Studies of the properties of diffusion flames

• Main Author: Avery, Derek Alan
• Published: University of Surrey 1956
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.751484

An exploratory investigation has been made of the combustion of town gas in a horizontal radiant tube of the type used by Gaz de France. 'In this system fuel gas is introduced into the tube so that it flows along its upper surface as a turbulence free layer and air for combustion forms a layer beneath the gas flowing with it. By this means an extended flame is produced which results in a fairly uniform temperature distribution along the tube. The distribution of heat flux and temperature along a radiant tube was investigated at a number of different values of heat input and pressure drop in the tube. The main part of this work was devoted to an investigation of the conditions inside the tube. By solution of the partial differential equation for diffusion a further equation was developed for the gas concentration at any point in the tube (assuming no combustion). Plots of this equation are presented for air/gas velocity ratios Va/Vg of 0.5, 1.0 and 1.5. The following equation for flame length in terms of the input variables of air and gas flow rates was also developed from this solutions- L = 0.47 G/D (G/D) 1.62 where L = Flame length (ft.) G = gas rate (cu. ft. /hr.). D = Diffusion coeff. (ins2/sec.) A = air rate (cu.ft./hr.). Experimental determination of flame length showed that it increased with air rate at constant gas rate instead of decreasing as predicted by this equation. Vertical traverses of gas analysis were carried out for CO, CO2 and O2 at a number of points along the tube and when plotted as concentration "contours" showed marked similarity in form to those derived from the diffusion theory.