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. It makes the structure of the whole fuel system simple and is of great significance for development and application of small two-stroke spark-ignition engine.
The basic idea and principle of DIC are described in the paper. Test results on a 30cm3 modified engine are presented, including characteristics of fuel supply and engine's performance comparison with carburetor engine.