Numerical and experimental study of the influence of CO₂ and N₂ dilution on soot formation in laminar coflow C₂H₄/air diffusion flames at pressures between 5 and 20 atm

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DOIResolve DOI: http://doi.org/10.1016/j.combustflame.2015.01.020
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TypeArticle
Journal titleCombustion and Flame
ISSN0010-2180
Volume162
Issue5
Pages22312247
SubjectSoot formation; Laminar diffusion flame; Pressure effect; CO2 chemical effect
AbstractThe effects of fuel dilution by CO₂ and N₂ on soot formation and the flame structure in laminar coflow C₂H₄/air diffusion flames at pressures between 5 and 20 atm were investigated both experimentally and numerically. Experimentally a constant ethylene flow rate and a constant dilution rate of 1:2 (fuel:diluent by mass) were maintained throughout the experiments. The flames were stable and non-smoking over the pressure range investigated. The radially-resolved soot volume fraction and temperature distributions were measured by the spectral soot emission (SSE) technique. Numerical calculations were conducted using two C₂ chemistry models with formation of PAHs up to pyrene and a soot model incorporating pyrene collision as the soot inception step and hydrogen-abstraction acetylene addition mechanism and PAH condensation as the surface growth processes. The two C₂ chemistry models were the ABF mechanism [Appel et al. (2000)] and the DLR mechanism [Slavinskaya and Frank (2009)]. The DLR mechanism predicted little or no chemical effect of CO₂ dilution, depending on the pressure, in the present context. Numerical results are in qualitative agreement with experimental measurements. Soot volume fractions and carbon conversion are lower in the CO₂-diluted flames due to the additional chemical effect of CO₂. CO₂ is still more effective than N₂ as a diluent to suppress soot formation at elevated pressures. The primary pathway for the chemical effect of CO₂ dilution is through the reverse reaction of CO + OH ↔ CO₂ + H. The chemical effect of CO₂ lowers the rates of soot inception, C₂H₂ addition, and PAH condensation. The effectiveness of the CO₂ chemical effect on soot formation suppression diminishes with increasing pressure. The diminishing effectiveness of the chemical effect of CO₂ dilution with increasing pressure is due to the significant decrease in the H radical mole fraction.
Publication date
PublisherElsevier
LanguageEnglish
AffiliationMeasurement Science and Standards; National Research Council Canada
Peer reviewedYes
IdentifierS0010218015000322
NPARC number23000071
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Record identifier1be0b73b-596f-4f65-a7e3-b7b6d0427961
Record created2016-06-01
Record modified2016-06-01
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