Homogeneous charge compression ignition

N.SACHIN

what is meant by Homogenous charge compression ignition(HCCI)?

Internal combustion engines fall into four categories based on how well air and fuel are mixed together in the combustion chamber and how the fuel is ignited :

• Gasoline engine
• Gasoline Direct Injection engine
• Diesel Engine
• HCCI engine

In HCCI engine, the best attributes of gasoline and diesel engines are combined. A premixed fuel-air charge undergoes tremendous compression until the fuel self-ignites. This is what happens in a photo-detonation engine, and because it employs a homogenous charge and compression ignition, it is often described as an HCCI engine. HCCI combustion results in virtually no emissions and superior fuel efficiency. This is because photo-detonation engines completely combust the fuel, leaving behind no hydrocarbons to be treated by a catalytic converter or simply expelled into the air.

The defining characteristic of HCCI is that the ignition occurs at several places at a time which makes the fuel/air mixture burn nearly simultaneously. There is no direct initiator of combustion. This makes the process inherently challenging to control. However, with advances in microprocessors and a physical understanding of the ignition process, HCCI can be controlled to achieve gasoline engine-like emissions along with diesel engine-like efficiency. In fact, HCCI engines have been shown to achieve extremely low levels of Nitrogen oxide emissions (NOx) without after treatment catalytic converter. The unburned hydrocarbon and carbon monoxide emissions are still high (due to lower peak temperatures), as in gasoline engines, and must still be treated to meet automotive emission regulations.
HCCI engines can operate using a variety of fuels.