Dual-mode (two-stroke/four-stroke) engine with controlled auto-ignition

摘要

An internal combustion engine is disclosed having exhaust 16 and intake 14 poppet valves in which the valve events relative to the rotation of the engine crankshaft are selectable such that the engine may be switched between a two-stroke mode and a four-stroke mode. In the invention, when the engine is operating under low load conditions in the two-stroke mode, the exhaust 16 and intake 14 valve events are timed to occur consecutively with little or no overlap between them. The resulting poor scavenging of burnt gases serves to retain a sufficient proportion of hot residual gases in the combustion chamber to support controlled auto-ignition.