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Your search keyword '"Guiberti, Thibault F."' showing total 179 results
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179 results on '"Guiberti, Thibault F."'

45. Effects of residence time on the NOx emissions of premixed ammonia-methane-air swirling flames at elevated pressure.

Author

Wang, Guoqing, Guiberti, Thibault F., Cardona, Santiago, Jimenez, Cristian Avila, and Roberts, William L.

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 O 2 , CO 2 , CO, NO, NO 2 , and N 2 O 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 O 2 concentration in the exhaust. Increasing the swirl number reduces emissions of NO, NO 2 , and N 2 O 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 NO 2 and N 2 O. This reduction is not reflected in a measurable increase in NO concentration because NO is present in much larger quantities than NO 2 and N 2 O 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. [ABSTRACT FROM AUTHOR]

Published
2023
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46. UV-visible chemiluminescence signature of laminar ammonia-hydrogen-air flames.

Author

Zhu, Xuren, Roberts, William L., and Guiberti, Thibault F.

Abstract

This work investigates the UV and visible chemiluminescence signatures of laminar ammonia-hydrogen-air flames. A counterflow burner was used to stabilize flat and steady premixed ammonia-hydrogen-air twin-flames for wide ranges of ammonia fuel fractions (0.55 ≤ X NH 3 ≤ 0.90), equivalence ratios (0.35 ≤ ϕ ≤ 1.70), and strain rates (50 ≤ a ≤ 300 / s). The chemiluminescence spectra in the UV and visible regions were measured. The important contributors to the chemiluminescence of ammonia-hydrogen-air flames were first identified and their sensitivities to equivalence ratio and ammonia fuel fraction were then quantified. Promising ratios of chemiluminescence intensities for the non-intrusive optical sensing of equivalence ratio and ammonia fuel fraction in premixed ammonia-hydrogen-air flames were also identified. Among the 36 ratios that could be formed with the 9 contributors to chemiluminescence that were defined, 3 are particularly promising, namely, OH*/NO*, OH*/ violet (violet refers to the 350 to 400 nm range), and red/blue (blue and red refer to the 450 to 500 nm and 650 to 750 nm ranges, respectively). Ratios OH*/NO* and OH*/ violet were found to provide suitable measures of equivalence ratio for lean and rich ammonia-hydrogen-air flames, respectively, because these ratios are very sensitive to equivalence ratio, are insensitive to ammonia fuel fraction, and are marginally sensitive to strain rate. Once equivalence ratio is known, the ammonia fuel fraction can then be measured with ratio red/blue because it is sensitive to the ammonia fuel fraction and it is globally insensitive to strain rate. [ABSTRACT FROM AUTHOR]

Published
2023
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