| 1. |
- Ji, Longjuan, et al.
(författare)
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Effects of secondary hydrogen injection on thermoacoustic instability of swirling premixed flames in a model combustor
- 2024
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Ingår i: Fuel. - 0016-2361. ; 377
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Tidskriftsartikel (refereegranskat)abstract
- Effects of pilot H2 injection on the thermoacoustic instability of premixed CH4/air flames were experimentally investigated with varied hydrogen injection rates and different injection strategies. The flames were stabilized on a swirl burner with a central pilot-fuel injection tube. The flame structure was captured using high-speed OH* chemiluminescence and OH-PLIF methods, while the CO and NOx emissions were also measured. It is validated that a minimal flow rate of the pilot H2 injection can significantly enhance flame stabilization. Comparatively, the other two strategies, including premixing H2 with CH4 and a pilot injection of the CH4, all exhibit nearly no improvement in the flame stabilization. The underlying reason is that the pilot H2 injection can modify the flame anchoring, reduce flame height, and even redistribute heat release in the flame. Moreover, the H2 injection suppresses the flame front roll-up, mitigates the heat release fluctuations, and ultimately leads to decoupled acoustic pressure and unsteady heat release. Furthermore, it appears that the CO emissions decrease with the pilot H2 injection while the NOx emissions significantly increase. Thus, although the pilot H2 injection can be effective to actively suppress the thermoacoustic instability, the elevated pollutant emissions should be a major drawback of this strategy. In the present work, the optimized trade-off between flame stabilization and NOx emission is achieved using a pilot H2 injection at a thermal power fraction of about 5%. These results are helpful to attain stable and clean combustion in the gas turbine based on hydrogen fuel.
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| 2. |
- Ji, Longjuan, et al.
(författare)
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Structure and thermoacoustic instability of turbulent swirling lean premixed methane/hydrogen/air flames in a model combustor
- 2024
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Ingår i: International Journal of Hydrogen Energy. - 0360-3199. ; 60, s. 890-901
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Tidskriftsartikel (refereegranskat)abstract
- The structure and thermoacoustic instability (TI) of premixed CH4/H2/air swirling flames were experimentally investigated for a range of hydrogen fraction (ηH2) up to 80% under different equivalence ratio (Φ) and swirl number (S) conditions. It is shown that the onset of TI is enhanced when increasing either ηH2, S, or Φ. The dominant frequency of TI increases dramatically with ηH2. The higher dominant frequency in the hydrogen-enriched flames can be attributed to a shorter flame length which results in a reduced flame convection time. It is observed that the unstable flames are always accompanied by the appearance of outer recirculation zone (ORZ) flame. Therefore, the flame kernel residing in the ORZ can be an indicator of the occurrence of TI. The flame front of thermoacoustic unstable flames was observed to be more wrinkled, e.g., with larger mean absolute curvature (κ abs) and local flame surface area ratio (δΣmax). Importantly, the phase-locked analysis shows that κ abs and δΣmax can be modified at different oscillation phases, and their maximum and minimum values are simultaneously achieved at phase angles θ of about 0° and 180°, respectively. Variations of κ abs and δΣmax are in phase with the heat release rate, indicating a strong correlation between the TI and flame structure modification; however, they show a phase lag of about 72° behind the pressure in this work. These results are vital when understanding and predicting the TI based on the flame structure, especially when adopting a visual detection method of the instability.
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