Active piston technique to optimize the chamber pressure in two-stage light-gas guns

We report a study in the field of gun design and optimization, paying particular attention to the issue of energy matching between the pump tube and the barrel. The objective was to set up a technique in order to obtain a nearly constant pressure at the projectile base, without using a highpressure tapered section in which the piston extrusion occurs. In a first step, it was analyzed the opportunity of using two separate pistons inside the pump tube, in which the back piston sustains the stroke of the first one for a longer time. Then, to cope with technological problems, the same idea was implemented by developing a single piston characterized by an active core. In the following, after having presented a general overview on the proposed technique, we describe the numerical model used for performance evaluation and a numerical comparison of the performance achievable with a single piston and with the proposed method. Finally, we report some experimental results that were used for the model validation and also for demonstrating the technological feasibility of an active-core free-piston for two-stage light-gas guns.