Reduced kinetic model for complex turbulent $n$-heptane flame simulations

In large-scale turbulent flame simulations, the exploitation of detailed chemistry and transport models often necessitates expensive memory and CPU requirements. To maintain the practicality and flexibility of such simulations, the combustion chemistry is commonly represented by reduced reaction mechanisms. The present paper describes the development of such a reduced short kinetic scheme for high-temperature oxidation of $n$-heptane suitable for application in complex turbulent flame simulations. Through a combination of the directed relation graph and quasi-steady state approximation methodologies, a skeletal 65-species kinetic model is formally reduced down to a 25-species derivative suitable for atmospheric lean to stoichiometric conditions. Further removal of appropriate reactions and species is facilitated by using the reaction path flux analysis, yielding a short chemical scheme of 25 species and 69 reactions. Particular attention is given to avoid addition of lumped reactions (for all isomer compounds) and artificial kinetic rates expressed as nonlinear algebraic combinations of excluded elementary steps. In addition, most of the original radical reaction pathways are duly preserved, and an adequate number of intermediate lighter-chain hydrocarbon species is represented in the reduced scheme to ensure a proper breakdown and oxidation of the main hydrocarbon. A series of 0D and 1D propagating and counterflowing premixed flames and axisymmetric coflowing laminar jet flames are computed throughout an iterative validation procedure. Complementary computations with the 65-species base scheme, as well as available experimental data are exploited for the assessment of the optimization effort. The comparisons demonstrate that the derived scheme ensures satisfactory agreement with these data over the investigated parameter space.