A new correlation between diluent fraction and laminar burning velocities : Example of CH4, NH3, and CH4 + NH3 flames diluted by N2
(2024) In Fuel 364.- Abstract
Modern combustion processes widely use exhaust gas recirculation, oxyfuel combustion, and other techniques that alter the concentration of diluent gases from that of the air. The dilution's impact on the laminar burning velocity, SL, is therefore a crucial effect that has been studied experimentally and numerically in the literature. However, an accurate fitting correlation with physical meanings is lacking, making it difficult to extrapolate SL data to real-application conditions. To address this gap, in the present work we have derived a novel correlation between diluent fraction and laminar burning velocity, SL, through new analysis of the maximum temperature gradient and heat release rate as... (More)
Modern combustion processes widely use exhaust gas recirculation, oxyfuel combustion, and other techniques that alter the concentration of diluent gases from that of the air. The dilution's impact on the laminar burning velocity, SL, is therefore a crucial effect that has been studied experimentally and numerically in the literature. However, an accurate fitting correlation with physical meanings is lacking, making it difficult to extrapolate SL data to real-application conditions. To address this gap, in the present work we have derived a novel correlation between diluent fraction and laminar burning velocity, SL, through new analysis of the maximum temperature gradient and heat release rate as lnSL/SL0=a1/Yu-1/Yu0, where Yu is the reactant mass fraction in the total unburnt mixture, and a being a constant when only the diluent concentration is varied. To provide data for the analysis and validation, SL of CH4 + O2 + N2, 40 %CH4 + 60 %NH3 + O2 + N2, and NH3 + O2 + N2 flames were measured using the heat flux method at varied oxygen ratio xO2 and equivalence ratio ϕ. Simulations were carried out using three kinetic mechanisms from Han, Konnov, and Okafor, which have been validated using both CH4 and NH3 burning velocities. Our experimental and simulation results for various fuel types and equivalence ratio conditions demonstrate good linearity with R2 > 0.985 over all ranges of xO2 spans, from the upper limit of xO2 = 1.0 to the lower limit where SL is below 5 cm/s, confirming the accuracy of the correlation equation. This correlation is also found valid under complex conditions with various unburned temperatures, pressures, diluent types, and fuel types, indicating its wide applicability. Sensitivity analyses revealed the kinetic origin of the linear lnSL vs. 1/Yu relationships. Specifically, the absolute values of a sensitivities are much smaller than those of SL, and they remain nearly the same for different oxygen ratios. Therefore, even by tuning the rate constants of the highly sensitive reactions, the a at different 1/Yu conditions will change uniformly, resulting in a linear lnSL vs. 1/Yu variation though with a different slope value.
(Less)
- author
- Han, Xinlu ; Feng, Hongqing ; Lin, Riyi and Konnov, Alexander A. LU
- organization
- publishing date
- 2024-05-15
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- Ammonia, Dilution, Kinetic mechanism, Laminar burning velocity, Methane
- in
- Fuel
- volume
- 364
- article number
- 131108
- publisher
- Elsevier
- external identifiers
-
- scopus:85184031585
- ISSN
- 0016-2361
- DOI
- 10.1016/j.fuel.2024.131108
- language
- English
- LU publication?
- yes
- id
- e408c8fe-b15c-454f-ad4c-025eb7647f9f
- date added to LUP
- 2024-03-08 10:47:12
- date last changed
- 2024-03-08 10:48:08
@article{e408c8fe-b15c-454f-ad4c-025eb7647f9f,
abstract = {{<p>Modern combustion processes widely use exhaust gas recirculation, oxyfuel combustion, and other techniques that alter the concentration of diluent gases from that of the air. The dilution's impact on the laminar burning velocity, S<sub>L</sub>, is therefore a crucial effect that has been studied experimentally and numerically in the literature. However, an accurate fitting correlation with physical meanings is lacking, making it difficult to extrapolate S<sub>L</sub> data to real-application conditions. To address this gap, in the present work we have derived a novel correlation between diluent fraction and laminar burning velocity, S<sub>L</sub>, through new analysis of the maximum temperature gradient and heat release rate as lnS<sub>L</sub>/S<sub>L</sub><sup>0</sup>=a1/Y<sub>u</sub>-1/Y<sub>u</sub><sup>0</sup>, where Y<sub>u</sub> is the reactant mass fraction in the total unburnt mixture, and a being a constant when only the diluent concentration is varied. To provide data for the analysis and validation, S<sub>L</sub> of CH<sub>4</sub> + O<sub>2</sub> + N<sub>2</sub>, 40 %CH<sub>4</sub> + 60 %NH<sub>3</sub> + O<sub>2</sub> + N<sub>2</sub>, and NH<sub>3</sub> + O<sub>2</sub> + N<sub>2</sub> flames were measured using the heat flux method at varied oxygen ratio x<sub>O2</sub> and equivalence ratio ϕ. Simulations were carried out using three kinetic mechanisms from Han, Konnov, and Okafor, which have been validated using both CH<sub>4</sub> and NH<sub>3</sub> burning velocities. Our experimental and simulation results for various fuel types and equivalence ratio conditions demonstrate good linearity with R<sup>2</sup> > 0.985 over all ranges of x<sub>O<sub>2</sub></sub> spans, from the upper limit of x<sub>O<sub>2</sub></sub> = 1.0 to the lower limit where S<sub>L</sub> is below 5 cm/s, confirming the accuracy of the correlation equation. This correlation is also found valid under complex conditions with various unburned temperatures, pressures, diluent types, and fuel types, indicating its wide applicability. Sensitivity analyses revealed the kinetic origin of the linear lnS<sub>L</sub> vs. 1/Y<sub>u</sub> relationships. Specifically, the absolute values of a sensitivities are much smaller than those of S<sub>L</sub>, and they remain nearly the same for different oxygen ratios. Therefore, even by tuning the rate constants of the highly sensitive reactions, the a at different 1/Y<sub>u</sub> conditions will change uniformly, resulting in a linear lnS<sub>L</sub> vs. 1/Y<sub>u</sub> variation though with a different slope value.</p>}},
author = {{Han, Xinlu and Feng, Hongqing and Lin, Riyi and Konnov, Alexander A.}},
issn = {{0016-2361}},
keywords = {{Ammonia; Dilution; Kinetic mechanism; Laminar burning velocity; Methane}},
language = {{eng}},
month = {{05}},
publisher = {{Elsevier}},
series = {{Fuel}},
title = {{A new correlation between diluent fraction and laminar burning velocities : Example of CH<sub>4</sub>, NH<sub>3</sub>, and CH<sub>4</sub> + NH<sub>3</sub> flames diluted by N<sub>2</sub>}},
url = {{http://dx.doi.org/10.1016/j.fuel.2024.131108}},
doi = {{10.1016/j.fuel.2024.131108}},
volume = {{364}},
year = {{2024}},
}