Comparative study of soot formation on the centerline of axisymmetric laminar diffusion flames: Fuel and temperature effects

Abstract The appearance of soot on the centerline of axisymmetric laminar diffusion flames has been studied by monitoring (i) the gas temperature by thermocouples; (ii) the soot particle field by laser scattering/extinction; (iii) the presence of polycyclic aromatic hydrocarbons (PCAH) by laser induced fluorescence. Four fuels were used: butene, acetylene, butadiene, and benzene. All but one flame were at the smoke height condition and were characterized by different levels of N 2 dilution aimed at controlling the temperature field. It was observed that (i) soot nucleation occurs at the centerline; (ii) the soot onset on the centerline occurs when a characteristic temperature of 1350K is measured, regardless of fuel type or level of dilution; (iii) butene and benzene have similar fluorescence patterns, in contrast with premixed flame environments. These last two observations are consistent with the proposal that, though the extent of conversion of fuel into soot may significantly change from fuel to fuel, there is a common mechanism of soot formation for all fuels. The centerline fluorescence measurements indicate that the fluorescing species may contribute to the nucleation phase or, to a minimal extent, to surface growth in these diffusion flames. Time resolved measurements indicate that the fluorescence decay time is ≤ 10 ns, consistent with a possible identification of the fluorescing species with polycyclics such as acenaphthalene and pyrene.

[1]  I. Fells,et al.  A scanning optical densitometer using deconvolution to measure soot concentrations in axisymmetric flames , 1982 .

[2]  Stephen J. Harris,et al.  Surface Growth of Soot Particles in Premixed Ethylene/Air Flames , 1983 .

[3]  A. F. Sarofim,et al.  Optical Constants of Soot and Their Application to Heat-Flux Calculations , 1969 .

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

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

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

[7]  B. Haynes,et al.  Sooting Structure in a Laminar Diffusion Flame , 1980 .

[8]  D. E. Rosner,et al.  Experimental studies of soot particle thermophoresis in nonisothermal combustion gases using thermocouple response techniques , 1985 .

[9]  Alan C. Eckbreth,et al.  Combustion diagnostics by laser Raman and fluorescence techniques , 1979 .

[10]  George Sidebotham,et al.  Sooting behavior in temperature-controlled laminar diffusion flames☆ , 1984 .

[11]  I. B. Berlman.  Handbook of flourescence spectra of aromatic molecules , 1971 .

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

[13]  B. Haynes,et al.  Identification of a source of argon-ion-laser excited fluorescence in sooting flames , 1981 .

[14]  B. Haynes,et al.  Optical Studies of Soot‐Formation Processes in Premixed Flames , 1980 .

[15]  Michael Frenklach,et al.  A conceptual model for soot formation in pyrolysis of aromatic hydrocarbons , 1983 .

[16]  S. A. Myers.  An improved line narrowing technique for a dye laser excited by a nitrogen laser , 1971 .

[17]  J. Langelaar,et al.  The effects of sequence congestion and weak coupling on the observed fluorescence lifetimes in different spectral regions in the case of intermediate strong coupling , 1974 .

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

[19]  E. Eckert,et al.  Analysis of heat and mass transfer , 1971 .