Structure of laminar sooting inverse diffusion flames

Abstract The flame structure of laminar inverse diffusion flames (IDFs) was studied to gain insight into soot formation and growth in underventilated combustion. Both ethylene–air and methane–air IDFs were examined, fuel flow rates were kept constant for all flames of each fuel type, and airflow rates were varied to observe the effect on flame structure and soot formation. Planar laser-induced fluorescence of hydroxyl radicals (OH PLIF) and polycyclic aromatic hydrocarbons (PAH PLIF), planar laser-induced incandescence of soot (soot PLII), and thermocouple-determined gas temperatures were used to draw conclusions about flame structure and soot formation. Flickering, caused by buoyancy-induced vortices, was evident above and outside the flames. The distances between the OH, PAH, and soot zones were similar in IDFs and normal diffusion flames (NDFs), but the locations of those zones were inverted in IDFs relative to NDFs. Peak OH PLIF coincided with peak temperature and marked the flame front. Soot appeared outside the flame front, corresponding to temperatures around the minimum soot formation temperature of 1300 K. PAHs appeared outside the soot layer, with characteristic temperature depending on the wavelength detection band. PAHs and soot began to appear at a constant axial position for each fuel, independent of the rate of air flow. PAH formation either preceded or coincided with soot formation, indicating that PAHs are important components in soot formation. Soot growth continued for some time downstream of the flame, at temperatures below the inception temperature, probably through reaction with PAHs.

[1]  George Sidebotham,et al.  Flame temperature, fuel structure, and fuel concentration effects on soot formation in inverse diffusion flames , 1992 .

[2]  KoHse-HoingHaus.  Applied Combustion Diagnostics , 2002 .

[3]  John Kent,et al.  Reaction path analysis of the formation of aromatics and soot in a coflowing laminar diffusion flame of ethylene , 2002 .

[4]  Robert J. Santoro,et al.  Generation of CO and smoke during underventilated combustion , 1994 .

[5]  Suk Ho Chung,et al.  Soot zone structure and sooting limit in diffusion flames: Comparison of counterflow and co-flow flames , 1997 .

[6]  Robert J. Santoro,et al.  The Transport and Growth of Soot Particles in Laminar Diffusion Flames , 1987 .

[7]  Ian M. Kennedy,et al.  Soot Formation In Laminar Inverse Diffusion Flames , 1994 .

[8]  Reginald E. Mitchell,et al.  Experimental and numerical investigation of confined laminar diffusion flames , 1980 .

[9]  Ian M. Kennedy,et al.  Models of soot formation and oxidation , 1997 .

[10]  S. Turns.  An Introduction to Combustion: Concepts and Applications , 2000 .

[11]  J. Kent,et al.  Soot measurements in laminar ethylene diffusion flames , 1982 .

[12]  E. Eddings,et al.  FT-IR and 1H NMR characterization of the products of an ethylene inverse diffusion flame , 2006 .

[13]  R. L. Wal,et al.  Simultaneous laser-induced emission of soot and polycyclic aromatic hydrocarbons within a gas-jet diffusion flame , 1997 .

[14]  Ömer L. Gülder,et al.  Determination of the soot absorption function and thermal accommodation coefficient using low-fluence LII in a laminar coflow ethylene diffusion flame , 2004 .

[15]  Robert J. Santoro,et al.  Soot inception in a methane/air diffusion flame as characterized by detailed species profiles , 1985 .

[16]  R. Dobbins,et al.  Soot inception temperature and the carbonization rate of precursor particles , 2002 .

[17]  J. R. Arthur,et al.  Carbonaceous Deposits from Hydrocarbon Diffusion Flames , 1952, Nature.

[18]  Christopher R. Shaddix,et al.  Aspects of soot dynamics as revealed by measurements of broadband fluorescence and flame luminosity in flickering diffusion flames , 1997 .

[19]  I. Glassman,et al.  Effect of Oxygen Addition to a Near-Sooting Ethene Inverse Diffusion Flame , 1992 .

[20]  Robert J. Santoro,et al.  Soot particle measurements in diffusion flames , 1983 .

[21]  Kathryn M. Butler,et al.  Generation and Transport of Smoke Components , 2004 .

[22]  W. Mallard,et al.  The observation of laser-induced visible fluorescence in sooting diffusion flames , 1982 .

[23]  C. Smith,et al.  Soot escape from laminar air-starved hydrocarbon flames , 1979 .

[24]  L. Blevins,et al.  Flame height measurement of laminar inverse diffusion flames , 2006 .

[25]  J S Lighty,et al.  Combustion Aerosols: Factors Governing Their Size and Composition and Implications to Human Health , 2000, Journal of the Air & Waste Management Association.

[26]  Eui Ju Lee,et al.  Soot formation in inverse diffusion flames of diluted ethene , 2005 .

[27]  F. G. Roper.  The prediction of laminar jet diffusion flame sizes: Part I. Theoretical model , 1977 .

[28]  R. Axelbaum,et al.  The Effect of Flame Structure on Soot-Particle Inception in Diffusion Flames , 1995 .

[29]  Alan C. Eckbreth,et al.  Effects of laser-modulated particulate incandescence on Raman scattering diagnostics , 1977 .

[30]  C. Shaddix,et al.  Laser-induced incandescence measurements of soot production in steady and flickering methane, propane, and ethylene diffusion flames , 1996 .

[31]  Anthony P. Hamins,et al.  Concentration measurements of OH· and equilibrium analysis in a laminar methane-air diffusion flame , 1990 .