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HCCI
It is a form ofinternal combustion in which well-mixedfuel andoxidizer (typically air) arecompressed to the point of auto-ignition. As in other forms ofcombustion, thisexothermicreaction releases chemical energy into a sensible form that can be transformed in an engineintowork and heat.
Introduction
HCCI has characteristics of the two most popular forms of combustion used in SI engines:homogeneous charge spark ignition (gasoline engines) and CI engines: stratified chargecompression ignition (diesel engines). As in homogeneous charge spark ignition, the fuel andoxidizer are mixed together. However, rather than using an electric discharge to ignite a portionof the mixture, the density and temperature of the mixture are raised by compression until theentire mixture reacts spontaneously. Stratified charge compression ignition also relies ontemperature and density increase resulting from compression, but combustion occurs at theboundary 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 whichmakes the fuel/air mixture burn nearly simultaneously. There is no direct initiator of combustion.This makes the process inherently challenging tocontrol. However, with advances inmicroprocessors and a physical understanding of the ignition process, HCCI can be controlledto achievegasoline engine-like emissions along withdiesel engine-like efficiency. In fact, HCCIengines have been shown to achieve extremely low levels of Nitrogen oxide emissions (NO
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