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IGNITION TIME DELAY OF HYDROGEN-OXYGEN-DILUENT MIXTURES AT HIGH TEMPERATURES

1963; American Institute of Aeronautics and Astronautics; Volume: 1; Issue: 10 Linguagem: Inglês

10.2514/3.2049

1533-385X

J. A. Nicholls, T. C. Adamson, Rebecca Morrison,

Combustion and flame dynamics

The motivation for this study arose from experiments on standing detonation waves wherein the flame front was visibly separated from the shock front. This physical separation corresponds to the ignition time delay. A theoretical analysis of the ignition time delay zone for hydrogen-oxygen-diluent mixtures is presented herein. A reaction scheme consisting of nine reactions, which should be valid for temperatures above about 1100°K, is considered. Assuming the initial mole fractions of H2 and (>2 to be of order unity and taking advantage of inequalities that should be valid to at least 2000 °K, it is possible to integrate the differential equations representing the kinetics. Thus time dependent expressions for all radical and water vapor concentrations behind the shock wave are obtained. A characteristic time, based on the initial concentration of H2 and the fastest reaction rate constant, is introduced. For times much greater than this characteristic time, the equations reduce to very simple forms. In order to arrive at an explicit analytical expression for the ignition time delay, a value for the mole fraction of H, characteristic of this delay time, is introduced. It is found that the delay time is dependent on the temperature, pressure, composition, and reaction rate constant for the rate controlling reaction. There is weak dependence on the reaction rate constants for the initiation reactions. A brief comparison between this theory and some experimental results on standing detonation waves is presented and good agreement found. The theory is also in good agreement with available shock tube results.