Automatically simplified chemical kinetics and molecular transport and its applications in premixed and non-premixed laminar flame calculations

Abstract

Among many other methods for simplifying chemical kinetics for laminar and turbulent flame calculations, the method of intrinsic low-dimensional manifolds (ILDM) has shown to be an efficient tool for the development of reduced kinetic schemes. Based on a numerical analysis, it identifies and decouples the fast relaxing timescales of the chemical system. The results, for example, the thermokinetic state of the system or the reaction rates, are then stored in terms of a small number of parameters (mixture fraction, reaction progress variables) for subsequent use in reacting flow calculations. Furthermore, together with the reduced mechanism, information about the coupling of the chemical kinetics with the physical processes (molecular transport, turbulent mixing) is obtained. In this paper, we present a method that allows an efficient implementation of the ILDM method in flame calculations and overcomes several problems that had been discussed in previous work. It is based on three ingredients: A robust numerical method to calculate the ILDM, a storage scheme that allows an easy implementation in CFD codes, and a model for the coupling of the chemical kinetics with transport processes. In this way, not only the chemistry can be calculated beforehand but also a reduced set of diffusion coefficients. The method is verified by simulations of laminar syngas-air flames with an emphasis on the non-premixed case.