Humidity compensated charge density control for an internal combustion engine

Apparatus and methods for determining a desired charge density for an engine (12) having an inlet air pathway (22). A first characteristic indicative of an engine speed of the engine (12) is determined. A second characteristic indicative of a load on the engine (12) is determined. A third characteristic indicative of a humidity of air in the inlet air pathway (22). A value indicative of a desired charge density of a combustion mixture for the engine (12) is determined as a function of the first, second, and third characteristics.