A new concept for high efficiency two-stroke cycle spark-ignition engines has been developed. The installation of the IFP-developed pneumatic fuel injection process in a two-stroke engine allows the introduction of the fuel separately from the scavenging air, in order to minimize fuel shortcircuiting. The process does not require an external air pump since the compressed air used to atomize the fuel is supplied at no expense by the crankcase. The premixed charge is delivered directly into the cylinder with a high spray quality, its stratification for the optimization of combustion is controlled by a valve. This process, therefore, provides the advantages of the direct injection but uses commercially available gasoline injectors.A single-cylinder engine has been developed first to verify the potential of the process. A very large area of fuel isoconsumptions below 260 g/kWh (0.43 Ib/hp-h) and consequently low unburned hydrocarbons emissions have been obtained with this new engine rated at a specific power of 50 kW/liter (67 hp/l) of displacement.