Autoignition of n-Butane/lsobutane Blends in a Knock Research Engine

Experiments were conducted using a single cylinder, spark ignition research engine to examine the effect of the branched chain alkane isobutane (RON 102) on the autoignition chemistry of straight chain n-butane (RON 94), Isobutane was added in increasing quantities from 10 to 48% by volume. Measurement of cylinder pressure and the analysis of end gas species were used as diagnostics to determine the knock point and ascertain the end gas reactivity. Increasing the amount of isobutane suppressed the chemical reactivity, decreased the knock intensity, and delayed the time to autoignition. Examination of the chemical species in the end gas suggests that (i) low temperature chemical reactions are occurring; and (ii) increasing the amounts of isobutane in the fuel mixture leads to higher yields of propene and chain terminating methyl radicals.