OCR Text |
Show In the detailed flame study radial and axial in-flame measurements were made of gas velocity, gas temperature and gaseous species concentration (CO, CO2, NOlO CnHm and O2) distributions. Experimental Results In the parametric tests, 98 flames were investigated for the effects of burner input variables upon NO. and CO emissions from the combustion tunnel. The input variables found to have effect upon NO. and CO emissions are: type of fuel nozzle fuel gun position within burner primary air fraction radial displacement of swirl from flame axis Type of Fuel Nozzle Two parameters, the exit velocity of the fuel jet from the gun and the angle of the jet relative to the flame axis, were considered in the design of the fuel nozzles. Several nozzles were built to allow the velocity of the fuel to range from 50 ft/sec. to 600 ft/sec. and the angle to vary from 00 to 25 0 • Results obtained from the combustion tests with these nozzles are shown in Figures 3 and 4. It is noteworthy that while CO emission levels were very low for all cases, they increased slightly with increasing fuel jet velocity. On the other hand, NO. emission levels were more influenced by the fuel jet angle: i.e., increasing the fuel jet angle from 0 to 25 0 increased NO. concentration at the exit by - 25 %. Fuel Gun Position The axial position at which the fuel is introduced within the burner is known to be important in determining the flame structure. Fluid dynamically it affects the interaction of the axial fuel jet and the swirling annular air flow. To investigate the effect of this parameter upon NO. and CO emissions, several flames were investigated in which the location of injection of fuel within the burner was varied. Figures 5 & 6 illustrate the effect of this variable for the cases of highly swirling and weakly swirling primary air. The negative values of the fuel gun positions shown in Figures 5 & 6 indicate the distance between the end of the burner face and the fuel gun tip. A negative value implies that the gun has been retracted into the burner throat It can be seen from Figures 5 and 6 that the fuel gun position has little effect on NO. concentration. However, CO emissions were observed to increase dramatically when the fuel gun was moved in the burner for certain burner configurations. PrimaI)' air fraction The conditions represented in Fig. 5 with 51 % of the air supplied as primary air give high NO. values, ranging from 110 to 135 ppm, while CO concentrations are understandably low because of the early aeration of the fuel in this case. It is the case illustrated in Fig. 6 that deserves further discussion. With the low primary fraction, NOx 4 |