The burning rate of propellants plays a vital role among the parameters controlling the operation of solid rocket motors, therefore, it is crucial to precisely measure the burning rate in the successful design of a solid rocket motor. In the present review, a brief description of the methods for the determination of the burning rate of solid rocket propellants is presented. The effects of various parameters on the burning rate of solid propellants are discussed and reviewed. This review also assesses the merits and limitations of the existing different methods for the evaluation of the burning rate of solid rocket propellants.

Various Methods for the Determination of the Burning Rates of Solid Propellants : an Overview

An experimental system is presented for the direct and continuous measurement of the burning rates of solid rocket propellants under conditions closely approximating those of a solid rocket motor. The system involves a positioning type servomechanism which moves a sample of solid propellant within a two dimensional rocket motor such that the receding burning surface of the sample is maintained at a fixed position with respect to the motor. Since the burning surface remains fixed, the direct measurement of the velocity of the propellant feed mechanism for adjusting the position of the propellant sample yields the burning rate. The servomechanism incorporated a 50 m Ci 137Cs source of gamma rays coupled with a scintillation probe for detecting the position of the burning propellant surface. The output of the probe was converted into a voltage by a ratemeter. It was then amplified and compared to a standard voltage which was proportional to a desired propellant surface position. The resulting difference was amplified for the purpose of driving a 0.6 hp servomotor which positioned the burning surface of the propellant sample. The size of the sample was approximately 2.5 cm square by 10 cm long. The experimental data were obtained with the above servomechanism for two composite propellant formulations. The data were obtained for a range of pressures from 8.8 to 35.5 kg/cm2, and for burning rates ranging from 0.40 to 0.8 cm/sec. The data correlated well with previously published data. A theoretical analysis of the servomechanism was performed to determine system stability and performance. An optimization analysis of the servomechanism system yielded optimum operating parameters.

Continuous Measurement of Solid Propellant Burning Rates

: A microwave continuous measurement technique has been utilized to measure burning rates of a CTPB and AP composite solid propellant during steady state and 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 which is receding at some unknown velocity. By continuously comparing the phse angle of this reflected signal with the 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. Accurate (plus or minus 10 percent) continuous burning rate data was obtained and shown to be within capabilities of the system for dP/dt values less than about 2500 psi/second. (Modified author abstract)

Measurement of Steady State and Transient Solid Propellant Burning Rates with Microwaves.

: 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.

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Measurement of solid propellant burning rates during rapid depressurization

Study on Stable Operation of Micro-thruster Using Stacked Solid Propellant Pellets

A technique for measuring the burning rate of solid propellants inside rocket motors is described. The technique consists of embedding wires in a specimen of solid propellant and then casting or bonding the specimen to the propellant in the rocket motor. The wires employed were made of 0.0045‐in.‐diam lead‐antimony which has a low melting point, a low thermal diffusivity, and a moderate electrical resistance. The technique involves measuring the time interval between successive interruptions of the wires caused by the burning surface of the propellant. The distance between these wires is determined from an x‐ray picture of the specimen prior to placing it in the rocket motor and prior to burning. Thus, with both the distance burned and the burning time known, the burning rate can be determined. When this technique is properly employed, it does not influence the burning rate, nor does it affect the flow field. Furthermore, it can be employed to study the influence on the burning rate of the port shape of a propellant grain inside a rocket motor, since the small specimen of solid propellant containing the resistance‐wire network can be cast into the grain of a solid rocket at any position in the port. This will permit measuring burning rates at selected locations and times in the rocket motor.

H. E. Bethel

Papers

Technique for Measuring Burning Rates of Solid Propellants