Time Series Analysis on the Emission of Light from Methane-Air Lean Premixed Flames: Diagnostics of the Flame Instability

This paper deals with time series analysis on the emission of light from methane-air lean premixed flames. Planar flames formed on a flat burner at the equivalence ratio of unity; Cellular flames formed at low equivalence ratios, because diffusive-thermal effects have a destabilizing impact in this range. We measured the light emission to get time series of intensity, and obtained the root mean square (RMS) and power spectrum density of the emission intensity normalized by its average value. The RMS increased as the equivalence ratio decreased, which is due to the increase in the instability level. The power spectrum density had a sharp peak at the frequency corresponding to the typical oscillation of premixed flames, and the I If spectrum appeared in the low frequency range. Moreover, we performed time series analysis on the normalized emission intensity. We obtained the attractor and correlation dimension to investigate the characteristics of the dynamic behavior of flame fronts. The characteristics depended strongly on the equivalence ratio, i.e. on intrinsic instability. Consequently, the obtained results suggest that time series analysis on the emission of light is applicable to diagnostics of the instability of premixed flames.