A Model of Erosive Burning of Composite Propellants

Abstract

(1) a result in high velocity flows of product gases across burning propellant surfaces (notably, nozzleValues of (r aft/rfore)iajtial as a function of the less rocket motors) is leading to increased occurerosivity constant ( k3) and the burning rate expon-:ence of erosive burning. In this paper , a physieat ( n ) are presented in Table I for y = .1.25. As cally realistic picture of the effect of such crossmay be seen, for the case of no erosion (k 3 = 0) -flows on composite propellant combustion , based on the af t end will recede more slowly than the fore the bending of columnar diffusion f lames by the end , due to lower pressure at the aft end. As k 3 crossflow , is presented. This bend ing results its increases , the r af~/rfore ratio also increases , shifting of the diffusion flame heat release zone going through unity (generally desirable) at a valuẽ~1 toward the surface , with consequent increased heat of k 3 which depends on the burning rate exponent. feedback flux from this flame to the surface andThe results of Table I give some indication of the thus increased burning rate. A relatively simple sensitivity of nozzleless motor design to the eroanalytical model based on this picture is developed sive burning characteristics of the propellant and for prediction of propellant burning rate as a functhus point out the importance 'f information regardtion of pressure and crossflow velocity, given only ing the propellant 's erosive burning characteriszero-cross flow burning rate versus pressure data, tics to the designer. Model predictions and experimental results are compared , with reasonably good agreement being found . performance repeatability and thrust misalignment. Development of a better understanding of the More than in any conventional motor , the exact eraeffects of crossflows on solid propellant combustion sive burn rate behavior must be held constant from is needed for accomplishment of accurate motor perbatch to batch if reproducibility is not to be a forsnance predictions in terms of both mean iatericr • problem. The performance sensitivity of a nozzleballistics analysis and prediction of motor stability less motor to erosion is due to the fact that the characteristics. With such understanding, the motor maximum erosion occurs at the choke point in the designer can either dasign his grains to compensate base. Since this point is the effective throat area , for mean erosive burning effects on grain burn patand the throat area versus time is thus a function tern , or , knowing how propellant formulation paraof regression rate , the result is a chamber pressure meters affect erosion sensitivity, vary propellant history which varies strongly with erosion, parameters in such a way as to optimize these e f f e c t s . A review of the literature indicates that there is In a nozzleless motor , two parameters which no unifying predictive model for erosive burning of affect bu rning rate , prcasure and crossflow velocity, solid prop~llants,~~ vary strong ly from the fore end to the aft end of the grain ...

Solid Rocket Motors Internal Ballistic Model With Erosive and Condensed Phase Considerations

“…Yet a more complex burn rate equation takes also in the account the velocity vector of the combustion gases that "wash" the surface of the solid propellant [14][15][16][17][18][19][20]:…”