Laser-ignition of laser-dispersed metal particles

The development of a lasershock technique for dispersing Al metal fuel particles at velocities closer to those expected in a detonating explosive is discussed. The technique is described in detail by quantifying how air drag affects the temporal variation of the velocity of the dispersed particle plume. The effect of particle size is incorporated by examining various polydispersed commercial Al powders at different dispersion velocities (380 - 640 m/s). A simplified theoretical analysis of particle motion is carried out in attempt to explain the experimental velocity trends. The technique is finally tested within a preliminary study of particle ignition delay and burn time, where the effect of velocity is highlighted for different particle sizes. It was found that plume velocity exhibits a quasiexponential temporal profile, where smaller particles are more susceptible to air drag than larger ones. Moreover, larger particles exhibit longer ignition delays and burn times than smaller ones. The travel velocity of a particle was found to affect its ignition delay and burn time, especially for particles in the diffusioncontrolled regime. Shorter ignition delays and burn times were observed at higher particle velocities. Emission spectroscopy and broadband photodiode collection were found to provide similar information, which allows for the use of photodiodes with good accuracy.