The vast majority of propellant ignition data has been collected and studied for heat fluxes in the typical, intentional ignition range. However, when a propellant contained within a rocket motor case is exposed to low fluxes in hazardous situations, such as close proximity to a fire, unwanted ignition can also occur. These studies set forth to model and study the conditions of such a situation, including ignition time and temperature profiles as a function of several constant incident low heat fluxes.A CO2 laser was used as the radiant heat source for ignition of aluminized and non-aluminized AP based propellants. A piece of blackened aluminum foil was bound to the top of the propellant to simulate the rocket motor casing and the propellant-metal interface. Once ignition time data and temperature profiles were collected, theoretical models were developed to model the behavior of the propellants under these low flux conditions.It was discovered that under these conditions the samples still roughly exhibited the classic -2 slope on a log time versus log flux plot. However, the ignition time did increase for the samples covered with foil, as expected, due to the absorptivity of the foil. The experimental temperature measurements during heating to ignition followed the classic transient, 1D, semi-infinite solid with constant heat flux condition temperature profile, and were theoretically modeled as such. The final ignition temperature of the surface of the propellant was much lower than expected for what was reported in many other higher flux, air-propellant surface condition studies. However, this ignition temperature remained consistent throughout all of the tests.
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Low flux radiative ignition studies of ammonium perchlorate composite propellants
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