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International Journal of Energetic Materials and Chemical Propulsion
ESCI SJR: 0.149 SNIP: 0.16 CiteScore™: 0.29

ISSN Imprimir: 2150-766X
ISSN En Línea: 2150-7678

International Journal of Energetic Materials and Chemical Propulsion

DOI: 10.1615/IntJEnergeticMaterialsChemProp.2012001433
pages 85-105


Fred S. Blomshield
Naval Air Warfare Center-Weapons Division, NAVAIR, China Lake, CA 93555


Solid rocket combustion instability has been a technical issue in the development of rocket motors since modern rocket motors were first developed in the late 1940s. These problems ranged from minor (causing no effect on the system) to major (leading to motor failure). Instability manifests itself as thrust oscillations that can couple with other motor components, including guidance, thrust vectoring, and structural components. Instability can cause unacceptable changes to the motor's ballistic pressure-time history. A motor's stability is determined by various acoustic gains and losses. Losses include nozzle damping, particle damping, vortex shedding, structural damping, and other acoustic flow losses. Driving factors include pressure coupling, velocity coupling, and distributed combustion. The most dominant driving mechanism is the pressure coupling, which is the coupling between acoustic pressure oscillations at the surface of a burning solid propellant with the combustion processes of the propellant. It is a function of frequency, pressure, and propellant formulation. This response is the key input to motor stability prediction programs. Measurements of the response function are often used to evaluate new propellant ingredients to parametrically examine formulation changes and look at propellant additives. The most common way to measure the pressure-coupled response is by using the T-burner. The T-burner technique has been used to successfully measure the response of propellants since the late 1950s. The current T-burner at China Lake was built in the mid 1980s and updated in 2005. It is capable of measuring the response function up to 27.6 MPa (4000 psi) over a frequency range of 300−4000 Hz. The cost of using the T-burner to understand the pressure response of a propellant can easily exceed $100,000 (US dollars), depending upon the formulation and pressures required. During motor development, estimations must be made to approximate the response function. These estimations can often be incorrect due to the vast differences among formulations. Burning rates, oxidizer types, reduced smoke, minimum smoke, metalized, inert binders, energetic binders, and other propellant properties can all affect the response. This paper will summarize the vast quantity of pressure-coupled response data that has been measured. The objective is to organize response data in one place, and to draw general conclusions about the pressure-coupled response for various families of propellants. Pressure-coupled response curves as functions of pressure and frequency are included. This paper will also include a review of response measurement techniques and data analysis, with particular attention to the "pulsed during burn after burn" technique used at China Lake. It is hoped that this document will aid in estimating response functions for future propellants. It is further hoped that this work will enable conclusions to be drawn on the functionality of solid propellant variables and allow general trends to be postulated.