Precision Flash X-Ray Determination of Density Ratio in Gaseous Detonations

An x-ray densitometer has been used to measure the density ratio across a detonation wave in a number of different gaseous mixtures involving C2H2, C2N2, or H2 with O2 and Kr. In a 3-in. i.d. tube at an initial pressure of 60 cm the density ratios observed were between 1.64 and 1.67. Investigations of the influence on density ratio of tube diameter at constant initial pressure and of initial pressure at constant tube diameter both indicate an extrapolated infinite diameter density ratio of 1.70 for a 0.3 C2H2 + 0.3 O2 + 0.4 Kr mixture. This result is significantly lower than the ratio 1.79 which corresponds to the tangent point on the equilibrium Hugoniot from the initial state. At the present time these observations cannot adequately be explained by detonation theory.