Abstract
We study the variability in the ignition delay time, tign, of n-butanol due to uncertainty in the enthalpies and entropies of the fuel and fuel radicals. A stoichiometric mixture reacting adiabatically at constant volume is considered, over a range of initial temperatures (700-10 00 K) and pressures (10-80 bar). We develop a thermodynamic class approach to account for the variability in the thermodynamic properties of species of interest, and to define associated uncertainty ranges. To gain insight into the impact of the variability of the thermodynamic properties of individual species, a brute force sensitivity analysis is first performed. The results show that large variations in tign are mainly due to perturbations in the enthalpies of six species belonging to two thermodynamic classes. A refined 1D analysis is then conducted of the uncertain enthalpies and entropies of these six species. In particular, a complex, nonmonotonic dependence of tign on species enthalpies is observed, highlighting potential limitations in extrapolating local sensitivity results. The 1D analysis also shows that uncertainties in species entropies have a weaker impact on the variability in tign than the species enthalpies. A global sensitivity analysis of the impact of thermodynamic class uncertainties is then performed, namely using surrogates constructed using an adaptive pseudo-spectral method. The results indicate that the variability of tign is dominated by uncertainties in the classes associated with peroxy and hydroperoxide radicals. Lastly, we perform a combined sensitivity analysis of uncertainty in kinetic rates and thermodynamic properties. In particular, the results indicate that uncertainties in thermodynamic properties can induce variabilities in ignition delay time that are as large as those associated with kinetic rate uncertainties. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.