The Institute's HBK-S high-pressure combustion chamber test rig allows combustion processes in gas turbines to be studied under realistic conditions. Large quartz windows in the casing, combined with the use of optically accessible combustion chambers, enable that all laser-based diagnostic techniques developed at the Institute can be applied in such studies. Special challenges in this regard include adapting measurement techniques to extreme combustion conditions (pressures of up to 40 bar, thermal output of up to 1 MW), and ways of cooling and keeping clean the quartz windows. When using collimated high-power laser radiation, for example when applying CARS or laser Raman scattering, the combustion chamber windows can easily be damaged by impurities.
Reaction zones and regions of hot exhaust gas can be visualised using planar laser-induced fluorescence (PLIF) imaging of OH radicals. This measurement technology has been used, for example, to characterise flame stabilisation and combustion oscillations in a scaled industrial gas turbine burner made by Alstom .OH-PLIF imaging can also be used to study the flameless oxidation combustion concept for gas turbine combustors at pressures up to 25 bar . Particle image velocimetry (PIV) was used, among other things, to precisely characterise the turbulent flow field in an industrial gas turbine burner made by Siemens . It was possible, in particular, to show the importance of small and medium-sized vortices for mixing and flame stabilisation. A special challenge in this respect involved using single-pulse Raman measurements for simultaneous determination of species concentrations and temperature in the HBK-S high-pressure test rig. By applying this technique, it was possible for the first time to quantitatively determine the mixing and effects of turbulence-chemistry interaction in a scaled industrial gas turbine burner [4,5].