Ulrich Stopper

Flow Field and Combustion Characterization of Premixed Gas Turbine Flames by Planar Laser Techniques

Lean premixed natural gas/air flames produced by an industrial gas turbine burner were analyzed using laser diagnostic methods. For this purpose, the burner was equipped with an optical combustion chamber and operated with preheated air at various thermal powers P, equivalence ratios Φ, and pressures up to p=6 bars. For the visualization of the flame emissions OH∗ chemiluminescence imaging was applied. Absolute flow velocities were measured using particle image velocimetry (PIV), and the reaction zones as well as regions of burnt gas were characterized by planar laser-induced fluorescence (PLIF) of OH. Using these techniques, the combustion behavior was characterized in detail. The mean flow field could be divided into different regimes: the inflow, a central and an outer recirculation zone, and the outgoing exhaust flow. Single-shot PIV images demonstrated that the instantaneous flow field was composed of small and medium sized vortices, mainly located along the shear layers. The chemiluminescence images reflected the regions of heat release. From the PLIF images it was seen that the primary reactions are located in the shear layers between the inflow and the recirculation zones and that the appearance of the reaction zones changed with flame parameters.

Flow field and combustion characterization of premixed gas turbine flames by planar laser techniques

Lean premixed natural gas/air flames produced by an industrial gas turbine burner were analyzed using laser diagnostic methods. For this purpose, the burner was equipped with an optical combustion chamber and operated with preheated air at various thermal powers P, equivalence ratios Φ , and pressures up to p = 6 bar. For the visualization of the flame emissions OH* chemiluminescence imaging was applied. Absolute flow velocities were measured using particle image velocimetry (PIV), and the reaction zones as well as regions of burnt gas were characterized by planar laser induced fluorescence (PLIF) of OH. Using these techniques, the combustion behavior was characterized in detail. The mean flow field could be divided into different regimes: the inflow, a central and an outer recirculation zone, and the outgoing exhaust flow. Single-shot PIV images demonstrated that the instantaneous flow field was composed of small and medium sized vortices, mainly located along the shear layers. The chemiluminescence images reflected the regions of heat release. From the PLIF images it was seen that the primary reactions are located in the shear layers between the inflow and the recirculation zones and that the appearance of the reaction zones changed with flame parameters.Copyright

Experimental Analysis of the Combustion Behavior of a Gas Turbine Burner by Laser Measurement Techniques

Experimental results from optical and laser spectroscopic measurements on a scaled industrial gas turbine (GT) burner at elevated pressure are presented. Planar laser induced fluorescence on the OH radical and OH* chemiluminescence imaging were applied to natural gas/air flames for a qualitative analysis of the position and shape of the flame brush, the flame front and the stabilization mechanism. The results exhibit two different ways of flame stabilization, a conical more stable flame and a pulsating opened flame. For quantitative results, 1D-laser Raman scattering was applied to these flames and evaluated on an average and single shot basis in order to simultaneously determine the major species concentrations, the mixture fraction and the temperature. The mixing of fuel and air as well as the reaction progress could thus be spatially and temporally resolved, showing differently strong variations depending on the flame stabilization mode and the location in the flame.

Experimental Investigations of Flame Stabilization of a Gas Turbine Combustor

While today’s gas turbine (GT) combustion systems are designed for specific fuels there is an urgent demand for fuel-flexible stationary GT combustors capable of burning natural gas as well as hydrogen-rich fuels in future. For the development of a fuel flexible, low-emission, and reliable combustion system a better understanding of the flow field – flame interaction and the flame stabilization mechanism is necessary. For this purpose, a down-scaled staged can combustion system provided with an optical combustion chamber was investigated in a high pressure test rig. Different optical diagnostic methods were used to analyze the combustion behavior with a focus on flame stabilization and to generate a comprehensive set of data for validation of numerical simulation methods (CFD) employed in the industrial design process. For different operating conditions the size and position of the flame zone were visualized by OH* chemiluminescence measurements. Additionally, the exhaust gas emissions (NOx and CO) and the acoustic flame oscillations were monitored. Besides many different operating conditions with natural gas different fuel mixtures of natural gas and hydrogen were investigated in order to characterize the flashback behavior monitored with OH* chemiluminescence. For selected operating conditions detailed laser diagnostic experiments were performed. The main flow field with the inner recirculation zone was measured with two-dimensional particle image velocimetry (PIV) in different measuring planes. One-dimensional laser Raman spectroscopy was successfully applied for the measurement of the major species concentration and the temperature. These results show the variation of the local mixture fraction allowing conclusions to be drawn about the good premix quality. Furthermore, mixing effects of unburnt fuel/air and fully reacted combustion products are studied giving insights into the process of the turbulence-chemistry interaction and reaction progress.Copyright