INDUSTRIAL AND ENGINEERING CHEMISTRY
3756
The data presented here should be generally applicable to conditions similar to those prevailing when these tests were carried QUt.
Vol. 41, No. 12
(3) Davidson, W. F., Bull. Am. Meteor. Soc., 27, 547-9 (1946). (4) Dept. Scientific and Industrial Research, Tech. Paper 1, At-
mospheric Pollution Research, London, H.M. Stationery Office, 1945. ( 5 ) Dobson, G. hl. (1948).
ACKNOWLEDGMENT
This report would not have been possible without the able assistance of a number of othws, especially C. A. Gosline, Jr., E. I . du Pont de Nemours & Company; J. F. Mattingly, U. S. Weather Bureau, Evansville, Ind.; and 0. H. Newton, U. 8. Weather Bureau, Brownsville, Tex. LITERATURE CITED (1) Bosanquet, C. H., and Pearson, J. L., Trans. Faraday SOC.,32, 1249-63 (1936) ( 2 ) Brooks, F.A,, Agr. Eng., 28, 233-40 (1947). e
B.,Quart. J . Roy. Meteor.
Soc., 74, 133-43
(6) Etkes, P. W., and Brooks, C. F., Monthly Weather Rev., 46, 45960 (1918).
(7) Frost, R., PFOC. Roy. Boo., A186, 20-35 (1946). (8) Hewson, E. W., IND. ENQ.CHEM., 36, 195-201 (1944) (9) Meetham, A. R., Weather, 1, 200-5 (1946). (10) Parker, A., Nature, 155, 682-5 (1945). (11) Roberts, 0. F. T., Proc. Roy. Soc., A104, 640-53 (1923). (12) Sutton, 0. G., Ibid., A135, 143-65 (1932). (13) Sutton, 0. G., Quart. J.R o y . Meteor. Soc., 73, 257-81 (19471 (14) Ibid., pp. 426-36. (15) Ibid., 74, 13-30 (1948) Rncmvm March 7 , 1949
rner
r
C
wit
S JOSEPH GRUMER Cent,ral Experinrent S t a t i o n , 77.S. B u r e a u of 'Mines, P i t t s b u r g h , P a .
T h e ability to interchange gas supplies has become important in the gas industry. New gases may not be able eo maintain stable flames in consumers' appliances. Recent studies have shown the fundamental principles of flame stabilization and entrainment of air in gas burners. This information is combined into relationships predicting the performance o f all burners in a community when fuel gases are changed, without requiring that the number of burners or their individual characteristics be known. Only certain readily obtainable data on the fuel gases concerned in the intcrchange are required. The method can be put to a practical test when data on actual fuel gases in use become available.
HE gas utility industry is occasionally forced to interchange fuel gases or supplement a low supply with gas of another kind. This may lead to serious problems, inasmuch 8s new mixtures are required to burn satisfactorily on a large number and on different types of gas appliances in use within a community. It is therefore necessary to develop a method for predicting the performance of interchanged furl gases, The A4merican Gas Association and the National Bureau of Standards ha,ve attempted to develop a method from an essentially empirical approach, but to date no completely satisfactory solution has been found ( 1 , 6). The practical method dcveloped in this paper can be used when certain readily obtainable basic data on fuel gases io be interchanged become available. The metliod is based on theoretical principles making use of the concept of boundary velocity gradients that define the flame-stability reglon and the principles of air entrainment by a fuel jet. These are combined t o develop relations which predict the rhange in burner performance when fuel gases are interchanged. FLAME-STABILITY DIAGRlJIS FOR VARIOUS FUEL GASES
Flash-back and blowoff characteristics may be studied with a burner consisting of a cylindrical tube with unrestricted port into which premixed fuel gas and air are iiitroduced a t different rates of flow. A burner flame is stable between two critical flow conditions, which are determined by the slopes of the curves of critical
stream velocity a t the boundary of the stream (10, 12, 16). If the stream-velocity distribution over the entire cross section is known, the desired slopes or, as termed by Lewis and von Elbe, critical boundary velocity gradients ( g F for flash back and g B for blowoff) can be calculated from measured critical flows for flash back and blowoff. For laminar (Poiseuille) flow, the boundary velocity gradient, g, is ( 1 2 ) g = limit (--dU/d.r) = 4Y/nR3 ?-+
? '
(1)
