THEORY OF UNSTEADY COMBUSTION OF SOLIDS - INVESTIGATION OF QUASI-STEADY ASSUMPTION

A numerical model was developed to investigate the applicability of ac tivation energy asymptotics (AEA) in unsteady combustion of solids, an d specifically, the quasisteady condensed phase (surface) reaction ass umption. It was found that while condensed phase global decomposition activation energies are typically large enough for accurate prediction of steady burning rate and surface temperature by AEA, the criterion for comparable accuracy in predicting unsteady burning rate (e.g., lin ear response function) is more stringent. For realistic material prope rties the error in the linear response because of the quasisteady cond ensed phase reaction assumption is significant, both in magnitude and phase. The results also show that st moderate pressures (10-100 atm), condensed phase reaction zone unsteadiness should be considered before , or at least in conjunction with, gas phase unsteadiness. Nonlinear c ombustion response was also investigated. The primary effect of nonlin earity was to convert low frequency response (particularly that near t he peak) to higher frequencies. Validation of numerical results was ac complished by comparing the linear surface reaction response with the predictions of analysis.