US Patent 7431024 Method and operation of an engine

An engine is disclosed which may operate in a first operating state wherein a spark ignited fuel is ignited in a combustion chamber with an igniter and a second operating state wherein a compression ignited fuel is ignited in a combustion chamber with an igniter. A compression ratio in the combustion chamber being up to about eight to one. The engine may be a four-stroke engine. The engine may include a piston having a top portion with a recessed central portion.