Reduced mechanisms for gasoline surrogates valid at engine conditions

Presented at 8th US National Combustion Meeting, Provo, Utah, USA, 19–22 May 2013.
A detailed mechanism for four-component gasoline surrogates, developed by Lawrence Livermore National Laboratory (LLNL), showed good agreement with experiments in engine-relevant conditions. However, with 1389 species and 5935 reversible reactions, the mechanism is far too large to use in practical engine simulations. Therefore, reduction of the mechanism was performed. First, the directed relation graph with error propagation and sensitivity analysis (DRGEPSA) method was used to generate skeletal mechanisms at varying levels of detail. This step produced significantly reduced skeletal mech- anisms, but those with tight error limits were still too sizable for practical use. Therefore, a second reduction step was employed, using the quasi-steady-state (QSS) approximation based on computational singular perturbation (CSP) analysis. The QSS species concentrations were solved analytically, rather than through an iterative solution approach. For error constraints of 10% and 30%, the final reduced mechanisms consist of 245 and 178 species, respectively. Both reduced mechanisms (and the corresponding skeletal mechanisms) were validated with homogeneous autoignition simulations over engine-relevant conditions, and both showed good agreement in predicting ignition delay.