Influence of Coexisting Lower Alkanes on Low Temperature Oxidation Reaction of N-Heptane

In this study, the influence of coexisting lower alkanes on n-heptane HCCI combustion was experimentally investigated. The experiments to compare n-heptane/methane HCCI and n-heptane/propane HCCI were carried out using a single cylinder HCCI engine. As the result, the low temperature reaction was more suppressed and the start timing of high temperature oxidation reaction was delayed in n-heptane/propane HCCI than in n-heptane/methane HCCI, though the octane number of propane was lower than that of methane. This inconsistency with octane rating was explained by numerical analyses on the basis of detailed kinetic mechanism that propane consumed more OH radicals as the chain carrier of low temperature oxidation mechanism since propane had higher reactivity with OH radical than methane.