Chinese scientists bring record-breaking Stirling generator to life while Nasa’s patent stays on paper

[Nan Yang]

Chinese scientists bring record-breaking Stirling generator to life while Nasa’s patent stays on paper​

• A prototype for a thermoacoustic Stirling generator has passed a milestone, in good news for space and submarine sectors
• But, though Nasa has a patent for a similar power system, it has not yet revealed any prototype or performance metrics

Zhang Tong
Published: 8:00pm, 11 Nov, 2023

Chinese scientists have taken a step forward in the race for alternative energy with the development of the most potent thermoacoustic Stirling generator to date.

Powered by heat, the highly efficient generator operates very quietly, which is ideal for applications where silence is critical, such as in submarines and the aerospace industry.

In a recent demonstration, the prototype delivered a groundbreaking 102 kilowatts of power from a heat source of 530 degrees Celsius (986 Fahrenheit). It marked the first time that type of generator had crossed the 100kW threshold – a milestone for practical application.

Historically, heat-to-electricity conversion has been dominated by steam turbines – devices known for their size, noise and maintenance demands. With the need for more reliable and quieter operation, especially in submarines, the new generator represents a significant breakthrough.

Though Nasa’s LEW-TOPS-80 patent aligns with this goal, proposing a thermoacoustic engine paired with an alternator to generate electricity in space, it has yet to unveil any prototypes or specific performance metrics.

The prototype of the thermoacoustic Stirling generator has had promising results. Photo: Handout

The Chinese generator was created by the Technical Institute of Physics and Chemistry (TIPC) at the Chinese Academy of Sciences (CAS) and is about 2 metres (6½ feet) in length with a dumbbell-like shape.

It operates with impressive efficiency, according to Professor Hu Jianying of the TIPC.

“The current thermoelectric conversion efficiency is about 28 per cent; with a hotter 600 degree thermal fluid, efficiency could reach 34 per cent,” he said.

Such efficiency can rival that of steam turbines.

Professor Luo Ercang of the TIPC highlighted the generator’s reliability, simple design, few moving parts and compatibility with various heat sources.

“It operates quietly and efficiently, and can use different types of heat, including solar energy, waste heat and biomass,” a CAS statement quoted Lou as saying.

The innovative system comprises a thermoacoustic Stirling engine and a linear motor encased in a rigid shell. The engine converts heat into sound waves that resonate to form a stable sound field. These waves then drive a piston, which in turn generates electricity.

“High-pressure helium at 15 megapascals serves as the working medium, and the absence of mechanical parts needing lubrication means the generator could exceed a decade of lifespan,” Hu said.

While the Stirling engine technology – first developed by Scottish engineer Robert Stirling in 1816 – faces manufacturing challenges due to material requirements for containing high-pressure gas, its low noise and high reliability remain appealing for specialised contexts.

Sweden’s use of it in submarines and China’s own advancements with Stirling engines for naval applications underscore the technology’s value. Modern air-independent propulsion (AIP) submarines, including the Chinese navy’s 039A/B type, use Stirling engines as power supplies.

The thermoacoustic generator developed by CAS not only breaks new ground for traditional Stirling engine designs but also integrates a motor that converts sound directly into electrical energy.

Hu noted that the motor’s design avoided harmful vibrations and maintained an airtight seal within the mechanism.

“The linear motor, consisting of a piston driven by sound waves, permanent magnets and coils, contributes to the high conversion efficiency. Its symmetrical design also eliminates some harmful vibrations,” he said.

“The linear motor keeps a very tiny space, about the thickness of a human hair, between the piston and cylinder. This prevents the parts from touching while maintaining the internal airtight environment.”

Despite the lack of an academic paper linked to the CAS announcement, the breakthrough underscores the potential of thermoacoustic Stirling generators to revolutionise power generation in diverse fields.

“It is a promising new generation technology for solar thermal, biomass power generation, and distributed energy systems,” Hu said.