Atmospheric Testing of Hydrogen Fuel Injectors for RQL Combustion within the Rolls-Royce Pearl 15 Hydrogen Demonstrator Engine Program Atmosphärische Untersuchung von Wasserstoff-Kraftstoffinjektoren für Fett-Mager-Verbrennung im Rolls-Royce Pearl 15 Wasserstoff-Demonstratortriebwerksprogramm

Abstract

Hydrogen in aviation is a potential candidate to achieve reduced CO2 emissions as well as satisfying the high energy demand for propulsion. The altered combustion characteristics of hydrogen, for example the higher flame speed, needs to be understood for application in aircraft combustors. A total of five swirl stabilized hydrogen injectors for well researched rich-quench-lean combustion were developed and provided by Rolls-Royce Deutschland to the DLR Institute of Propulsion Technology in Cologne. The injectors are tested at atmospheric pressure and otherwise combustor-like test conditions for flame stabilization, weak extinction and thermoacoustic response. The optical measurements to record the rich primary zone consist of cameras in the infrared and ultraviolet wavelengths, which are tuned for water-vapor and OH* radiation respectively. The images are averaged, deconvoluted and overlayed to study the injector designs. All injectors are found to stabilize at all test conditions. The injectors are shown at a lean and at a rich air-fuel-ratio. The thermoacoustic response is low and the weak extinction levels remarkably high. Flame stabilization was observed in the shear layer of the inner recirculation zone and, in some cases, in the shear layer of the outer recirculation. In variant 1 and 2, the fuel is introduced within two air flows and interacts with both, which leads to an elongated heat release zone. The design objective of these two variants was to achieve fast mixing of air and fuel. Contrary, variant 3 to 5 are designed to achieve locally fuel rich and thus colder regions. Variant 3 shows an extraordinarily low fuel velocity in its central fuel injection and produces a V-shaped flame. Variant 4 and 5 also feature a central fuel injection, but achieve a radial velocity component in the fuel by means of a swirler. Fuel and air mix more intense than in the case of V3 and distinct combustion zones form. Lastly, variant 2 and 5 are shown with a shortened seal which eliminates flame anchoring on the seal, but also removed the flow widening effect of the seal. Based on the experimental results, it is concluded that hydrogen flames stabilize well in a kerosene-derived swirl injector at fuel rich and lean conditions. Flame blow off is not expected to be a challenge in hydrogen combustion. The design objective of good mixing for variant 1 and 2 was achieved, as well as locally fuel rich regions created for variant 3 to 5