Investigation of Flame Stabilization in a High-Pressure Multi-Jet Combustor by Laser Measurement Techniques

Abstract

In this contribution, comprehensive optical and laser based measurements in a generic multi-jet combustor at gas turbine relevant conditions are presented. The flame position and shape, flow field, temperatures and species concentrations of turbulent premixed natural gas and hydrogen flames were investigated in a high-pressure test rig with optical access. The needs of modern highly efficient gas turbine combustion systems, i.e., fuel flexibility, load flexibility with increased part load capability, and high turbine inlet temperatures, have to be addressed by novel or improved burner concepts. One promising design is the enhanced FLOX® burner, which can achieve low pollutant emissions in a very wide range of operating conditions. In principle, this kind of gas turbine combustor consists of several nozzles without swirl, which discharge axial high momentum jets through orifices arranged on a circle. The geometry provides a pronounced inner recirculation zone in the combustion chamber. Flame stabilization takes place in a shear layer around the jet flow, where fresh gas is mixed with hot exhaust gas. Flashback resistance is obtained through the absence of low velocity zones, which favors this concept for multi-fuel applications, e.g. fuels with medium to high hydrogen content. The understanding of flame stabilization mechanisms of jet flames for different fuels is the key to identify and control the main parameters in the design process of combustors based on an enhanced FLOX® burner concept. Both experimental analysis and numerical simulations can contribute and complement each other in this task. They need a detailed and relevant data base, with well-known boundary conditions. For this purpose, a high-pressure burner assembly was designed with a generic 3-nozzle combustor in a rectangular combustion chamber with optical access. The nozzles are linearly arranged in z direction to allow for jet-jet interaction of the middle jet. This line is off-centered in y direction to develop a distinct recirculation zone. This arrangement approximates a sector of a full FLOX® gas turbine burner. The experiments were conducted at a pressure of 8 bar with preheated and premixed natural gas/air and hydrogen/air flows and jet velocities of 120 m/s. For the visualization of the flame, OH* chemiluminescence imaging was performed. 1D laser Raman scattering was applied and evaluated on an average and single shot basis in order to simultaneously and quantitatively determine the major species concentrations, the mixture fraction and the temperature. Flow velocities were measured using particle image velocimetry at different section planes through the combustion chamber.

Experimental and numerical investigation of spray characteristics in a new FLOX®based combustor for liquid fuels for Micro Gas Turbine Range Extender (MGT-REX)

“…6 of Ref. 13. This leads to an intense mixing of burnt gas with fresh fuel/air mixtures, and thus stabilization of the flame.…”

High Momentum Jet Flames at Elevated Pressure: B — Detailed Investigation of Flame Stabilization With Simultaneous PIV and OH-LIF

“…The turbulent high speed pipe flow inside these nozzles provides sufficient premixing and high flashback resistance at a wide range of operation conditions and fuels. Previous research demonstrated operation with pure hydrogen is possible at gas turbine relevant conditions with low NO x emissions and without flashback [7,8]. A key feature of a FLOX ® burner is the large inner recirculation zone, which brings hot burnt gas back to the combustor nozzles, where it supports the ignition of the incoming high momentum jet of fresh unburned fuel/air mixture.…”

“…The simplest model combustor is a lab-scale single nozzle burner, that has extensively been investigated at atmospheric conditions, both experimentally [11,12] and numerically [13]. Furthermore, a 3-nozzle model combustor has been investigated at high pressure [8]. All of these model combustors were down-scaled compared to full size gas turbine combustors, and therefore it was challenging to perform measurements with sufficient spatial resolution in order to resolve structures in context of flame stabilization.…”

Injector-coupled transverse instabilities in a multi-element premixed combustor

“…This injector configuration is similar to the FLOX V R combustion experiments, which have been widely studied. 34,41,42 The combustion chamber has cross-section dimensions of 238 mm and 30 mm in the x-and z-directions, respectively. In the flow (y-) direction, the crosssectional area is constant for the first 115 mm and is followed by a 92 mm long converging section where the chamber aspect ratio is held constant.…”

“…This injector configuration is similar to the FLOX® combustion experiments, which have been widely studied. 34,41,42…”