This 1990s Engine Turns Sound Into Electricity FOREVER— It's 40% More Efficient Than a Gas Generator

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[00:00:00]In 1992, NASA flew a thermoacoustic refrigerator aboard space shuttle Discovery, a device with no compressor, no refrigerant, no moving parts of any mechanical kind, and a documented coefficient of performance exceeding that of the conventional refrigeration system it replaced. Los Alamos National Laboratory's thermoacoustic Stirling heat engine, documented by physicist Greg Swift in peer-reviewed publications spanning two decades, [music] it converts temperature differentials into acoustic energy and then converts acoustic energy into electricity at efficiencies approaching 40% of the theoretical Carnot maximum with zero mechanical friction loss. A gas turbine operating between the same temperature limits achieves 25 to 35% of Carnot.

[00:00:41][music] The thermoacoustic engine significantly outperforms it with nothing moving. With nothing moving inside the pressure vessel except a column [music] of pressurized gas oscillating at the speed of sound. By the end of this video, you will understand exactly why this engine is in zero power plants and zero homes [music] and what it would take to change that.

[00:01:00]The phenomenon that powers this engine was first documented not by a physicist but by a physician investigating an entirely unrelated question. Byron Higgins, a British physician working in London in the 1770s, had constructed a glass tube open at both ends for use in a chemistry demonstration. When he suspended a small hydrogen flame inside the tube and heard it begin to produce a sustained musical tone, the flame was not merely burning, it was vibrating.

[00:01:25]The heat of the flame was driving an acoustic oscillation in the air column of the tube that reinforced itself and continued indefinitely. Higgins published his observation in 1777 in a pamphlet titled Experiments and Observations Relating to Acidous [music] Acid, documenting the singing flame phenomenon without offering any theoretical explanation for why. This is the story of why. That naming arrived in 1859 when Pieter Rijke, a Dutch physicist at the University [music] of Leiden, conducted a systematic investigation. Rijke replaced the flame with a heated wire mesh positioned inside the pipe and found that the mesh produced an intense [music] sustained tone whenever the mesh was positioned in the lower half of the pipe with [music] the pipe oriented vertically. He documented his results in the Annalen der Physik in 1859, confirming that heat introduced at the correct position drove a self-sustaining sound wave. He did not know why the position mattered. [music] He knew precisely that it did and he measured it. Lord Rayleigh, the British physicist [music] whose work on wave phenomena earned him the Nobel Prize, provided the theoretical explanation in 1877, published in his two-volume treatise The Theory of [music] Sound. Rayleigh's criterion stated that acoustic oscillations are amplified when heat is added to a gas at the moment of maximum acoustic compression and are damped when heat is added at the moment of maximum rarefaction. The position of Rijke's heated mesh placed it precisely where the acoustic cycle was in its compression phase. The engineering application arrived at Los Alamos National Laboratory in the 1980s when physicist John Wheatley recognized a potential that a correctly designed acoustic resonator could extract useful power from a temperature differential.

[00:03:02]Greg Swift spent the following two decades refining the thermoacoustic Stirling heat engine, the TASE, at Los Alamos, publishing systematic performance data documenting conversion efficiencies of 18% rising to 42% of the Carnot efficiency limit in the most optimized configurations. In 1992, NASA selected a thermoacoustic refrigerator for a flight experiment, the first thermoacoustic device to operate in space.

