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Homogeneous Charge Compression Ignition (HCCI)
● HCCI is an alternative piston-engine combustion process that can provide efficiencies as high as compression-ignition, direct-injection (CIDI) engines (an advanced version of the commonly known diesel engine) while, unlike CIDI engines, producing ultra-low oxides of nitrogen (NOx) and particulate matter (PM) emissions.
WORKING PRINCIPLE OF HCCI
Homogenous charge is drawn in to the cylinder during suction and compress to high enough temperature to achieve spontaneous ignition of the charge.
After Combustion initiation the temperature rapidly increases and whole fuel burn simultaneously.
As whole mixture burns simultaneously and no flame propagation, combustion temp can be controlled less than 700° Centigrade and thus NOx formation is avoided.
Advantages of HCCI:
● HCCI engines are more efficient thus eliminating of throttling losses, the use of high compression ratios, and a shorter combustion duration.
● HCCI engines also have lower engine-out NOx than SI engines.
● Lower emissions of PM and Nox
● Because flame propagation is not required, dilution levels can be much higher than the levels tolerated by either SI or CIDI engines.
● The combustion duration in HCCI engines is much shorter than in CIDI engines since
it is not limited by the rate of fuel/air mixing. This leads to higher efficiency.
● HCCI engines may be lower cost than CIDI engines since they would likely use lower-pressure fuel-injection equipment.
Challenges of HCCI:
● Controlling Ignition Timing over a Range of Speeds and Loads.
● Extending the Operating Range to High Loads.
● Cold-Start Capability.
● Hydrocarbon and Carbon Monoxide Emissions.
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