Detonation formation in H-2-O-2/He/Ar mixtures at elevated initial pressures

In this paper the formation of detonation in H-2-O-2/He/Ar mixtures at elev ated initial pressures was investigated in an initiation tube for a detonat ion driver with an exploding wire as the ignition source. In most experimen ts the detonation wave was formed by a DDT process in which a reactive shoc k wave accelerates behind the leading shock wave and eventually leads to th e onset of detonation. The onset position was found to be at the leading sh ock wave or behind it. Only in very sensitive mixtures at high initial pres sure the direct initiation of detonation was observed. The influence of ign ition energy, initial pressure and composition on the detonation induction distance was determined. The results show that the detonation induction dis tance increases with the decrease of ignition energy and initial pressure a nd 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 %; respectiv ely, and the upper limits for helium and argon in stoichiometric H-2-O-2 mi xtures are 40 % and 36 %, respectively. High pressure peaks generated by th e DDT process were measured, especially in mixtures near the DDT limits. St atistical results show that such peak pressures can be up to 6 times of the CJ-pressures.