[00:03:28]>> [music] >> It worked exactly as the ground testing predicted. The thermoacoustic engine works through the Rayleigh criterion, the conversion of a temperature differential into acoustic oscillation through the thermodynamic interaction between a resonating gas column and a porous solid matrix positioned inside a sealed pressure vessel. The core component is the regenerator, a tightly packed porous matrix of fine wire mesh, metal foam, or fibrous material positioned inside a resonant tube filled with a pressurized working gas, typically helium or a helium-argon mixture. One end of the tube is connected to a heat source, a combustion chamber, waste heat exhaust, solar thermal collector, or any other surface maintained at elevated temperature. The opposite end is connected to a heat sink maintained at a lower temperature, ambient air, water cooling, or ground coupled heat exchanger. As the temperature gradient establishes itself across the regenerator, the gas parcel nearest the hot end is heated and expands. [music] The expansion displaces the gas column toward the cold end. As the gas parcel approaches the cold end, it is cooled and contracts. The contraction displaces the gas column back toward the hot end. The regenerator captures the heat from each gas parcel as it moves toward the cold end and returns that heat to the same gas parcel as it moves [music] back toward the hot end. A heat exchange cycle that occurs at acoustic frequency, [music] typically 60 to 100 h, many times per second. Each complete cycle is thermodynamically close to a [music] Stirling cycle. The accumulation of those cycles at acoustic frequency produces a high-amplitude standing wave in the sealed tube, a pressure oscillation [music] whose power is proportional to the square of the pressure amplitude and the cross-sectional area of the tube.

[00:05:08][music] That acoustic power is extracted by a linear alternator, a magnet attached to a piston whose motion is driven by the acoustic pressure oscillations, [music] moving through a coil to generate alternating current. The linear alternator >> [music] >> is the only component in the system that experiences mechanical motion. Greg Swift's 2002 paper in the Journal of the Acoustical Society [music] of America, the most cited reference in the thermoacoustic engine literature, documented [music] a Tachi prototype achieving 30% conversion of heat input to acoustic [music] work output at a hot end temperature of 650° C with acoustic to electric conversion efficiency of 85% through the linear alternator stage. Combined system efficiency of approximately [music] 25% heat to electricity, comparable to a small gas turbine, from a sealed vessel containing no mechanical components subject to wear. But, does it hold under real operating conditions across real temperature sources at the scale relevant to residential and industrial power generation? The most publicly documented thermoacoustic system performance evaluation occurred not in an engineering laboratory, but in a commercial kitchen. Ben & Jerry's Homemade Ice Cream, seeking to eliminate the hydrofluorocarbon refrigerant from its commercial freezer fleet in response to the Montreal Protocol's phase-out schedule, contracted with a thermoacoustic refrigeration development company called Cryenco in the late 1990s to evaluate a thermoacoustic freezer capable of maintaining commercial ice cream storage temperatures without HFC refrigerants. Cryenco's prototype, powered by a natural gas burner at the hot end and ambient air at the cold end, maintained [music] a freezer interior at -26° C, standard [music] commercial ice cream storage temperature, with a measured coefficient of performance of 1.2. [music] A conventional HFC compressor freezer of equivalent capacity achieves a coefficient of performance of 1.0 [music] to 1.4 under the same conditions. The thermoacoustic system matched the performance of its conventional counterpart with no compressor, no refrigerant, and no mechanical wear surface in the cooling circuit. Ben & Jerry's published their evaluation results and expressed interest in proceeding to commercial deployment.

[00:07:27]>> [music] >> Cryenco filed for bankruptcy in 2000 before the commercial program could proceed. The Space Shuttle Discovery flight experiment of 1992, [music] designated STAR, the Space Thermoacoustic Refrigerator, operated continuously for 12 days in the microgravity environment of low earth orbit. [music] This experiment, documented by Steven Garrett and Steven Backhouse in a paper published in Physics Today in 2000, [music] confirmed that the absence of gravity-driven convection produced no degradation in thermoacoustic performance. The United States [music] Department of Energy's ARPA-E awarded a $2,800,000 research grant [music] to Penn State in 2012 to develop thermoacoustic engine technology.

[00:08:15]The team documented system efficiencies of 22% [music] heat to electricity conversion. When the electrical grid serving Puerto Rico collapsed in September 2017 following Hurricane Maria, the absence of locally available fuel was a documented cause of prolonged outage. A thermoacoustic generator operating on waste heat from a wood fire, a solar thermal collector, or any consistent temperature differential would have continued generating during the entire recovery period. Temperature differences are available everywhere, always, at zero cost. Every documented test confirms the same performance outcome. So, why has not a single thermoacoustic [music] power generator been manufactured at commercial scale in the 40 years since Wheatley's [music] team published their first results? The global gas turbine market was valued at $23.4 [music] billion in 2023.

