Nonlinear dynamic combustion in solid rockets: L* effects

Nonlinear combustion and bulk-mode (L*) chamber gasdynamics in homogeneous solid propellant rockets are simulated computationally, A relatively new no nlinear simplified-kinetics combustion model is used. Quasi-steady gas and surface decomposition are assumed. Linear, oscillatory analytical results a re recovered (as numerical validation),In general, the calculated results e xhibit motor behavior in agreement with that observed experimentally for di fferent L* values, as summarized by Price (Price, E, W., "L* Instability," Nonsteady Burning and Combustion Stability of Solid Propellants, edited by L, De Luca, E, W Price, and M, Summerfield, Vol. 143, Progress in Astronaut ics and Aeronautics, AIAA, Washington, DC, 1992, Chap. 9, pp, 325-361) incr eases from low, <L-0*, to high, >L-0*, values burning rate and motor pressu re go from erratic and/or oscillatory to steady and stable. Several nonline ar combustion phenomena that have been observed experimentally but that are beyond the capability of linearized models are also predicted. These inclu de rapid initial (over-) pressurization, propellant extinction, and dual-fr equency and limit-cycle oscillations. The results suggest that some of thes e combustion phenomena could be due to nonlinear (but still quasi-steady) d ynamic burning and mass conservation effects within the classical bulk-mode framework rather than more complicated fluid and flame dynamic effects tha t have been proposed. In particular, the rapid rate of initial pressurizati on and the ignition spike commonly attributed to erosive burning may be due to nonlinear dynamic burning at low L*. Even without an overpressurization spike, it appears that the rapid pressurization rate in solid rockets is a t least partly due to the inherent L* instability of the initial state wher e L*< L-0*(alpha > 0) because of large values of L-0* at low pressures.