Autoigniton of n-Butanol at Low to Intermediate Temperature and Elevated Pressure

Autoignition delay experiments were performed for n-butanol in a heated rapid compression machine. Experiments were performed at pressures of 15 and 30 bar, in the temperature range 650-900 K, and for equivalence ratios of 0.5, 1.0, and 2.0. Additionally, the initial fuel mole fraction and initial oxygen mole fraction were varied independently to determine the influence of each on ignition delay. Over the conditions studied, it was found that the reactivity of the mixture increased as equivalence ratio, initial fuel mole fraction or initial oxygen mole fraction increased. A non-linear correlation to the experimental data was performed and showed nearly second order dependence on the initial oxygen mole fraction and nearly first order dependence on initial fuel mole fraction and compressed pressure. This was the first study of the ignition of n-butanol in this temperature and pressure range, and contributes to a better understanding of the chemistry of this fuel under the conditions relevant to practical devices. Experimentally measured ignition delays were compared against the ignition delay computed from several reaction mechanisms in the literature. The agreement between experiments and simulations was found to be unsatisfactory. Sensitivity analysis was performed and indicated that the uncertainties of the rate constants of parent fuel decomposition reactions play a major role in causing the poor agreement. Further path analysis of the fuel decomposition reactions supported this conclusion and highlighted the particular importance of certain pathways. Based on these results, it was concluded that further investigation of the fuel decomposition, including speciation measurements, will be required.