In this first paper of a two part study, the ignition response to arc image radiative heating (5 to 100 cal/cm sec) of several double-base propellants is examined; comparisons with certain AP and HMX propellants are made also. Ignition delay is affected by chemical factors in propellant formulation (stability of the condensed phase, reaction rate in the gas phase) and by optical factors in propellant formulation (opacifiers affecting reflectivity and in-depth absorption). The results show that comparisons of the chemical factors in the formulation can only be made properly when the optical factors are minimized (as by carbon addition). When optical factors are minimized by opacifying the propellant, one finds, in order of increasing ease of ignitability, the formulations tested fall as follows: HMX composite, AP composite, double base (noncatalyzed), double base (catalyzed).

Radiative Ignition of Double Base Propellants: I. Some Formulation Effects

The experimental and theoretical literature pertaining to the ignition of solid propel 1 ants over the period 1966-1980 is reviewed. The purpose is to present a cohesive description and evaluation of the research in solid-propellant ignition to date. Experimental research papers are reviewed first, then the theoretical papers are introduced; finally a summary is presented. As a result it seems clear that,while previously detailed experimental work was required, it now appears that further theory is necessary. It is finally evident, however, that the establishment of a sustained exothermic reaction in the gas phase is a necessary condition for the ignition of both homogeneous and composite propellants. Finally, needed experimental and theoretical research is indicated.

Solid-Propellant Ignition Theories and Experiments

Extinction Theories and Experiments

Publisher Summary This chapter discusses the solid propellant combustion and internal ballistics of motors. The combustion of a solid propellant is characterized by the way its surface regresses once it begins to burn. The burning rate is the distance traveled by the flame front per unit of time, measured normally to the burning surface. The burning rate is obtained by the strand useful length and the duration of the firing. The latter is determined by monitoring the noise created by the combustion. The advantage of this method is that a preliminary lateral restriction of the strand is not necessary. The introduction during the manufacturing of ballistic catalysts in propellant compositions allows the regulation of the burning-rate level and a significant decrease in the values of temperature coefficients and pressure exponents. Heterogeneous propellants contain a mixture of these ingredients, while decomposition releases gaseous products whose nature is either oxidizing or reducing. The addition of low-particle content, as ingredients in the propellant, is often successful in stabilizing motor combustion. This is particularly true in the case of tangential instabilities.

Solid Propellant Combustion and Internal Ballistics of Motors

Burning stability analyses of solid propellants are performed, within the framework of a thermal theory of monodimensional heterogeneous deflagration waves, from a linearized point of view. The frequency response function is determined both for pressure and radiation driven combustion waves. Two limiting schemes for the quasi-steady gas phase are implemented: distributed and sharp flame models. Work available from the literature in this field is reviewed, corrected, and extended. Particular attention is given to the connection between pressure and radiation driven admittance functions. Burning stability properties predicted from linear and nonlinear theories are compared. A way to rate experimentally the dynamic burning stability of condensed substances with optically opaque condensed phase and transparent flame is suggested.

Frequency response function of burning solid propellants

: Experimental and analytical investigations were conducted to understand the ignition and nonsteady burning processes that occur at and near the propellant surface, to determine the connection between the ignitability of a propellant and its other nonsteady combustion characteristics, to quantify the peculiarities of radiative ignition, and to develop a means of ranking propellant ignitability. As a result of these investigations, radiative ignition processes have been explained for a wide variety of propellant and test conditions. The stability properties of heterogeneous combustion waves were considered for linear and nonlinear situations. Nonlinear (large disturbances) solid propellant stability boundaries can be immediately defined from the knowledge of the associated restoring function. The restoring function is a property strictly dependent on the nature of the solid propellant.

L. H. Caveny

Papers

Solid Propellant Ignition and Other Unsteady Combustion Phenomena Induced by Radiation

Ignition Dynamics of Double Base Propellants