Due to climate change concerns, hydrogen is being considered for future aviation, but its commercial availability is limited, storage is bulky and its combustion with 100% concentration still poses numerous technical challenges. This leads to a certain interest in multi-fuel systems using both hydrogen and kerosene to facilitate the transition without completely redesigning the existing engines. Within the HOPE project, the present study focuses on an innovative multi-fuel combustion concept for aircraft propulsion, considering a laboratory-scale combustor hosted at TU Delft. Such a device, originally fueled with hydrogen and methane, is schematically composed of an axial swirler, four ducts for gaseous fuel injection, a mixing tube and a cylindrical combustion chamber. To avoid flashback, also an axial air injection duct is present that bypasses the swirler and directly reaches the air-fuel mixture in the mixing tube.
In this work, reactive CFD simulations are used to explore different spray injection configurations and assess the impact of kerosene on the flow field, the flame shape and the NO emissions of the modified system. In particular, three different injection positions are studied, featuring injection points on the backplane of the combustion chamber, inside the fuel/air mixing tube or on the axis of the burner. It is found that the most suitable position for kerosene injection is on the axis of the burner, so that the spray is surrounded by the swirling flow and undergoes a rapid mixing with the oxidising stream, limiting the maximum temperature reached by the mixture. Moreover, in this case, the addition of hydrogen leads to reduced NO emissions since it decreases the size of the hot spots generated by the combustion of kerosene.