3D particle sizing, thermometry and velocimetry of combusting aluminized propellants

Due to the unique advantages of high specific impulse, high thrust, simplicity and reliability, solid propellant with metal powder additives has emerged as a promising energy carrier for rockets in aerospace engineering. In-situ characterization of the metal particle combustion is crucial for the validation of numerical models and optimization of the propellant formulas. Previous studies mainly focused on the measurement of particle size and velocity near the combusting propellant surface with holography. Whereas, the behavior of the particles away from the surface is also essential for the full understanding the combustion and agglomeration mechanisms. Nevertheless, holography suffers from inaccurate depth estimation due to the large depth-of-focus. To overcome this limitation, a hybrid method which combines three-dimensional (3D) fiber optic imaging with two-color pyrometry is developed to realize simultaneous 3D localization, velocimetry, sizing, and thermometry of combusting aluminum particles in a large field of view. The method is validated both with numerical studies and experiments for a field of view of ∼60 × 50 × 50 mm3. According to the experimental results, the particle size follows a log-normal distribution which agrees with the specification of the propellants. In addition, the evolution of particle temperature and velocity were recorded for a duration of ∼13.9 ms. The results suggest that the temperature of most particles were between 2000 and 3500 K, while particle velocities were between 1 and 10 m/s. The measurement method proposed here is promising for the quantitative analysis of the complicated combustion process of aluminized propellants.