Steady-State Combustion of Nitramine Propellants

The temperature sensitivity of burning rate defined in Eq. (35) is also examined, giving the result shown in Fig. 9. 

The temperature sensitivity stays around 0.0028 fC for most cases. At elevated pressures, the heat feedback from the gas phase to the condensed phase is higher, and thus the effect of initial temperature on the interfacial energy balance becomes less important. A numerical analysis on the temperature sensitivity for low-pressure conditions was further performed by Beckstead and co-workers [35]. The predicted temperature sensitivity was determined to be too low compared to the measurements, mostly due to the uncertainties associated with the treatment of the condensed phase in the model. 

The combustion wave structure at 100 atm is shown in Figs. 13 and 14, exhibiting a close similarity to that at 1 atm except for the shorter flame-standoff distance (6 vs. 600 pm) and molten-layer thickness (2.1 vs. 66 pm). 

The major difference lies in a smaller void fraction. The shorter molten-layer thickness and higher burning rate yield a shorter residence time for condensed-phase reaction. Also, high pressure tends to retard the RDX evaporation, which dominates the gasification process in the two-phase layer. As evidenced by the large ratio of HCN to CHiO mole fraction, the endothermic decomposition, (R2), appears more profound at high-pressure conditions. This can be attributed to the higher surface temperature and heat transfer into the condensed phase. 

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Modeling Development of Steady-State Combustion of Nitramine Propellants... 

Studies on the physical properties, sublimation, decomposition, ignition, and self-deflagration of nitramine propellants conducted prior to 1984 are summarized by Boggs [44] and Fifer [45], and the state of understanding of steady-state combustion of nitramine propellants up to 1990 is given by Alexander et al. [46]. A summary of the latest development is covered in a volume edited by Yang et al. [47]. 

The theoretical model and numerical method outlined in the above sections were implemented to study steady-state combustion of nitramine monopropellants [33.34], laser-induced ignition of RDX [39,40], and steady-state combustion of nitramine/GAP pseudo-propellants [37-39]. The analyses were carried out over a broad range of operating conditions. Various important burning and ignition characteristics were investigated systematically, with emphasis placed on the detailed flame structure and the effect of the subsurface two-phase layer on propellant deflagration. 

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