The criticality of detonation transmission across hydrogen interfaces with non-uniform dilution

Abstract

The present work considers the transmission of a detonation wave in hydrogen–oxygen from one gas to another where there is a different concentration of some inert diluent—inert gases nitrogen and argon were considered in this study. The problem was first addressed analytically. A classic gasdynamic wave analysis was performed to calculate the shock which is transmitted into the downstream reactive gas. Then, a simple criterion for autoignition was defined. This criterion is based on the second explosion limit of hydrogen, where chain-branching and chain-terminating reactions compete. It was predicted that the transmission of the detonation wave from one gas to another would fail under certain conditions. One- and two-dimensional computational simulations based on the reactive Euler equations were then performed. The simulations give results that are overall consistent with analytic predictions. The most noteworthy result was that, for a sufficiently diluted upstream gas, adding more diluent to the downstream mixture tended to improve the ability of the detonation wave to successfully transmit, rather than suppressing it. This seemingly counter-intuitive behavior was attributed to the fact that adding diluent to the downstream gas increases its density (and shock impedance), resulting in a stronger transmitted shock wave, which is more prone to re-initiate a detonation wave. In addition for the case of argon dilution, additional argon results in a lower mixture heat capacity and higher specific heat ratio, ultimately resulting in higher post-shock temperatures. In essence, the wave behavior with the diluent mixtures considered in this study was found to be dominated by the aforementioned gasdynamic effects; however, for other diluents, competing kinetic effects may play a role. In addition, in the limit of an extremely diluted downstream gas, the successful transmission predicted by the analysis loses its practical relevance due to the assumption of an inviscid and adiabatic flow.

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ORCID for Ralf Deiterding: orcid.org/0000-0003-4776-8183

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