Raman measurements and joint PDF modeling of a nonpremixed bluff-body-stabilized methane flame
- General Electric Research Center, Schenectady, NY (United States)
- Cornell Univ., Ithaca, NY (United States)
Mixture fraction, temperature, and major species in a recirculation-stabilized nonpremixed methane-air flame are (1) measured using laser Raman scattering and (2) calculated using the joint velocity-composition probability density function (PDF) model, appropriately combined with an elliptic mean flow solver. The Raman system was modified to account for the significant levels of laser-induced fluorescence (LIF) and incandescence encountered in the rich sooty zone of the flame. The joint PDF contains three velocity components, which are modeled by Langevin equations, and five thermochemical scalar variables with mixing given by linear deterministic relaxation to the mean and chemistry by a four-step steady-state reduced scheme. The flame is characterized by significant finite-rate chemistry, including, unlike a CO/H{sub 2}/N{sub 2} fuel in the same apparatus, strong bimodality in the temperature-mixture fraction scatter plots. Calculations are compared with Raman data on temperature and major species. The agreement is in general reasonable, with the largest discrepancies being caused by the breakdown of the assumption of a chemical steady state for the cool fuel-rich gas at the core of the flame. Large discrepancies are found on the peak CO, as in other similar studies, confirming a need for better measurements of CO than Raman spectroscopy can provide. The model overpredicts the degree of extinction. The radial flux of the mixture fraction calculated directly from the joint PDF is compared with the flux given by an a posteriori gradient diffusion calculation, indicating no (radial) counter-gradient diffusion and a ``turbulent Schmidt number`` of about 0.4.
- OSTI ID:
- 93267
- Report Number(s):
- CONF-940711--
- Country of Publication:
- United States
- Language:
- English
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