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Show 180 160 140 120 ..-D E 100 Q. ..::: 0: z 80 60 40 2: 1 0 o • 2 3 4 12 5 riD 5500egC --0- 750 OegC 6 7 8 9 Fig. 10 Radial variation of thermal NO concentration at x/D=41.45 To calculate an EINOx figure from the computational results, for comparison with the experimental measurements, values for the NO and C02 concentrations were taken from the end of the computational domain which is 1 m from the burner exit. The EINOx shows a reduction of nearly 6 0/0 when the methane is preheated from 550°C to 750 0c. Conclusions Experiments have been performed into the role that fuel preheat can play in the soot loading and the radiative heat transfer and NOx emissions from turbulent oxygen enriched methane diffusion flames . The experiments indicate that the effect of methane preheat may be split into two regimes: 1. At lower degrees of methane preheat the effect is chiefly to reduce the radiant fraction and cause an unchecked rise in the flame temperature serving to increase NOx emissions. 2. At preheat temperatures above 550°C the total quantity of soot produced in the flame was seen to be enhanced causing the radiant fraction to increase thus countering the upwards drive on the flame temperature. As a consequence at the higher preheat temperatures NOx emissions were seen to decrease. The present modelling of soot is based on a simple approach that does not seem to capture the effect of fuel preheat on pyrolysis reactions. In order to account properly for this we need to calculate accurately the soot precursors (e.g. acetylene benzene and PAH), however consideration of the computational tractability in turbulent diffusion flame modelling precludes the use of more sophisticated models. The present computation shows an increase in the maximum soot concentration which leads to a reduction in the local flame temperature, as a result of preheating the fuel from 550 to 750°C. This results in the final EINOx reducing by as much as 6 % as a result of this preheating the fuel. References 1. Wagner, H. Gg., Seventeenth Symposium (International) on Combustion, 3, The Combustion Institute (1980). 2. Missaghi. M. Pourkashanian M., Williams, A., and Yap, T.L. , Proc. of Second International Conference on Environment and Combustion Technology, Portugal (1993) . |
