At least two gas combustion tubes disposed in an end-to-end relationship provide an elongate combustion chamber closed at both ends. A fuel mixture admitted alternatively into each closed end is ignited for generating positive pressure pulses traveling from one end of the chamber to the other. The combustion energy at one end compressed the fuel mixture from the other to permit ignition. A standing wave thus is formed having a pressure anti-node at each of the closed ends. The combustion chamber length is fixed relative to the frequency of the alternating ignitions to produce in the chamber a standing wave having an even number of quarter wave lengths with pressure anti-nodes and velocity nodes at its ends. The wave form thus has a pressure node and velocity anti-node at its mid-point. Combustion gases are discharged at this mid-point to a storage reservoir and, from the reservoir, to the propulsion turbine. High combustion pressures effectively cancel at the pressure node discharge point to permit cancellation of pressure pulse noise from the turbine exhaust. High velocity gases discharged into the reservoir are smoothed by storage to permit delivery to the turbine at a relatively fixed and high velocity.