Comparative IQT™ ignition delay times of the isomeric butanols

Ignition Quality Tester (IQT)™ derived cetane numbers (DCNs) of blends of n-, s-, i-, and tbutanols and ethanol with n-heptane have been measured using the ASTM D6890-07a protocol. Although the IQT ignition delays are not purely kinetic, instead involving the coupled processes of spray injection, evaporation, mixing, and ignition chemistry, trends in DCNs have been shown to correlate to oxidation kinetics governed by molecular structure. Co-oxidation with the more reactive gasoline primary reference fuel, n-heptane, further elucidates application-relevant blending behaviors, relevant in this case to fuel oils. For the n-, s-, and i-butanols, results for each blend series indicate DCNs generally trending with the relative reactivities of the pure isomeric butanols at lower oxidation temperatures. Surprisingly, t-butanol, which has been shown in other studies to be the least reactive butanol as a pure component, shows the highest blend reactivity at comparable mixture fractions. This result is explained in a discussion of alcohol/heptane blending kinetics, and is related to the lack of easily abstractable H atoms in positions α to the OH group in t-butanol.