Controlled Auto-Ignition (CAI) and Homogeneous Charge Compression
Ignition (HCCI) combustion are radically different from the conventional
spark ignition (SI) combustion in a gasoline engine and compression ignition
(CI) diffusion combustion in a diesel engine. The combination of a diluted
and premixed fuel and air mixture with multiple ignition sites throughout the
combustion chamber eliminates the high combustion temperature zones and
prevents the production of soot particles, hence producing ultra-low NOx
and particulate emissions. The use of lean, or more often diluted, air/fuel
mixture with recycled burned gases permits unthrottled operation of a CAI/
HCCI gasoline engine, thus yielding higher engine efficiency and better fuel
economy than SI combustion. Therefore, CAI/HCCI combustion represents
for the first time a combustion technology that can simultaneously reduce
both NOx and particulate emissions from a diesel engine and has the capability
of achieving simultaneous reduction in fuel consumption and NOx emissions
from a gasoline engine.