Effect of Nitrogen Dilution on the characteristics of HCCI Combustion

Ignition delay timesand combustion times ofiso-octane/air mixture andnitrogendiluted/non-dilutedgasoline/air mixturewere measured by usinga rapid compression machine undertheconditionsequivalent to practical engines .The dilutionratioswere0,20 and 50% byexternalpercentage.For the case ofiso-octane,thepressurerangeis1.77 to 2.37 MPa, and temperaturerangeis732to1046K.Forthe case ofgasoline,the pressurerangeis 2.14 to2.45 MPa, and temperature rangeis659 to 1108 K.The results show the existence of two ignition regimes.In oneregime,mixture spontaneouslyignites at multiple points sequentiallyin the combustion chamber.Another regime yields reaction front formation and propagationinsidethe combustion chamber prior to multiple pointignition.Being diluted with nitrogen,HCCI combustion becomesslowand ignition delay time sbecome long inthe entire temperature range ,especiallyin NTC.For allthe nitrogen dilutionratios,the combustion time increasedin proportion to the ignition delay time .Combustion time can be related tothe difference of localignition delay time which is caused by local inhomogeneity of temperature.