where V is the flow in a cylindrical tube of radius R and si is the stream velocity a t distance T from the axis of the tube. For turbulent flow of Reynolds number Re (8, 1 6 ) g = limit +R
(-dU,ldr) = V2/103R4R~1'4
(2)
The advantage of this theoretical treatment of flame stability can be seen by examining Figures 1t o 4 t)aken from ( 1 2 ) * The critical flows of natural gas-air mixtures a t \+hich flash back and blovioff were observed. with various burners are presented in Figures 1 and 2. There is a, different set of curves for each burner size. However, by plotting the data against g B instead of V F , subslantially a single curve is obtained for the burners of various size except for very small tube diameters approaching quenching distances (the minimum t.ube diameter through which flame will just pass) and for very large t,ube diameters that show tilted flames (12, 15). This is shown in Figure 3. A similar unification is obtained by plotting g B instead of VB. Figure 4, in which both g p and g B are plotted, defines the flame-stability region of natural gas-air mixtures. Similar flame-stability diagrams may be obtained for all combustible constituents of commercial fuel gases, which are hydrogen, carbon monoxide, methane, ethane, ethylene, propane, propene, and but'ane. The same is true for mixtures of these constituents with one another and with noncombustibles, such as oxygen, nitrogen, and carbon dioxide. Thus it is clear that, in principle, there is no difference between supplemeiiting fuel gases and interchanging them. A desired simplification is obtained by plott,ing fuel gas percentage as the fraction of the stoichiometric. In this way the
December 1949
2757
INDUSTRIAL AND ENGINEERING CHEMISTRY
13
has been derived by von Elbe and Grumer (14) from the Bernouilli and momentum theorems. It is
12
V2/V3
11
+ z u
2 9
2 U u
$8 a
2 z
7
6
5
4 0
GAS FLOW, CUBIC CENTIMETERSPER SECOND
Figure 1. Critical Flows for Flash Back of Natural Gas-Air Flames in Cylindrical Tubes of Different Diameters a t Room Temperature
LI
p
V,/V].
Y
flame-stability curves of, for example, the saturated hydrocarbons coincide fairly closely (Figure 5 ) . For all practical purposes, therefore, saturated hydrocarbons may be represented by a single flame-stability diagram (Figure 6). There are not enough data to determine whether similar groupings hold for other gases. Figure 7 shows the stability region for hydrogen-air flames (16). The relative tendency of natural gas-type fuels to blow off and that of predominantly hydrogen fuels t o flash back is seen by comparing Figures 6 and 7. The inert-gas content of a fuel gas becomes important if the h a 1 mixture with air contains more than a few per cent of inert gas. This is demonstrated in Figure 8, where gF of stoichiometric methane flames is plotted against the ratio of 0 2 / 0 2 f i\Jz in the mixture from 100% oxygen t o air. The curve ie steep in the "air" region. ge is similarly affected by inert gases (10, 18). Increasing stream temperature (IS) and barometric pressure (9) increase both gR and g ~ . Despite the large amount of work that has been done on flash back and blowoff, lack of data prevents plotting stability regions for many of the gases 14 enumerated above and for mixtures of them. This will have to be done before the flame13 stability part of this problem can be completely evaluated. 12
(31
poA/~Ao
- (1 - po/p.fr)is the density and A is the area of the stream at the port. Subscript o refers to the fuel gas at the orifice. This equation shows the fuel-gas percentage (100 V J V ) to be a function of the densities and the port and orifice areas. Actual air entrainment is generally somewhat smaller than calculated. Though the factors causing this discrepancy are only partly understood a t present, they appear to depend largely on burner geometry (3-5, 7 , 11) and are not likely to change significantly for any one burner because of the interchanging of fuels. Therefore, when fuels a and x are interchanged on a burner without adjustment, the ratio of the air entrainment for both fuels is approximated, using Equation
where
10
-
= pslr[l
p
3, as
(VIVO): -
(P"/P)Z
(VlV0)Z
(POlP).
