Hochdrucktests von Wasserstoff-Kraftstoffinjektoren in einer Dreisektor-Fett-Mager-Brennkammer für das Rolls-Royce Pearl 15 Wasserstoff-Demonstrator-Triebwerksprogramm

Abstract

The effect of air traffic emissions on earth’s radiative forcing is substantial. Considering the continued projected growth of demand for air travel, novel solutions for the reduction of emissions, which go beyond incremental increases in system efficiency, are necessary. The integration of H2 as fuel for aircraft engines is one possible pathway to drastically lower emissions. While H2-combustion omits the formation of carbonaceous emissions like CO2, UHC and soot, its effect on the formation of NOx under conventional engine operating conditions is still not well understood. Considering the high impact of non-CO2-effects on the radiative forcing, the inhibition of NOx attains a new importance in the design of H2-injectors and combustion chambers. In this context, Rolls Royce is exploring direct H2-combustion in Rich-Quench-Lean (RQL) mode within Germany’s LuFo 6 program ’WOTAN’. Two H2-injectors were selected from previous testing under atmospheric conditions and were then tested at elevated pressures and preheat temperatures in the High-pressure Optical Triple Sector (HOTS) in the high-pressure test facility HBK1 at the DLR Institute of Propulsion Technology in Cologne. The results of the test campaign served as an additional safety check for the following full-annular test of both H2-injectors at take-off operating condition. Methods and results of the atmospheric and full-annular tests are presented elsewhere. Two H2-injectors with different fuel injection methods were tested at 7% take-off load. There an injector air-to-fuel ratio (AFRinj) variation was conducted to investigate the effect of stoichiometry on the flame shape and NOx-emissions. OH* is a marker of the heat release zone and water vapor is a combustion product. Superimposed OH* and water vapor images can indicate the reaction progress in the combustion chamber. Therefore, the flame was imaged in its ultra-violet (UV)-, near-infrared (NIR)-, and visible spectrum, thereby visualizing the line-of-sight OH* and water vapor occurrence, as well as the flame luminosity. The exhaust gas probe was located downstream of the convergent section of the combustion chamber. O2, CO2, and NOx were measured dry. A dynamic pressure probe was placed at the convergent section of the combustion chamber. Both injectors showed stable combustion over the investigated power range, with constant flame shape and position regardless of pressure, temperature, injector pressure drop or AFR. A significant absolute difference in the emission index (EI) of NOx between both injectors was observed for all the test points. The AFR variation showed a dissimilar sensitivity of EI NOx with respect to AFR between the two injectors. The absolute difference of NOx-emissions is found to be the result of different flame stabilization mechanisms. The flame of the injector with higher emissions showed flame anchoring at the injector exit, while the other injector established a lifted flame. The difference in NOx-sensitivity was attributed to the disparate fuel placement and local stoichiometry. Because of this one of the injectors formed a second heat release zone in the inner recirculation zone with increasing AFR.