Measurement of the temperature of burning aluminum particles using multi-spectral pyrometry

Aluminum is part of the composition of a vast number of high explosives and contributes to enhancing their blast. During the expansion of the fireball and the afterburning phase, aluminum particles indeed burn with both air and the detonation products, thus releasing energy into the flow. However, due to the short characteristic time of the afterburning phenomenon and the extreme conditions in the fireball, the combustion mechanism of aluminum during this phase is not precisely known. The aim of this study is to provide reliable and accurate information on the temperature of aluminum particles and the surrounding gas during the afterburning phase in order to improve combustion models. It is therefore necessary to study the combustion of aluminum particles in an atmosphere close to afterburning conditions. This work focuses on the use of an electrostatic levitator coupled with a multispectral pyrometry diagnostic. The levitator allows studying the combustion of a single particle in the size range 30 ~ 50 μm in an arbitrary atmosphere, whose pressure and composition are chosen to be close to the ones encountered in a fireball. The use of the levitator allows avoiding the disturbance that could be present in other experimental setups (heat furnace, Bunsen burner, etc.). The multispectral pyrometry diagnostic allows us to determine the temporal evolution of the integrated temperature of the condensed phase during the combustion of the aluminum particle. The photomultipliers are used to follow the temporal evolution of the light emission of the particle during combustion and are assembled into a pyrometer which is used to trace back to the temperature. The choice of wavelengths has been investigated and selected specifically for our case study. An investigation of the measurement error has been made. The obtained temperature information provides crucial experimental data without disturbance, thanks to our experimental device. These data also allows verifying the assumptions made in combustion models