| OCR Text |
Show - 5 - from 2 kHz to 12.5 kHz are similar. For ¢ = 1.14, the intensities at around 7 kHz seenl slightly lower than those of other equivalence ratios. The components of the sound pressure of turbulent flames are divided into two groups, one is that which intensity depends on the equivalence ratio and the other is independent of that. This range of frequencies where the effect of an existing of a turbulent premixed flanle on the sound emission correspond fairly well with that of observed flame front movements[10,11J. It can be assumed that the components below 2 kHz are of the former group. The frequency components in this range were examined in detail. Intensities of sound pressure components below 2 kHz are plotted against equivalence ratio, ¢, and the results are shown in Fig. 4. The dotted lines of 62 dB and 65 dB are sound pressure levels without flame at the mixture velocities of 4.5 m/s(bottom line) and 6.5 m/s(top line), respectively. As the equivalence ratio increases, the in tensity of sound pressur~ increases to a maxim urn of 85 dB at ¢ 1.1 and decreases. For ¢ 0.6 or 1.5, the intensities of sound pressure beconle as low as that without flame. For ¢ < 0.6, no steady flame could anchor on the burner. Intensities of sound pressure components below 2 kHz are plotted against logarithms of burning velocities as shown in Fig. 5[9J. It is seen that the intensity of sound pressure increases with the burning velocity. In this figure, the intensity Spi of sound pressure seems to be proportional to the logarithm of burning velocity. The gradient of lines representing the relation between Spl and the burning velocity S is estimated to be 33 dB, and the relation can be approximately u expressed as S pl = Q + 331og( SJ, (2) where a IS a constant, and the units of Spl and S u are dB and cm/s, respectively. Equation (2) can be rewritten as P = {3S 1.65 S u ' (3) |
