An Industry Approach of Aero-Engine Fuel Spray Nozzle Optimization for Thermoacoustics

Abstract Thermoacoustic instabilities pose a challenge in many combustion systems. From an industry point-of-view it is important to have the right tools at hand, in best case to reliably predict the occurrence of instabilities upfront of an engine development program or at least to be able to quickly react during the development phase, or in worst case even later. In an industrial context these tools need to be as simple, as quick, and as cheap as possible while still delivering a consistent and reliable output. Such a tool chain typically combines numerical, experimental, and low order modelling methods. Rolls-Royce has established a set of tools for the thermoacoustic evaluation and validation of fuel-spray-nozzles (FSN) and the whole combustion system before testing it on an engine. This paper demonstrates our approach by example of an aero-engine fuel spray nozzle optimization. This process takes several steps. First some worthwhile modifications to the FSN needs to be identified. This can either be based on previous experience, engineering judgement (e.g. based on CFD), or a dedicated parameter study. Then, the proposed modifications are tested in the Rolls-Royce thermoacoustics rig SCARLET to extract the flame-transfer-function (FTF). While some conclusions can already be drawn from these test results alone, the next step applies the measured FTF in a low order thermoacoustic network model (LOTAN) of the engine combustion system for stability prediction. Based on the SCARLET results and the stability prediction the most promising configurations are selected for validation in a full annular combustion test (FANN). The results from each of these steps illustrate how the FSN improvements can be successfully evaluated from low to high TRL (Technology Readiness Level) testing, so that only the most appropriate candidate is brought forward into the final product design. The methods and processes, while demonstrated here by example of a kerosene fueled aero-engine FSN, can be applied in the same way to other types of fuels like sustainable aviation fuel (SAF) or hydrogen.