The accuracy of laser-induced incandescence (LII) measurements is significantly influenced by the calibration process and the laser profile degradation due to beam steering. Additionally, the wavelength used for extinction measurements, needed for LII calibration, is critical and should be kept as high as possible in order to avoid light absorption by molecular species in the flame. The influence of beam steering on the LII measurement was studied in turbulent sooting C 2 H 4 /air flames at different pressures. While inhomogeneities in the laser profile become smoothed out in time averaged measurements, especially at higher pressure, the corresponding single shot beam profiles reveal an increasing effect of beam steering. In the current configuration it was observed that the resulting local laser fluence remains within certain limits (30% to 200%) of the original value. A sufficiently high incident laser fluence can thus prevent the local fluence from dropping below the LII threshold value of approximately 0.3 J/cm 2 at the cost of increased soot surface vaporization. A spatial resolution in the dimension of the sheet thickness of below 1 mm cannot be guaranteed at increased pressure of 9 bars due to beam steering. A feasibility study in a combustor at technical conditions demonstrates the influence of both effects beam steering and choice of calibration wavelength and led to the conclusion that, however, a shot to shot calibration of LII with simultaneously measured extinction can be realized.

Laser-induced Fluorescence / Thermometry / Lean Combustion / Gas Turbine A method for measurements of planar temperature distributions based on planar laser-induced fluorescence (PLIF) of the OH radiacal is described. The technique was developed specifically for the application in lean combustion systems, where OH equilibrium concentrations are largely independent on equivalence ratio and a function of temperature only. It is thus possible to derive a temperature information from measurements of absolute OH concentration, which can be obtained from a combined PLIF/absorption measurement. This paper discusses the basics of the method, and describes validation experiments in high pressure laminar premixed flames which were performed to asses its applicability and accuracy. Therefore, we compared our LIF based results with CARS measurements performed in the same flames. Finally, an example for the application in a lean gas turbine model combustor is discussed.

In this contribution, an overview of the progress in the design of an enhanced FLOX® burner is given. A fuel flexible burner concept was developed to fulfill the requirements of modern gas turbines: high specific power density, high turbine inlet temperature, and low NOx emissions. The basis for the research work is numerical simulation. With the focus on pollutant emissions, a detailed chemical kinetic mechanism is used in the calculations. A novel mixing control concept, called HiPerMix®, and its application in the FLOX® burner are presented. In view of the desired operational conditions in a gas turbine combustor, this enhanced FLOX® burner was manufactured and experimentally investigated at the DLR test facility. In the present work, experimental and computational results are presented for natural gas and natural gas+hydrogen combustion at gas turbine relevant conditions and high adiabatic flame temperatures (up to Tad=2000 K). The respective power densities are PA=13.3 MW/m2 bar (natural gas (NG)) and PA=14.8 MW/m2 bar(NG+H2), satisfying the demands of a gas turbine combustor. It is demonstrated that the combustion is complete and stable and that the pollutant emissions are very low.

An experimental analysis of confined premixed turbulent methane/air and hydrogen/air jet flames is presented. A generic lab scale burner for high-velocity preheated jets equipped with an optical combustion chamber was designed and set up. The size and operating conditions were configured to enable flame stabilization by recirculation of hot combustion products. The geometry of the rectangular confinement and an off-center positioning of the jet nozzle were chosen to resemble one burner nozzle of a FLOX V Rbased combustor. The off-center jet arrangement caused the formation of a pronounced lateral recirculation zone similar to the one in previously investigated FLOX V R -combustors (Lückerath et al., 2007. "FLOX V R Combustion at High Pressure with Different Fuel Compositions," ASME J. Eng. Gas Turbines Power, 130(1), pp. 011505; Lammel et al., 2010. "FLOX V R Combustion at High Power Density and High Flame Temperatures," ASME J. Eng. Gas Turbines Power, 132(12), p. 121503ff). The analysis was accomplished by different laser measurement techniques. Flame structures were visualized by OH* chemiluminescence imaging and planar laser-induced fluorescence of the OH radical. Laser Raman scattering was used to determine concentrations of the major species and the temperature. Velocity fields were measured with particle image velocimetry. Results of measurements in two confined jet flames are shown. The mixing of fresh gas with recirculating combustion products and the stabilization of the methane flame are discussed in detail. The presented findings deliver important information for the understanding of confined jet flames operated with different fuels. The obtained data sets can be used for the validation of numerical simulations as well.

An experimental analysis of confined premixed turbulent methane/air and hydrogen/air jet flames is presented. A generic lab scale burner for high-velocity preheated jets equipped with an optical combustion chamber was designed and set up. The size and operating conditions were configured to enable flame stabilization by recirculation of hot combustion products. The geometry of the rectangular confinement and an off-center positioning of the jet nozzle were chosen to resemble one burner nozzle of a FLOX®-based combustor. The off-center jet arrangement caused the formation of a pronounced lateral recirculation zone similar to the one in previously investigated FLOX®-combustors [1, 2]. The analysis was accomplished by different laser measurement techniques. Flame structures were visualized by OH* chemiluminescence imaging and planar laser-induced fluorescence of the OH radical. Laser Raman scattering was used to determine concentrations of the major species and the temperature. Velocity fields were measured with particle image velocimetry. Results of measurements in two confined jet flames are shown. The mixing of fresh gas with recirculating combustion products and the stabilization of the methane flame are discussed in detail. The presented findings deliver important information for the understanding of confined jet flames operated with different fuels. The obtained data sets can be used for the validation of numerical simulations as well.