Abstract
In a previous paper, a technique for measuring transverse turbulence intensity in flames by means of helium diffusion was described. The intensity is estimated from the concentration distribution of helium (determined by sampling) downstream of a ‘point source’ injection tube immersed in the main stream. Results were reported of the effect of various parameters on the intensity measured at a single location in highly turbulent flames stabilized on baffles in a 2 in. × 8 in. rectangular duct. The present paper contains additional results obtained at several other positions in the same duct. The data include heat release combustion efficiencies and turbulence intensities under both cold flow and burning conditions for each of two different values of approach flow turbulence intensity (approximately 5 per cent and 10 per cent). Premixed pentane-air at an equivalence ratio of 0·7 and a pressure of 0·85 atm was used. The twofold increase in approach turbulence caused an approximately twofold increase in the rate of flame spreading. By comparing the absolute intensities of turbulence during burning and cold flow it is shown that in regions of actively burning gas the turbulence is higher than in cold flow, but in regions of completely burnt gas the intensity may be reduced and may even become laminar. Cold gas regions adjacent to flame zones are essentially unaffected by the presence of flame.
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