Experimental study of mixture formation on a DISI engine

Based on a horizontally opposed flat-four engine which was previously fuel-supplied by carburetor, a transparent optical engine bench equipped with low-pressure direct injection system was developed aiming at adopting the low-pressure DI system on the prototype engine. To make a good match between the combustion system and the DI system a decentralized-cavity piston was designed that formed a new kind of geometrical shape of the combustion chamber. Using high-speed photography technology the mixture formation process was filmed and different mixture formation patterns were analyzed and compared in conditions of different combustion chamber geometry. The results showed that the piston with decentralized cavity top surface can effectively conduct the fuel spray forming a vortex motion upward to the top of chamber that would subsequently form stratified mixture near the plugs, and it can effectively avoid wall-wetting phenomenon which was found in the original combustion system.