Laser technology for measurement of solid propellant transient burning rates during rapid depressurization

A laser technique of transient burning rate measurement of solid propellant has been investigated. A photocell detects a laser beam passing through the propellant strand, and the cross-section of the laser beam is regulated so that the laser energy varies linearly along the height of the strand. Using a photo-controlled depressurization system, it is desirable to set up the starting time of depressurization in advance, and the initial rate of depressurization can be easily reproduced. Experimental results show that: (1) for a short time after depressurization begins, the burning rate remains unchanged; (2) during the depressurization process, the burning rate, while continuously decreasing in magnitude, exhibits low frequency oscillations; (3) the amplitude and the frequency of the burning rate oscillations, referenced to a smooth rate-time curve, increases as the depressurization rate increases; (4) for a short time after depressurization, the transient burning rates is higher than the steady state burning rate at the corresponding pressure, and then the transient burning rates oscillate around the quasi-steady rate. The experimental dynamic burning rates are compared with those available by microwave and capacitance methods. The discrepancies in the three experimental results have been discussed.