In Flameless Oxidation (FLOX®) the combustion is distributed over a large volume by a high internal flue gas recirculation. This technology has been successfully used for many years in technical furnaces under atmospheric conditions with very low NOx emissions. In the work presented here, FLOX® combustion was for the first time investigated at high pressure in order to assess its applicability for gas turbine combustors. A FLOX® burner was equipped with a combustion chamber with quartz windows and installed into a high pressure test rig with optical access. The burner was operated under typical gas turbine conditions at pressure of 20 bar with thermal powers up to 475 kW. Natural gas as well as mixtures of natural gas and H2 were used as fuel. The NOx and CO emissions were recorded for the different operating conditions. OH* chemiluminescence imaging and planar laser-induced fluorescence of OH were applied in order to characterize the flame zone and the relative temperature distributions. The combustion behaviour was investigated as a function of equivalence ratio and fuel composition, and the influence of the gas inlet velocity on mixing and emissions was studied. For various operating conditions the lean extinction limits were determined.

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 is 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 (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.

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.