Showing papers on "Burn rate (chemistry) published in 1971"

Nonlinear longitudinal combustion instability - Influence of propellant composition

Abstract: : Current stability criteria for longitudinal combustion instability were tested for generality using data from 54 different propellants. These included formulations containing polyurethane and carboxyl-terminated polybutadiene binders, ammonium perchlorate, aluminum, and rate modifiers. The propellants were tested at 70F in 4- and 8-in. diam, tubularly-perforated motors which were pulsed to initiate the instability. It was found that for a particular propellant system, well-defined behavioral trends could be established as the formulation was varied. A considerable variability in such trends was observed, however, for grossly different propellant systems. Consequently, a generalized correlation of motor behavior with the details of propellant formulation was not achieved. Similarly, the stability criterion proposed by Capener, Dickinson, and Kier, which features a power law relation between a 'threshold' burning rate and the corresponding chamber pressure, was found to be invalid in the general case. (Author)

An experimental investigation of rapid depressurization extinguishment

Abstract: Results are presented from an experimental study of solid propellant extinguishment by rapid depressurization. Systematic variations in propellant binder, oxidizer loading level, burning rate catalyst, metal loading, and exhaust pressure level were studied. The effects of motor configuration on extinguishment and reignition are discussed. Results indicate that combustion extinguishment requirements are determined by the binder type, percentage of ammonium perchlorate oxidizer, motor geometry, and exhaust pressure level as well as the pressure and depressurization rate. The von Elbe model with a coefficient of one provides a rough correlation of extinguishment requirements.

The Response of a Burning Solid Propellant Surface to Thermal Radiation

Abstract: : A new technique for the study of processes related to propellant combustion instability has been employed in which burning rate variations produced by a periodic radiant heat flux are measured. The phase angle between the perturbing flux and the burning rate response and the dependence of the magnitude of the response on the driving frequency are obtained. As the frequency of the perturbing flux increases, magnitude of the reaction is observed to first increase and then to pass through a maximum. In general, the experimental results tend to confirm the theoretical models for transient burning rate response, although the observed maximums in the response functions appear to occur at higher frequencies than is predicted by the simpler gas-phase models. (Author)

Effects of the acceleration vector on transient burning rate of an aluminized solid propellant.

Abstract: Experimental results concerning the transient burning-rate augmentation of a 16% aluminum polybutadiene acrylic acid (PBAA) propellant burned in a 2-in. web motor at pressure levels from 300 to 1200 psia with centrifugal accelerations from 0 to 140 g. The orientation of the acceleration vector was varied to determine its effect on the transient burning rate. The burning-rate augmentation was strongly dependent on (1) acceleration level, (2) propellant distance burned (or burn time), and (3) orientation of the acceleration vector with respect to the burning surface. This transient rate augmentation resulted from the retention of molten metallic residue on the burning surface by the normal acceleration loading. The presence of the residue altered the combustion zone heat transfer and caused increased localized burning rates, as evidenced by the pitted propellant surfaces that were observed from extinction tests conducted at various acceleration levels.

Nonstationary burning of propellants with variable surface temperature

Abstract: The author examines nonstationary processes (combustion at varying pressure, quenching, and ignition) for a model propellant whose burning rate u and surface temperature t1 depend on pressure p and initial temperature T0. All the processes in the surface reaction zone and the gas phase are assumed inertialess. It is shown that a theory of nonstationary combustion for such a model can be constructed by analogy with the Zel'dovich theory [1, 2], in which the surface temperature of the powder is assumed fixed. The variation of burning rate with time has been investigated for small sudden pressure changes. It is shown how a sufficiently large and steep pressure drop may cause quenching of the propellant. The process of propellant ignition is subjected to a qualitative analysis.

Solid propellant rocket motor

Abstract: A solid propellant rocket motor having a controlled rate of thrust buildup to a desired thrust level by the combined utilization of a regressive-burning controlled flow solid propellant igniter and a progressive-burning main solid propellant charge wherein the igniter is capable of operating in a vacuum and sustaining the burning of the propellant below its normal L* combustion limit until the burning propellant surface and motor chamber pressure has increased sufficiently to provide a stable motor chamber pressure.

Micro-Rocket Impulsive Thrusters

Abstract: : Light weight solid propellant motors which supply high thrusts (greater than 500 lbf) for durations on the order 0.010 sec. (referred to as impulsive thrusters) require special analysis of items such as internal ballistics, propellant combustion, ignition stimuli, exhaust plume envelope, and inert hardware. A survey of the rocket motor concepts revealed that the desired thrust versus time program can be achieved by internal burning grains and existing high burning rate composite propellants. The mathematical model for transient internal ballistics developed during the study can be applied to a wide range of high preformance rocket motors which experience rapid ignition and pressurization transients.

Measurement of solid propellant burning rates during rapid depressurization

Abstract: : A microwave continuous measurement technique has been used to measure burning rates of a carboxyl-terminated polybutadiene and ammonium perchlorate composite solid propellant during rapid decompression. A microwave signal oscillating at a known source frequency is passed through the end of a burning propellant strand opposite the burning surface and allowed to reflect off the burning surface. By continuously comparing the phase angle of this reflected signal with the phase angle of another signal oscillating at the original source frequency, a relative phase angle of another signal oscillating at the original source frequency, a relative phase angle between the two signals is obtained. The rate of change of this relative phase angle with time is proportional to the propellant's burning rate. Possible errors were investigated and conclusions reached concerning them.

Low acceleration solid propellant rocket ignition study

Abstract: A study was conducted to develop a solid-propellant rocket igniter system that would build up thrust at a controlled rate of less than 0.2 G/sec. The system consisted of a long burning, regressive burning, controlled flow igniter and an inhibited progressive burning surface in the main rocket motor. The igniter performed the dual role of igniting, under vacuum backpressure and low L* (motor free volume/nozzle throat area ratio) conditions, the nonrestricted portion of the propellant and providing the mass addition necessary to sustain combustion until the propellant burning area had increased sufficiently to provide a stable motor-chamber pressure. Two series of tests were conducted with existing small test motor hardware to: (1) demonstrate the feasibility of the concept, (2) determine the important parameters governing the system, and (3) obtain design guidelines for future scaled-up motor tests. A quasi-steady-state mass balance for the ignition system was written and programmed for use as a motor design tool.

Combustion Termination of Solid Propellant Motors.

Abstract: : An extensive analysis has been made of published characteristic chamber length instability data using a linearized form of the model The steady-state burning rate exponent has been shown to be the most sensitive propellant parameter governing marginal stability conditions Data for different propellants have been quantitatively compared with theoretically predicted marginal stability conditions Comparison between the predicted and measured characteristic chamber lengths and frequencies versus operating pressure was found to be relatively good, and it is encouraging to note that the kinetic parameters found to correlate the characteristic chamber length instability data are of the same order of magnitude as those previously found to correlate extinguishment data A device for measuring the effect of external thermal radiation on steady-state burning rates has been designed, fabricated, and assembled (Author)

Development of a Rocket Motor Burn Rate Measurement System.

Abstract: : The technique chosen to develop into a microwave burn rate sensor was that of the microwave interferometer. Microwave engery is beamed through a 'window' in the rocket motor case and into the propellant. At the burning propellant surface, this microwave energy is reflected and beamed back through the 'window' to a detector system. At this detector system, the combination of transmitted and reflected energy produces a standing wave of energy which is monitored by the detectors. As the burning surface moves, the standing wave will also move a proportional amount. Thus, by monitoring the motion of the standing wave, the motion of the burning surface is obtained. (Author)