This study reports on experimental investigations on isothermal and reacting swirled nonpremixed flows under varying pressure conditions. In this configuration, a central high speed fuel jet was surrounded by a heated swirling air flow. For the reacting case natural gas served as fuel whereas for isothermal conditions fuel was replaced by a mixture of helium and air to achieve Reynoldssimilarity. The optically accessible combustor allowed for application of laser diagnostics. Here we report on Laser Doppler Anemometry and planar laser-induced fluorescence (PLIF) experiments used to characterize the flow field and visualize selected scalars, respectively. Acetone served as a fluorescence marker for mixture fraction investigations. The hydroxyl radical was used to provide general features of the reaction zone such as flame shape and mean stabilization. To expose the influence of pressure on the flame structure three different operating points were investigated varying the combustor pressure between 2 and 6 bar while the inflow bulk velocities remained the same. Striking features of the present configuration are a detached flame, multiple recirculation zones, and complex coherent flow structures.

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This study reports on measurements in a generic non-premixed gas turbine combustor segment. Flow and scalar field were characterized using advanced laser diagnostic methods. The optically accessible burning chamber allowed for measurement of inflow conditions close-by the nozzle important for comparisons with numerical simulations. The generic nozzle design is sufficiently simplified to be precisely reproduced by block structured computational grids but shows typical features of gas turbine applications. To expose the influence of heat release on the flow field properties both isothermal and combusting conditions were investigated. Striking features of the present configuration are a detached flame, multiple recirculation zones, and complex coherent flow structures.

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.

The lean premixed combustion system was scaled from Siemens 60Hz engine application and optimized for implementation in the new SGT5-8000H 50Hz engine. The Siemens H-class engine is air cooled, uses a pressure ratio of 19:1 and is designed to achieve an efficiency of >60% efficiency in combined cycle operation. This improved dry low NOx system is of can annular type and consists of 16 cans in the SGT5-8000H. It was developed and tested in a full scale, high pressure rig test program. The single can high pressure rig simulates closely the flow conditions upstream of the combustor in the SGT5-8000H midframe and downstream of the combustor at the turbine inlet. The combustion system uses 5 fuel stages which allow flexible tuning over the whole range of engine operation conditions (ignition, idling, part- and base load). The system is designed to operate over a wide range of fuel quality and preheat temperatures. The test program is carried out over multiple years and encompasses rig / engine tests. This paper describes the combustion system in more details and the testing methodology. The test rig results showed that the performance targets are fully achieved in terms of emissions and operational requirements. Furthermore, the development / validation program will continue to reduce emissions through extended programs for future engines.

Lean premixed combustion technology became state-of-the-art in modern gas turbines for power generation to reduce NOx emissions. In these systems, thermo-acoustic oscillations are easily excited in the combustion chamber. Due to the high heat release density, extreme amplitudes can occur which reduce component life or may even cause damage to the engine. Knowledge of the acoustic behavior is required in order to understand and predict these instabilities. This study of the combustor-turbine interaction is focused on the reflection coefficient analysis. The interface between the combustion system and the first turbine stage is the focus area of this study. The rotating components need to be included as outlook of this work. Compressible Large Eddy Simulation (LES) resolving acoustics is applied based on the open source CFD code OpenFOAM. Five cases of increasing complexity are presented. The main idea is to begin the study based on simple geometries such as a convergent-divergent nozzle and two nozzles respectively convergent and divergent, to proceed with increased complexity by adding a vane section, and finally to investigate the behavior of a realistic turbine design. The real engine case consists of an authentic geometry including a can annular combustion chamber and turbine vane section. These cases are studied as basic generic tests in order to validate analytical formulae and to test the CFD methods applied. Calculations with acoustic excitation and non reflecting boundary conditions (NRBC) at the computational inlet and outlet domains are carried out to verify the plausibility of the acoustic set up. The forced response approach is applied provoking a wave excitation at the inlet of the combustion chamber. Multi-harmonic excitation with small amplitudes is used to stay in the linear range. The post-processing for all cases is performed using the two-microphone method in order to calculate the reflection coefficient and the acoustic impedance taking into account the effects of the mean flow.

This work contributes to the understanding of mechanisms that lead to increased carbon monoxide (CO) concentrations in gas turbine combustion systems. Large-eddy simulations (LES) of a full scale high pressure prototype Siemens gas turbine combustor at three staged part load operating conditions are presented, demonstrating the ability to predict carbon monoxide pollutants from a complex technical system by investigating sources of incomplete CO oxidation. Analytically reduced chemistry is applied for the accurate pollutant prediction together with the dynamic thickened flame model. LES results show that carbon monoxide emissions at the probe location are predicted in good agreement with the available test data, indicating two operating points with moderate pollutant levels and one operating point with CO concentrations below 10 ppm. Large mixture inhomogeneities are identified in the combustion chamber for all operating points. The investigation of mixture formation indicates that fuel-rich mixtures mainly emerge from the pilot stage resulting in high equivalence ratio streaks that lead to large CO levels at the combustor outlet. Flame quenching due to flame-wall-interaction are found to be of no relevance for CO in the investigated combustion chamber. Post-processing with Lagrangian tracer particles shows that cold air—from effusion cooling or stages that are not being supplied with fuel—lead to significant flame quenching, as mixtures are shifted to leaner equivalence ratios and the oxidation of CO is inhibited.

An upgrade of the lean premixed combustion system installed in the SGT5-8000H in Irsching/Germany was developed for the 50 Hz and 60 Hz versions of the SGTX-8000H gas turbines. It features lower CO and NOx emissions by improving combustion aerodynamics and reduction of the air consumption of the combustion system. Furthermore an improved secondary air managing system increases the amount of air, which can be supplied in a controllable way to the turbine in part load operation and, thus, increases the combustor temperature. This is done in stepwise increasing the air mass flow to the turbine by feeding compressor exit air to different distinct turbine stages. All in all this system extends the turn down capability beyond the level achievable by the new combustion system alone. The new combustion system and the secondary air managing system were installed in full scale and tested in the SGT6-8000H test facility of the Siemens Gas turbine plant in Berlin. The results have subsequently successfully been validated in the first commercial application on a customer site. This paper presents the technical features of the systems, the development program and the test results.