Pre-evaporated Stratified Injection (PSI) is a low-cost mechanical fuel injection system which dramatically reduces exhaust gas emissions in small IC engines. In two-stroke engines, this is achieved by incorporating a mechanically driven coaxial air-fuel injector within the upper half of an engine's main piston. In four stroke engines the injector cylinder is located in the cylinder head with the injector piston driven by the valve cam. In both configurations, the relative motion of the injector piston draws a rich air-fuel mixture from the carburetor, captures and compresses for sufficient time under most operating conditions to substantially evaporate fuel before direct injection into the cylinder.
This technology allows for stratified charge combustion without wall wetting (spray impingement), leading to lower hydrocarbon (HC) and carbon monoxide (CO) emissions in four-stroke engines, and for the first time allowing low cost, small two-stroke engines to meet non-handheld emission standards.