On Gas Turbine Diagnostics with Emphasis on Combustion Chambers
Abstract: The thesis aims to analyse the gas turbine based energy conversion systems with the emphasis on combustion chambers. The investigation is mainly experimental at a component level. The majority of investigations concentrate on gaseous fuel firing. The influence of swirl, heat release and combustor geometry on the turbulent flows in a generic premixed gas turbine combustor, is investigated using particle image velocimetry (PIV), laser Doppler velocimetry (LDV). The goal is to characterize the main flow structures and turbulence in a model combustor that is relevant to gas turbines during Natural Gas firing. An explanation for the underlying mechanisms is presented to describe the effect of swirl, heat release and outlet contraction on the flow field. CO, NOx and total unburned HC were measured at the outlet of the combustor, and the influence of mass flow rate, inlet temperature, and addition of CO2– diluent was investigated. The combustor’s behaviour, particularly in the lean part of its range of operation, was investigated to assess some of the problems associated with combustion in suggested power plants for CO2 rich bio-fuels and CO2 capture/sequestration. The partially reformed mixtures can be formed using biomass. Before combusting these mixtures in a gas turbine, experimental work was done on the generic combustion chamber to examine the off-design combustor behaviour when switching from natural gas to the wet and dry generic hydrogen-rich mixtures. The thesis reports work on liquid atomisation. Although technical applications make use of well distributed and finely dispersed sprays, the injectors may operate under off-design conditions of low Weber numbers. A low We water spray subjected to an air cross-flow which similar to pre-vaporisers of lean premixed pre-vaporising (LPP) burners is studied. PIV and PDA have been used to quantify both the continuous and dispersed phases. A long range microscope has been used to characterize the column breakup process. Investigation of synthetic liquid fuel combustion in the generic combustor has been a part of this thesis. An experimental comparison of the synthetic jet fuel and jet A1 is performed. Emissions of NOX, CO and HC, ignition and extinction points, liner temperatures, soot levels in the combustor are studied. Modern gas turbine compressors are sensitive to changes in profile shape and to surface roughness with their highly loaded blades. The remedy to fouling problem is washing. The thesis work includes an investigation of the two-phase flow in the bellmouth of the compressor during off-line washing conditions. The main emphasis has been on studying the characteristics of the injected spray used for cleaning of the compressor. The used nozzles are akin to pressure swirl nozzles for liquid fuel injection. To provide with accurate boundary conditions for the spray, laser-based measurements of a spray, originating from an authentic wash nozzle, have been conducted. The other branch of this study aims to describe the behaviour of a generic combustor under off-design conditions that are reflecting the current trend of bio-fuels in the gas turbine power industry. Since it is rather rare to have custom-built gas turbines for low calorific value operation, the engine will be forced to operate outside its design envelope. Typical restraints are decrease in Wobbe-index and surge- and flutter-margins for turbomachinery. In this study, an advanced performance deck has been used to quantify the impact of firing low calorific value gases in a generic type gas turbine. A single-shaft gas turbine characterized by a compressor and an expander map is considered. Emphasis has been put on predicting the off-design behavior. The combustor is discussed and related to previous experiments which include investigation of flammability limits, Wobbe-index, flame position, etc.
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