Sarich orbital engine

The Sarich orbital engine is a type of internal combustion engine invented in 1972 by Ralph Sarich, an engineer from Perth, Australia. Instead of reciprocating pistons it has a central prismatic piston that orbits the axis of the engine without rotating, which sets it apart from the similar Wankel engine and its spinning trilobular rotor. The compact arrangement of combustion chambers promised an engine about one third the size and weight of a conventional piston engine, with no high-speed contact between the piston and the walls, but the vanes that divide the chambers were hard to seal. The Orbital Engine Company, funded by partner BHP and Australian federal research grants, worked on the concept from 1972 until 1983 and had a 3.5 litre four-stroke engine performing as well as ordinary petrol engines of the day. Because commercialising the engine needed at least 100 million dollars of further development, the company instead adapted its patented injection and stratified combustion system to existing two-stroke and four-stroke engines, which became the Orbital Combustion Process.