Application of Laser Techniques in Combustion Environments of Relevance for Gas Turbine Studies

Abstract: In the work presented in this thesis, different laser-based techniques were employed for measurements in different combustion devices. Laser-based techniques enable non-intrusive and in-situ measurements to be carried out, in which high spatial and temporal resolution can be obtained. Different parameters related to combustion research can be visualized, such as species concentrations, temperature, velocities and particle sizes. The combustion devices investigated can be related in one way or another to gas turbine combustion, the measurements being performed in devices ranging from laboratory-scale burners to industrial gas turbine burners. The Triple Annular Research Swirler (TARS) is a laboratory burner that simulates the character of a gas turbine, in terms of both fuel injection and flame stabilization. Studies using planar laser-induced fluorescence (PLIF) were carried out here to demonstrate how different swirler configurations affect flame and flow dynamics and how flashback depends on different operating conditions. Simultaneous measurements of OH PLIF and of acetone PLIF were employed to visualize flame position and fuel distribution, respectively, the measurements being carried out simultaneously with velocity measurements involving particle image velocimetry (PIV). Visualization of flame position and of fuel distribution through use of OH PLIF and acetone PLIF was applied to several industrial gas turbine burners to investigate their combustion characteristics. The measurements were performed on-site at Siemens in Finsp {a}ng, in burners fueled with natural gas or with a mixture of natural gas and hydrogen. The aim of the experimental investigations was to obtain a better understanding both of the mixing of air and fuel and of the flame dynamics, knowledge of which can hopefully be used to further reduce the emission levels from gas turbines. Part of the experimental results was used for the validation of computational fluid dynamics (CFD) models, used to simulate the flow and the turbulent combustion inside the combustion chamber. A Multi-YAG laser system which can generate a rapid burst of laser pulses, and a high-speed framing camera capable of recording sequences of up to eight images, were used to study fuel vaporization, and its consequent mixing with air, in a Jet A or biojet fueled gas turbine pilot burner under elevated pressure conditions. Fuel PLIF was used to visualize both the liquid and the gas phase of the fuel, Mie scattering being used to visualize only the liquid phase of the fuel. The liquid phase of the fuel was found, as expected, to be close to the burner nozzle and the evaporated fuel to be found a distance downstream from the burner nozzle. High-speed OH PLIF was also employed for visualizing the flame position. Additional work carried out included characterization of partially premixed and diffusion flames in a high-pressure vessel and burner (HPVB) using OH PLIF and PAH PLIF for the visualization of flame position and of polyaromatic hydrocarbon distribution, respectively. Flames using liquid fuels (n-heptane, n-decane and ethanol) as well as gaseous (methane) fuels were studied. The results are intended to be used as data base for kinetic mechanisms and as validation data for CFD models.