A numerical study of planar detonations.

Abstract

A one dimensional numerical study on the build-up and propagation of planar detonation waves in H2 and Air combustibles mixtures is presented. To describe the motion of a traveling detonation the unsteady Euler equations coupled with source terms to account for a finite rate chemical activity, are used. The algorithm for computing the numerical hyperbolic fluxes is based on the Harten-Yee TVD scheme. Since the source terms lead to stiff differential equations, an implicit treatment of these terms is implemented. The computer solver works with 13 chemical species and 33 different one step reactions of a H2 - O2 - N2 combustion mechanism. The detonation process is initiated via the energy provided by an igniter made of hot and high pressure helium which acts as a driver of a shock tube driving through a combustible mixture a blast (or strong shock), accompanied by exothermic chemical changes. It is shown that for each equivalence ratio of the combustible mixture, the detonation can only be triggered if the igniter energy deposition is equal or exceeds a computed minimum value. When the igniter energy deposition is less than this minimum, the combustion zone decouples from the blast wave. This blast, as it travels downstream becomes weaker and no longer induces chemical reactions across it, however, a chemical activity still remains being now started by a reaction front located at some distance behind the leading wave. Finally, a particular way of generating an overdriven detonations is considered.