Combustion of reactive metal particles in high-speed flow of detonation products.

摘要

It is common practice to add reactive metal particles to high-explosive formulations in order to increase the total energy output. The present study is an effort to increase the understanding of metal particle combustion in detonation products.;Furthermore, a simple analytical model is developed to predict ignition of magnesium particles in nitromethane detonation products. The flow field is simplified by considering the detonation products as a perfect gas expanding in a vacuum in a planar geometry. This simplification allows the flow field to be solved analytically. A single particle is then introduced in this flow field. Its trajectory and heating history are computed. It is found that most of the particle heating occurs in the Taylor wave and in the quiescent flow region behind it, shortly after which the particle cools. By considering only these regions, thereby considerably simplifying the problem, the flow field can be solved analytically with a more realistic equation of state (such as JWL) and a spherical geometry. The model is used to compute the minimum charge diameter for particle ignition to occur. It is found that that the critical charge diameter for particle ignition increases with particle size. These results are compared to experimental data and show good agreement.;Aluminum and magnesium particles ranging from 2 to 100 microm are subjected to the flow of detonation products of a stoichiometric mixture of hydrogen and oxygen. Luminosity emitted from the reacting particles is used to determine the reaction delay and duration. It is found that the reaction duration increases as dn with n ≈ 0.5, more consistent with kinetically controlled reaction rather than the classical diffusion controlled regime. Emission spectroscopy is used to estimate the combustion temperature, which is found to be well below the flow temperature. This fact also suggests combustion in the kinetic regime. Finally, the flow field is modelled with a CFD code and the results are used to model analytically the behaviour of the aluminum particles.