Chemometric analysis of a detailed chemical reaction mechanism for methane oxidation

A widely used detailed reaction mechanism for methane oxidation (Gas Research Institute (GRI) mechanism 2.11) has been analysed, in order to evaluate if reactions were to be added to the mechanism. This mechanism consists of 279 reversible elementary reactions between 48 different species, each with a temperature dependence described by a modified Arrhenius expression. The mechanism was transformed to 558 irreversible reactions, and the rate constants were analysed at a fixed temperature, to reduce the complexity of the analysis. A partial least squares (PLS) model was generated, which estimated reaction rate constants as a function of a reaction descriptor vector. This vector characterized the different chemical bonds in the reactants and products of a chemical reaction. The model was validated through full cross validation. The original mechanism was unable to correctly predict oxidation of methane in a natural gas engine exhaust manifold: Oxidation of 2300 ppm methane in the presence of 300 ppm NO, 9% oxygen and 2% water. Therefore, these conditions were used for evaluation of the reaction mechanism. The potential reactions for expanding the mechanism were selected among reactions with one or two reactants and one or two products. A stepwise analysis combining rate of production (ROP) analysis with sensitivity analysis was used to reduce 2138 potential elementary reactions to nine important reactions, which were added to the mechanism. The analysis was based on PLS estimates of the reaction rate constants, but in the final model, Literature values were included where available. This modification of the mechanism improved model predictions. (C) 1998 Elsevier Science B.V. All rights reserved.