Detonation formation in H $_2$-O $_2$/He/Ar mixtures at elevated initial pressures

Abstract.

In this paper the formation of detonation in H$_2$-O$_2$/He/Ar mixtures at elevated initial pressures was investigated in an initiation tube for a detonation driver with an exploding wire as the ignition source. In most experiments the detonation wave was formed by a DDT process in which a reactive shock wave accelerates behind the leading shock wave and eventually leads to the onset of detonation. The onset position was found to be at the leading shock wave or behind it. Only in very sensitive mixtures at high initial pressure the direct initiation of detonation was observed. The influence of ignition energy, initial pressure and composition on the detonation induction distance was determined. The results show that the detonation induction distance increases with the decrease of ignition energy and initial pressure and with the increase of the mole fraction of helium or argon. With the same mole fraction, argon increases the induction distance more than helium. In the facility utilized the DDT upper and lower limits of hydrogen in H$_2$-O$_2$ mixtures are in the ranges from 36 to 40 % and from 78 to 82 %, respectively, and the upper limits for helium and argon in stoichiometric H$_2$-O$_2$ mixtures are 40 % and 36 %, respectively. High pressure peaks generated by the DDT process were measured, especially in mixtures near the DDT limits. Statistical results show that such peak pressures can be up to 6 times of the CJ-pressures.