Considerations for Hydrogen Fueled Aerospace Gas Turbine Combustion Sub-System Design

Abstract As part of its commitment to the decarbonization of the aviation sector and the UN Race to Zero global campaign, Rolls-Royce is actively developing hydrogen combustion gas turbine engine technology capable of powering a range of aircraft from 2035 onwards. These innovative technologies are undergoing integration and validation through a demonstrator project, which involves the modification of a Pearl15 engine for ground testing with gaseous and liquid hydrogen. The design of an aerospace combustor needs to satisfy conventional requirements such as cost, weight, aero-thermal performance, and lifespan. However, the introduction of hydrogen as the primary fuel introduces additional challenges, including potential novel failure modes, operability considerations and pollutant emissions. The NOx emissions resulting from hydrogen combustion are currently the subject of extensive research and are considered, to be one of the key considerations which will ultimately influence the design of the optimum hydrogen combustion sub-system for aerospace applications. This paper describes the development of the first prototype combustion technology at Rolls-Royce. Innovative fuel injection concepts were investigated to enable operation with 100% hydrogen on the Pearl 15 combustor architecture which is to serve as the test vehicle for ground demonstration in the Clean Aviation Project “CAVENDISH”. The paper details the process which began with prototype development and validation on a single sector atmospheric test rig to map the design space and understand sensitivities. This allowed the selection of four leading configurations based on NOx emissions, flame stability (measured using optical methods), ignition and weak extinction performance. The four configurations were then tested in a single sector, intermediate pressure rig testing at engine-representative low power conditions. This testing aimed at identifying challenges related to flame stability and combustor temperature distribution, thereby mitigating risks associated with engine combustor testing. Finally, tests were undertaken in a full annular, high pressure combustion rig at engine-representative maximum takeoff conditions. Aerothermal performance, as measured by NOx emissions, weak extinction and exit temperature traverse, demonstrated promising comparisons to kerosene-based fuel. These results demonstrate that a retrofittable combustion solution is credible and realistic for a minimum viable hydrogen gas turbine product.