Session: 04-16 Hydrogen Emissions I

Submission Number: 174740

Stabilization of Premixed Swirled Hydrogen-Air Flame at Elevated Pressures 

Large eddy simulations (LES) have been performed to develop and optimize a premixed hydrogen-air injector at high pressure for aeronautical applications. Due to its high flammability and flame speed, concepts involving hydrogen are usually not operated with premixed combustion to avoid the risk of flashback. Instead, injection strategies are mainly based on non-premixed flames, thus leading to high temperature regions favoring the formation of nitrogen oxides (NOx).  However, premixing hydrogen and air allows the mixture to burn at very lean conditions, thus decreasing the flame temperature, which is the key parameter to reduce NOx formation. Numerical simulations, along with comparisons to experimental data, of two ultra low-NOx injector concepts will be presented in this paper for an operating condition of 9 bar. The first concept was designed to fully operate with premixed combustion. This concept gave satisfactory results for some numerically tested conditions, but lacked of flexibility in operating range and could become unstable and lead to blow-off at certain conditions. Therefore, a second concept, by adding a pilot injection of hydrogen, has been investigated and it resulted that only a small proportion of pilot injection is required to stabilize the combustion for a wider range of operating conditions. Simulations were carried out with a detailed mechanism for hydrogen-air (9 species and 21 steps) and the Zeldovich model for nitrogen oxide formation. Dynamic thickened flame model was used to model the flame-turbulence interaction in premixed regions using the Takeno flame index. Finally, experiments were conducted on the MICADO high pressure high temperature test bench at ONERA, operated under the same conditions as the simulations. The chamber was equipped with optical accesses allowing OH* chemiluminescence and OH-PLIF to be implemented during the tests. NOx and residual hydrogen could be measured using gas sampling probes at the exit of the combustion chamber. Comparisons between simulation and experimental results exhibit a good agreement thus validating the numerical approach used to design the injection system.

Presenting Author: Jiangheng Ruan ONERA

Presenting Author Biography: 2019 : Ph.D. in numerical combustion at CORIA laboratory (Rouen, France)
Since 2020 : Research scientist at ONERA Palaiseau (France), specialized in numerical simulations of combustion chambers, conception of hydrogen-air injectors

Authors:

Jiangheng Ruan ONERA
Guillaume Pilla ONERA
Sylvain Petit ONERA
Axel Vincent-Randonnier ONERA