Oscillatory Behavior of Fine AP/HTPB Composite Propellants
Hickman, Scott Ralston
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Permalink
https://hdl.handle.net/2142/83975
Description
Title
Oscillatory Behavior of Fine AP/HTPB Composite Propellants
Author(s)
Hickman, Scott Ralston
Issue Date
1998
Doctoral Committee Chair(s)
Quinn Brewster
Department of Study
Mechanical Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Aerospace
Language
eng
Abstract
The steady and oscillatory combustion of wide distribution AP/HTPB composite propellants containing coarse AP and fuel-rich, fine-AP/HTPB pocket regions has been investigated experimentally and theoretically. These propellants are of special interest because they are similar to many wide distribution bi-modal tailorable plateau propellants. The unsteady combustion response was measured using the laser-recoil method. It was found that at 1 atm monomodal fuel rich propellants containing fine AP (representative of the pocket propellant in the bimodal propellants) exhibit both a low frequency combustion response peak (∼10 Hz) due to the thermal relaxation in the solid and a secondary peak at a higher frequency (50--300 Hz). The frequency of this second peak has a strong correlation with particle size; it only appears for small AP (≤ 50 mum) and its frequency increases with decreasing AP size, even down to the smallest size tested to date (2 mum). The addition of coarse AP (which results in a nearly stoichiometric overall mixture but still has a reasonably large Peclet number, of order 10) suppresses the second peak. The frequency of the second peak was found to scale linearly with mean burning rate to AP particle size ratio (rb/d) except in the case of very fuel rich propellants. At 2 atm, it was found that the frequency of the second peak for the pocket propellant formulation doubled in frequency with very little change in mean bum rate. Also, the weak second peak found at 1 atm for a bimodal formulation was larger, on the order of the magnitude of the thermal relaxation peak, at 2 atm. Microthermocouple tests at 1 atm in pocket propellant formulations showed oscillatory flame temperatures in the gas phase with a frequency that corresponded to that of the second peak in the combustion recoil response function. An investigation of the mechanism of the second peak in the response function was conducted. The mechanism of the second peak in the response function was concluded to be a coupling between selective pyrolysis of the AP and binder and gas phase compositional (stoichiometry) fluctuations.
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