Impact of thermochemistry on optimized kinetic model predictions: Auto-ignition of diethyl ether

Abstract

Diethyl ether (DEE) is considered a potential diesel substitute because of its advantageous properties, such as high cetane number and liquid state at ambient conditions. In the present study, an optimized kinetic model for auto-ignition of DEE is developed based on a mechanism from the literature (Sakai et al., 2017). By means of sensitivity and uncertainty analyses, the impact of kinetic and thermochemical parameters on model predictions is compared first. It is found that enthalpies of formation of the most sensitive species have an even larger impact on ignition delay times than the most sensitive reactions. This motivates the joint optimization of both thermochemical parameters and reaction rate constants within their respective uncertainty limits against the experimental targets. In addition to conventional model modification, which often only considers the rate coefficients of elementary reactions as uncertain, this study thus also takes the enthalpies of formation, standard entropies, and heat capacities of species into account, and calibrates the rate rules instead of elementary reactions, when needed. For comparison, a second model is developed by modifying rate coefficients alone. Both optimized models show good agreement with the experimental ignition delay times at low and high temperatures, with slightly improved predictions by the model with additionally optimized thermochemistry. However, modified model parameters and the resulting reaction fluxes at intermediate temperature exhibit notable differences between the two models, which highlights the effect of the shifted chemical equilibria of important reactions when the thermochemistry is optimized as well.