Hydrodynamic Breech Window Design Concept for Laser Ignition of Large-CaliberGuns

摘要

Laser ignition is becoming a viable method of igniting a propellant bed(especially for large-caliber guns). However, problems still are present at the optical interface of the laser and the round to be fired. The most obvious problem to the casual observer is the deposits left on the window from the ignition of the igniter material and propellant. If the window is obscured (by an opaque coating or by opaque particles), ignition of subsequent rounds may not be possible. Therefore, a method of keeping the window clean for an extended number of firings is needed. Instead of physically wiping the window after each firing, this study examined the use of hydrodynamic flow of the igniter gases to keep the obscuring particles and hot gases from making contact with the window. Initial experiments used visualization by water jets to validate theoretical predictions for deflecting the particle-laden fluid flow. Improvements to the basic design included a cyclonic chamber in the window region to remove particles. Predictions indicated that the maximum pressure in the cyclonic chamber would be about 75% of the maximum breech pressure. Designs were tested in both subscale (76-ram I.D.) and full-scale (155-ram I.D.) simulators made of optically clear polymer resins. Several of these designs dramatically reduced the amount of particles that reached the window area.