An experimental study on the liftoff of a co-flowing non-premixed turbulent methane flame: effect of the fuel nozzle geometry
Notice bibliographique
Résumé
The effect of the fuel nozzle geometry on the liftoff phenomenon of turbulent methane diffusion flame with and without a co-airflow is investigated experimentally. This investigation consists of two parts. In the first part, the effect of the internal geometry of a circular nozzle is examined. This was accomplished via varying the nozzle diameter, orifice length to diameter ratio (L/D), and (3) the contraction angle. These geometrical parameters were aimed to create a wide range of test conditions of the ensuing jet flow. The strength of the co-airflow was also varied to evaluate its impact on the jet flame liftoff parameters. The second part consists of investigating the effect of the fuel nozzle exit orifice geometry on the flame liftoff. This was achieved by employing a rectangular nozzle with an exit aspect ratio of 2 and a circular nozzle. Particle Image Velocimetry (PIV) technique was used to characterize the velocity field of the turbulent jets issuing from these nozzles. Also, a high speed imaging technique was employed to determine the flame liftoff height. The flame results showed that the fuel nozzle having the greater L/D or smooth contraction has higher liftoff velocity. In addition, the results revealed that the rectangular nozzle has a lower liftoff velocity. The effect of the nozzle diameter on the liftoff, however, was found to depend on the co-airflow strength. The corresponding turbulent jet flow characteristics showed that higher levels of jet near-field turbulence results in a lower flame liftoff velocity regardless of the nozzle internal geometry. Moreover, the results showed that a nozzle with the lowest L/D or with smooth contraction has the lowest flame liftoff height. The PIV results revealed that a circular jet, which spreads faster and generates higher near-field turbulence, generates a flame with its base sitting closer to the nozzle. The results revealed also that the rectangular fuel nozzle, which, in general, has lower liftoff height, produces higher turbulence intensity in the jet near-field and faster spread along the minor axis of the nozzle which is an indication of the presence of relatively more turbulent flow structures (which is induced by the nozzle’s exit asymmetry). The results confirmed that higher jet spread rate in the near-field in conjunction with higher turbulence level result in an increased flame propagation speed (in line with Kalghatgi’s lifted diffusion flame stability theory), and hence make it possible for a flame to stabilize at a relatively lower height from the nozzle.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».