Development of a Lumped Parameter Model for a Monopropellant Hydrazine Reaction Chamber 670545

Catalytic decomposition of hydrazine and hydrazine blend propellants has been recognized as an efficient means of providing warm gas for direct thrust or auxiliary power in many current and future applications. In most of these applications, the dynamics which relate propellant inlet flow to gas output flow have a significant influence on the overall system design. It therefore becomes essential that these dynamics be predicted and tailored for each system.

In general, the approach to date to this problem has been from two extremes: the empirical evaluation of specific configuration and the analytical study of a completely distributed parameter microscopic model. The first approach does not lend itself to tailoring of the reaction chamber for specific systems. The second approach could produce both prediction and tailoring capability if accurate values of reaction and diffusion rates as a function of numerous environmental and geometric parameters were available. The experimental measurement of these parameters during actual reactor operation does not presently appear practical. It is the objective of the paper to present a compromise approach to this problem. A lumped parameter model which includes an overall mass and energy balance for the reaction chamber is developed. This model is based upon empirically determined reaction and diffusion rate coefficients. These coefficients can be obtained directly from conventional engine test data. The range of values of the coefficients as a function of mission parameters is summarized in a table which, with the model, can be used to estimate the hydrazine reaction chamber dynamics for a wide variety of mission requirements.

The basic material in this paper has been developed as a part of Hamilton Standard's internally funded research and development program on hydrazine monopropellants; it has not been previously published except for portions of the work which appear in several Hamilton Standard technical proposals.