An Experiment on Solid Propellant Combinations; Evaluate the Propellant Properties using Ultrasonic Impulse Measuring System

Abstract

Impulse force is the key for all high speed aero propulsion system. Solid propellants are uncontrollable once it ignited because it has the ingredients (fuel, oxidizer) for combustion within the chamber in which they are ignited. Since an entire solid propellant motor performance depends on propellant choice, chamber pressure, and nozzle design, the evaluation of propellant properties is highly needed. In the proposed Ultrasonic Impulse measuring system, the solid propellant motor, when fired, produces a thrust force which makes a bending moment in the simply supported beam. A sensitive Ultrasonic sensor will calibrate the bending moment, proportional to the Impulse force. The effective burning time is noted. Thermocouple reading, load cell reading, and the effective burning time value is used for calculating the mass flow rate, effective exhaust velocity, and specific impulse. The different fuel – oxidizer combinations with catalysers, binders are made. The small scaled propellant motor with length 0.12m, Diameter 0.025m, Exit Nozzle Diameter 0.003m, Empty Motor weight 20grams are used. The Recrystallation method is used for propellant preparation. The pyrotechnic ignition is adapted. The Grain test, Rope test are carried out. We have chosen high molecular weight, and low heat of formation value propellants. There are 4 different propellant combinations are tested with the proposed impulse measuring system. The Specific impulse reading of KNO3 + C12H22O11 + Al powder combination has highest value among all the propellants. It has 87seconds of specific impulse. The proposed impulse measuring system gives the reasonable readings with minimum error. We have compared the experimental results with the theoretical results and got the specific impulse of 90 seconds. The heat of formation of potassium nitrate and sucrose combination gives a low heat of formation value. The heat of combustion value and the characteristic velocity of the solid propellant combination (KNO3 + C12H22O11 + Al powder) are decreased.