A Study on Combustion Characteristics and Reduction of Emissions in a Swirl Pre-mixed Combustor : A StudyonCombustion CharacteristicsandReductionof EmissionsinaSwirlPre-mixed Combustor
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In recent decades, conventional power-generation systems have consumed fossil fuels as their source of energy. Several solutions, such as gas turbine combustor technology, have been demanded due to environmental restrictions and efficient use of energy. A gas turbine combustor has efficient performance and uses LNG, etc. for fuel. These are clean fuels for which three methods of combustion have been suggested: a lean pre-mixed flame, a quick-quench-lean-burn combustion, and catalytic combustion. The method of interest in this paper is a lean pre-mixed flame. A lean pre-mixed flame is one in which a large amount of excess air is supplied into the primary nozzle with the fuel. Hence, the combustion approaches the condition of the lower limit of flammability, which leads to a decrease in the flame temperature and harmful emissions, such as the thermal generation of NOx. The experimental and numerical analyses of lean pre-mixed combustion methods in this paper about flame characteristics and decreasing harmful emissions have been confirmed using two types of combustor. First, the experimental results of an EV burner showed that with an increasing inlet air temperature, the NOx emission increased due to a higher adiabatic flame temperature, while the CO emission increased or decreased at the low or high A/F ratio regime, respectively. The CO emission is dependent on the flame location. When the load was decreased from the design condition, the NOx emission decreased as the thermal load was reduced. With an increasing load, however, the NOx emission increased due to along residence time. The CO emission decreased or increased with decreasing load. This is because the flame extinction limit is extended by an increasing the inlet air temperature that induces an enhancement of the recirculation strength. Second, experimental and CFD studies have been carried out to investigate how a vortex generator affects the mixing and combustion characteristics of a swirl-stabilized premixed flame of a gas-turbine combustor. CFD analyses reveal that the vortex generator induces shear stress, weakens the swirl intensity, and consequently, changes the flow pattern of the premixed flame. The results also reveal that the vortex generator improves mixing between the air and the fuel. The emissions and chemiluminescence signals for various operating conditions are experimentally measured, and it can be concluded that the vortex generator positively affects the emissions and air/fuel mixing only when there is a sufficiently high flow velocity at the interface between the vortex generator and the fluid flow. Otherwise, the vortex generator has a slightly negative effect on the emissions and flow mixing. Third, as a result of a numerical study of a gas turbine combustor with a vortex generator Ⅱ, in the case of a combustor equipped with a vortex generator that configured the screw figure, a vortex generator in the combustor effectively generated a vortex that was maintained until the front of the combustor. It also led to a fluctuation in the pressure at different areas inside the combustor. Furthermore, the fuel/air mixing rate was enhanced upstream of the front of combustor, which was induced by decreasing the fuel-rich zone. As a result, the overall NOx emission decreased. According to the flame configuration, the swirl number was decreased by the effect of the vortex generator. These results were induced by the repeated change of flow velocity by the vortex generator.