German university builds zero-emission hydrogen engine with over 60% efficiency — matching fuel cells via combustion

Researchers at Otto-von-Guericke University Magdeburg have developed a hydrogen engine that operates in a closed cycle and achieves over 60 percent thermal efficiency — without releasing any exhaust to the environment. The project was funded by Germany's Federal Ministry for Economic Affairs and Energy and carried out in collaboration with research partner WTZ Roßlau gGmbH.

How the closed loop works

The key difference from a conventional combustion engine lies in what happens to the combustion gases. A standard engine draws in air, burns it with fuel, and expels exhaust. The Magdeburg engine does not. After each power stroke, most of the gas mixture stays inside the system — it is cooled, reconditioned, and fed back in. The water produced during the reaction is separated and liquefied. The working gas simply keeps circulating, with no conventional exhaust leaving the engine.

The engine runs on a carefully balanced blend of three gases: hydrogen as the fuel, oxygen to enable the combustion reaction, and argon as a stable carrier gas. Argon is an inert noble gas — it does not burn and does not react with oxygen under operating conditions. It creates favourable thermodynamic conditions for controlled and efficient combustion. In technical circles, this principle is known as the Argon Power Cycle.

Better than diesel — and on par with fuel cells

The test bench results are striking. Modern petrol engines typically achieve 30 to 40 percent thermal efficiency. Diesel engines in commercial vehicles reach around 45 percent at best. Conventional open hydrogen combustion engines are generally expected to fall in the 40 to 45 percent range.

The Magdeburg closed-loop engine exceeds 60 percent — territory previously reserved for hydrogen fuel cells. The difference is the pathway: fuel cells convert hydrogen into electricity through an electrochemical reaction, while the Magdeburg engine achieves comparable efficiency through direct combustion. The researchers describe this as a significant technological breakthrough.

Target applications: heavy industry, not passenger cars

Prof. Dr. Hermann Rottengruber, who led the project at the Institute for Engineering of Products and Systems (IEPS), is clear about the intended use cases: not cars or motorcycles, but sectors where battery-electric solutions still fall short. He specifically names marine propulsion, stationary power generators, tractors, large construction and harvesting machines, wheel loaders, and long-haul trucks.

The maritime sector is showing particular interest. According to Rottengruber, leading manufacturers of marine propulsion systems have already signalled strong demand — unsurprising, given the growing pressure on the shipping industry to decarbonise by 2050, with very few viable alternatives to diesel currently available.

Economic case: no exhaust aftertreatment needed

Beyond efficiency, the closed system offers a meaningful economic advantage. Because no conventional exhaust gases are produced, expensive catalytic converters and filter systems are not required — components that would still be necessary on open hydrogen engines. Over an engine's operational lifetime, this could offset the greater technical complexity of the closed-loop design.

Remaining challenges

The researchers are candid about the hurdles that remain. Power density is currently limited by the amount of hydrogen that can be injected into the combustion chamber during each cycle. Carbon dioxide can also accumulate in the closed loop, produced by the combustion of lubricating oil. Both factors affect efficiency and performance and must be resolved before the concept can move from laboratory prototype to series production. No concrete timeline for vehicle deployment currently exists.

What this means for hydrogen mobility

The closed-loop engine demonstrates that the ceiling of hydrogen combustion technology has not yet been reached. While public debate often frames the choice as battery-electric versus fuel cell, the Magdeburg team shows that combustion engines running on hydrogen can match fuel cell efficiency levels through an entirely different technical route. That makes the technology particularly relevant for heavy transport and maritime applications — sectors where electrification remains years away from being practical.

Sources:

• Fuel Cells Works (01-05-2026)
• Motorcycles.News
• Interesting Engineering
• GaGadget
• IndexBox
• Otto-von-Guericke University Magdeburg