(4)
The gas percentage that will result in a burner with a new fuel,
x, can be predicted by means of Equation 4, if the gas percentage formed by the current fuel, a, and the densities of both fuels are known. Experimental values of ratios of VIVOfor several nonideal Venturi burners using interchanged fuels were derived from data obtained by Kowallce and Cea$sBe (11). As shown in Table I, these are well matched by values calculated with Equation 4,over a wide variation in specific gravities of the filrls. The air-entrainment equation for burners with cylindrical ducts has been derived by von Elbe and Grumer ( 1 4 ) as
V2/VI = ( P ~ I ~ A / P L-~PA, L~, )A ~ / P Q
(5 1
11
EFFECT OF INTERCHANGE O F FUEL GASES ON AIR ENTRAINMENT IN A BURNER
To predict whether a burner operating at given air-shutter, gas-orifice, and line-pressure settings will maintain a stable flame, the flame-stability diagram for the fuel, the composition of the mixture in the burner, and the boundary velocity gradient, g, at the burner port must be known. The Iatter two quantities are determined in an atmospheric gas burner by the air-entrainment process. Most atmospheric burners contain Venturi ducts which serve to distribute the stream uniformly over a multihole port. An equation for the air entrainment in an ideal Venturi burner
c
82 10 3 3
2 8 7 6 5 0
20
40
60
80
100 120 140 160 180 200 220 240 GAS FLOW CUBIC CENTIMETERS PER SECOND
260
280
300
320
Figure 2. Critical Flows for Blowoff of Natural Gas-Air Flames from Cylindrical Tubes of Different Diameters a t Room Temperature Flames surrounded by air except as indicated
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 41, No. 12
and subscript o to the plane of the gas orifice, as before. Pressure p , is composed of the sum of pressures due to friction at the tube wall, flame thrust, and gravitational buoyancy, each of which can be determined independently either by calculation or experiment. Before ignition, pressure p , is smaller by the amount corresponding t o flame thrust, and air eiitrainment is correspondingly larger. When the fuel gas is lighter than air and the burner is in an upright position, buoyancy decreases p , and correspondingly increases air entrainment. It has the opposite effect in invelted burners and no effect in horizontal burners The experimental points fit the theoretical curves well. Flashback and blowoff curves for theae burners are shown in Figures 9 and 10 as dotted curves. They have been obtained from the data in Figure 4 by means of the equation V , = R3g/4V/V0, using experimental values of g and V I V Ocorreiponding to flash bark and blowoff, respectively. Stable flames are possible only in the region between these curves. In the example illustrated by Figure 10 the stable-flame reglon is very narrow, axid because B o m C fluctuations in mixture coniposiiion are inherent in the airentrainment process (1.6) it is hardly possible in practice to oblain a permanently stable flame. Figures 9 and 10 demonstrate that burner performance can be predicted theoretically by comparing the air-entrainment curve with the stable-flame region of the fuel gas.
