The future is set to see hydrogen-powered planes taking flight globally. For this to happen, engineers need to create the jet engines that will drive them. Recent experiments conducted by researchers at ETH Zurich are laying the groundwork for these engines to be both powerful and resilient.
Europe is gearing up for eco-friendly flying powered by hydrogen produced in a sustainable way. Last year, the European Union initiated a project to assist industries and academic institutions in developing a medium-haul aircraft powered by hydrogen. This involves modifying jet engines to function with this new fuel, as current engines are optimized for kerosene combustion.
“Hydrogen combusts significantly quicker than kerosene, leading to more compact flame structures,” states Nicolas Noiray, a Professor in the Department of Mechanical and Process Engineering at ETH Zurich. This characteristic must be factored into the design of hydrogen engines. The recent findings from Noiray’s team provide critical insight into this matter, recently published in the journal Combustion and Flame.
A significant issue is vibrations, which engineers aim to reduce. In standard jet engines, around twenty fuel injection nozzles are placed around the annular combustion chamber. The turbulent combustion process produces sound waves that bounce off the chamber walls, creating a feedback mechanism for the flames. This interaction could result in vibrations that put considerable stress on the engine’s combustion chamber. “Such vibrations may weaken the material and potentially cause cracks or damage,” explains Abel Faure-Beaulieu, a former postdoctoral researcher in Noiray’s team. “Therefore, it’s crucial to ensure that these vibrations don’t occur during normal operations when designing new engines.”
Simulating conditions at cruising altitude
When the current kerosene engines were created, engineers needed to control these vibrations. They accomplished this by refining the flame shapes along with the combustion chamber’s design and acoustics. However, the type of fuel significantly influences the relationships between sound and flames. Consequently, it’s essential for engineers and researchers to prevent vibrations from developing in the new hydrogen engines. A sophisticated testing and measuring setup at ETH Zurich enables Noiray to assess the acoustics of hydrogen flames and anticipate potential vibrations. As part of the EU’s HYDEA project, he collaborates with GE Aerospace to evaluate hydrogen injection nozzles manufactured by the company.
“Our facility allows us to simulate the temperature and pressure conditions typical in an engine during cruising flight,” Noiray describes. The researchers at ETH can also mimic the acoustics of various combustion chambers, which facilitates extensive measurements. “This study is groundbreaking in its effort to measure the acoustic behavior of hydrogen flames under real flight conditions.”
The researchers initially utilized a single nozzle and then modeled the acoustic properties of an array of nozzles configured for a future hydrogen engine. This research aids GE Aerospace engineers in refining the injection nozzles and sets the stage for a high-performance hydrogen engine. They expect to conduct initial ground tests of the engine in a few years, and it could eventually power the first aircraft fueled by hydrogen.
ETH Professor Noiray believes that developing the engines and hydrogen storage tanks for aircraft is not the most significant obstacle in transitioning aviation to utilize hydrogen. “Humans have traveled to the moon; there’s no doubt engineers will be able to create hydrogen planes,” he remarks. However, solely having planes is insufficient. Noiray emphasizes the necessity of establishing an entire hydrogen aviation infrastructure, which includes generating climate-neutral hydrogen in adequate quantities and transporting it to airports. Accomplishing this in a timely manner demands a collective effort starting now.
