Flickering characteristics and temperature field of premixed methane/air flame under the influence of co-flow

•Flickering characteristics and temperature field of premixed methane/air flame are studied in co-flow.•The temperature is measured by improved flame reaction technique by correcting the number density of metal atoms.•The temperature calibration is conducted by sodium D-line reversal method.•The oscillation amplitude of flame decreases and the frequency increases with co-flow velocity.•The oscillation amplitude increases with equivalence ratio.

The flickering characteristics and the temperature field of an axisymmetric premixed methane/air flame under the influence of co-flow are studied experimentally using the image analysis and the flame reaction technique. The premixed flame is visualized by the alkali metal solution of sodium (Na) for characterizing the flickering characteristics. The temperature measurement of the flame is carried out using the flame reaction technique combined with the relationship between the local intensity of the flame and the temperature from the sodium D-line reversal method, and the influence of the number density distribution of Na on the measured temperature field is corrected by the measurement integrated analysis of the flame with the iterative procedure. This technique is validated by the local temperature measurement in the steady flame under the influence of co-flow using the thermocouple calibrated by the sodium D-line reversal method. The flame visualization and temperature measurement in the flickering flame of the premixed methane/air flame indicates that the flame contour and the temperature field oscillate periodically with the flickering frequency due to the Kelvin–Helmholtz instability of the flame. The oscillation amplitude decreases and the frequency increases gradually with the co-flow velocity increases similar to the observation in the diffusion flame in literature, while the oscillation amplitude grows with the equivalence ratio increases. These changes in the flickering characteristics of the flame are caused by the variations of the temperature field in the premixed flame.