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A new type direct-injection stratified-charge combustion system for gasoline engines is developed by the authors. In the system, gasoline is directly injected into a cylinder near the end of compression stroke by a nozzle with the injection holes unequally spaced on its tip. The angles among sprays in the vicinity of spark plug are small, and become larger downstream along the direction of air swirl motion. Therefore the circularly concentration stratification form rich to lean of air-fuel mixture is mechanically realized to ensure the reliable ignition and smooth flame propagation in the inhomogeneous mixture after sparking. The selection of main parameters of the system, the performance and the combustion characteristics of the engine after optimization of those parameters are introduced in detail in this paper.

Proper fuel supply system is the crux to realize the stratified scavenging for small type of two-stroke gasoline engine. A simple and effective diaphragm fuel injection system (DFI) is developed in the paper, which mainly consists of diaphragm pump and injector, the DFI utilizes the crankcase pressure which reflects the inlet flow rate to meter and inject fuel. As low short-circuit at low load operation, stratified scavenging seems not necessary, so the conventional carburetor is preserved to function at low load. This makes the whole fuel system simple and effective. The paper describes the operation principle of the DFI, and results of test on a 30cm3 modified engine are also presented, including the performance of fuel supply and contrast of complex engine performance with the original carbureted engine.