OCR Text |
Show OPERATING CONDITIONS The operating conditions selected for the present study are as follows: Table 1: Operating Conditions Fuel: natural gas Load: 100,000 Btulhr (0.07 lbs/min) Excess Air Range: 0-32.5% (0-1.6 lbs/min) Swirl Air Range: 0.8 - 1.2 lbs/min Axial Air Range: 0- 0.6 lbs/min PERFORMANCE INDEX Identification of burner operating conditions (i.e., excess air and swirl strength) that produce an unusually "favorable" response, as well as the more typical "adverse" response, is frrst required, then the reasons for this performance can be discerned. In order to compare and determine the performance for different injector geometries, swirl intensities, and excess air levels, a consistent criterion must be applied. A cost function, or "performance function," is used to weight the relative importance of NOx and combustion efficiency based on prescribed limits for each. The performance function, J, is defmed as J = wNOz • f([NO .. J)+ w7J' g(7]) (3) The functions f and g are selected to give a maximum J value when combustion efficiency is high and NOx is low. The terms WNOx and wll are weighting factors whose sum is equal to 1. For the results presented here, NOx and efficiency were equally weighted at 0.5. The NOx and efficiency functions are defmed as follows, f([NOxD = 1-0.75{[~~.]J g(7]) = l[ 11 ~ ~nU. ]1/2 100% 7]miD [NOx1> 25 ppm 1] < 99.8% 1] ~ 99.8% (4) (5) Both of these functions vary from 0 to 1, with high values indicating low NOx and high efficiency. The important feature of the performance function is that it returns a high value when performance is "favorable" (i.e., low NOx and high combustion efficiency). The performance function is described in detail in Reference 8. 6 |