Modeling Auto Ignition Transients in Reacting Diesel Jets

Abstract

The objective of the present work is to establish a framework to design simple Arrhenius mechanisms for simulation of diesel engine combustion. The goal is to predict autoignition over a selected range of temperature and equivalence ratio, at a significantly reduced computational cost, and to quantify the accuracy of the optimized mechanisms for a selected set of characteristics. The methodology is demonstrated for ndodecane oxidation by fitting the autoignition delay time predicted by a detailed reference mechanism to a twostep model mechanism. The preexponential factor and activation energy of the first reaction are modeled as functions of equivalence ratio and temperature and calibrated using Bayesian inference. This provides both the optimal parameter values and the related uncertainties over a defined envelope of temperatures, pressures, and equivalence ratios. Nonintrusive spectral projection (NISP) is then used to propagate the uncertainty through homogeneous autoignitions. A benefit of the method is that parametric uncertainties can be propagated in the same way through coupled reacting flow calculations using techniques such as large eddy simulation (LES) to quantify the impact of the chemical parameter uncertainty on simulation results.