Orbital engine - Definition

An Orbital engine is a type of internal combustion engine, featuring rotary rather than reciprocating motion of its internal parts. It differs from the conceptually similar Wankel engine by using a shaped rotor that rolls around the interior of the engine, rather than having a trilobular rotor that spins "in place". The advantage is that there is no high-speed contact area with the engine walls, unlike in the Wankel where edge wear is an ongoing engineering problem.

The orbital engine was invented by Ralph Sarich, an engineer from Perth, Australia, in 1972. He worked on the concept for years, but the original concept has never resulted a production engine. The company has since given up work on the design.

However, a related piece of the design, an air-assisted direct fuel injection system, continues to be developed by the company. The system allows for stratified charge injection under light loads, but can switch to traditional fuel injection operation (the "air assist") when more power is needed and normal stratified charge designs have problems. The injection system can be applied to both four stroke and two-stroke engines.