Experimental Investigation of Pressure Influence On A Swirled Stabilized Premixed Hydrogen-Air Flame For Aeronautical Applications Using Optical Diagnostics

Abstract

Reducing carbon footprint of the aviation sector is essential for its sustainability. A promising solution for short-to-medium-haul flights is to replace kerosene with hydrogen combustion. This switch leads to significant changes in the architecture of the combustion chamber, whose design requires a detailed understanding of the dynamics of reactive flows. Due to thermophysical properties of hydrogen, H2 flames are prone to flashback and could be difficult to stabilize, thus reducing the operability range. When operated in lean premixed conditions, H2 flames are also subject to instabilities. Besides, due to the higher adiabatic flame temperature and differences in chemistry-turbulence interactions, mitigating NOx emissions remain challenging. Therefore, to guarantee optimal operation over a wide operability range, it is necessary to have a detailed understanding of the injection system operation. This study reports a novel injector design of premixed ultra-low NOx swirl-stabilized H2-air flame. This concept has been tested on the ONERA MICADO test rig. Various operating conditions have been explored up to 19 bar and global equivalence ratio between 0.2 and 0.3. Flame dynamics and topology have been characterized using OH* chemiluminescence imaging and OH-PLIF. NOx emissions and combustion efficiency are measured by exhaust gases sampling. Results show very low NOx levels for all tested operating conditions. Though fully premixed conditions are limited due to flashback phenomena, the introduction of a pilot injection demonstrates the capacity to extend the safe operation range of such technology, without degrading NOx emissions or combustion efficiency.