Abstract
In this study, a bespoke single-stage swirl burner was used to experimentally investigate the effects of residence time on emissions from premixed ammonia-methane-air flames. The residence time was altered in two ways: by modifying the combustion chamber's length or by modifying the swirl number. Exhaust emissions of O2, CO2, CO, NO, NO2, and N2O were measured at an absolute pressure of 2 bar for equivalence ratios between 0.50 and 0.95 and ammonia fractions in the fuel blend between 0 and 100%. Spatial distributions of NO and OH radicals were also imaged using PLIF inside the combustion chamber at different heights above the nozzle. Data shows that increasing residence time can further advance chemical reactions, as evidenced by a reduction in O2 concentration in the exhaust. Increasing the swirl number reduces emissions of NO, NO2, and N2O more efficiently than tripling the chamber's length. However, a decrease in the combustion efficiency may be responsible for a fraction of this NOx reduction when the swirl number is increased for some equivalence ratios. NO emissions are not modified when the chamber's length is increased, which is consistent with the fact that the NO-LIF signal does not decay when the distance from the nozzle increases. Therefore, NO formation is somehow restricted to within the main reaction zone of the swirling flame, that is, the zone whose height does not exceed 60 mm for this burner. Conversely, tripling the chamber's length reduces the concentrations of NO2 and N2O. This reduction is not reflected in a measurable increase in NO concentration because NO is present in much larger quantities than NO2 and N2O in flames examined here. Consistent with the fact that OH promotes NO formation via fuel-NOx pathways, a positive correlation is found between NO- and OH-LIF intensities.
Original language | English (US) |
---|---|
Pages (from-to) | 4277-4288 |
Number of pages | 12 |
Journal | Proceedings of the Combustion Institute |
Volume | 39 |
Issue number | 4 |
DOIs | |
State | Published - Jan 2023 |
Bibliographical note
Funding Information:This research was supported by the King Abdullah University of Science and Technology (KAUST) under grant numbers BAS/1/1370-01-01 and BAS/1/1425-01-01 .
Publisher Copyright:
© 2022
Keywords
- Adjustable swirler
- Laser-induced fluorescence
- NO-PLIF
- NOx emissions
- Residence time
ASJC Scopus subject areas
- General Chemical Engineering
- Mechanical Engineering
- Physical and Theoretical Chemistry