Panoramic vision analysis of burning aluminum droplet and oxide cap with 360-degree microscopic photography

The aluminum agglomerate surfaces serve as the essential interfaces for heat and mass transfer processes during combustion, with the attached oxide cap exerting a significant effect on the asymmetrical spatial distribution of agglomerate physical properties. Therefore, understanding the surface characterization and its dynamic evolution during aluminum combustion is important. However, significant challenges exist in visualizing and measuring agglomerate surfaces due to the micrometer-scale size, extremely rapid dynamic evolution, asymmetric three-dimensional morphology, and complex combustion behaviors. Traditional methods are limited in providing three-dimensional, in situ measurements of agglomerate surfaces under the propellant-burning environment. Thus, a panoramic vision analysis method is proposed to achieve 360-degree visualization and measurement of agglomerate surfaces. A high-speed panoramic microscopic imaging system up to 30 kHz is established, composed of two high-speed cameras positioned opposite each other to capture the panoramic view of agglomerates. A data processing pipeline, incorporating an artificial intelligence segmentation algorithm and an ellipsoid geometric model, is developed to reconstruct three-dimensional models of agglomerates with varying diameters over time. The oxide cap distributions and dynamic behaviors, such as rotation and drift on the droplet surface, are visualized. Quantitative measurements of oxide cap and droplet areas are also obtained, with oxide cap area ratios ranging from 10% to 40%. This study provides a method for visualization and quantitative measurement of agglomerate surfaces, offering a tool for further research on the mechanism of oxide cap dynamics on surfaces. Novelty and significance statement The novelty of this work lies in proposing a 360-degree panoramic vision analysis method, which enables three-dimensional surface visualization and quantitative measurement of burning droplets and oxide caps. A high-speed panoramic microscopic imaging system, operating at up to 30 kHz, is established by positioning two high-speed cameras opposite each other to capture the front and back sides of the agglomerates simultaneously. The experimental results demonstrate that the proposed method is competent in reconstructing three-dimensional models of agglomerates with varying diameters over time, allowing for visualizing the evolution of the oxide cap distribution and drift on the droplet surface. Quantitative measurements of the oxide cap and droplet areas are obtained, with the oxide cap area ratio ranging from 10% to 40%. This method provides technical support for deeper insights into the analysis of oxide cap dynamics.