The global extinction limits of non-premixed nitrogen/ammonia-substituted methane– and ethylene–air counterflow flames were experimentally evaluated. In comparison to nitrogen substitution, ammonia substitution reduced the extinction strain rates more. Measurements of OH* chemiluminescence, of which the intensity correlates with extinction limits, suggest that ammonia substitution reduces OH* production. The effects of transport, thermal and chemical properties on flame extinction of the ammonia-substituted flames were assessed, and it was found that their lower extinction limits were due to reactions that consume radicals, which hinder the chain-branching reactions. To mimic the effect of exhaust gas recirculation on the extinction limits of ammonia-substituted flames, carbon dioxide was added to the oxidizer stream. Lower extinction limits were observed with carbon dioxide addition as a result of thermal and chemical effects. Carbon dioxide addition lowered flame temperatures and, like ammonia substitution, introduced reactions that consume radicals. Nitric oxide (NO) production was quantitatively analyzed by simulations. It was found that, for ammonia flames, NO production was promoted by ammonia oxidation with OH, whereas for carbon dioxide addition, NO production was suppressed by the reduction of OH production.
Bibliographical noteKAUST Repository Item: Exported on 2023-09-07
Acknowledged KAUST grant number(s): URF/1/4688-01-01
Acknowledgements: The study is supported by KAUST Competitive Research Grants (URF/1/4688-01-01). The authors thank Prof. Thibault Guiberti of KAUST for the assistance on chemiluminescence measurements and Dr. Et-touhami Es-sebbar and Earnesto Thachil for technical support.
ASJC Scopus subject areas
- Energy Engineering and Power Technology
- Chemical Engineering(all)
- Fuel Technology