Simplifying Chemical Kinetics Using Intrinsic Low-Dimensional Manifolds

Abstract

During the last years the interest in the numerical simulation of reacting flows has grown considerably. Numerical methods are available which allow to couple chemical kinetics with flow and molecular transport. However, the use of detailed physical and chemical models, involving more than 100 chemical species, is restricted to very simple flow configurations with very simple geometries, and models are required which simplify chemistry without sacrificing accuracy. As early as one hundred years ago Bodenstein observed that some chemical reactions are so fast that some chemical species in the reaction system are in a quasi-steady state. This observation has been the basis for practically all attempts to simplify the description of chemical reaction systems. We discuss a mathematical method, which can be used for the simplification of chemical kinetics. The method is simply based on local time scale analyses of chemical reaction systems. In this way the fast (and thus not rate limiting) chemical processes are identified and decoupled, and the chemistry can be described in terms of a small number of governing reaction progress variables. Examples for reacting flow calculations are shown and verify the approach.