Flame height measurement of laminar inverse diffusion flames

Abstract

Flame heights of co-flowing cylindrical ethylene-air and methane-air laminar inverse diffusion flames were measured. The luminous flame height was found to be longer than the height of the reaction zone determined by planar laser-induced fluorescence (PLIF) of hydroxyl radicals (OH) because of luminous soot above the reaction zone. However, the location of the peak luminous signals along the centerline agreed very well with the OH flame height. Flame height predictions using Roper's analysis for circular port burners agreed with measured reaction zone heights when using values for the characteristic diffusion coefficient and/or diffusion temperature somewhat different from those recommended by Roper. The fact that Roper's analysis applies to inverse diffusion flames is evidence that inverse diffusion flames are similar in structure to normal diffusion flames.2

Comparative flame structure investigation of normal and inverse turbulent non-premixed oxy-fuel flames using experimentally recorded and numerically predicted Rayleigh and OH-PLIF signals

“…Previous investigations on laminar air flames already found structurally similar flames for IDF and NDF [4,8]. However, when differential diffusion was strong, differences between IDF and NDF start to emerge, e.g.…”

“…Whilst some studies of laminar air flames have found that inverse and normal diffusion flames are similar in structure [4,8], other authors have observed differences in the measured temperature in air combustion [7] and in the OH* chemiluminescence fields in oxy-fuel combustion [9]. To our knowledge, a similar comparison of turbulent normal and inverse diffusion flames has not been published.…”

“…In the present investigation, we focus on analyzing the differences between non-piloted IDFs and NDFs, extending previous laminar studies [4,[7][8][9] towards turbulent oxy-fuel flames. The influence of turbulence on flame structure in both configurations is studied using experimental and numerical data.…”

“…Takagi et al [7] investigated N 2 -diluted H 2 normal and inverse diffusion flames at the same jet and coflow velocity. Mikofski et al [8] experimentally investigated the flame length in relation to the jet velocity. Zhang et al [9] identified differences between IDFs and NDFs based on OH* chemiluminescence in a CH 4 -O 2 mixture.…”

Control of the structure and sooting characteristics of a coflow laminar methane/air diffusion flame using a central air jet: An experimental and numerical study

“…The structure and soot formation characteristics of coflow laminar normal diffusion flames (NDF) (fuel jet is issued into air) have been experimentally investigated by many researchers, e.g., Mitchell et al [7], Santoro and co-workers [8], Faeth and co-workers [9], among many others, and numerically studied using relatively detailed chemistry by Kaplan and Kailasanath [10], Smooke et al [11,12], and Guo et al [13], among others. Coflow inverse diffusion flames (IDF) have also been investigated experimentally by various researchers [14][15][16][17][18][19]. It has been made clear that IDFs exhibit remarkably different soot formation features from those of NDFs due to the very different temperature, chemical environment, and residence time experienced by incepted soot particles [10].…”