Effect of ammonia addition on suppressing soot formation in methane co-flow diffusion flames

Matthew J. Montgomery*, Hyunguk Kwon, Jochen A.H. Dreyer, Yuan Xuan, Charles S. McEnally, Lisa D. Pfefferle

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


Due to issues surrounding carbon dioxide emissions from carbon-containing fuels, there is growing interest in ammonia (NH 3 ) as an alternative combustion fuel. One attractive method of burning NH3 is to co-fire it with hydrocarbons, such as natural gas, and in this case soot formation is possible. To begin understanding the influence of NH3 on soot formation when co-fired with hydrocarbons, soot volume fractions and mole fractions of gas-phase species were computationally and experimentally interrogated for CH4 flames with up to 40% NH3 by volumetric fuel fraction. Mole fractions of gas-phase species, including C 2 H 2 and C 6 H 6 , were measured with on-line electron impact mass spectrometry, and soot volume fractions were obtained via color-ratio pyrometry. The simulations employed a detailed chemical mechanism developed for capturing nitrogen interactions with hydrocarbons during combustion. The results are compared to findings in N 2 -CH 4 flames, in order to separate thermal and dilution effects from the chemical influence of NH3 on soot formation. Experimentally, C 2 H 2 concentrations were found to decrease slightly for the NH 3 -CH4 flames relative to N 2 -CH4 flames, and a stronger suppression of C 6 H 6 was found for NH3 relative to N 2 additions. The measured results show a strong suppression of soot with the addition of NH3 , with soot concentrations reduced by over a factor of 10 with addition of up to 20% or more NH3 by mole fraction. The model satisfactorily captured relative differences in maximum centerline C 2 H 2 , C 6 H 6 , and soot concentrations with addition of N 2 , but was unable to match measured differences in NH3 -CH4 flames. These results highlight the need for an improved understanding of fuel-nitrogen interactions with higher hydrocarbons to enable accurate models for predicting particulate emissions from NH3 /hydrocarbon combustion.

Original languageEnglish
JournalProceedings of the Combustion Institute
Issue number2
Pages (from-to)2497-2505
Publication statusPublished - 2021


  • Ammonia
  • CFD simulations
  • Color-ratio pyrometry
  • Soot


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