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

An experimental study of the penetration and breakup of liquid jets injected normal to high subsonic speed (A/=0.45 and 0.75) airstreams through injection ports of various geometries and sizes is reported. The measurement techniques were primarily optical, employing 2.5 x 10 ~3-sec photos to produce "streak" pictures for penetration measurements and 10 6 and 10 ~8-sec spark photos to show the details of the breakup process and some droplet size measurements. The penetration data were successfully correlated using groupings of the variables and parameters suggested by a simple analysis.

Penetration and Breakup of Liquids in Subsonic Airstreams

Experimental results are presented on the formation of condensed combustion products (CCPs) at the burning surface of aluminized solid propellants. A number of experimental techniques were developed for describing the characteristics of the CCPs as a function of the oxidizer particle size and pressure. The results of this investigation provide qualitative descriptions of the CCPs formed at the propellant burning surface as functions of oxidizer particle size and pressure. Nomenclature ak = oxidizing potential of gas mixture (mole share of oxidizing components in the mixture) D = diameter of agglomerate D43 = mass-medium diameter of agglomerates D AP = mass-medium diameter of ammonium perchlorate particles d = diameter of e ne oxide particle d HDO 43 = mass-medium diameter of e ne oxide particles Fm.D/ = mass function of agglomerate size distribution fm.D/ = mass function of agglomerate size distribution density fm.d/ = mass function of e ne oxide particle size distribution density P = pressure r = propellant burn rate T = temperature Zm = share of unburned metal in the agglomerates relative to the initial aluminum in the propellant Z a = share of initial metal in the propellant used to form the agglomerates as a whole Z HDO = share of initial metal in the propellant used to form the e ne oxide particles Z ox = share of initial metal in the propellant used to form oxide in the agglomerates ° = edge angle of wetting ´ = mass share of oxide in agglomerates

Condensed Combustion Products at the Burning Surface of Aluminized Solid Propellant

The transient effects of the breakup and atomization of liquid jets in a crossflow on the size of droplets within the plume were experimentally determined. Water and water/methanol mixtures were injected normal to an air stream at Mach numbers 0.48 and 3, at ambient temperature and at stagnation pressures of 1.4 and 4.3 a tin, and at liquid-to-gas momentum flux ratios from 4-12. Droplet size distributions at sampling rates of up to 9 kHz were obtained using a Fraunhofer diffraction technique. The transients in the liquid mass flow rates were inferred from measurements of the extinction of a laser beam passing through the aerosol. The droplet sizes were found to fluctuate with frequencies of the order of 1-15 kHz. The fluctuations were characterized by a sudden and relatively brief increase in the mean diameter of the droplets caused by the passage of fractured clumps. Also evident was the very small size of the droplets that had been sheared off the windward surfaces of the jet. The jet fracture frequency was related to the frequency of waves propagating along the initial jet column. The axial column waves are postulated to have been caused by jet perturbations created by vortices in the air flow around the jet column.

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Transient behavior of liquid jets injected normal to a high velocity gas stream

The mean droplet diameter in the spray resulting from transverse injection of liquid jets into supersonic airstream was investigated in detail by the use of the diffractively scattered light method. The effects of viscosity, surface tension, jet/freestream dynamic pressure ratio, injector diameter, and location in the plume on the mean droplet diameter were determined. AH tests were performed at A/^ =3.0, with P0 4.2 atm and T0 = 300 K. The injectants used were water, various solutions of glycerine and ethanol in water, and Fluorinert to produce wide variations in viscosity and surface tension. The important results can be summarized as follows: 1) the droplet size has an inverse relation with respect to jet/freestream dynamic pressure ratio, 2) the droplet diameter decreases as the measurement station moves downstream, 3) the smallest droplets are formed at the outer edge of the spray plume, 4) droplet size has a direct relation with respect to surface tension and viscosity of the injectant, and 5) at very high viscosities the jet does not break up into nominally spherical particles. For a certain range of viscosity and dynamic pressure ratio, the breakup of the jet is into ligaments rather than droplets.

Effects of properties and location in the plume on droplet diameter for injection in a supersonic stream

A model is developed which correlates the experimentally observed burning rates of composite nonmetallized propellants subjected to acceleration fields normal to the burning surface. The model attributes the increased burning rates to additional energy transfer to the propellant surface from the combustion of ammonium perchlorate particles retained on the propellant surface by the acceleration forces. A method for predicting, with limited experimental data, the burning rate of a propellant as a function of pressure and acceleration is described.

An investigation of the acceleration induced burning rate increase of nonmetallized composite propellants

The average burning rates of a parametric series of propellants were determined in acceleration fields up to 1000 g using a combustion bomb mounted on a centrifuge. The propellant strands were burned at 500, 1000, and 1500 psia with the acceleration field directed normal and into the burning surface. Acceleration caused a time-dependent increase of as much as 100% in the burning rate of relatively slow-burning aluminized propellants. The relative amount of burning-rate increase for the various propellants was strongly dependent on the amount of aluminum retained on the propellant surface during burning. The burning rates of two very fast-burning propellants were found to be essentially accelerationindependent. OLID-PROPELLANT rocket motors are currently being used in applications which subject the metallized propellant grains to acceleration fields. The propellant burning rates increase appreciably when the acceleration field is imposed normal and into the burning surface.1'2 Postfire inspections of motors containing metallized propellants have revealed the presence of metal and/or metal oxide residue in the motor cases. The propellant burning-rate increase and the retention of residue appear to be interrelated. The review and abstracting of the literature on the effects of acceleration on solid-propell ant performance are presented in Refs. 3 and 4. Although progress has been made toward an understanding of some aspects of burning-rate augmentation in acceleration fields, it was believed that additional experimental studies with well-controlled propellant parameters would yield valuable insight. A parametric series of aluminized propellants was formulated to establish the importance of some of the propellant parameters that could be controlled to minimize the effects of acceleration. The objectives of this investigation were twofold. The first objective was to obtain the quantitative effect of acceleration on the burning rate of the propellants as a function of propellant composition, acceleration level, and time. The second objective was to obtain quantitative information on the amount of aluminum and/or aluminum oxide residue retained in the inhibitor case as a function of propellant -composition, acceleration level, pressure level, and propellant burning rate.

Aluminized composite solid-propellant burning rates in acceleration fields

A technique was developed to ascertain the magnitude of combined erosive and acceleration induced burning rate increases of aluminized composite solid propellants as a function of acceleration. The results indicate that a propellant exhibits a decreased erosion sensitivity when subjected to an acceleration field which is directed normal and either into or out of the propellant burning surface.

E. J. Sturm

Papers

An investigation of the acceleration induced burning rate increase of nonmetallized composite propellants

Aluminized composite solid-propellant burning rates in acceleration fields

An experimental investigation of solid propellant erosive burning inan acceleration field

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