Caractéristiques des détonations instables près des limites d'extinction et mécanismes de compétition de la détonation galopante

Abstract

We present the results of a study aimed at characterizing the unsteady propagation of near extinction limit gaseous detonations. Experiments were performed in a circular detonation tube with a stoichiometric propane-oxygen mixture, diluted or not with argon or helium. Other results from Lee et al. (1995) study were also used to characterize unstable detonations. The velocity of the combustion wave vs. position history is measured continuously with a microwave Doppler interferometer technique improved by Lee (1992) that uses a co-axial waveguide. Diagnostics also include piezo-electric pressure transducers and photodiodes to obtain respectively the shock front and the reaction zone evolutions. Four propagation regimes were identified: stable,"stuttering", galloping, and extinction. For each mode, we determined the limiting initial pressures and the limiting dilution for the appearance of the galloping detonation. For the undiluted mixture, it was found that features of the galloping detonation were independent from the initiation conditions, apart from a delay between the initiation of the detonation and the first reinitiation peak. Influence of dilution and diluent on the onset of the galloping regime is also discussed with computed induction times. A simple analytical model to account for the coupling between the reaction zone and the shock front of the detonation was elaborated. This model is validated for two analytical known results. En [i.e. In] particular, it is found that, under certain conditions, shock deceleration can lead to reaction zone acceleration and vice versa. This might explain the cyclic behavior of galloping detonation waves.