Experimental Investigation of a Non-Premixed H2/Air Swirled Flame at Elevated Pressure Using Optical Diagnostics

Abstract Hydrogen is a promising solution for decarbonizing aviation, but its unique properties pose technical challenges for its integration into traditional combustion systems. This requires the development of innovative injection systems and combustion chambers tailored to high-pressure aeronautical conditions. This study investigates a non-premixed hydrogen jet flame with swirled air injection under representative aeronautical conditions (high pressure and high temperature) using the test bench MICADO at ONERA. Flame dynamics is analyzed through high-speed OH* chemiluminescence. Planar laser-induced fluorescence on OH radicals (OH-PLIF) reveals the local flame front topology. Aerodynamics is also studied using 2D-2C high-speed particle image velocimetry (PIV), while NOx concentrations in the burned gases are measured using a gas analyzer. The experiments are conducted with an air temperature maintained at 575 K, a constant inlet air velocity, and a fixed injection equivalence ratio of 0.14, while the chamber pressure varies from 4 to 15 bar. These results provide a unique experimental database on the behavior of an H2/air flame under high-pressure conditions. It is observed that pressure has a limited effect on flame topology and flow dynamics. However, NOx production increases with pressure, which appears to be primarily linked to mechanisms involving the NNH and N2O pathways.