There always exists the possibility that acoustic combustion-instabilities take place in the combustion chamber of a solid-propellant rocket motor. This is a phenomenon that the energy-gain of a standing acoustic wave in the combustion chamber exceeds the energy-loss of that wave, the pressure amplitude of that wave increases because of the surplus energy, and this increase causes the unstable combustion of the propellant. The response function of a solid propellant indicates the inclination of the propellant to cause the acoustic combustion-instability. Therefore, those engaged in the engineering of the solid-propellant rocket must clearly understand the meaning of the response function and roughly know about the experimental methods for its measurements. This article gives them necessary knowledge. First, fundamentals of acoustics are described. Next, the expression of the coefficient of the exponential increase of the acoustic pressure amplitude caused by the interaction of oscillatory pressure with oscillatory velocity of gas particles at the propellant surface [Culick and Yang, Progress in Astronautics and Aeronautics, Vol. 143, pp. 719-747] is presented. Then, the relation between this coefficient and the response function is explained. Last, the experimental methods for the measurements of the response function are presented.
2017 Combustion Society of Japan