Homogeneous Charge Compression Ignition

Homogeneous charge compression ignition, or HCCI, is a form of internal combustion in which a well-mixed fuel and oxidizer, typically air, are compressed to the point of auto-ignition, and as in other forms of combustion the resulting exothermic reaction produces heat that can be transformed into work in a heat engine. HCCI combines characteristics of conventional gasoline engines, which combine a homogeneous charge with spark ignition, and modern direct-injection diesel engines, which combine a stratified charge with compression ignition; like a spark-ignition engine, HCCI injects fuel during the intake stroke, but rather than using a spark to ignite part of the mixture, it raises density and temperature through compression until the entire mixture reacts spontaneously. Controlling HCCI requires microprocessor control and a physical understanding of the ignition process, and the technology can achieve gasoline engine-like emissions with diesel engine-like efficiency, including extremely low oxides of nitrogen without a catalytic converter, though unburnt hydrocarbons and carbon monoxide still require treatment to meet emissions regulations.