Suppression of NOx emissions by intensive strain in lean premixed hydrogen flamelets

Alessandro Porcarelli*, Boris Kruljević, Ivan Langella

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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NOx formation in premixed, highly-strained, pure hydrogen-air flamelets is investigated at lean conditions. Detailed-chemistry, one-dimensional and two-dimensional simulations are performed on a reactants-to-products configuration with varying applied strain rate. The results highlight for the first time for lean pure-hydrogen flamelets that NOx emissions are suppressed as strain rate is increased. The most substantial decrease is observed across the thermal NOx formation pathway. Here the suppression of NOx is triggered by a redistribution across the flamelet of the radicals involved in the pathway reactions. A comparison with methane flamelets is further performed to understand to what extent the observed trends with strain can be specifically linked to hydrogen burning features. Similar NOx suppression trends with strain are also observed for increased pressure and different equivalence ratios, although with different rates of decrease. A correlation is proposed based on the observed results and further theoretical considerations, to predict NOx emissions according to applied strain rate and equivalence ratio.

Original languageEnglish
Pages (from-to)413-431
Number of pages19
JournalInternational Journal of Hydrogen Energy
Publication statusPublished - 2023


  • CFD
  • Hydrogen
  • Premixed combustion
  • Strained flames


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