Relative reactivities of the isomeric butanols and ethanol in an ignition quality tester

Ignition quality tester (IQT) derived cetane numbers (DCNs) of binary blends of each individual alcohol (1-, 2-, iso-, and t-butanol and ethanol) with each second component (n-heptane and a real distillate fuel) have been measured to explore the autoignition behavior of these mixtures. This study pays particular attention to the effect of physical property variation within and among families of mixtures on their apparent reactivities. The relative reactivities of these blends are dominated by chemical kinetics, while blend-specific physical properties affect relative ignitability only slightly. The results firmly support DCN measurement as a means of characterizing mechanistic ignition chemistry behaviors among fuels and their blends. Surprisingly, t-butanol, which has been shown in other studies to be the least reactive pure C₄ alcohol, shows the least suppression of reactivity when blended with heptane or diesel fuel for most mixture fractions. This result is related to the lack of easily abstractable H atoms in t-butanol, relative to the other alcohols investigated, an explanation hitherto applied only to pure component butanol reactivity. Measured DCN values are shown to fit well a one-parameter cetane number blending model. Predictions from this model show that up to several percent of the considered alcohols can be blended into diesel-like fuels without significant deterioration of the cetane number.