Seminar presented by Shigeru Tachibana, JAXA

wednesday 9 October at 13:00
Place: Navier meeting room (large meeting room in the building adjacent to the library).

Dynamic behaviors of inhomogeneous mixture flames in a lean premixed combustor (~60kW) under self-excited combustion instabilities are investigated by optical diagnostics. Detailed measurements have been performed in 4 fuel split (to upstream/downstream injections) conditions while keeping the total equivalence ratio constant at 0.69. The combustion stability was very sensitive to the fuel split condition (i.e. local equivalence ratio distribution). In the strong oscillations case, a bulge of fresh gas, which is considered a traveling vortex ring of fresh gas mixture, is periodically moving along the outer shear layer and merging with the stationary vortex flame near the wall. The level of the vortex-flame interaction is very sensitive to the local equivalence ratio distribution, and it seems that the strong oscillations occur when  richer mixtures locate about the inner shear layer region. These observations indicate that the driving force of the instability is the vortex-flame interaction, but the strength of the instability is modified by the local distribution of equivalence ratio.

Other recent studies, such as a combustion instability in a staged fuel jet engine combustor under pressurized conditions and utilization of the non-linear time-series analysis of dynamic pressure data for monitoring combustor stability margin, will be briefly introduced as well.

References:
1. Tachibana, S., Fukumoto, A., Kanai, K., Yoshida, S., Suzuki, K. and Sato, T., “Combustion instability in a lean premixed low-swirl combustor with mixture inhomogeneity ”, ECM2013, Lund, Sweden, June, 2013.
2. Tachibana, S., Fukumoto, A., Kanai, K., Yoshida, S., Suzuki, K., Sato, T. and Gotoda, H., ”Characteristics of dynamic pressure data and flame structures in an unstable lean premixed combustor with mixture inhomogeneity.” n3l workshop, Munich, Germany, June, 2013.
3. Tachibana, S., Kanai, K., Yamamoto, T., Shimodaira, K., Suzuki, K. and Sato, T., “Unsteady flame structures in a lean staged combustor under combustion instability”, 41st Annual Meeting of Gas Turbine Society of Japan, Okinawa, Japan (to be presented).
4. Gotoda, H., Nikimoto, H., Miyano, T. and Tachibana, S. (2011) “Dynamic properties of combustion instability in a lean premixed gas-turbine combustor”, CHAOS 21, 013124.

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