Solid-Fuel Regression Rate Modeling for Hybrid Rockets

Abstract

One of the primary parameters in the analysis of the performance of the hybrid rocket engine is the regression rate of the solid fuel. Many studies in the past few years have theoretically claimed, or experimentally shown, a possible dependence between the regression rate itself and the chamber total pressure, but no agreement has

Review of Classical Diffusion-Limited Regression Rate Models in Hybrid Rockets

“…In the interest of clarity, the different solutions for the radiation correction are plotted in Figure 3 along with the numerical solution to Equation (26). Note that each approximation has its own merits: While being the least accurate, Equation (27) remains adequate over the entire domain and results in unitary coefficients, as per Equation (28). Equation (29) remains the most accurate over the entire domain, and Equation (30) remains nearly indiscernible from the numerical solution for smaller radiative contributions while remaining simple to apply, as long asQ rad /Q c ≤ 2/3.…”

“…For systems with low values ofQ rad /Q c , Marxman et al [6] note that the tradeoff between the new terms in Equation (28) is "nearly exact, andṙ can be calculated with little error by usingQ c alone". IfQ rad =Q c , then Equation (28) predicts that approximately three quarters of the heat actually transferred to the wall will be due to radiation but thatṙ will be only 35% higher than the case with no radiation. While useful for illustrative purposes, this result should be treated with care: If the majority of heat transferred is radiative, the dependencies on geometry will no longer be the same as those already considered for the purely convective case.…”

“…While useful for illustrative purposes, this result should be treated with care: If the majority of heat transferred is radiative, the dependencies on geometry will no longer be the same as those already considered for the purely convective case. Furthermore, the accuracy of Equation (28) degrades rapidly once radiative heat flux overtakes that due to convection, as evidenced in Figure 3.…”

“…They developed a correlation that normalized the regression rate by its maximum value before pressure effects appeared in a manner to make it possible to predict whether a particular set of conditions was kinetically or diffusively limited, in addition to successfully matching experimental data. More recently, Favaro et al [28] performed experiments designed to illuminate the role of heterogeneous reactions, thus leading to the development of a semi-empirical model.…”

Analytical Prediction for Grain Burn Time and Burning Area Kinematics in a Solid Rocket Combustion Chamber

“…The formulation tested was hydroxyl-terminated polybutadiene in gaseous oxygen at pressures ranging from 4 to 16 bars. A simplified analytical model, which retains the essential physics and accounts for pressure dependency, was developed for hybrid rockets in conjunction with the corresponding numerical simulation reported in [9]. However, the results of its simplified analytical model may not translate directly for use with solid rockets.…”