"Hydrogen burns much faster than kerosene, resulting in more compact flames," said Nicolas Noiray, Professor of Mechanical and Process Engineering at ETH Zurich. His team's experiments, recently published in 'Combustion and Flame', are pivotal for designing these new engines.
A significant challenge in hydrogen engine development is managing vibrations. Jet engines typically feature around twenty fuel injection nozzles arranged within the combustion chamber. The turbulent combustion of fuel produces sound waves that reflect off the chamber walls, potentially feeding back into the flames and causing vibrations. "These vibrations can fatigue the material, which in the worst case could lead to cracks and damage," explained Abel Faure-Beaulieu, a former postdoctoral researcher in Noiray's team. Therefore, new engines must be designed to avoid these vibrations during operation.
Managing vibrations in kerosene engines involved refining the flame shape and adjusting the geometry and acoustics of the combustion chamber. However, with hydrogen's different combustion properties, researchers must ensure these solutions are still effective. ETH Zurich's advanced testing facility plays a key role in this, allowing for the simulation of engine conditions at cruising altitude. As part of the EU project HYDEA, Noiray and his team, collaborating with GE Aerospace, have been testing hydrogen injection nozzles.
"Our facility allows us to replicate the temperature and pressure conditions of an engine at cruising altitude," Noiray said. It can also simulate the acoustics of different combustion chambers, facilitating comprehensive measurements. "Our study is the first of its kind to measure the acoustic behaviour of hydrogen flames under real flight conditions."
The research involved analyzing a single nozzle and modeling the acoustics for an array of nozzles as they would appear in future hydrogen engines. These findings assist GE Aerospace engineers in refining nozzle designs and setting the stage for high-performance hydrogen engines. Initial ground tests for the engine are anticipated in the coming years, with future prospects of powering hydrogen-fueled aircraft.
According to Professor Noiray, while developing hydrogen engines and tanks is challenging, it is achievable. "Humanity has flown to the moon; engineers will undoubtely be able to develop hydrogen planes," he stated. However, he emphasized that planes alone are insufficient. Establishing the infrastructure to produce and transport climate-neutral hydrogen to airports is a significant obstacle. A coordinated effort is essential to achieve this within a practical timeline.
Research Report:Measuring acoustic transfer matrices of high-pressure hydrogen/air flames for aircraft propulsion
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