: This book has several purposes, including a broad historical summary of combustion instabilities in propulsion systems; a concise compilation of the main mechanisms for instabilities in liquid and solid fueled rockets, ramjets, thrust augmentors and gas turbines; development of a theoretical framework for investigating unsteady motions in combustion systems; and accessible surveys of the basic material required to understand the subject. Emphasis is placed throughout the book on observed behavior. For well-understood reasons, the best, and in many respects most useful quantitative data, have been obtained for solid propellant rockets. Hence that type of device occupies a special position in the subject. The book comprises nine chapters and eight annexes. Material in the annexes is not essential for reading and broadly understanding the main part of the book, but is likely interesting for those choosing to do research on the subject. The nine chapters divide into three parts.

Unsteady Motions in Combustion Chambers for Propulsion Systems

Metal-based nanoenergetic materials: Synthesis, properties, and applications

Experimentally determined values of the critical Weber number available from the literature are scattered over a very wide range ofWec from 2.2 to 99.6. To study one possible source of these discrepancies an experimental investigation was made of the deformation and breakup of water droplets at nearly critical Weber numbers. Experiments were conducted in a small horizontal wind tunnel. A continuous stream of uniform water droplets was allowed to fall perpendicularly to the continuous stream of air. The time histories of water droplets were recorded by using a high speed camera. Five different basic behaviours of water droplets were recorded in the range ofWe = 11 to 14. It was found that an increase in the Weber number in this region resulted in an increased percentage of droplets with regular bag type breakup.

Deformation and breakup of liquid drops in a gas stream at nearly critical Weber numbers

Direct combustion of recyclable metal fuels for zero-carbon heat and power

This volume brings together international scientists in the field of solid rocket propulsion. Thirty-nine papers present in-depth coverage on a wide range of topics including: advanced materials and non-traditional formulations; the chemical aspects of organic and inorganic components in relation to decomposition mechanisms, kinetics, combustion and modelling; safety issues, hazards and explosive characteristics; and experimental and computational interior ballistics research, including chemical information and the physics of the complex flow field.

Solid propellant chemistry, combustion, and motor interior ballistics

A comprehensive analytical model which considers time and space development of the flow field in solid propellant rocket motors with high volumetric loading density is described. The gas dynamics in the motor chamber is governed by a set of hyperbolic partial differential equations, that are coupled with the ignition and flame spreading events, and with the axial variation of mass addition. The flame spreading rate is calculated by successive heating-to-ignition along the propellant surface. Experimental diagnostic studies have been performed with a rectangular window motor (50 cm grain length, 5 cm burning perimeter and 1 cm hydraulic port diameter), using a controllable head-end gaseous igniter. Tests were conducted with AP composite propellant at port-to-throat area ratios of 2.0, 1.5, 1.2, and 1.06, and head-end pressures from 35 to 70 atm. Calculated pressure transients and flame spreading rates are in very good agreement with those measured in the experimental system.

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Starting Transient of Solid-Propellant ocket Motors with High Internal Gas Velocities

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

In this second paper of a two-part study, emphasis is on the pressure dependent pre-ignition events in double base propellants and the influence of radiation source (arc image vs laser) on observed ignition behavior. The pressure-dependent (< 21 atm) ignition domain of a PNC/MTN double base propellant is examined using controlled exposure lengths together with high speed movies and an infrared detector to monitor flame development. There is a brief flux-dependent period of transient flame development after gasification begins; this is followed by a relatively long, flux-dependent period of steady-state, radiation assisted burning before a selfsustaining condition is reached. The nature of this condition for self-sustainment is not yet well-defined. The ignition behavior seen with an arc furnace or a laser is generally quite close for both double base and composite propellants, if optical effects (reflection, penetration) are factored out. An exception is fast deradiation extinction, seen only with the laser; greater radiation penetration in the arc image wavelength region precludes this phenomenon. I. Introduction A S pointed out in the companion paper,l thermal zmradiation is a convenient energy input for studying solid propellant ignition behavior. By varying such factors as radiant flux, ambient pressure, and propellant compositions, much can be learned about the processes underlying the macroscopic ignition response, e.g., which of these factors controls that behavior in differing ambient conditions and what is needed to predict ignitability quantitatively in new circumstances. At the same time, one must be aware that the unique nature of radiation and the characteristics of the devices used to produce it can affect the test results. The present study is a systematic survey of radiation ignition behavior of a variety of propellants, intended to illustrate both these positive and negative aspects. In the companion paper,1 a generalized ignition behavior 4'map'* (log °f irradiation time vs log of radiant flux) was presented. The boundaries on this map were discerned by go/no-go testing and by monitoring of IR radiation from the developing flame. For clarity, we summarize them again here in the order they are encountered as irradiation time increases: Lla = first gas evolution; Llb = first IR signal from the surface region indicating the beginning of exothermicity; L]c = incipient flame indicated by a roughly 50-fold increase in IR signal; Lld = self -sustained flame indicated by steady burning if flux is removed; L2 = deradiation extinction boundary indicated by disappearance of a well-developed flame when radiation is removed too quickly. The companion paperl concentrated on certain propellant formulation effects; it illustrated how these boundaries are shifted strongly by the optical properties of the propellants. This was shown to obscure the comparison of different types of propellants, but unmodified double base propellants

Radiative Ignition of Double Base Propellants: II. Pre-ignition Events and Source Effects

Aluminum powders added to conventional rocket propellants burn either as single particles or agglomerates which contain hundreds or even thousands of the original particles. Combustion efficiency and acoustic stability characteristics are very dependent on the final Al/Al2O3 particle size injected into the chamber flowfield. High-speed photographs of burning homogeneous propellants provided data on agglomeration size and visualization of the flow processes as a function of pressure (1 to 10 MPa), initial particle size (5 to 100 μm), and aluminum mass fraction (0.1 to 13%). Photomicrographs of extinguished surfaces revealed the importance of particle accumulation in a thin mobile reaction layer adjacent to the burning surface. A model was developed that interpreted data and observations from several sources. The model accounts for accumulation of aluminum particles in the mobile reaction layer, retention of particles by surface tension forces, melting, and ignition at the surface. The following agglomeration and particle behavior items are categorized: decreasing agglomerate size with increasing pressure, minimum mass loading required for agglomeration, prominent agglomeration for particles with diameters less than the reaction layer thickness, and sharply reduced agglomeration for larger particles. The model provides an approach for controlling and interpreting agglomerate size behavior.

Agglomeration and ignition mechanism of aluminum particles in solid propellants

Certain metal organic salts (e.g., lead or copper salicylate) when used in double-base propellants induce desirable insensitivities of burning rate to pressure and initial temperature. To understand this, the combustion wave zones (luminous flame, dark, fizz, and surface reaction zones) were examined by means of photography and fine thermocouples (4fi bead). The metal salts significantly alter the surface and fizz zones. The surface zone accumulates carbonaceous material coincident with the appearance of an accelerated burning rate in the catalyzed case. No attendant change in surface heat release is detected. Coinciding with this carbonaceous layer occurrence are substantial (50-100%) increases in conductive feedback from the fizz zone. This latter effect is believed directly responsible for the altered burning behavior though its origin may lie in the altered surface chemistry.

Leonard H. Caveny

Papers

Starting Transient of Solid-Propellant ocket Motors with High Internal Gas Velocities

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

Radiative Ignition of Double Base Propellants: II. Pre-ignition Events and Source Effects

Agglomeration and ignition mechanism of aluminum particles in solid propellants

Site and Mode of Action of Platonizers in Double Base Propellants