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

TL;DR

This study investigates n-butanol autoignition at elevated pressures and various temperatures, revealing monotonic ignition delay decrease, reaction mechanism sensitivities, and highlighting the need for improved fuel decomposition data.

Contribution

The paper provides new experimental ignition delay data for n-butanol under specific conditions and analyzes the discrepancies with existing reaction mechanisms, emphasizing the importance of fuel decomposition pathways.

Findings

Ignition delay decreases with increasing temperature.

Simulation models do not accurately predict experimental delays.

Fuel decomposition rate uncertainties significantly affect model accuracy.

Abstract

Autoignition experiments for n-butanol have been performed using a heated rapid compression machine at compressed pressures of 15 and 30 bar, in the compressed temperature range of 675-925 K, and for equivalence ratios of 0.5, 1.0, and 2.0. Over the conditions studied, the ignition delay decreases monotonically as temperature increases, and the autoignition response exhibits single-stage characteristics. A non-linear fit to the experimental data is performed and the reactivity, in terms of the inverse of ignition delay, shows nearly second order dependence on the initial oxygen mole fraction and slightly greater than first order dependence on initial fuel mole fraction and compressed pressure. Experimentally measured ignition delays are also compared to simulations using several reaction mechanisms available in the literature. Agreement between simulated and experimental ignition delay is found to be unsatisfactory. Sensitivity analysis is performed on one recent mechanism and indicates that uncertainties in the rate coefficients of parent fuel decomposition reactions play a major role in causing the poor agreement. Path analysis of the fuel decomposition reactions supports this conclusion and also highlights the particular importance of certain pathways. Further experimental investigations of the fuel decomposition, including speciation measurements, are required.