Crankcase scavenged two-stroke engines

Abstract

A two-stroke engine of crankcase scavenged type includes a piston reciprocably mounted in a cylinder, an exhaust port, an inlet port arranged to supply combustion air to the crankcase and a transfer port comprising two or more transfer passages extending between the crankcase and the cylinder. The transfer port is arranged to open before the exhaust port closes whereby, in use, the cylinder is scavenged. Fuel metering means communicates with at least one but not all of the transfer passages and is arranged to supply fuel into the said transfer passage at a rate which is directly determined by the mass flow rate of air through the inlet port. The fuel metering means includes a metering valve connected to actuating means, which is arranged to modulate the valve in response to the mass flow rate of air through the inlet port and fuel supply means arranged to supply pressurised fuel continuously to the metering valve. The transfer passage includes a non-return valve arranged to prevent the flow of fuel from the transfer passage into the crankcase.