Onset of convective burning in picric acid

Based on simultaneous optical registration and measurement of the pressure at several points along the height of a sample, we have studied the onset of convective burning in picric acid when it is ignited from a closed end. We have investigated the effect of the particle size and density of the explosive (0.7–1.1 g/cm$^3$), the height of the sample, the power of the igniter, and the parameters of the channel in the shell. We have obtained the spatial profiles of the pressure distribution. We have determined the dependence on the investigated parameters of the critical height of the bed at which convective burning begins. We have determined two typical cases realized in the initial stage of development of the process. For one case, a smooth increase in pressure before and after the luminosity front is characteristic; for the other case, the presence of a peaked pressure distribution close to the front is characteristic. We have established the conditions under which a specific case is realized. We suggest an explanation for the results obtained.