Factors Determining the Flame Configuration and Affecting Combustion Stability in Gas-Turbine Combustors
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Vol. 54, No. 4, November, 2020
FACTORS DETERMINING THE FLAME CONFIGURATION AND AFFECTING COMBUSTION STABILITY IN GAS-TURBINE COMBUSTORS L. A. Bulysova,1 A. G. Tumanovskii,2 M. N. Gutnik,2 and V. D. Vasil’ev2 Translated from Élektricheskie Stantsii, No. 6, June 2020, pp. 2 – 5.
The possibilities of influencing combustion stability during changeover to low-emission combustion and ways of extending the stable combustion range are analyzed. The flow velocity, temperature, and pressure in the low-emission combustor (LEC) are considered as influencing factors. A premixed swirl-stabilized combustor is considered. The burner unit consists of main and pilot burners. The main burner has two fuel channels that allow controlling the quality of the air-fuel mixture. The LEC developed for an aeroderivative gas turbine was tested at an inlet air pressure of 2 MPa and an inlet air temperature of 475°C and an exhaust gas temperature of up to 1320°C. Keywords: low-emission combustor; gas turbine; air-fuel mixture; nitrogen oxide; stable combustion; experimental studies; control algorithm.
Because of the complex geometry of the outlet channel and the developed end of the burner, the swirl of the flow is not so strong and its opening is not so significant. This allows the recirculation zone to form along the axis of the combustion chamber to which the air exiting the main burner is hardly admixed. This flow structure, on the one hand, allows achieving stable combustion and high combustion efficiency with the PB, even at low fuel flows in it, because cold air from the main burner is hardly admixed to the combustion region. On the other hand, this flow structure creates problems for stable combustion when feeding fuel to the MB after changeover to
Low-emission combustors (LEC) of gas turbines must ensure reliable and effective operation of power-generating installations. One of the ways to reduce the NOx emission is to decrease the flame temperature by burning a well-mixed lean air-fuel mixture (AFM). The necessity of meeting the operational and energy requirements simultaneously severely complicates the issue because this reduces the reliability of the system as a whole because of possible thermoacoustic pulsations, lean blowoff, and backfire to the mixing zone. An important task in developing a LES is to assess the combustion stability margin and the possibilities to control it. A schematic of LEC, its principle of operation, and fuel control can be found in [1]. Here we will analyze the influence of such factors as velocity, pressure, and temperature in the combustion region on the combustion stability margin. Figure 1 shows the velocity field in a longitudinal section of the LEC after the burner units (BU). The solid arrows indicate the main flow directions that form three recirculation/stabilization zones of the flame. It can be seen that the velocity field has complex structure and separates the airflows from the pilot and main zones. Exiting the main burner (MB), the swirling flow opens and moves at high velocity toward the l
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