Stabilization of Premixed Swirled Hydrogen-Air Flame At Elevated Pressures

Abstract

Large eddy simulations have been performed to develop and optimize a premixed hydrogen-air injector at high pressure for aeronautical applications. Hydrogen injection strategies are usually based on non-premixed flames, thus leading to high temperature regions favoring the formation of NOx. Premixing hydrogen and air allows the mixture to burn at very lean conditions, therefore decreasing the flame temperature, which is the key parameter to reduce nitrogen oxides formation. Numerical simulations of two ultra low-NOx injector concepts, along with comparisons to experimental data, will be presented in this paper for an operating condition of 9 bar. A first concept was previously designed to fully operate with premixed combustion. This concept gave satisfactory results for some tested conditions, but exhibits limited flexibility in operating range and could become unstable and lead to blow-off at certain conditions. Therefore, a second concept, incorporating a pilot injection of hydrogen, has been tested, showing a stabilization of the combustion for a wider range of operating conditions with a small ratio of pilot injection. Simulations were carried out with a detailed mechanism for hydrogen-air and the Zeldovich model for nitrogen oxide formation. Finally, OH* chemiluminescence and OH-PLIF could be performed during the experiments conducted on the MICADO test bench at ONERA. NOx and residual hydrogen were 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.