Development of adaptive kinetics for application in combustion systems

In this paper, an automatic method for reducing chemical mechanisms during run time based on the quasi-steady-state assumption (ASSA) is presented. The method uses a lifetime analysis of the chemical species which can be set to steady state according to a ranking procedure. Steady-state species concentrations are computed by algebraic rather than differential equations, thus yielding a significant reduction in the computational effort. In contrast to previous reduction schemes in which chemical species were selected only when they were in steady state throughout the whole process, the present method allows for species to be selected at each operating point separately generating an adaptive chemical kinetics scheme. The mechanism can change during the simulation run. This ensures that the optimal reduced mechanism is used at each time step leading to a very efficient and accurate procedure. The method is used for calculations of a natural gas fueled engine operating under homogeneous charge compression ignition (hCCI) conditions. We discuss criteria for selecting steady-state species and the influence of these criteria on the results, such as concentration profiles and temperature. A full mechanism with 53 species can be reduced to a minimun of 14 non-steady-state species while still reproducing the physical behavior of the detailed mechanism with good agreement