Evaluation of Dynamic Burn Rate from the Extinction Compliance of Solid Rocket Motors

THE modeling of solid propellant combustion serves a number of useful purposes in the scheme of propellant development. Composite propellant burn-rate modeling has developed to a point where it can and does make useful contributions to combustion research and practical propellant development [1-18]. The available models are able, at least qualitatively, to explain the burn-rate characteristics of a wide variety of propellants of interest. However, deficiencies do remain and there is work yet to be done to improve the quantitative aspects and predictive capability in general [15]'. A modeling restriction that is common to most works is the quasisteady gas phase and homogeneous solid, one-dimensional flame (QSHOD) model, which neglects the gas-phase thermal inertia. The validity of the QSHOD model is limited to pressure perturbations within a low frequency range of below 1 kHz [10]. An analysis considering finite gas-phase thermal inertia, as well as the effects of nonlinear stability becomes formidable, and numerical methods have to be adapted. In spite of some attempts, fully workable solutions are not available [10]. Examination of frequency response function reveals that the role of gas-phase thermal inertia is not only to stabilize the burning near the first resonant mode but also to destabilize the burning near the second resonant mode. Calculations made for different amplitudes of driving pressure show that the nonlinear effects could be important in the dynamic behavior of burn rate. These are succinctly reported by Anil Kumar and Lakshmisha [10]. Thermal Inertia,' Proceedings of the Second International High Energy Materials Conference and Exhibit, Madras, India, edited by S. Krishnan, and S. K. Athithan, Allied Publishers, New Delhi, India, 1998, pp. 187-192.