|M.Sc Thesis||Department of Aerospace Engineering|
|Supervisor:||Prof. Emeritus Gany Alon|
|Full Thesis text - in Hebrew|
The use of metallic powders, mainly aluminum, to increase the blast effect and the incendiary effect of explosives is common. The aluminum in such explosives reacts with the detonation products, or with oxygen in the shocked air. The aluminum characteristic behavior depends, among other things, on the particle size and charge size. Reaction with the detonation products takes place at grater pressure, meaning greater portion of the energy goes to the blast. On the other hand, combustion with oxygen in the air releases more heat. Hence, when designing such a charge, it is important to make sure that aluminum will ignite where it gives the best performances.
The objective of the present research is to calculate the location and time of ignition of aluminum particles adjacent to a TNT charge. In order to perform this task a computer code was written. This code calculates first the surrounding condition of the gases around the particle, based on data from the literature, and then calculates the particle location and temperature at any given time. The locus and time of the particle ignition is determined using two bounding temperatures, which ignition is expected to take place somewhere between them. As part of the research we examined the influence of the particle size on the ignition time and location. In addition, we studied the influence of the charge weight on these parameters.
From the results we noticed that particles adjacent to an explosive charge heat up in two phases: After the blast wave passes through the particle cloud, and after the particles exceed the contact surface between the detonation gases and the shocked air. Opposed to intuition, the latter is the dominant heating phase.
As predicted, the larger the particle the farther and later it will ignite. Above a certain size, the particle will not ignite at all. We also saw that the bigger the charge, the bigger are the particles that can be ignited and the shorter is their ignition time.
The main conclusion of this research is that by making the right combination of particle size and charge size, the location of ignition can be determined, as well as the condition it will take place in. An appropriate combination can determine whether a particle will ignite with oxygen in the shocked air, or will react with the detonation products.