4L-I 0 100
ZOO
300
VFLOCITV G G D l t N T PT HOUNOARY,
400
500
500
4 v
“**R (-%)= ; ;?, SECONDS I dr
P-
Figure 3. Flash back
CritieaI Velocity Gradients at Boundary of Gas Stream of
natural gas-air flames in cylindrical tubes of different diameters at rmom temperature
wfiero p is the static pressure and the numbers L are “momentum coefficients,’’ with values usually between 0.7 and 1. Subscript m refers to the plane of maximum static pressure in the burner
For the usual case of a rather short, cylindrical tube burner, slow-burning mixture, and high fuel Aow the second term in Equation 5 can be neglected. The equation reduces substantially to the form of Equation 3, and Equation 4 represents the ratio of air entrainment for two interchanged fuels a and z with good approximation for both cylindrical and Venturi duct burners. When fuels are interchanged, boundary-velocity gradient g in the flame port may also change. To calculate the effect, it may be assumed that Poiseuille flow is established a t the flame port, so that g is determined by Equation 1. For cylindrical burners this approximation is justified, as shown by the agreement between experiment and calculation (IC). For Venturi burners the approximation depends upon the diameter-to-depth ratio of the portholes. An investigation of this subject appears desirable, though it is very probable that for the usual range of porthole dimensions Equation P is closely fulfilled. The equation for the efflux of the fuel through the orifice i s
10,000 8.000
7Lo 6,000 n
7.
2 4.000 *A
c’
z
2 2.000 Y W
c
G
s
1,000
’ 800
W
cc
2
z
600
3
8
400
_1
3
r0: 200
100 0.2 0.6 1.0 1.4 GAS CONCENTRATION FRACTION OF STOICHIOMETRIC
Figure 1. Flame-Stability Diagram for Natural Gas-Air Mixtures
Figure 5 .
Flame-Stability Diagram for Paraffin-Air Mixtures
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
December 1949
2759
critical boundary velocity gradients for flash back and blowoff)
TABLEI . COMPARISON OF EXPERIMENTAL AND CALCULATED versus mixture composition (expressed as fractions of stoichioAIR ENTRAINMENT RATIOS FOR INTERCHANGED FUELGASES metric). The performance point changes when the adjustment (Experimental values calculated from data of Kowalke and Ceaglske, 11) Specific Gravity ( V / V o )x/( V / V o b Burner of Fuel Gases Calculated Orifice Sine (pam = 1) Experimental (Equation 4) 0.582 0.575 fiO 1.406 0.667 0.630 1.160 1.00 1.00 Fuel a 0.440 1.32 1.26 0.273 1.56 1.55 0.174 1.406 0.555 0.580 56 1.160 0.639 0.618 0 845 0.630 0.845 0.440 1.00 1.00 0.273 1.27 1.25 0.174 1.55 1.54 0.585 0.571 1.406 50 0.639 0.632 1.160 0.848 0.883 0.030 1.00 1.00 0.440 1.24 1.32 0.273 1.53 1.74 0.174 0.592 0.560 I . 406 15 0.647 0.644 1.160 0.850 0.878 0.630 1.00 1.00 0.440 1.24 1.29 0.273 1.53 1.57 0.174 0.606 0.592 1.406 30 0.646 0.647 1.160 0.858 0.863 0.630 1.00 1.00 0.440
__
where u: is the discharge coefficient and p , represents the line pressure. Combining Equation 6 with Equations 1 and 4, one obtains
(7) Equations 4 and 7 determine the change of air-entrainment performance as defined by the values of g and the mixture composition in the burner. INTERCHANGEABILITY OF FUEL GASES IN A COMMUNITY
Equations 4 and 7 can be applied to any burner in a community. The air-entrainment performance of every burner can thus in principle be represented by a point in a diagram of
of the air shutter, the gas orifice, or line pressure is changed. I n a community which has been serviced satisfactorily by fuel a all burners are adjusted t o give stable flames with fuel a a t the prevailing line pressure, so that the performance points of all burners fall statistically within the stable-flame region represented by the re ion between curves gF and BE of fuel a. (It is felt that the yel?oow tip and incomplete combustion limits can be incorporated in the flame-stability diagram, although the means of representation are not known at present. The present discussion of the role of flame stability and air entrainment in fuel gas interchangeability does not depend upon yellow tip and incomplete combustion limits, as suoh flames are stable and can be used for heatine;.) The burners will not be distributed uniformly within this region. Most of them will be located on the rich side, away from the flash-back and blowoff limits according t o normal practice in appliance adjustment. When fuel x is substituted for fuel a without any burner adjustments (5 can be a mixture of a and a supplementing fuel) the shift of the limits of the region of air-entrainment performance can be calculated by appl ing Equations 4 and 7 t o the two flame-stability limits of fuera, and solving for (VIVO),and, (g)=. The resultino two curves are not the flame-stability limits of fuel z but tEe new limits of the air-entrainment performance region of this particular statistical roup of burners. The flame-stability limits of fuel z must be 