Model Reduction for Combustion Chemistry

The description of chemically reacting systems leads very often to reaction mechanisms with far above hundred chemical species (and, therefore, to more than a hundred partial differential equations), which possibly react within more than a thousand of elementary reactions. These kinetic processes cover time scales from nanoseconds to seconds. Due to these scaling problems the detailed simulation of three-dimensional turbulent flows in practical systems using detailed kinetics is beyond the capacity of even today’s super-computers. Using simplified sub-models for the chemical kinetics is a way out of this problem. The question arising in mathematical modeling of reactive flows is then: how detailed, or down to which scale has the chemical reaction to be resolved in order to allow a reliable description of the entire process? The aim is the development of models, which should be as simple as possible in the sense of an efficient description, and also as detailed as necessary in the sense of reliability. In particular, an oversimplification of the coupling processes between chemical reaction and turbulent flow should be avoided by all means to allow a predictive character. This chapter describes different methodologies for the reduction of chemical mechanisms for subsequent use in reacting flow calculations.