An interpretation of L' combustion instability in terms of acoustic instability theory.

A theoretical model is presented which describes the conditions leading to instability in a solid rocket motor in terms of both the combustion characteristics of the propellant and the characteristics of the chamber. The characteristics of the propellant are denned quantitatively in terms of its usual steady-state burning rate constants a and n, corresponding to the equation r = aP, two new constants A and B (termed transient constants), and the mean thermal diffusivity of the solid, a. The transient constants result from a comprehensive model of the chemical reactions occurring during combustion. The characteristics of the chamber are defined quantitatively in terms of its characteristic length L*. This theory is applied successfully to interpret existing L* instability data and to define the relationship between L* instability and acoustic instability through the acoustic admittance parameter. Thus, the L* burner, as well as the acoustic-mode-type burners, can be used as a tool with which to understand solid propellant transient combustion behavior.