Analysis of a systematical reduction technique

The systematical reduction of chemical reaction mechanisms is studied by using a first-order sensitivity analysis. Two important aspects in the reduction strategy are considered here: the identification of the steady-state species and the truncation of the resulting algebraic equations for these species. The analysis is applied to the four-step model of Peters et al. based on the skeletal mechanism for lean methane-air combustion. The identification of the steady-state species with the sensitity analysis confirms the choices made bySeshdri and Peters. Even more, with the analysis it is predicted that the differences in burning velocity between the four-step mechanism and the skeletal mechanism can be reduced, by taking CH3 not in steady state, effectively yielding a five-step model. The effect of truncation is also investigated, and the differences of several approximations in the fourstep model are studied systematically. With the sensitivity analysis introduced here, we are able to predict the qualitative effect of truncation. Applied to the truncation of the expression for OH mole fraction, it shows that the performance of the four-step model can be improved considerably if another reaction is included in this expression. The computations of the burning velocity with this extended OH expression confirm the prediction. It can be concluded that the presented sensitivity analyses can be used effectively to analyze and determine systematically reduced mechanisms