Study of unsteady combustion processes controlled by detailed chemical kinetics

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

Our understanding of the fundamentals of combustion processes to large extent was heavily based on the use of a fairly simplified one-step Arrhenius kinetics model. However, the chemical mechanisms are an important factor significantly influencing the processes. The range of validity of simplified chemical schemes is necessary very limited. Furthermore, it became clear that the use of a one-step Arrhenius model may lead to only a very basic picture describing qualitatively a few major properties of the combustion phenomena with some poor accuracy if any, often rendering misinterpretation of a verity of combustion phenomena. Moreover, many important features of combustion can not be explained without account of the reactions chain nature. An accurate description of unsteady, transient combustion processes controlled by chemical kinetics requires knowledge of the detailed reaction mechanisms for correct reproducing combustion parameters in a wide range of pressures and temperatures. The availability of such models is essential for gaining scientific insight into the most fundamental combustion phenomena and it is an essential factor for design of efficient and reliable engines and for controlling emissions. 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 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.