Soot nucleation and growth in acetylene air laminar coflowing jet diffusion flames

Abstract

The objective of the present investigation was to extend recent measurements of soot nucleation and growth within acetylene/air laminar jet diffusion flames. Several factors motivated this extension. First, the measurements of Ref. 1 were limited to soot processes along the axes of laminar jet diffusion flames, where soot nucleates near the cool core of the flow and moves directly toward the flame sheet; therefore, it was of interest to consider other soot paths in order to investigate the generality of these results, especially for paths where soot nucleates near the flame sheet and initially moves toward more fuel-rich regions of the flow, which account for most of the soot production in buoyant diffusion flames. In particular, nucleation near the cool core of the flames generally is accompanied by observations of translucent objects but whether these objects are still observed for soot paths beginning at higher temperatures in the vicinity of the flame sheet must still be resolved. Secondly, measurements of hydrocarbons in Ref. 1 were limited to acetylene; therefore, information about the concentrations of other hydrocarbons is needed in order to establish their potential role in processes of soot formation within acetylene/air diffusion flames. Additionally, although several test flames weremore » considered in Ref. 1, the available range of characteristic flame residence times (taken as the time for a fluid parcel to convect along the axis from the burner exit to the flame sheet) was rather narrow (17--23 ms); therefore, consideration of a broader range of flame conditions was of interest. Finally, a problem concerning measurements of O{sub 2} concentrations at fuel-rich conditions was discovered, motivating reconsideration of effects of soot oxidation rates on measurements of soot growth rates.« less