The combustion-wave structures of azide polymers were examined based on the data obtained by burningrate and temperature-profile measurements. The energetic azide polymer evaluated in this study was bis-azide methyl oxetan (BAMO), which contains two —N3 bonds in the molecular structure. BAMO polymer was copolymerized with tetrahydrofuran and cured with an isocyanate and cross-linked to formulate BAMO copolymer. The results indicate that the burning rate of BAMO copolymer increases with increasing the energy density contained within the unit mass of BAMO copolymer samples. The temperature sensitivity of burning rate is three or four times greater than that of conventional solid propellants. The rate of heat release in the gas phase increases as initial temperature increases at constant pressure. The heat transfer process in the combustion wave is correlated with the observed burning-rate characteristics.

Combustion of energetic azide polymers

Passage en revue des mecanismes qui affectent la sensibilite a la temperature: les mecanismes directs traites dans les modeles analytiques, les aspects non ideaux du processus de combustion, la derive des mecanismes de controle

Mechanisms and models of solid-propellant burn rate temperature sensitivity - A review

A burning rate law is proposed to relate the overall burning rate of composite solid propellant to the burning rates of individual components and the geometry of the burning surface. The complex three dimensional burning surface structure is simplified into unit cells in order to allow computational investigation of the mixing mechanism near the burning surface. The conservation equations of mass, momentum and mixture fraction have been solved numerically to obtain the velocity and mixture fraction field above the surface. The averaged mixture fraction on the burning surface of oxidiser and of the binder is correlated with both the surface geometry and Reynolds number. Experimental results for detailed surface structure and burning rate for specially formulated ammonium perchlorate (AP) composite propellant grains have been obtained at different pressure. The experimental results are explained using the averaged mixture fraction on the surface. It is concluded that the combustion of AP composite propellan...

Theoretical and Experimental Study of Composite Solid Propellant Combustion

This paper presents current work on improving the accuracy of solid composite propellant modeling to include catalytic additives and using it to develop a better understanding of the working mechanism of burning rate enhancement. To this end, isolating the physical mechanism where the catalyst impacts the composite propellant burning rate was studied. To accomplish this goal, a parametric study was conducted by systematically varying different aspects of the burning that are covered by the simple model. The results from the model were compared to experimental data collected from propellants formulated in the authors’ laboratory both with and without catalytic nanoparticle additives, namely TiO2. Some variations of the TiO2 additive tested included powder that was produced by spray-drying with and without heat treating as well as titania that was premixed into the binder before making the ammonium perchlorate (AP)/binder mixture. The propellants are compared to two ammonium perchlorate and hydroxyl-terminated polybutadiene (HTPB) baselines with 80% and 85% solids loading. Advancements on the Beckstead-Derr-Price (BDP) model to incorporate catalytic additives were accurately demonstrated using the technique outlined in this paper. This study determined that the catalyst primarily impacted the condensed phase by increasing the reaction rate of the condensed-phase AP; this conclusion was based on the fact that only changes in the condensed-phase AP reaction rate produced the pressure dependence and absolute magnitude of the increased burning rates due to the TiO2-based additive that were seen in the data. In contrast, an unrealistically high increase in the pressure dependence was found if the binder kinetics were modified to match the observed burning rates, and changes in the primary flame kinetics only varied the slope of the burning rate curve; these results are not supported by the experimental data. Furthermore, an empirical constant (Ωc) was found to model the effect of the additives on the AP reaction rate in the form of a burning-ratemagnitude modifier. Typically, an increase of around 50 to 60% in the reaction rate was observed for the use of nano-titania in an 85% AP propellant.

J.R. Osborn

Papers

Temperature sensitivity of propellant burning rates

Reply to comments of Rastogi, singh, and Rao on erosive burning models