Abstract
This paper will shed some light on the area of signal processing analysis, and hopefully gives rise to more work in combustion instability field, which will lead to a better understanding of this very important aspect. Flickering frequency mode could be an indication of flame instability. In this paper is a light cell as an alternative optical chemiluminescence emission technique and a high-speed camera which is considered as a conventional technique to acquire a flame flicker are used. To study the effect of burner diameter on the flame flicker mode, an experimental study on free jet propane diffusion flame with different diameters is performed, while keeping the fuel flow rate constant. The results show that the laminar flame flickering mode has a frequency in the range of 10 to less than 15 Hz, and 15 Hz occurred at transitional condition (Re=1200). The results of the power spectra of both techniques show that many of the strong sub-harmonics occurred at laminar flame mode. On the other hand, the sub-harmonic frequencies start to disappear at high Reynolds number (above the transitional value of 1200). Results also show that the typical flickering frequency is 13Hz, which agrees well with other published data. In this paper, a family of auto-correlation curves of the chemiluminescence emission at different Re number are presented. The auto-correlation curves of the Chemiluminescence emission signals of both techniques at laminar conditions are very strong correlation of laminar Re numbers conditions; their trends are similar to autocorrelation of the theoretical sine wave. In the transitional condition; auto-correlation started to drop to zero, which mean that the signal has started to become a weak correlation, and the signals became turbulent flame. KEYWORDS: Diffusion Flame; Chemiluminescence Emission; Flame Flicker; Combustion Iinstability.