Characterisation of piloted single-nozzle lean direct injection burners with angled hydrogen jet injection

Hydrogen presents a viable route to decarbonising gas turbine engines; however, its significantly different combustion characteristics, as compared to conventional hydrocarbons, necessitate the need to develop new combustor designs which mitigate issues of flame instability, thermoacoustics and high Nitrogen Oxide (NO X ) emissions. This study is conducted on a piloted single-nozzle hydrogen Lean Direct Injection (LDI) burner, where the fuel jet is injected in a cross-flow of air, close to the combustor inlet, resulting in a partially premixed mixture with good fuel–air mixing whilst mitigating flashback. The design and arrangement of fuel injection have been shown to considerably influence hydrogen-air mixing in LDI burners. The work aims to understand the effect of the angle of hydrogen fuel injection on flame behaviour, combustor dynamics and NO X emissions. Three hydrogen jet injection angles (45°, 90° & 135°) were investigated for a range of air velocities, 30 m/s to 90 m/s, and global equivalence ratios, 0.1 to 0.6. Fuel–air mixing, flame behaviour and emissions characteristics were determined using Laser-Induced Breakdown Spectroscopy, OH* high-speed chemiluminescence, dynamic pressure and NO X measurements. The results show that the hydrogen jet injection angle has a considerable influence on fuel–air mixing characteristics, flame macrostructure and dynamic behaviour. The transverse fuel injection configuration produces stable, lifted flames as shown in the modified progress variable figures, which result in lower levels of NO X emissions at an air velocity of 40 m/s, due to the lower residence time. On the other hand, upstream angled fuel injection resulted in attached flames, a more uniform fuel–air mixture profile, and relatively lower acoustic amplitudes. This research yields new insights into hydrogen flame stabilisation mechanisms, provides crucial data for numerical validation, and informs the design of fuel injectors for 100% hydrogen combustors, thereby enhancing the practical value of this research. • Jet penetration effects on mixture fraction and flame position were characterised. • Transverse injector (90°) predominantly showed lifted flames with flat root profile. • Upstream-angled injector (135°) produced anchored flames at all tested conditions. • Downstream-angled injector (45°) gave lifted flames with inverted V-shaped roots. • Anchored flames exhibited the lowest dynamic pressure amplitudes.