US Patent 7363911 Humidity-based combustion control in a multiple combustion mode engine

A system and method for controlling operation of a gasoline internal combustion engine capable of running in a spark ignition mode and a homogeneous charge compression ignition mode. The method and system implementation include determining humidity of air to be drawn into a combustion cylinder of the engine, and controlling an operating parameter of the engine that affects the homogeneous charge compression ignition mode of operation.