NASA's Glenn Research Center has developed a novel Double-acting Extremely Light Thermo-Acoustic (DELTA) converter that operates at high frequencies (>400 Hz) with greatly increased specific power and no moving parts. Conventional engine power systems grow substantially in size and weight as their power level increases, as they manage their required reactive force, produced centrifugal force, or achievable current flow. In contrast, the DELTA converter enables an order of magnitude improvement in specific power compared to conventional engines.
The DELTA converter harnesses the power of thermoacoustics by relying on the relationship between the temperature and pressure oscillations present in sound waves. By using thermoacoustics to drive a double-action piston, this revolutionary DELTA converter enables a lightweight, maintenance-free, high-specific-power system ideal for unmanned aircraft vehicles, next-generation aircraft, mobility on-demand, and any power system in which efficiency, size, and weight are critical.
Glenn's innovative DELTA converter uses a double-action push/pull piston, in which an acoustic wave — or sound wave generated by heat — pushes both ends of a single piston. When sound waves are propagated down a narrow tube, they transfer energy along the tube. Conversely, when a heat gradient is introduced, it will generate sound waves that will cause the push/pull piston to oscillate. Using thermoacoustics to oscillate the push/pull piston simplifies engine operation by eliminating moving parts such as hot displacers and heavy springs. The double-action piston is contained by multiple thermoacoustic stages in series that form a delta-shaped triangular loop. One side of the piston creates an acoustic wave while simultaneously receiving acoustic power on the opposing side, enabling increased power on the single piston as compared to a single-action piston.
The simple design consists of a helium-filled tube, heat exchangers, regenerators, and a single, non-contact, oscillating piston. Operating at 400 Hz, this converter can produce four times more power than conventional engines operating at 100 Hz, with no hot moving parts, maintenance, lubrication, or electric feedback required. At this higher frequency, the output current is minimized and the specific power is maximized, enabling an order of magnitude increase in specific power over conventional engines. Glenn's novel DELTA converter offers this significantly increased specific power in a compact, lightweight, maintenance-free package that has considerable commercial potential.