The influence of detonation cell size and regularity on the propagation of gaseous detonations in granular materials

This paper presents results from an experimental study of transmission of gaseous detonation waves through various granular filters. Spherical glass beads of 4 and 8 mm diameter and crushed rock of 7.5 mm volume averaged diameter were used as filter material. Varying the initial pressure of the detonating gas mixture controlled the detonation cell size. Dilution with argon was used to vary the detonation cell regularity. The complete range from almost no detonation velocity deficit to complete extinction of the combustion wave was observed. The existing correlation for gaseous detonation velocity deficit V/V-CJ = [1 -0.35 log(d(c)/d(ps))] +/-0.1 where d(c) is the critical diameter for the gaseous detonation and d(ps) is the pore size, is found to be applicable for both smooth spherical particles and irregular crushed rock when considering irregular detonation structures. Soot films and pressure measurements show that as the detonation cell size is increased, reinitiation of a regular CJ-detonation moves further downstream from the granular filter until it finally no longer occurs at V/V-CJ approximate to 0.4-0.45. Complete extinction of the combustion wave occurs at V/V-CJ approximate to 0.25-0.3. These two limits appear to be about the same for irregular and regular detonation cell structures. For irregular structures without argon dilution, d(c)/d(ps) approximate to 50 can be found for detonation wave failure, and d(c)/d(ps) approximate to 100 can be found for complete extinction of the combustion wave. For argon dilution these limits are changed to d(c)/d(ps) approximate to 10 and d(c)/d(ps) approximate to 40, respectively. The data are a bit scarce as a basis for proposing a new correlation for regular structures, but as a first approximation V/V-CJ = [0.8-0.35log(d(c)/d(ps))] +/- 0.1 is suggested for regular structures. The detonation or combustion wave is found to approach a constant velocity in the granular filter if not extinguished.