Experimental Study of Hydrogen Addition Effects on a Swirl-Stabilized Methane-Air Flame
Abstract
:1. Introduction
2. Experiments and Method
2.1. Flow Path and Equipment
2.2. Operating Condition, LBO, and CO Emission Measurements
2.3. Investigation of the Flame and Flow Field
2.4. Mathematical Description for the Proper Orthogonal Decomposition (POD)
2.5. Computational Implementation: Method of Snapshots
3. Results and Discussion
3.1. LBO Limits and The Averaged Features of Flames and Flow Field
3.2. Instantaneous Velocity Fields
3.3. Identification of Precessing Vortex Core by POD Analysis
3.4. CO Emissions
4. Conclusions
- The flame LBO limits can be extended to lower equivalence ratios by adding H2 in the fuel flow and improving the combustor inlet temperature. Higher H2 molar fraction in the fuel mixture can benefit the combustor operation with an extended equivalence ratio range.
- Time-averaged CH chemiluminescence indicated that the flame reaction zone traveled and stabilized upstream with the increase of equivalence ratios and H2 molar fraction in the fuel mixture. The attached ‘V’ shape flame, ‘M’ shape flame, and a lifted ‘V’ shape flame was found along the decrease of the equivalence ratio without H2 addition. With 25% and 50% H2 addition, the flame shape changed from the attached ‘V’ shape to the lifted ‘V’ shape. The ‘M’ shape flame was not found.
- The time-average velocity field of non-reacting flow revealed the presence of center recirculation zone (CRZ) and outer recirculation zone (ORZ) due to the vortex breakdown and the geometry of the dump combustor, respectively. An annular jet flow was found to be located between the CRZ and ORZ. The velocity in the CRZ, ORZ, and the annular jet flow was enhanced by improving the combustor inlet temperature from 384 K to 484 K.
- The time-average velocity field of reacting flow indicated that the H2 addition could lead to a velocity increase in the flow field at equivalence ratio 0.7. However, at a lower equivalence ratio 0.54, this effect was not observed. Reducing equivalence ratio resulted in a size reduction of CRZ for both the CH4 flame and 75%CH4/25%H2 flame. By using inverse Abel transform, it could be observed that the flame with 25% H2 addition was able to stabilize at the ISL at a lower equivalence ratio when compared to the CH4 flame.
- Unlike the average flow field, the instantaneous velocity field of the reacting flow revealed the unsteady vortices structures, which indicated the presence of a coherent helical vortex. Such a helical vortex often appears in swirling flow and it is commonly referred to as the precessing vortex core (PVC).
- In the non-reacting flow, the structure of POD spatial mode and their relevant time coefficients indicated that the first two POD modes were associated with a self-excited single helical instability which features a PVC. In the reacting flow, the flame of CH4 and 75%CH4/25%H2 were studied at the equivalence ratio of 0.70 and 0.54. Fast Fourier transform showed that the PVC was suppressed by the combustion.
- The CO emission measurement showed that the equivalence ratio operation range with low CO (under the UDL) was extended by H2 addition and improving the combustor inlet temperature. In addition, adding H2 made it possible to operate a low CO combustion at lower adiabatic flame temperatures. However, increasing H2 molar fraction from 25% to 50% did not significantly extend the margin of adiabatic flame temperature for low CO operation.
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Items | Units | Operating Parameter | Uncertainty |
---|---|---|---|
Fuel | - | CH4/H2 blends | - |
H2 molar fraction | - | 0–50% | - |
Air flow rate | g/s | 2.96 | ±0.02 |
Equivalence ratio | - | 1–LBO (lean blowout) limits | 0.01 |
Swirl number | - | 0.58 | ±0.01 |
Preheated temperature | K | 384/484 | ±2 |
PIV System | Lavision |
---|---|
Camera | Phantom V611 |
Recording resolution | 1280 × 800 pixels |
Recording frequency | 2 kHz |
Laser | ND:YLF |
Laser sheet thickness | ≈1 mm |
Laser wavelength | 527 nm |
Laser pulse interval | 50 µs |
Seeding particles | TiO2 |
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Li, M.; Tong, Y.; Klingmann, J.; Thern, M. Experimental Study of Hydrogen Addition Effects on a Swirl-Stabilized Methane-Air Flame. Energies 2017, 10, 1769. https://doi.org/10.3390/en10111769
Li M, Tong Y, Klingmann J, Thern M. Experimental Study of Hydrogen Addition Effects on a Swirl-Stabilized Methane-Air Flame. Energies. 2017; 10(11):1769. https://doi.org/10.3390/en10111769
Chicago/Turabian StyleLi, Mao, Yiheng Tong, Jens Klingmann, and Marcus Thern. 2017. "Experimental Study of Hydrogen Addition Effects on a Swirl-Stabilized Methane-Air Flame" Energies 10, no. 11: 1769. https://doi.org/10.3390/en10111769