ABSRACT
HCCI has characteristics of the two most popular
forms of combustion used in IC engines: homogeneous charge spark ignition
(gasoline engines) and stratified charge compression ignition (diesel engines).
As in homogeneous charge spark ignition, the fuel and oxidizer are mixed
together. However, rather than using an electric discharge to ignite a portion
of the mixture, the concentration and temperature of the mixture are raised by
compression until the entire mixture reacts spontaneously. Stratified charge
compression ignition also relies on temperature increase and concentration
resulting from compression, but combustion occurs at the boundary of fuel-air
mixing, caused by an injection event, to initiate combustion.
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 aftertreatment 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.
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