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A simple diaphragm injection carburettor (DIC) is developed and patented by the author in the paper. The principle is that, as the function of the diaphragm mechanism, the pressure difference between two sides of the metering hole equals the vacuum of the Venturi, so it can realize the pressurized fuel metering, by the fuel metering hole and vacuum from the Venturi, and fuel injection. The fuel is injected into the feed port and mixes with the small fraction of air through the port, the main port of fresh air from the crankcase is injected to the cylinder with the scavenging organized so that a separating layer is created between the exhaust and feed port, it can substantially reduce short-circuit. According to the characteristics of low short-circuit at low delivery ratio, the low load fuel supply system of conventional carburettor is preserved and combined with DIC which functions at high load operation.

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.

Early Intake-Valve Closing (EIVC), which has been suggested to control the load of SI engines for a long time, is applied in this paper to control the load and the boost pressure of a turbocharged SI engine. Load control by means of EIVC reduces the pumping loss at the part load, and boost pressure control by means of EIVC eliminates the disadvantages of the conventional boost control system with wastegate and reduces the pumping loss at high speeds and loads. Another advantage of this control concept is the possibility to utilize the internal cooling effect of the charge when the intake-valve is closed before BDC. The lower compression temperature of the EIVC engine in comparison with the conventional engine is very helpful to reduce the tendency to knock and can be effectively utilized to improve the thermal efficiency.