High-pressure testing of hydrogen fuel injectors in a triple-sector RQL-rig for the Rolls-Royce Pearl 15 Hydrogen Demonstrator Engine Program

Abstract As part of Germany’s LuFo 6 program ’WOTAN’, Rolls-Royce Deutschland (RRD) investigated direct H 2 combustion in Rich-Quench-Lean (RQL) mode. Two H 2 -injectors, previously tested under atmospheric conditions, were evaluated at elevated pressures and preheat temperatures in the High-pressure Optical Triple Sector (HOTS) at DLR’s HBK1 facility. These tests served as a safety check for the following full-annular test at take-off operating condition. Both injectors were tested at 7% take-off load, with variations in air-to-fuel ratio (AFR) to examine the effects of stoichiometry on flame characteristics and NO x emissions. Flame imaging was conducted using ultra-violet (UV)-, near-infrared (NIR)-, and visible spectrum diagnostics to visualize OH*, water vapor and flame luminosity. Exhaust gas measurements were performed downstream of the combustion chamber’s convergent section. Both injectors demonstrated stable combustion across all test conditions, maintaining consistent flame position and shape despite changes in pressure, temperature and AFR. However, significant differences in NO x emission index (EI) were observed between the injectors. The injector with higher NO x emissions exhibited flame anchoring at the injector exit, while the other maintained a lifted flame, reducing thermal NO x formation. Additionally, AFR variation revealed different sensitivities of EI NO x , attributed to distinct fuel placement and local stoichiometry. One injector developed a second heat release zone in the inner recirculation region at higher AFRs, further contributing to elevated NO x .