This paper outlines updates made to a method for chemical kinetic model reduction. The original method used the directed relation graph with error propagation to generate a skeletal model, and the solution mapping method to tune the remaining rate constants to match reduced model responses to those of the original detailed model. In the current work, skeletal model generation is performed using a path flux analysis, and changes have been made to the optimization process, by including an intermediate steepest-descent method in order to make the optimization process more efficient. The new method is then applied to the reduction of a methane-air model for two different sets of initial conditions. Results show rapid optimization of the model is possible as compared to previous work. Results for the optimized models also are able to predict the perfectly-stirred reactor response better than the optimized models generated using the older method. Nomenclature A i= preexponential constant for i th forward reaction rate constant b 0 = zero-order response function fit coefficient b p = first-order response function fit coefficients b p,q = second-order response function fit coefficients b p,q,s = third-order response function fit coefficients C A = consumption rate of species A C AB = consumption rate of species A to form species B E i = activation energy for i th forward reaction rate constant F i = correction term for i th forward reaction rate constant based on third body efficiencies, etc. f p = half-span of variation for the p th active parameter f = set of functions describing state of chemically reacting system g = set of differential equations describing time evolution of chemically reacting system I = number of reactions i = reaction index J = number of species j = species index k fi , k bi = forward and backward rate constants for i th reaction M = number of targets for optimization m = target index n = summation index P = number of active parameters for optimization P A = production rate of species A P AB = production rate of species A from species B p, q, s = active parameter indices R = universal gas constant r AB = interaction between species A and species B r ABT = temperature-averaged value of r AB S = sensitivity coefficient = laminar flame speed T = temperature t = reaction time t 50% = reaction time to achieve 50% of total temperature rise X p = factorial variable x j = concentration of j th species Y p = transformed factorial variable y = responses (composition, temperature, flame speed, critical times, etc.) in a chemically-reacting system α m = weighting factor for m th target in objective function β i = temperature exponent for i th forward reaction rate constant δ Bi = 1 if i th reaction contains species B; 0 otherwise η m = value of m th target in objective function ζ = vector of initial conditions θ = vector of parameters describing reacting system (rate constants, mass diffusivities, etc.) ν ij = signed stoichiometric coefficient of j th species in i th reaction ν′ ij , ν″ ij = forward and rever...
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