Quenching and pollutant emissions in side-wall and head-on NH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si69.svg" display="inline" id="d1e710"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> /H <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si71.svg" display="inline" id="d1e718"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> /N <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si71.svg" display="inline" id="d1e726"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> premixed laminar flames
Bibliographic record
Abstract
We present quenching distance, wall heat loss, and pollutant emission results from a series of simulations of NH 3 /H 2 /N 2 premixed laminar flames in side-wall and head-on quenching configurations. Conditions cover lean to rich mixtures (equivalence ratio from 0.3 to 1.2) at both atmospheric and moderate (10 atm) pressures. For each set of conditions, two-dimensional “V”-flame simulations with side-wall quenching (SWQ) and with symmetric boundary conditions are compared to isolate wall heat loss from curvature effects. Simulations of one-dimensional head-on quenched (HOQ) flames covering the same range of conditions are also included for further comparison. First, a non-monotonic relationship between quenching Peclet number and equivalence ratio is found at 10 atm for both SWQ and HOQ, attributed to a significant change in flame structure at lean conditions, with the Jiang chemical kinetics mechanism. Second, wall heat loss normalized by laminar flame power is lower for HOQ flames, compared to SWQ, at lean conditions and higher at rich conditions, which is attributed to the effect of flame curvature on heat release rate in SWQ flames. Yet, normalized wall heat loss shows a similar correlation with quenching Peclet number for both pressures and quenching configurations. Third, similar to previously reported experimental results, we find that ammonia slip increases due to wall heat loss and curvature effects, while hydrogen slip departs negligibly from that of unstretched laminar flames. The contrast with ammonia slip is striking at low equivalence ratio and is attributed to the strongly diverging flux of hydrogen near the quenching point, promoting its consumption. Fourth, both wall heat loss and negative flame curvature at the wall significantly reduce NO emissions as the rates of NO forming reaction pathways are diminished. In the SWQ cases, NO consuming pathways are comparatively less inhibited, being in part fed by NO diffusing towards the wall from non-quenched regions. Finally, both negative curvature at the wall and wall heat loss increase N 2 O emissions. A non-monotonic relationship between N 2 O emissions and equivalence ratio is observed at elevated pressure, as the rate of the N 2 O consuming reaction increases for equivalence ratios below 0.6. Novelty and significance statement We present the first flame-resolved simulations at elevated pressure of side-wall quenching (SWQ) and head-on quenching (HOQ) in NH 3 /H 2 flames. The range of equivalence ratios covered also extends to leaner conditions than previously investigated in both HOQ and SWQ NH 3 /H 2 flames (relevant to staged gas turbine combustors). The one-to-one comparison between 1D HOQ, 2D adiabatic, and 2D SWQ NH 3 /H 2 flames is also novel, and reveals key insights on the effect of preferential diffusion on flame quenching and emissions. The results provide foundational insights that can be used to better understand and model flame-wall interaction in practical NH 3 /H 2 combustion devices.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.006 | 0.007 |
| Meta-epidemiology (narrow) | 0.005 | 0.008 |
| Meta-epidemiology (broad) | 0.002 | 0.005 |
| Bibliometrics | 0.003 | 0.005 |
| Science and technology studies | 0.005 | 0.006 |
| Scholarly communication | 0.004 | 0.006 |
| Open science | 0.007 | 0.008 |
| Research integrity | 0.009 | 0.009 |
| Insufficient payload (model declined to judge) | 0.063 | 0.003 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; both teacher heads agree on what is shown here.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".