A Direct Comparison of Flame-Transfer Matrices Measurements Between Hydrogen and Kerosene Flames in the Same Combustor at Realistic Aero-Engine Conditions

To model and predict thermoacoustic instabilities of a combustion system it is common practice that a flame transfer function (FTF) describes the flame dynamics. Therefore, Rolls-Royce developed a high-pressure single sector rig (SCARLET) to acoustically measure flame-transfer matrices (FTM) at realistic engine-operation conditions along the whole flight cycle. From the FTM measurement the FTF can be extracted for modelling purposes, by taking only the two-two-element of the matrix into account — that element describes the transfer of velocity fluctuations before the flame into velocity fluctuations after the flame front. As part of our net zero initiative to decarbonise future aviation, Rolls-Royce is developing hydrogen technologies. As part of the development of a new and interchangeable hydrogen fuel injector for an existing combustion system environment (a demonstrator engine), measurements of flame transfer matrices have been performed in the SCARLET rig to de-risk the occurrence of thermoacoustic instabilities. These measurements allow a direct comparison of transfer matrices of kerosene and hydrogen flames within the same combustor environment. The study allows a direct assessment between gaseous hydrogen and liquid kerosene fuel preparation to see how sensitive the FTF is to the fuel changes. Additionally, the direct influence on gains and time delays for selected operation conditions will be provided.