Design and Validation of a Novel Test-Rig for RQL Flame Dynamics Studies

In this paper a novel test-rig for the investigation of low-frequency thermoacoustic instabilities in aero-engines with air-staging RQL (rich-quench-lean) is presented. The new approach is to separate the rich primary zone from the lean secondary zone to allow for an isolated thermoacoustic characterization of each combustion zone. In addition the test-rig offers the possibility to combine both zones to judge the transferability of the findings from the separated to the compact configuration. The high modularity of the test-rig is already considered in the design-phase and allows a cost and time efficient manufacturing. Heat losses in the primary zone and the transition duct between the two zones play a crucial role for the functionality of the facility and are estimated during design to guarantee a stable re-ignition in the secondary zone. The main design steps in the secondary zone for achieving complete burn-out of the hot primary combustion gases are described. The realization of the acoustic excitation via loudspeakers is described and damping measures to improve combustor stability are explained. The operation of both zones, their acoustic behavior and the operational limits of the test-rig are demonstrated experimentally. They include first thermoacoustic measurement data of naturally occurring instabilities, the corresponding eigenfrequencies and the validation of the test-rig design. Finally an outlook on the future work in the research project concludes this paper.