[00:09:14]GE Vernova, [music] Siemens Energy, and Mitsubishi Power collectively supply the majority of utility and industrial gas turbine installations worldwide.

[00:09:24]>> [music] >> Each company's revenue depends on a product category with specific mechanical characteristics, [music] rotating compressor stages, turbine blades, and lubrication systems.

[00:09:36]That a sealed vessel of pressurized helium oscillating at acoustic frequency does not share. A thermoacoustic generator has no compressor blades to replace, no bearing lubricant to degrade, no turbine stage to fail at operating temperature. It has no scheduled replacement event. GE Vernova's gas turbine service contracts, valued at approximately 60% of the company's total turbine business revenue, exist because gas turbines require continuous maintenance. A sealed helium vessel does not. Underwriters Laboratories has no listing standard [music] for thermoacoustic electrical generators. UL 1741 covers inverters for distributed generation systems.

[00:10:17]UL 2200 covers stationary engine generator sets. Neither standard addresses an acoustic resonance device generating alternating current through a linear alternator because no such device has reached commercial production in a form that manufacturers have submitted for listing evaluation. Without a UL listing, a thermoacoustic generator cannot be specified by a licensed electrical contractor, cannot receive a building permit in most American jurisdictions, [music] and cannot be connected to a grid-tied system without voiding the interconnection agreement. [music] The regulatory infrastructure for installing one legally does not exist because the commercial infrastructure for manufacturing one has [music] never been established. The Dutch company Sound Energy, founded in Amsterdam in 2009 [music] specifically to commercialize thermoacoustic generation for industrial waste heat recovery, [music] completed a field demonstration of a 40 kW thermoacoustic generator at a natural gas processing facility in Morocco in 2016, [music] the largest thermoacoustic power generation system ever operated in a commercial setting. The demonstration confirmed 22% heat-to-electricity conversion efficiency from waste heat at 350° C. Sound Energy ceased operations in 2020 when its commercial rollout financing failed to close following the COVID-19 economic disruption. The Morocco installation's performance data remains in the published literature. No successor company has resumed commercial development at equivalent scale. The practical path for anyone seeking to build and operate a thermoacoustic device at residential scale begins with Greg Swift's 2002 textbook Thermoacoustics: A Unifying Perspective for Some Engines and Refrigerators, available through the Acoustical Society of America. The design environment for low amplitude thermoacoustic energy conversion, Delta EC, [music] is a free software package developed at Los Alamos National Laboratory for thermoacoustic system design, available for download from the Los Alamos website. Small-scale demonstration thermoacoustic engines operating on a temperature differential as low as 30° C >> [music] >> are buildable from standard plumbing components and speaker driver components for under $100 in materials. [music] No one failed to commercialize this technology because it did not work. The Morocco installation proved it worked at 40 kW.

[00:12:31]The problem is that it worked without generating a service contract. When Puerto Rico's grid stayed down for 11 months after Hurricane Maria and fuel for conventional generators ran out within weeks, the temperature differential between a [music] wood fire and the ambient air of the surrounding forest was generating no electricity anywhere on [music] the island. Every fire that burned for warmth or cooking in the recovery period was exhausting its heat into the atmosphere [music] instead of through a helium column oscillating at 60 Hz into a linear alternator. The acoustic oscillation Lord Rayleigh described [music] in 1896 would have converted a fraction of that wasted heat into power. It did not because the sealed vessel containing the helium was not there.

[00:13:11]>> [music] >> The gas turbine industry spent $23.4 billion last year selling machines with compressor blades that erode, bearings that wear, and service contracts that are more profitable than the turbines themselves. John Wheatley's team at Los Alamos documented a sealed vessel with no moving parts generating electricity from a temperature difference in 1985.

[00:13:32]Greg Swift refined it for 20 years and published every result. NASA flew it on the space shuttle in 1992. The helium still oscillates at the speed of sound.

[00:13:41]The Rayleigh criterion still holds exactly as Lord Rayleigh stated it in 1896.

[00:13:47]The temperature difference between a fire and the air above it has not changed. The question was never whether it works. The question is why we're still asking why we don't use it. This is off the meter. Subscribe so you never miss the next solution the world forgot to use.