship between the in-cylinder flow and the fuel behavior is important to improve the thermal efficiency and to reduce the exhaust emission. Three-dimensional drop size and volume distributions in a fuel spray injected by a swirl type gasoline injector were measured by using a pulsed laser holographic method. The spray formed hollow-cone structure under 0.1-0.25Mpa of ambient pressure. The spray cone angle decreased and the drop volume distribution became to compact with elevated ambient pressure. Furthermore, in order to clarify the mixing process of DI-SI engine with the deep cavity combustion chamber in the piston, In-cylinder flow and fuel behaviors were measured by using a laser-induced fluorescence technique and particle image velocimetry. The fuel spray mainly impinged on the cavity bottom surface and the fuel flow toward the spark plug was formed by it's own momentum. The vapor fuel was distributed near the spark plug by the fuel flow rolled up along the cavity wall. After then, the vapor fuel was transported into the piston cavity by the swirl flow. A part of fuel drops, that lost momentum and left behind the spray, was evaporated and directly transported to the spark plug with the swirl flow. The stratified mixture was formed around the spark plug by this mixing process.