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Despite significant developments and widespread theoretical and practical interest in the area of Solid-Propellant Nonsteady Combustion for the last fifty years, a comprehensive and authoritative text on the subject has not been available. Theory of Solid-Propellant Nonsteady Combustion fills this gap by summarizing theoretical approaches to the problem within the framework of the Zeldovich-Novozhilov (ZN-) theory. This book contains equations governing unsteady combustion and applies them systematically to a wide range of problems of practical interest. Theory conclusions are validated, as much as possible, against available experimental data. Theory of Solid-Propellant Nonsteady Combustion provides an accurate up-to-date account and perspectives on the subject and is also accompanied by a website hosting solutions to problems in the book.
Non-steady burning of solid propellants was investigated both theoretically and experimentally, with attention to combustion instability, transient burning during motor ignition, and extinction by depressurization. The theory is based on a one-dimensional model of the combustion zone consisting of a thin gaseous flame and a solid heat up zone. The non-steady gaseous flame behavior is deduced from experimental steady burning characteristics; the response of the solid phase is described by the time-dependent Fourier equation. Solutions were obtained for dynamic burning rate, flame temperature, and burnt gas entropy under different pressure variations; two methods were employed. First, the equations were linearized and solved by standard techniques. Then, to observe nonlinear effects, solutions were obtained by digital computer for prescribed pressure variations. One significant result is that a propellant with a large heat evolution at the surface is intrinsically unstable under dynamic conditions even though a steady-state solution exists. Another interesting result is that the gas entropy amplitude and phase depend critically on the frequency of pressure oscillation and that either near-isentropic or near-isothermal oscillations may be observable. Experiments with an oscillating combustion chamber and with a special combustor equipped for sudden pressurization tend to support the latter conclusion. (Author).
The research carried out under the grant was aimed at furthering the scientific understanding of nonsteady propellant combustion behavior in rocket motor chambers. Controlled nonsteady flow and burning conditions were produced in laboratory-scale solid rocket motors by developing a device that modulated the throat area of the primary nozzle. Modulation frequencies up to 2400 Hz were obtained. The modulated throat rocket motor is being used to acquire data using AP composite propellant grains. Cold flow tests were used to study the acoustic modes and nozzle discharge characteristics. Computerized techniques were developed for conducting spectral analyses of head-end and nozzle-end pressure data. In addition, the equations describing the nonsteady one-dimensional gas dynamics and propellant combustion were formulated, and a comprehensive numerical solution was developed. The present solution takes into account the couplings among the oscillating nozzle flow, the nonsteady chamber flow, and erosive burning. Since pressure and velocity oscillations can be made to occur and decay in high loading density rocket motors with realistic grain configurations, the experiment is expected to produce propellant/chamber response functions that are relatively easy to interpret, compared to the difficult to interpret T-burner response functions.
This report describes progress on a collaborative research program combining the expertise of individuals from several universities to develop a new ability to predict the propulsion performance of solid rocket motors. The focus of the research on nonsteady behavior is unique and the overall project is not possible at any one of the institutions participating in this coordinated research. The individual tasks which we are studying will pursue solid propellant decomposition under unsteady conditions, nonsteady aspects of gas phase flame structure measurements, numerical modeling of multidimensional flame structure, propellant/flame interactions and overall nonsteady propellant combustion characteristics in realistic rocket motor environments. Our goal has been to develop general models of fundamental mechanisms of combustion instability that can be applied to a variety of new energetic materials.
Analytical models were developed for the linearized pressure-coupled and velocity-coupled combustion response functions of composite propellants. The theory is that compositional fluctuations occur in the course of composite propellant burning, that these fluctuations originate from the inherent heterogeneity of the propellant microstructure, and that they will contribute to the nonsteady combustion under oscillating pressure (and velocity) conditions. Properties of the response to compositional fluctuations were determined and compared with responses to pressure and velocity fluctuations in series of parametric studies. The response to compositional fluctuations was found to be relatively strong response. Each response tended to increase with increasing AP particle size and pressure, and with decreasing mean crossflow velocity. A series of experiments was carried out with three propellants to determine whether or not certain features of the microstructure could be measured and correlated with response function behavior. Additional tasks pertaining to nonlinear combustion response and high frequency combustion response were performed and are described in the text. A list of publication generated by or in the course of this program is presented.
Solid Propellant Rocket Research