Reduced Chemical Kinetic Mechanisms for Hydrocarbon Fuels

Several reduced chemical kinetic mechanisms for combustion of ethylene and nheptane have been generated using CARM (Computer Aided Reduction Method), a computer program that automates the mechanism-reduction process. The method uses a set of input test problems to rank species by the error introduced by assuming they are in quasi-steady state. The reduced mechanisms have been compared to detailed chemistry calculations in simple homogeneous reactors and experiments. Reduced mechanisms for combustion of ethylene having as few as 10 species were found to give reasonable agreement with detailed chemistry over a range of stoichiometries. Much better agreement with detailed chemistry was found for ethylene ignition delay when the reduced mechanism was tuned through selection of input test problems. The performance of reduced mechanisms derived from a large detailed mechanism for n-heptane was compared to results from reduced mechanisms derived from a smaller semi-empirical mechanism. The semi-empirical mechanism was clearly advantageous as a starting point for reduction for ignition delay, but the differences were not as notable for perfectlystirred-reactor (PSR) calculations. Reduced mechanisms with as few as 12 species gave excellent results for n-heptane/air PSR calculations but 16-25 or more species are needed to simulate n-heptane ignition delay.