Abstract
Green hydrogen produced by electrolysis offers a high potential for reducing CO2 emissions and thus represents a promising approach for the decarbonization of aviation. However, propulsion systems based on direct hydrogen combustion require modified fuel injectors and combustion chambers to account for the particular combustion characteristics of hydrogen. Engineering those modifications requires the acquisition of experimental and numerical tools especially suited for this task and in the end validating them in a suitable environment. In this context, hydrogen combustion and its numerical simulation is presented with a dual-swirl burner in an optically accessible atmospheric combustor as an intermediate step. The fuel injector was originally designed to simulate kerosene combustion with natural gas at atmospheric conditions by producing a gas film with mixing properties similar to a kerosene film. In this study, this natural gas fuel injector is adopted for combustion of pure hydrogen. To ensure safe operation and to reduce the risk of flashback, fuel and air are injected non-premixed. Good flame stability and mixing, which leads to potentially low NOx values, is achieved by introducing a swirling motion into the flows. Therefore, the air is fed through a co-rotating dual-swirler configuration. In the circumferential shear layer in-between, hydrogen is injected axially with a co-rotating velocity component. In this study, the combustor is operated under atmospheric pressure at a globally lean equivalence ratio. While hydrogen and cooling air are injected at ambient temperature, the burner air is preheated to 376.2 K. Cooling air is lead along the inner walls of the heat shield for convective cooling and enters the combustion chamber at the outer walls where it forms a cooling film for the side walls. Further cooling air is introduced via downstream located dilution ports to reduce the temperature at the combustor exit. Measurements of OH* radical chemiluminescence as well as infrared radiation as a marker of the hot water vapor distribution have been carried out to identify the flame location and shape. The configuration is further analyzed by means of reacting Large-Eddy-Simulations using the Flamelet-Generated-Manifolds combustion model in combination with the Dynamic Thickened Flame model. The comparison of the simulation results with the experimental reference data shows that the flame lift of height and global flame spread are correctly predicted by the simulation for both operating conditions. However, the combustion model does not precisely capture the flame stabilization mechanism, leading to a radial offset of the flame front.
