Unsteady Combustion Processes Controlled by Detailed Chemical Kinetics

A correct description of unsteady, transient combustion processes controlled by chemical kinetics requires knowledge of the detailed chemical reaction mechanisms for reproducing combustion parameters in a wide range of pressures and temperatures. While models with fairly simplified gas-dynamics and a one-step Arrhenius kinetics in many cases makes possible to solve the problem in question in explicit analytical form, many important features of combustion can not be explained without account of the reactions chain nature, describing qualitatively a few major properties of the phenomena in question with some poor accuracy if any, often rendering misinterpretation of a verity of combustion phenomena. However, for modeling real three-dimensional and turbulent flows we have to use reduced chemical kinetic schemes, since the use of detailed reaction mechanisms consisting up to several hundreds species and thousands reactions is difficult or practically impossible to implement. In this lecture we consider the option of a reliable reduced chemical kinetic model for the proper understanding and interpretation of the unsteady combustion processes using hydrogen-oxygen combustion as a quintessential example of chain mechanisms in chemical kinetics. Specific topics covered several of the most fundamental unsteady combustion phenomena including: the regimes of combustion wave initiated by initial temperature non-uniformity; ignition of combustion regimes by the localized transient energy deposition; the spontaneous flame acceleration in tubes with no-slip walls; and the transition from slow combustion to detonation.