Abstract
The effect of forced oscillations on the behaviour of non-premixed swirling methane flames close to the lean blow out limits was investigated using experiments in a lab-scale burner. Two different fuel injection geometries, non-premixed with radial -NPR- and non-premixed with axial -NPA- fuel injection, are considered. The flame behaviour is studied using 5 kHz OH∗ chemiluminescence and OH Planar Laser Induced Fluorescence (OH PLIF) imaging. In both systems, acoustic forcing reduces the stability of the flame, and in particular, the stability was found to decrease with the increase in forcing amplitude. Flame lift-off was observed in both configurations, with the magnitude of the effect of forcing depending on the fuel injection configuration. The results provide insight on the effect of superimposed flow field fluctuations in systems operating close to the lean blow out limits and offer useful data for the development and validation of numerical models for the prediction of the dynamic behaviour of flames of industrial interest.
Highlights
In order to reduce the environmental impact of combustion systems, and in particular to reduce NOx emissions, gas turbine manufacturers are developing technologies based on the use of lean flames
The study of the flame behaviour in the presence of flow field fluctuations is very important for the understanding of combustion instabilities and in general for the development of modern combustors based on lean burn technology
The results suggest that the presence of velocity fluctuations has a strong impact on the flame behaviour, and both the blow-off mechanism and stability limits of forced flames can be different from the one observed in unforced flames
Summary
In order to reduce the environmental impact of combustion systems, and in particular to reduce NOx emissions, gas turbine manufacturers are developing technologies based on the use of lean flames. Combustion instabilities can cause vibration and additional noise [2], and in the case of large fluctuations, flame quenching, flashback and damages of the combustor components [3]. The study of the flame behaviour in the presence of flow field fluctuations is very important for the understanding of combustion instabilities and in general for the development of modern combustors based on lean burn technology. The understanding and prediction of flame blow-off is of crucial importance for the design of modern combustors that often operate close to the lean blow out limits. It is of great interest to study the impact of periodic motions on the local and global extinction of flames of practical interest
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