Development of an Experimental Combustor for Hybrid Electric Gas Turbines

Future aircraft will require innovative propulsion architectures, such as hybrid electric gas turbines, for improvements in emissions and fuel economy. Hybridized propulsion systems impose novel operational constraints for the gas turbine, such as lower turndown ratios or sub-idle operation. Recent system-level studies have shown the feasibility of such architectures, but not the detailed combustor-level considerations. One particularly promising future aviation combustor concept is axially staged partially-premixed fuel injection, which is enabled by advances in additive manufacturing and sustainable aviation fuels. This paper describes facilities to develop a better understanding of axial fuel staging and the potential benefits it may provide. Two facilities have been developed to investigate different subsets of the relevant fundamental physics behind fuel staging. In particular, the success of fuel staging is highly dependent on both the nature of the fuel atomization in the coflowing staged air, but also the mixing of this staged air-fuel mixture into a vitiated crossflow. One facility was designed to study hybridized spray-in-coflow and spray-in-crossflow configurations and the second facility to assess the impacts of staged-fueling strategies on key combustor operability and turbine durability metrics, including flame shape, CO and NOx emissions, and turbine inlet temperature pattern. The facilities employ proven high-speed optical diagnostics and standard emission sampling methods to study the associated fluid mechanics and combustion dynamics. Additionally, innovative laser absorption-based measurement techniques can similarly be applied to resolve previously inaccessible spatial and temporal temperature profiles of the combustion products impinging on the turbine vane. This testbed can simulate a range of practical hybrid engine operating conditions. The contribution of this paper is to introduce new experimental testbeds for axially staging liquid fuels in aviation combustors and to detail the considerations that drive the facility and test design.