Abstract
An experimental study was performed to investigate the combustion instability characteristics of swirl-stabilized combustors. A premixed gas composed of ethylene and air was burned under various flow and geometric conditions. Experiments were conducted by changing the inlet mean velocity, equivalence ratio, swirler vane angle, and combustor length. Two dynamic pressure sensors, a hot-wire anemometer, and a photomultiplier tube were installed to detect the pressure oscillations, velocity perturbations, and heat release fluctuations in the inlet and combustion chambers, respectively. An ICCD camera was used to capture the time-averaged flame structure. The objective was to understand the relationship between combustion instability and the Rayleigh criterion/the flame structure. When combustion instability occurred, the pressure oscillations were in-phase with the heat release oscillations. Even if the Rayleigh criterion between the pressure and heat release oscillations was satisfied, stable combustion with low pressure fluctuations was possible. This was explained by analyzing the dynamic flow and combustion data. The root-mean-square value of the heat release fluctuations was observed to predict the combustion instability region better than that of the inlet velocity fluctuations. The bifurcation of the flame structure was a necessary condition for combustion instability in this combustor. The results shed new insight into combustion instability in swirl-stabilized combustors.
Highlights
Conventional gas turbine engines used for electric power generation have mainly employed diffusion-flame-type combustors because of their high reliability and stability [1]
The first objective of the present study is to investigate the effects of flow and geometric conditions on the dynamic combustion characteristics of swirl-stabilized combustors
The dynamic combustion characteristics (p, q, u′) and flame structure of turbulent premixed flames in swirl-stabilized combustors were studied by changing the inlet mean velocity (10, 15, and 20 m/s), equivalence ratio (0.55–0.80), swirl numbers (SNs) (0.43, 0.65, 0.99), and combustion chamber length (95, 320 mm)
Summary
Conventional gas turbine engines used for electric power generation have mainly employed diffusion-flame-type combustors because of their high reliability and stability [1]. This type of combustion causes high temperatures in the local flame zones, increasing the formation of thermal NOx and soot. Recent gas turbine engines have often been operated under lean premixed or partially premixed conditions, to overcome increasingly stringent emission regulations [2,3]. Self-excited thermo-acoustic instability is likely to occur under fuel-lean premixed conditions. Combustion instability can lead to structural defects or failures in the combustor, in addition to severe problems in terms of heat transfer and combustion efficiency. The necessary condition for this phenomenon was provided by Rayleigh [4] and is summarized as follows:
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