Study on the particle size and velocity near Al/Al-Li based propellant surface using digital holography technology

Solid propellants typically incorporate approximately 15%–20% aluminum particles to enhance energy density. The transport behavior of aluminum particles, such as agglomeration, ignition and combustion near the propellant combustion surface, significantly impacts propellant combustion efficiency. To observe burning particles, this study developed a digital in-line holographic (DIH) laser testing system with a 4 f optical amplification component and a coaxial holographic reconstruction algorithm based on angular spectrum analysis. Calibration using standard particle size plates demonstrated particle size measurement errors within 5% and z -axis positioning errors within 2.2%. Ignition and high-speed digital holographic tests were conducted on aluminum (Al) and aluminum-lithium alloy (Al-Li) based solid propellants to evaluate the irregular morphology and agglomeration dynamics of particles near the combustion surface. Statistical analysis of high-speed data acquisition yielded the particle size distribution. The average particle size of the Al-Li propellant is 24.10% smaller than that of traditional pure Al propellant demonstrating a reduction in agglomeration. Furthermore, a depth-of-field extension algorithm was developed to obtain particle position information along the laser direction, enabling the calculation of three-dimensional velocity vectors for particles near the combustion surface.