Propulsive Performances of Pulsed Detonations

Abstract

The propulsive potential of a reactive mixture that uses detonation as a combustion process is studied. An experimental set up is built up to determine the thrust and the impulse developed in single and multi-operating cycles by the detonation products of a reactive mixture contained in a cylindrical combustion chamber (CC). One end of the CC, called the thrust wall (TW), is closed and supports the thrust. The other end is open into atmosphere for the exhaust of the detonation products. The detailed flow features are experimentally investigated by means of pressure gauges inside the CC and in the immediate vicinity of open-ended of CC. The specific impulse Isp reached in our device, with C2H4 = 3 O2 as a detonative mixture, is about 200 s. The overpressure profiles recorded on the TW show clearly that the flow inside the CC is self-similar. Consequently, a relationship between Isp and the Chapman Jouguet's characteristics of the detonative mixture is established. The maximum operating frequency can be linked to the scale of the reactive mixture contained in CC and the maximum averaged thrust is deduced. The atmospheric shock wave produced is found to be equivalent to that of a strong point source of explosion of energy EO liberated by the reactive mixture. For the pulsed detonation results, the same thrust and impulse profiles as in single shot was obtained, but it was found a deficit about 30% in the level of thrust and consequently on the specific impulse. This deficit is mainly due to the quality of the filling of the CC and of the renewing the reactive mixture because of low value of length to diameter ratio of CC.