Analyse de la stabilisation, structure et des émissions de flammes hydrogène-air sur un injecteur coaxial pour la propulsion aéronautique

Due to the rising challenge of climate change, more and more industries are looking for ways to decarbonize their activities. The aeronautical industry is no different, and hydrogen-fuelled engines, among others, appear as a solution to reduce the carbon footprint of commercial flights. Hydrogen is absolutely carbon-free, producing only water vapor when burned, and contains the most energy per kilogram of any fuel, making it the ideal clean fuel at first glance. However, using a hydrogen as a fuel is a challenge in many ways. In addition to being difficult to store, the combustion properties of hydrogen are unique: it is extremely flammable and burns hotter than most other fuels. This in turn causes two main issues when burning it in an engine: safety, as hydrogen can ignite in zones where combustion is unwanted, and pollution, as hotter flames can lead to production of nitrogen oxides (NOx). This work focuses on this second issue by studying a novel injection mode on swirled coaxial injectors. These injectors are very modular, allowing different diameters and variable swirls.After conducting a parametric study on flame stabilization and NOx emissions for non-premixed hydrogen flames stabilize on our injector, we investigate the effects of injecting a rich mixture instead of pure fuel on flame structure and NOx. After observing that this different injection mode is capable of reducing flame volume and emissions, scaling laws relating flame characteristics and NOx are derived, first for jet flames and then for more complex swirled flames, using additional insight from Large Eddy Simulation. In addition, an inventory of the different flame structure produced with rich mixture injection with different degrees of swirl and different diameter combinations is generated. To go further, fine observations of flames using OH Planar Laser-Induced Fluorescence synchronized with Stereo Particle Image Velocimetry are made to give insight into how partial-premixing affects flame structure and strain profiles. These diagnostics are employed over multiple flames with diverse structures and configurations, giving insight into the different interaction between swirl-induced flow structure and flame stabilization in the different flame zones, in both lifted and attached flames. With the knowledge gathered, a new injector, consisting of three swirled coaxial channels to reduce flame volume is designed and studied using chemiluminescence imaging and gas analysis. This first study on this type of injector validates the broad design cues extracted from the rest of the work.