Multiscale Analysis of Powder-Propellant Conveying Stability Through a Nozzle

The conveying stability of the powder propellant is significant for the feeding-system design and particle-combustion performance of powder engines. In this study, a nozzle structure was employed to increase the conveying stability in a pipeline. The gas–solid flow through the nozzle was visualized, and the pressure signals were analyzed using multiscale methods: the standard deviation, wavelet transform, and higher order statistics. The nozzle structure helped to reorganize the downstream gas–solid by accelerating the gas–solid two-phase flow. The results for the standard deviation indicated that the upstream was more stable and less affected by the downstream at higher fluidized pressures. Through wavelet analysis, the energy fraction of the frequency band was used to represent the gas–solid characteristics, and the particle collision and nonlinear drag of the gas–solid interaction represented by the low-frequency band were determined to be the main factors affecting the downstream stability. Additionally, a high fluidized pressure (>2 MPa) yielded a relatively stable downstream flow. The higher order statistics method provided a better result than the standard deviation because of its high resolution and strong noise suppression. The analysis results indicate that increasing the particle size enhances the downstream stability.