Comparison of automatic reduction procedures for ignition chemistry

In this paper, we present a comparison between the reduced mechanisms obtained through a computational singular perturbation method (CSP) and the reduced mechanisms obtained through a lifetime analysis based only on the diagonal elements of the Jacobian matrix and a species sensitivity The two methods are used for the analysis of autoignition, which is an interesting test situation because of the sensitivity of ignition to the radical pool and the smaller range of timescales expected. It is found that the steady-state species selected by the two methods are in good agreement. The mechanisms are reduced to a 10-step mechanism when CSP is applied and an 11-step mechanism in the case of the simpler lifetime analysis. Both mechanisms are compared with the detailed mechanism and experimental data and are found to reproduce the physical and chemical parameters very well. This shows that for a large part of the timescale range, the system is close to linear. The comparison shows the advantage of the CSP method as being somewhat more accurate. However, the simpler lifetime analysis is of sufficient accuracy and of more convenience when applied to a system requiring a considerable reduction in computational time, as is the case when applying online reduction.