Spontaneous Raman-Rayleigh measurements of species concentration-temperature have been made in turbulent nonpremixed flames of methane near extinction. The means and rms of fluctuations of temperature, density, mixture fraction, and the mass fractions of CH4, O2, N2, H2O, H2, CO, and CO2 are presented in this paper. The mean Raman-Rayleigh results compare favorably with probe measurements of species concentrations and temperature made in similar flames. At a given axial location, unreactedness (finite rate kinetics) and not unmixedness [high (ξ″2) 1 2] explains almost entirely the change in the flame structure. As the flame approaches extinction, the Favre averaged mass fractions of CH4 and O2 increase while those of the products H2O, H2, CO, and CO2 decrease. The rms of fluctuations in the temperature and mass fractions O2, H2O, H2, CO, and CO2 decrease as well. Although these results favor the concept of a diffuse flame structure, the existence of partially premixed laminar diffusion flamelets cannot be excluded.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology
- Physics and Astronomy(all)