Diffusion flames turbulent fuel jets

Diffusion Flames in the Transition Region. As the velocity of the fuel jet increases in the laminar to turbulent transition region, an instabihty develops at the top of the flame and spreads down to its base. This is caused by the shear forces at the boundaries of the fuel jet. The flame length in the transition region is usually calculated by means of empirical formulas of the form (eq. 13) where I = length of the flame, m r = radius of the fuel jet, m v = fuel flow velocity, m/s and and are empirical constants. 

Diffusion Flame. When a slow stream of fuel g s flows from a tube into the atmosphere, air diffuses across the boundary of the stream and Brms an envelope of expl mixture around a core of gas. The core decreases in height until it disappears at some distance above the tube. It thus assumes the shape of a cone. On ignition, a flame front spreads thru the mixture and stabilizes itself around the cooe of fuel gas. The hydrocarbons in common fuel gases crack to form free C H. The shell of carbon-bearing gas so formed gives such flames their luminosity Turbulent Jet Flame. When a gas stream issues from an orifice above a certain critical velocity, it breaks up into a turbulent jet that entrains the surrounding air. The flame of such a jet consists of random patches of combustion and no cohesive combustion surface exists... 

We have chosen the latter approach, and show in Fig. 6 a sketch of a movable fan-induced co-flowing turbulent jet combustion tunnel. The working section is a 15 cm x 15 cm square pipe with large glass windows giving clear optical access to the turbulent diffusion flame produced on a 3-mm-diameter fuel tube. 

A turbulent jet diffusion flame was investigated. The apparatus and experimental procedure are described in detail in the article by Rambach et al. (11). The fuel jet had the following properties diameter of 1.6 mm, Reynolds number of 4400, and a fuel composition of 37% methane and 63% hydrogen. 

Mantzaras, J., and Van Der Meer, T. H. "Coherent Anti-Stokes Raman Spectroscopy Measurements of Temperature Fluctuations in Turbulent Natural Gas-Fueled Piloted Jet Diffusion Flames." Combustion and Flame 110 (1997) 39-53. 

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