The influence on the soot distribution within a laminar flame of radiation at fluxes of relevance to concentrated solar radiation

An assessment of the influence of high intensity radiation on the distribution of soot within a laminar ethylene flame is performed. Radiation at fluxes of up to 4.3 MW/m2, of a similar order encountered with concentrated solar radiation, is provided by a CO2 laser at 10.6 μm. Radiation at this wavelength, in the configuration used in this paper, allows effective isolation of three possible mechanisms of influence: molecular excitation of the fuel, irradiation of the soot, and irradiation of soot precursors. The influence of the radiation on the soot distribution is assessed by laser induced incandescence (LII) imaging in a plane that intersects with the CO2 laser beam. It is found that the high intensity radiation has a dramatic influence on the flame. The high energy radiation acts to increase the peak volume fraction of the soot by up to 250%. The results show that whilst the effect is most pronounced due to heating of the fuel, heating of the soot can also be significant.