Temperature field measurement of a burning aluminum droplet

In a diffusive combustion regime, an aluminum droplet undergoing combustion forms an oxide cloud that surrounds the burning droplet. Thorough characterization of this cloud is crucial to the validation of the subsequent modeling. This paper makes a significant contribution to the field by providing an experimental procedure to resolve the spatial temperature profile within the oxide cloud. An electrodynamic levitator is used to observe the self-sustained combustion of aluminum particles with a radius of $35\mu m$ in atmospheric air, with negligible convective effects. The levitating device is coupled to an optical apparatus that allows for a light extinction method, thereby enabling the determination of size and concentration profiles of the nanometric alumina droplets, as introduced in previous works. The data from the previous study are employed in conjunction with a modulated absorption–emission (MAE) technique to ascertain a temperature profile that does not rely on the grey-body assumption. This technique is further enhanced by an optimization method to account for gaseous phase emissions, which typically hinder conventional temperature evaluation. Consequently, a spatially resolved temperature profile of the oxide cloud surrounding the burning droplet is obtained. Close to the surface of the droplet, a temperature of 2580 K is assessed. Then, a maximum temperature of about 3615 K is measured. As an additional outcome, gaseous emission profiles are obtained for three wavelengths and exhibit a notable correlation with a simulated gaseous suboxide concentration profile. The results presented in this work demonstrate a relatively high degree of consistency with expected temperatures.

Novelty and Significance Statement

This work presents a novel experimental method to obtain an unique temperature profile surrounding an isolated aluminum droplet in combustion. In conjunction with previous work, a non-intrusive, complete, and instantaneous characterization of the oxide smoke is now made possible, with the addition of the temperature profile to the known alumina particle size and concentration profiles. This comprehensive data set is presented for a fundamental case of a single levitating particle. The incorporation of the temperature profile provides an incomparable insight into alumina condensation processes and a detailed reference case for simulation purposes. The results presented in this work document the intricate condensation process of nanoparticles and highlight the limitations of current simulation methods.