8etermined separately by experiments as was done for fuel a. If the new limits of the airentrainment performance region are within the stable flame region of fuel x, fuels a and x are interchangeable. If the new limits are outside the stable flame region, it appears generally possible t o judge whether the fuels are not interchangeable a t all or whether the situation can be remedied by changes such as minor burner adjustments? minor adjustments in composition of fuel x, or minor changes in line pressure. For example, in a community satisfactorily using as fuel a a natural gas of specific gravity 0.63, heating value 1100 B.t.u. per cubic foot and stoichiometric value 0.085, the performance region of all burners is represented by the area bounded by the flame-stability curves of this fuel. These are obtained from Figure 6. If fuel a is t o be supplemented with mixtures of propane and air, the heating value of the send-out gas can be held constant at 1100 B.t.u. er cubic foot if the ratio of propanepropane air = l100fi590. [The heating value of a fuel is another limiting factor from the point of view of the gas industry and the consumer. It is not physically involved in air entrainment or flame stability (la, 1 4 ) and must therefore he
+
I
boundary-velocity gradients a t the flame port (not the
,---T---T---Tl
10,000 5,000 7
6000
6 Y
4.000
z
2
g x
2.000
d ys
9
1,000
800 600
D
8
400
6
200
dc
LOO
02
06 10 1.4 1.8 GAS CONCENTRATION. FRACTION OF STOICHIOMETRIC
Figure 6. Composite Approximate FlameStabilitv Diagram for Paraffin-Air Mixtures
HYDROGEN CONCENTRATION, FRACTION OF STOICHIOMETRIC
I
Figure 7.
Flame- Stability Diagram for Hydrogen-Air Mixtures
INDUSTRIAL AND ENGINEERING CHEMISTRY
2760
Vol. 41, No. 12
60,000 14
40,000
" v)
n z
12
8 20,000 w
'?, c
g
2
10 10,000
8
z2 0
8000
8
6000
4000
W
E 6
z
2
2
U
2,000
e
m' 14 L?
U i
_I
cc
0
E
1,000
0
800
K
2 12 z
600 10
400 02
04
06
08
10
02 -
OZfN2
Figure 8. Critical Boundary Velocity Gradients, g p , for Flash Back of Stoichiometric MethaneOxygen Mixtures
S
6
Effect of nitrogen dilution 4
treated separately. This is done very simply by rejecting any fuel having a n unacceptable heating value, regardless of its merits in other respects.] With a new send-out gas-fuel x, containing 32% propane, 43% air, and 25% natural gas, of specific gravity 1.08, stoichiometric value 0.0922, and the same line pressure as before-the performance region is represented by curves 12 and 22 of Figure 11, which were obtained by applying Equations 4 and 7 t o the flame-stability curves of fuel a and solving for (V/V,), and (g)=. The flame-stability limits of fuel x are obtained from Figure 6. When the stable-flame region of fuel x and the new performance region are compared, the latter region is found t o fall very largely within the former. This shows that most burners in the communlty R.ill perform satisfactorily with fuel 2 . ~h~ number of burners that will flash back 01 blow off mil] be relatively feqr, as these have t o be the appliances that were burning with lean or near stoichiometric flames or near flash back or blowoff when fuel a was supplied. A more exact estimation would be possible if data were gathered showing the probability distribution in any community of burners across the stable flame region of any fuel. It is also apparent from Figure 11 that all burners performing unsatisfactorily with fuel x would form stable flames If less air were entrained. As the air port area can be easily decreased in practically all air-entraining burners, it can be predicted that the new fuel will be completely satisfactory after some minor burner adjustments. Furthermore] yellow-tipped flames are not expected, as all burners will operate leaner than xtith fuel a. After adjustment of all burners t o fuel 2 , the two flamestability limits of fuel x mill bound the performance region of all burners in the community, replacing curves 12 and 22 of Figuro 11. When the community leturns to fuel a, the buiners that had not required adjustment to fuel x would return t o their original performance with fuel a; some of those that had been adjusted would form stable flames, some would not. This is shown in Figure 12. Curves l a and 2a were obtained by applying Equations 4 and 7 to the flame-stability limits of fuel x and , (g).. These are the limits of the airsolving for ( V I V O ) and entrainment region for the burners in the community returning to fuel a after adjustment to fuel 2 Figures 11 and 12 show that, after one period of adjustment t o fuel x, the community could be serviced satisfactorily by either fuel 2 or a , with only very minor readjustment demands. The example chosen is particularly severe, in t h a t only 25% of fuel a is retained in the send-out gas. The feasibiIitg of this method is indicated by the data in Table I and in Figures 9 and 10. These are sufficient t o justify further development.
