Effects of initial grain temperatures on homogeneous propellant rocket motor operation with special emphasis on combustion instability

The purpose of this paper is to give an overview of our main experimental results on combustion instabilities and pressure oscillations in Double-Base (DB) homogeneous propellant grain rocket motors (SPRM-01, 02 and 03). We recorded some particular pressure-time traces, at extreme grain initial temperatures (223-233 K and 313-323 K), with significant perturbed pressure signal that was FFT analysed. On the basis of an improved mathematical model it was explored how the derived nonlinear pressure coupled response function, depending on time and frequency, behaves at extreme initial grain temperatures. Dynamic response of the propellant combustion under operating motor conditions was also investigated and the results were related to combustion stability and motor efficiency. The study model incorporates unsteady rotational sources and sinks in the acoustic energy assessment and thus a more precise formulation of the acoustic instability in SRM can be achieved. This method involves the calculation of minimum 11 growth rate terms that arise in the dynamics of an oscillating complex flow. The susceptibility of the tested motors with a DB propellant to get a significant perturbed working and to go unstable with pressure especially at extreme low initial grain temperatures has been conclusively emphasized and this risk has to be better evaluated.