Influence of pressure on near nozzle flow field and soot formation in laminar co-flow diffusion flames

Abstract

Soot formation from combustion devices, which tend to operate at high pressure, is a health and environmental concern, thus investigating the effect of pressure on soot formation is important. While most fundamental studies have utilised the co-flow laminar diffusion flame configuration to study the effect of pressure on soot, there is a lack of investigations into the effect of pressure on the flow field of diffusion flames and the resultant influence on soot formation. A recent work has displayed that recirculation zones can form along the centreline of atmospheric pressure diffusion flames. This present work seeks to investigate whether these zones can form due to higher pressure as well, which has never been explored experimentally or numerically. The CoFlame code, which models co-flow laminar, sooting, diffusion flames, is validated for the prediction of recirculation zones using experimental flow field data for a set of atmospheric pressure flames. The code is subsequently utilised to model ethane-air diffusion flames from 2 to 33 atm. Above 10 atm, recirculation zones are predicted to form. The reason for the formation of the zones is determined to be due to increasing shear between the air and fuel steams, with the air stream having higher velocities in the vicinity of the fuel tube tip than the fuel stream. This increase in shear is shown to be the cause of the recirculation zones formed in previously investigated atmospheric flames as well. Finally, the recirculation zone is determined as a probable cause of the experimentally observed formation of a large mass of soot covering the entire fuel tube exit for an ethane diffusion flame at 36.5 atm. Previously, no adequate explanation for the formation of the large mass of soot existed.

Keywords:

• recirculation
• laminar diffusion flame
• soot model
• ethane

Acknowledgments

This research was undertaken, in part, thanks to funding from the Canada Research Chairs programme. The authors acknowledge NSERC of Canada for additional financial support. Computations were performed on the Ryerson University Sandy Bridge computing cluster and the GPC supercomputer at the SciNet HPC Consortium. SciNet is funded by: The Canada Foundation for Innovation under the auspices of Compute Canada; the Government of Ontario; Ontario Research Fund – Research Excellence; and the University of Toronto.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was undertaken, in part, thanks to funding from the Canada Research Chairs program. The authors acknowledge Natural Sciences and Engineering Research Council (NSERC) of Canada for additional financial support. Computations were performed on the Ryerson University Sandy Bridge computing cluster and the GPC supercomputer at the SciNet HPC Consortium. SciNet is funded by: The Canada Foundation for Innovation under the auspices of Compute Canada; the Government of Ontario; Ontario Research Fund - Research Excellence; and the University of Toronto.