58602 - 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) is presented. The new approach is to separate the rich primary zone from the lean secondary zone and, therefore, allowing for an isolated thermoacoustic characterization of each combustion chamber. The test rig also offers the possibility to combine both zones to assess the transferability of the findings from the separated to the compact configuration. Different combustion modes and their realization with a pressure-swirl aero-engine injector in the rich primary zone are shown and range from perfectly premixed natural gas combustion to a non-premixed kerosene flame. Heat losses between the combustion chambers, whose minimization is crucial for the reignition of the partially burned gases from the primary zone, are estimated. In the lean secondary zone, the design challenges include the theoretical verification of re-ignition and the main design steps for achieving complete burn-out of the hot primary combustion gases. Considering a high modularity of the test-rig already in the design phase explains the potential for saving costs and manufacturing time. The layout and design of the acoustic excitation via loudspeakers, the measurement and the reconstruction of the acoustic pressure field in the corresponding impedance measurement tubes are described. The ignition of both zones, the acoustic behaviour and operational limits of the test rig are demonstrated experimentally and include first measurement validation data and also the approach for damping certain self-excited thermoacoustic instabilites. Finally an outlook of the future work in the research project concludes this paper and underlines the ability of the new RQL-test-rig for low-frequency thermoacoustic investigations in the two separated combustion chambers.