Abstract: A system includes a combustion chamber that has a throat, and a regulator for changing area cross-sectional area of the throat. The regulator includes a first piston in fluid connection with the combustor, and a second piston that is moveable with the first piston. The second piston at least partially defining the throat.

Abstract: A piston tank with elongated contact between the piston and the tank bore to prevent piston cocking and preserve alignment is equipped with a compound piston that includes a carriage (or glider) and a barrier that is movable relative to the carriage. The carriage is an elongate ring with sealing and contact sites between the ring and the tank bore and axially spaced apart, and the barrier moves or changes shape in response to pressure differentials across the barrier imposed by a pressurized driving fluid. The barrier and carriage can thus move between a position allowing the full volume of the tank to be occupied by fuel or other functional fluid and a position ejecting all of the fuel or functional fluid out of the tank through an outlet port. Two examples of the barrier are disclosed—a plate that is movable within the ring and a diaphragm affixed to the ring and deformable in both directions.