Mixing and combustion in free and enclosed turbulent jet diffusion flames

Abstract

Experimental results of the concentration of nozzle fluid along the axis of the free jet can be expressed by the formula 1 C m =0·22( x d 0 )−1·5 . When the nozzle fluid is at a different temperature to the surrounding fluid the curves can be made to coincide with isothermal ones provided the jet diameter is replaced by an equivalent diameter d 0( T a T 0 ) 1 2 and experimentally this theory is found to be correct. Apart from a pressure effect which is not yet fully elucidated the half-jet angle is found to be independent of temperature and pressure of the jet nozzle at 6·45 degrees. When the free jet is actually burning, the concept of the equivalent nozzle diameter still gives a reasonable account of the effect of combustion. When the jet is enclosed by a comparatively large chamber, the dimensions of this chamber (l) and the proportion of air available become significant parameters, but if the mixing results are plotted in the form of ( 1 c m ) ( d′ 0 l )=∫( x l ) then they become a set of curves with the single parameter ( 1 C ∞ ) ( d′ 0 l ) where C ∞ is the concentration of burner fluid after it is completely mixed. The present experimental work shows that for high values of this parameter mixing can actually be faster over a certain portion of the distance than it is with a free jet.