Within the ESTiMatE project, comprehensive experimental datasets are required to validate the newly developed numerical models. For this purpose, two different test rigs are operated at TU Berlin: a turbulent counterflow burner and a swirl combustor based on an RQL (rich burn, quick mix, lean burn) architecture. The latter test rig underwent a commissioning period and achieved first fire in October 2020. At the heart of the test facility, a fuel-flexible two stage swirler provides a fuel-air mixture to the combustion chamber. Figure 1 shows a photograph of the combustion lab.
The test rig was operated at a nominal thermal power of 30 kW and an equivalence ratio of 0.8 using natural gas, while an electric heater provided air of up to 400°C to the combustor. A number of non-intrusive experimental techniques were then integrated in the lab: particle image velocimetry, OH* chemiluminescence, and high-speed video of the flame. At the aft end, the exhaust gas was continuously monitored for NOx and CO emissions. The downstream termination of the hot gas tube had to be equipped with an orifice plate to suppress acoustic resonance. The delivery system for secondary, quenching air, which is injected through circular holes behind the fused silica combustion chamber, was also put to test. Figure 2 shows the PIV laser sheet at low energy and the natural gas flame in the optically accessible combustion chamber.
Liquid fuel (Jet A-1) is fed to the combustor from a high-pressure reservoir through a water-cooled fuel lance. A best practice for fuel switchover was developed as the combustor can only be ignited on natural gas. After tens of operating hours the initially well distributed liquid fuel flame became unstable due to insufficient cooling of the fuel atomizer. Therefore, in a next step, the thermal management strategy for the liquid fuel lance will be adapted so that the test rig can be used for the planned experiments.
Overall, the commissioning period was a success and showed that the combustor design works well in conjunction with the sophisticated experimental methods.