Adapt aircraft jet engines to use hydrogen as fuel

Engineers are well underway in adapting aircraft jet engines to use hydrogen as fuel instead of the ubiquitous kerosene.

Europe is preparing to make regular non-polluting flights a reality using planes powered by sustainably produced hydrogen. Last year, the European Union launched a project to support industry and universities in the development of a medium-haul aircraft powered by hydrogen. Among other things, jet engines will have to be adapted to run on the new fuel. Current engines are optimized to burn kerosene.

Hydrogen burns much faster than kerosene, so the flames are more compact. This must be taken into account when designing hydrogen engines.

The team made up of, among others, Nicolas Noiray and Abel Faure-Beaulieu, from the Swiss Federal Institute of Technology in Zurich, has carried out experiments in this regard, the results of which provide very clarifying information on the modifications that must be made to jet engines.

One of the problems is vibrations, which engineers try to minimize. In typical jet engines, about twenty fuel injection nozzles are arranged around the annular combustion chamber of the engine. The turbulent combustion of fuel generates sound waves. These waves are reflected from the walls of the chamber and exert a feedback action on the flames.

This coupling between the sound wave and the flames could give rise to vibrations that would induce a strong load in the engine’s combustion chamber. These vibrations punish the material, which in the worst case can cause cracks and other damage. Therefore, when engineers create new engines, they make sure that these vibrations do not occur, at least not under typical operating conditions.

When engineers developed today’s kerosene engines, they had to control these vibrations. They achieved this by optimizing the shape of the flames, as well as the geometry and acoustics of the combustion chamber. However, the type of fuel greatly influences the interactions between sound and flame. This means that engineers must now ensure that they do not occur in new hydrogen engines.

A special laboratory at the Swiss Federal Institute of Technology in Zurich allows Noiray and his colleagues to measure the acoustics of hydrogen flames and predict possible vibrations. As part of the HYDEA project, in which the team participates together with the company GE Aerospace, Noiray and his colleagues test hydrogen fuel injection nozzles produced by the company.

Fuel injection nozzles for hydrogen-fueled jet engines being tested in this chamber in a laboratory at the Swiss Federal Institute of Technology in Zurich. Here researchers can replicate the flight conditions of a hydrogen jet engine aircraft at a cruising altitude. (Photo: Nicolas Noiray / ETH Zurich)

“In our laboratory we are able to replicate the temperature and pressure conditions of a jet engine at cruising altitude,” explains Noiray. Researchers at the Swiss Federal Institute of Technology in Zurich can also recreate the acoustics of several combustion chambers, allowing a wide range of measurements to be made. “Our study is the first of its kind to measure the acoustic behavior of hydrogen flames under flight conditions.”

The study is titled “Measuring acoustic transfer matrices of high-pressure hydrogen / air flames for aircraft propulsion.” And it has been published in the academic journal Combustion and Flame. (Fountain: NCYT by Amazings)