OCR Text |
Show furnace at various axial and radial locations. As can be seen on axis and near the furnace entrance the width of the PDF is relatively small. Far from the furnace entrance and off axis the PDF begins to flatten out and become bimodal with a minimum in the centre. It is well known that the rate of formation of thermal NOx significantly increases above 1600 to 1800 K. In most cases the PDF of the gas temperature extended above 1600 K. If the mean temperature were below 1600 no thermal NOx would be predicted even though the gas temperature was spending a portion of its time above this limiting temperature. Whereas the gas temperature was measured at many axial and radial locations, some comparisons can be made with the simulation results. It should be noted, however, that both the measurements and simulations are currently in a preliminary state. As such they do have limitations. An absorption coefficient of 0.1 was assumed in the simulation since there is very little soot in the flame. A turbulence intensity of 2% is assumed at the entrance to the furnace. In order to gain an understanding of the'confidence in the way in which the temperature fluctuations are estimated through the equations for the variance of enthalpy, the entrance PDF of temperature was unrealistically set to a very small value. The growth of the temperature fluctuations and the decay of the mean temperature were then compared to that measured. Figure 7 is typical of the comparison between the measure and predicted radial profiles. As seen in Figure 7 they correspond well; however, no measurements are shown beyond 0.9 cm. The reason 1800 1400 g 1200 i 1000 i 800 ~. 800 400 200 0.00 METHAN: FlAME TEMPERATlAlE RADIAL PROFILES $1m. )( -1 .870 em o Mea. )( -1.905 em 0.01 0.02 0.03 0.04 RadIal DIstance (m) Fiqure 7: Typical comparison between measurements and simulation near the axial location 1.9 cm from the furnace entrance. |