Visualization of fuel impingement on the piston top in a DISI engine

An experimental research was performed to investigate the macro- and micro-scopic behavior of fuel spray impingement and atomization characteristics of a multi-hole injectors used in direct injection spark ignition (DISI) engines. In a DISI engines, soot caused by pool combustion of fuel film at piston top caused by fuel spray impingement is one of the problems under cold start condition. It is necessary to investigate the spray impingement phenomena to reduce HC and PM emissions. Spray impingement strongly affects the mixture formation inside a cylinder. In this study, spray impingements are visualized with a high-speed camera in a Rapid Compression Expansion Machine (RCEM) attached to the piston top. High-speed visualization of liquid film on the top of piston can be carried out using a frosted glass. Luminous flame due to pool combustion on the piston top can be visualized using a side-view through a cylinder head window. Moreover microscopic high-speed visualization of fuel spray impingement on a surface on the flat plate in Constant-Volume Vessel (CVV) were carried out using high-speed video camera with 125kfps. Using the imaging results, as injection pressure rises, Weber number increases which decides whether particles deposit, rebound or splash; the imaging results are used to identify those behaviors.