The chemistry of pre-ignition of n-pentane and 1-pentene

The pre-autoignition chemistry of n-pentane and 1-pentene was studied by ra pid compression in the low temperature range (600-900 K). The pressure trac es, light emissions, intensities of cool flames, autoignition delays, and h ydrocarbon conversions before final ignition indicate that there are simila rities of behavior, but a lower reactivity of 1-pentene over the whole temp erature range. Chemical analysis of the stable intermediate species after t he cool flame; but before final ignition, shows marked differences in selec tivities for O-heterocycles and aldehydes. Relatively high amounts of propy loxirane and butanal in the oxidation of 1-pentene suggest additions of oxi dizing radicals to the double bond. The classical low temperature peroxidat ion scheme of alkanes can be applied, not only to n-pentane, but also to 1- pentene, if the higher reactivity of the allylic hydrogens and direct addit ion of OH and HO2 radicals are taken into account. Some peroxy radicals are common to both fuels and are responsible for their similar features of pre -autoignition chemistry. However, oxidation of 1-pentene is still deeply ma rked by the presence of an olefinic bond. (C) 1999 by The Combustion Instit ute.