OCR Text |
Show The source of the continuum observed in FIG. 5 is believed to predominately result from the recombination reaction C O + O -> C 0 2* * where CO2 (* designates an excited state species) emits light over a continuum from 300-500 nm [2]. Excess O2 results in higher availability for O atoms to react with CO, thus producing stronger emission. Under lean O2 conditions less O atoms are available resulting in weaker emission. The origin of the O H emission is more complex. From air-fuel combustion work it is widely agreed upon that O H emission results from the chemiluminescence reaction [3,4,5 ] CH+02->OH*+CO with the contribution from thermal excitation being negligible. However, for oxy-fuel conditions the flame temperature (adiabatic flame temperature for stoichiometric O2/CH4 is 3050 K, compared to air/CFL*, which is only 2222 K ) and radical concentrations are much higher. The higher temperature and radical concentration in oxy-fiiel flames introduce additional chemiluminescence reactions such as H+0+M-»M+OH* H+OH+OH->H20+OH* which are know to occur in H2 flame systems [6]. In addition, the thermal excitation contribution is 6000x stronger in an oxy-fuel flame compared to air-fuel1. It is not clear which of these mechanisms are dominate if any, but certainly the strong O H emission from an oxy-fuel flame makes it a reasonable choice to monitor and correlate to the burners operating conditions. Monitoring the burners operating conditions using the configuration in FIG. 3 integrates the flame radiation along the axial gas flow direction. As discussed above, the intensity of the emitted flame radiation detected depends on the wavelength region that is being observed. This wavelength 1 Estimated using Boltzmann distribution factor and Einstein transition probability [7] for adiabatic O2/CH4 and air/CIi, flames. 7 |