| OCR Text |
Show AFRC - 1996 Int. Symposium Baltimore 1800 __ 1600 u -.,... 1400 ~ 13 1200 ~ QJ E 1000 ~ QJ 800 E .:: 600 ~ 1~3 400 )0( 'e 200 a O~ 1~ Flame temper - ---•- x. 1--...... ........ .., ........... ....... No combus 2% 3~ ature .--.--:: ~ .... ".fa.""."., .. .. Ion ~ ~ ,La combu ....' .... , .... ......... ...... ...-. 1 .11 September 30 - October 2 1996 Page 7 of 14 --~ ~ t Ion "' ........ 0 ........ 6~ 7% 8~ 9% 10% fuel fraction ("wet") (m3/m3) • 02 12% a 02 14~ • 02 16% • 02 19% -.-cal ulated (Su = 0.3 m/s) • mea ured data ~cal ulated data (Su = 0.3 m/s) Figure 3: boundaries of stability of combustion and associated adiabatic flame temperatures. Same data as in figure 2. flame temperature, while the unburnt mixture temperature is being increased to preserve the flame stability. The explanation for this observation is as follows: an increase of the proportion of flue-gases decreases the burning velocity (and thus the stability) essentially linearly (see also Blint, 1988). However, increasing the mixture temperature increases the burning velocity of the mixture as r, where O! varies from 2 without flue-gases to > 3 at large proportions of flue-gases (Blint). This allows the maintenance of a constant flame stability upon high dilution with flue-gases by only a modest increase in mixture temperature. Whereas the decrease in flame temperature is essentially proportional to the degree of dilution, increase in mixture temperature, necessary to maintain a constant burning velocity, results in only a modest increase in flame temperature. As a rule of thumb, an increase in the mixture temperature of 100 °C results in a flame temperature that is only 50°C higher. The net effect is a reduction in flame temperature with increasing dilution, at constant burning velocity. 4.2 NOx production In this paper, the NOx production is expressed in units of gram NOx per gigajoule fuel. A quantity of 1 g/GJ NOx is equivalent to a flue NOx emission of 2 ppm (at 0% OJ. The NOx production due to combustion of a natural gas/air/flue-gas mixture in the flame tube has been calculated by subtracting the NOx, measured in the flue-gas upstream of the |
