The burning regimes and conductive burn rates of titanium subhydride potassium perchlorate (TiH1.65/KClO4) in hybrid closed bomb-strand burner experiments

A hybrid closed bomb-strand burner is used to measure the burning behavior of the titanium subhydride potassium perchlorate pyrotechnic with an equivalent hydrogen concentration of 1.65. This experimental facility allows for simultaneous measurement of the closed bomb pressure rise and pyrotechnic burn rate as detected by electrical break wires over a range of pressures. Strands were formed by pressing the pyrotechnic powders to bulk solid volume fractions between 0.58 and 0.88 theoretical maximum density. The burn rate dependence on average pressed powder density and initial vessel pressure are measured. Data from the strands with a 0.68 theoretical maximum density are compared to available literature. At all initial strand densities, the burn is observed to transition from a steady conductive burn to an unsteady convective burn within the strand. The conductive burning regime is analyzed following traditional closed bomb methods used with propellants and incorporating a relevant instantaneous burning surface area for the pyrotechnic powder bed. The transition to convective burning is analyzed and a relationship between the initial material characteristics of the pyrotechnic powder bed and the critical pressure at transition is developed.