Abstract
The present work investigates the effects of outer stage flare angle on ignition and kernel propagation in a centrally staged optical model combustor based on the kernel dynamics analysis and laser diagnostics of flow and spray fields. Three outer stage flare angles of 8°, 16°, and 25° are researched, respectively. The better ignition performances are found for larger outer stage flare angles. Key properties such as the kernel velocity, kernel trajectory extracted from 6 kHz high-speed flame images are analyzed in combination with the flow and spray measured via Particle Image Velocimetry (PIV) and Planar Mie Scattering (PMie). Results show that the larger outer stage flare angle imposes a larger opening angle of outer swirl jet (SWJ), shifting the vortex in outer recirculation zone (ORZ) and inner recirculation zone (IRZ) upstream. The spray distribution of a smaller flare angle exhibits a fuel-lean zone near the igniter and this is attributed to the presence of low-angle outer swirl jet that prevents the fuel droplets from arriving at the igniter vicinity. The flame kernel propagates along the path where the strain rate and velocity decrease and the spray droplet density is within the flammable limits. A lower outer stage flare angle increases the strain rate and velocity at the early phase of flame propagation, leading to a longer propagation route and thus increasing the risk of ignition failure.
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Abbreviations
- c :
-
gray intensity
- d :
-
distance to the origin/m
- FAR:
-
fuel to air ratio
- L :
-
kernel propagation distance/m
- P* :
-
total pressure/Pa
- R :
-
radial coordinate
- R v :
-
swirl radial velocity ratio
- S :
-
strain rate/s−1
- SMD:
-
sauter mean diameter/m
- T* :
-
total temperature/K
- t :
-
time/s
- V :
-
air velocity/m·s−1
- Y :
-
axial coordinate
- α :
-
half spray cone angle/(°)
- θ :
-
outer stage flare angle/(°)
- σ :
-
total pressure drop across the combustor
- ω :
-
vorticity/s−1
- 1:
-
combustor inlet
- 2:
-
combustor outlet
- ref:
-
reference value
- YR :
-
tensor in the Y-R plane
- ICAO:
-
international civil aviation organization
- IRZ:
-
inner recirculation zone
- ISL:
-
inner shear layer
- LDI:
-
lean direct injection
- LLO:
-
lean light off
- LPP:
-
lean premixed prevaporized
- LRZ:
-
lip recirculation zone
- ORZ:
-
outer recirculation zone
- OSL:
-
outer shear layer
- PIV:
-
particle image velocimetry
- PMie:
-
planar mie scattering
- RR:
-
rolls royce
- SWJ:
-
swirl jets
- TAPS:
-
twin annular premixing swirler
- TeLESS:
-
technology of low emission of stirred swirl
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Acknowledgements
This work was supported by National Natural Science Foundation of China (Grant No. 91641109) and National Science and Technology Major Project (2017-III-0004-0028).
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Yang, S., Hui, X., Zhang, C. et al. Mechanistic Insights into Effects of Outer Stage Flare Angle on Ignition and Flame Propagation of Separated Dual-Swirl Spray Flames. J. Therm. Sci. 31, 1642–1662 (2022). https://doi.org/10.1007/s11630-022-1656-z
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DOI: https://doi.org/10.1007/s11630-022-1656-z