Detonation in heterogeneous mixtures of liquids and particles

The mechanisms of detonation propagation in heterogeneous systems comprisin g closely packed particles and a liquid explosive are not fully understood. Recent experimental work has suggested the presence of two distinct modes of detonation propagation. One mode is valid for small particles (which is the regime we will address in this paper) with another mode for large parti cles. In this work we model numerically the detail of the wave interactions between the detonating liquid and the solid particles. The generic system of interest in our work is nitromethane and aluminium but our methodology c an be applied to other liquids and particles. We have exercised our numeric al models on the experiments described above. Our models can now qualitativ ely explain the observed variation in critical diameter with particle size. We also report some initial discrepancies in our predictions of wave speed s in nominally one dimensional experiments which can be explained by detail ed modelling. We find that the complex wave interaction in the how behind t he leading shock in the detonating system of liquid and particles is charac terised by at least two sonic points. The first is the standard CJ point in the reacting liquid. The second is a sonic point with respect to the sound speed in the inert material. This leads to a steady state zone in the how behind the leading shock which is much longer than the reaction zone in the liquid alone. The width of this region scales linearly with particle size. Since the width of the subsonic region strongly influences the failure dia meter we believe that this property of the how is the origin of the observe d increase in failure diameter with particle size for small inert particles .