Jet engines fit for the hydrogen age

Researchers at ETH Zurich have now provided an important contribution for the development of clean hydrogen aircraft engines: they have tested the acoustic behaviour of hydrogen injection nozzles in the lab under conditions similar to those prevalent at cruising altitude

“Hydrogen burns much faster than kerosene, resulting in more compact flames,” explains Nicolas Noiray, Professor in the Department of Mechanical and Process Engineering at ETH Zurich. This has to be taken into account when designing hydrogen engines. Experiments by Noiray’s team now provide an important basis for this. The team has just published its results in the journal external page Combustion and Flame.

One problem is vibrations, which engineers try to minimise. In typical jet engines, about twenty fuel injection nozzles are arranged around the annular combustion chamber of the engine. The turbulent combustion of the fuel there generates sound waves. These waves are reflected back from the walls of the chamber and have a feedback action on the flames. This coupling between the sound wave and the flames could give rise to vibrations that would induce a heavy load on the engine combustion chamber.

“These vibrations can fatigue the material, which in the worst case could lead to cracks and damage,” says Abel Faure-Beaulieu, a former postdoctoral researcher in Noiray’s group. “This is why, when new engines are being developed, care is taken to ensure that these vibrations do not occur under operating conditions.”

When engineers developed today’s kerosene engines, they had to get these vibrations under control. They achieved this by optimising the shape of the flames as well as the combustion chamber’s geometry and acoustics. However, the type of fuel has a major impact on the interactions between sound and flame. This means engineers and researchers must now make sure that they will not arise in a new hydrogen engine. An elaborate test and measurement facility at ETH Zurich allows Noiray to measure the acoustics of hydrogen flames and predict potential vibrations. As part of the EU project HYDEA, in which he is involved together with GE Aerospace, he tests hydrogen injection nozzles produced by the company.