An experimental, theoretical and kinetic modelling study on the reactivity of a lignin model compound anisole under engine-relevant conditions

Abstract

In this study, fundamental ignition delay time (IDT) experiments of anisole covering several compressed pressures (pc=1,2,4MPa) for stoichiometric (ϕ=1.0), lean (ϕ=0.5),and rich (ϕ=2.0) compositions at undiluted, fuel-in-air conditions to reflect application-relevant conditions, were investigated for the first time in the RCM. In addition, to increase the examinable range of temperatures and of IDTs, fundamental experiments in the shock tube (ST) covering the same compressed pressures and stoichiometric and lean conditions were conducted. Overall IDTs were measured in ranging from 0.07 to 274 ms. For all conditions an Arrhenius behavior was observed. Anisole showed lower reactivity than ethanol which is in accordance to the RON of both species. H-atom abstraction reactions on the methyl sidechain were calculated with a CBS-QB3 method. These rates were used in the model developed of this study. The calculated rates are generally lower compared to previously used rates in anisole models, especially for the H-atom abstraction by ȮH. The newly measured experimental data were used to validate a detailed chemical kinetic model. Further, literature available data (jet stirred reactor and flow reactor) were used to tighten the validation framework increasing the confidence in the mechanism. The newly developed model is capable of predicting the reactivity of anisole over the whole investigated RCM regime, the majority of the investigated ST regime and at the same time predicting JSR speciation measurements of available literature data. The analyses of model reveal the crucial role of the phenol sub-chemistry in the oxidation of anisole.