Nonlinear dynamic combustion in solid rockets: L*-effects

Nonlinear combustion and bulk-mode (L*) chamber gas dynamics in homogeneous solid propellant rockets are simulated computationally. A relatively new nonlinear simplified-kinetics combustion model is used. Quasi-steady gas and surface decomposition are assumed. Linear, oscillatory analytical results are. In general, the calculated results exhibit motor behavior in agreement with that observed experimentally for different L*-values, as summarized by Price. As L* increases from low (< L_o*) to high (> L_o*) values burning rate and motor pressure go from erratic and/or oscillatory to steady and stable. Several nonlinear combustion phenomena that have been observed experimentally but which are beyond the capability of linearized models are also predicted. These include rapid initial (over-) pressurization, propellant extinction, and dual-frequency and limit-cycle oscillations. The results suggest that some of these combustion phenomena could be due to nonlinear (but still quasi-steady) dynamic burning and mass conservation effects within the classical L*-framework rather than more complicated fluid and flame dynamical effects that have been proposed. In particular the rapid rate of initial pressurization and the "ignition" spike commonly attributed to erosive burning may be due to L*-nonlinear dynamic burning. Even without an over-pressurization spike it appears that the rapid pressurization rate in solid rockets is at least partly due to the inherent L*-instability of the initial state where L* < L_o* (α > 0) because of large values of L_o* at low pressures.