Light-diffraction particle size measurements in small solid-propellant rockets

Abstract

An experimental investigation was conducted to determine the effects of operating pressure and position within the motor and exhaust nozzle on the particle size distribution for a reduced smoke propellant. Light-diffraction measurements were made in a small solid-propellant rocket motor and high-speed motion pictures of strand burners were taken. Particle sizes were measured near the propellant surface of the end-burning grain, at the nozzle entrance, and at the nozzle exit. The results indicated that much of the ZrC reacts on or very near to the propellant surface to form ZrOz. Small particles (probably ZrC) were ejected from the propellant surface without agglomeration and were consumed, whereas the large agglomerates (probably ZrCh) remained almost constant in size along the length of the motor. The particulates broke up in the nozzle converging section to a monomodal distribution with a Dyi between 15 and 19 pun, independent of the particle size entering the nozzle. Aft of the nozzle in the expanding plume, the particles were significantly smaller and had multimodal distributions. It was also found that assuming a monomodal distribution of particles, when the distribution is actually multimodal, can lead to significant errors in measuring D-& from scattered light-intensity profiles.