Smoke Limits of Bunsen Burner Ethylene-Air Flames SIR: Smoke limits ( 7 ) and yellow-tip limits ( 2 , 3) of gaseous fuel-air flames may be correlated by a simple assumption-namely, that for a given burner and same total flow for both limits? the difference in fuel flow bet\veen the value a t which yellow first appears in a flame (the )ellow-tip limit) and the value a t which smoke is first emitted (the smoke limit) is directly proportional to the latter fuel flow. IVhen the data lvere reported ( 7 ) . no correlation between smoke limits on various burners had been found. In Figure 1 or this addendum these same data are now correlated for all instances uhere corresponding yellow-tip limits were available. For a given burner diameter and same total flow of fuel plus primary air, the ordinate
(
1 -
2)
~
equals the ratio of
the difference in fuel flow betiyeen the smoke and yellow-tip limits to the furl flow at thr smoke limit. F is the fraction of stoichiometric for the fuel-air mixture flowing from the burner port-the per cent gas divided by the stoichiometric
gas percentage. T h e subscript s designates the yello\v-tip limit and S.L. the smoke limit. The experimental points are divided into tkvo groupsthe group through \vhich the solid curve is dra\vn includes almost all points where F , is nonconstant (2. 3 ) . For these points the plot is of the form 1 - (T x) l's. .x, T h e solid points include all those where Fv is the constant yellolv-tip limit 11.88 for ethylene. (2. 3 ) ] . For these the plot is 1 - (-4 x ) 28s. x . not meaningful in itself. However. these points [all in with the others and therefore are included. For points \vhere F , exceeds the constant yelloiv-tip limit. the following procedure can be used to compute smoke limits of ethylene-air flames: 1 . Consider a given burner port diameter and total flo~v. the latter expressed for convenience in terms of the corresponding critical boundary velocity gradient ( g s , L , = gg). Determine experimental values of F, from Figure 2. 2. _Issume values of Fs.L. and obtain from the solid curve in Figure 1 rorresponding values for F,. 3. Choose the value of Fs.L. so that Fv from step 2 is about equal to F,
from step 1. If a small range of values of FS.L. meets this condition, a midpoint of the range should be taken. This value of Fs.L, and g,Y./~. defines one smoke limit for ethylene on the selected burner. T h e procedure can be repeated to obtain a curve of smoke limits. Solid curves in Figure 3 were computed in this way and fit the experimental points fairly well. The computed dashed curves i n 1;igure 3 are for points where E; = 1.88 (constant > ello\t.-tip limit for ethylene) and ivere obtained b>- the empirical relation t;,y.L.
=
1.88 f
D -c
D.Y.L.
\\here D, is the minimum burner diameter (cm.) for which I;, equals 1.88. It is 0.6 for ethylene ( 2 . .?). I).s./,. is the burner diameter for which F . Y . / , . is being sought. Acknowledgment
This research \vas supported i n part by the American Gas Association (Project ZC-20). Literature Cited (1) Grumer, J.. Harris. M. E . , I s n ESC. CHEM. 51, 570-2 (1959). (2) Grumer. J.. Harris, M. E.. Kojvc, V. R.. Zbid.. 48, 2052--62 (1956). (3) Grumer, .J., Harris, M. E.. K o i r e . V. R., Bur. M i n e s Rept. Inwst. 5 2 2 5 , 199 pp.. 1956. JOSEPff GKC\fl:R E. H A R R I S
hf4RCARET
Explosives Research Laboratory Bureau of Mines Pittsbur5h. Pa.
4 Figure 1. Correlation of smoke and yellow-tip limits of ethylene-air flames
.
a,.
A.A
247 143 891
x
611
v
390 249
0
!It
1 Figure 2. Curves of yellowtip fractions for ethylene-air Fc = 1.88
b Figure 3. Comparison of calculated curves and experimental points for smoke limits of ethylene-air flames on long cylindrical tubes
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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