Forming a stratified charge in a direct-injection spark-ignition i.c. engine

摘要

A stratified charge is formed in a direct injection engine by injecting fuel at a predetermined velocity, a predetermined droplet size, and forming the injected fuel with a hollow cone (50) having a predetermined initial cone angle. The injected fuel thereby shallowly penetrates the combustion chamber (24) so as to float therein to reduce wall-wetting and subsequent soot formation. A substantially flat top piston (16) forms the injected fuel into a ball-shaped kernel (52) during a compression stroke of the engine. The ball-shaped kernel (52) remains substantially unmixed with the inducted air, thereby producing the stratified charge. The continued motion of the piston (16) causes the ball-shaped kernel to move toward the spark plug (30) for ignition. The injection velocity (axial) may be 9 to 12.5 m/s, the droplet size may be 8 to 10 Ám and the initial cone angle may be 80 to 100 degrees.