Atmospheric testing of hydrogen fuel injectors for RQL combustion within the Rolls-Royce Pearl 15 hydrogen demonstrator engine program

Abstract Five swirl stabilized hydrogen injectors for aviation propulsion rich-quench-lean combustion were provided by Rolls-Royce Deutschland to the DLR Institute of Propulsion Technology. The injectors are tested at atmospheric pressure and combustor-like test conditions. Cameras in the infrared and ultraviolet wavelengths are applied to record water-vapor and OH* radiation respectively. The images are averaged, deconvoluted and overlaid. All injectors are found to stabilize at lean and rich test conditions. 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. Fast mixing of air and fuel was the design objective. Variant 3–5 are designed to achieve locally fuel rich and thus colder regions. Variant 3 is designed for centrally injected low velocity fuel and produces a V-shaped flame. Variant 4 and 5 also feature a central fuel injection, but with a radial velocity component. Fuel and air mix more intense than in V3 and distinct combustion brushes form. Variant 2 and 5 are shown with a shortened seal which eliminates flame anchoring on the seal, but also removed the flow widening effect. Based on the experimental results, it is concluded that hydrogen flames stabilize well in a kerosene-derived swirl injector with high blow-off resilience. The objective of good mixing for variant 1 and 2 was achieved, likewise locally fuel rich regions created for variant 3–5.