2 NATIIRAL
Figure 9.
GAS FLOW CLJBlC CENTlMfTERS PER SECOND
Effect of Ignition on Air Entrainment
Calculated curves and experimental points SUMMARY
The performance of every burner in a communitj can be represented for any adjustment by a point in a diagiam of boundary velocity gradients a t the flame port verrus gas-alr ratlo. Burner flames are stable between two criticat limits of the boundary velocity gradients which correspond to flash back and blowoff and depend primarily on the composition of the fuel gas and the a community that has heen serviced gas-air ratio. factorily by gas a,the performance points of all burners fall statistically within the stable-flame region of fuel a. By means of previously derived theoretical equations it is possible t o calculate with good approximation the change of burner performance
10
8 t0 w
E 6 v)
0
2 4 2
i
z
0
2
0
Flash back on ignition Blow-off on ignition Flash-back limit
20 40 0 20 40 60 NATURAL GAS FLOW CUA'C CENTIVETEAS PER S f C O N D
Figure 10. Burner Operating within Flame Instability Calculated curyes and experimental points
December 1949 20.000
INDUSTRIAL AND ENGINEERING CHEMISTRY
I
Fuel gas a, natural gas Fuel gas X, ‘25% natural gas 1 132% Dropane I
2761
ACKNOWLEDGMENT
The author wishes t o thank Bernard Lewis and Guenther von Elbe for suggestions received during the course of the work. Measurements of flame-stability limits of hydrocarbon-air mixtures were made by M. E. Harris of the Explosives Branch of the Bureau of Mines. NOMENCLATURE
g p
= boundary velocity gradient, sec.-I
r A R Re U
= distance from axis, cm. = cross-sectional area, sq. cm. = radius, cm. = Reynolds number
V 01
= rate of flow of stream, cc. per second. = orifice discharge coefficient
p
coefficient, dependent on velocity profile of stream = density, grams per CC.
= static pressure head, cm.
= velocity in a cross-sectional element d A , cm. per
second
= momentum
GAS CONCENTRATION. FRACTION OF STOICHIOMETRIC
Figure 11.
Predicted Burner Performance in Community Exchanging Fuel Gas a for x
that results when one fuel gas is substituted for another. Thus, when fuel x is substituted for fuel a without any burner readjustments, the shift of the limits of the region of burner performance can be calculated. If the new limits of the region of burner performance are within the stable-flame region of fuel L, fuels a and x are interchangeable. If the new limits are outside the stable-flame region, it appears generally possible t o judge whether the fuels are not interchangeable or whether the situation can be remedied by minor burner adjustments, minor adjustments in composition of fuel 2, or minor changes in line pressure. Present information indicates the feasibility of the method. I t s application to all fuel gases in use requires considerable expansion of the present body of data.
Figure 12. Predicted Burner Performance in Community Returning to Fuel Gas a after Adjustment to x
Subscripts: a = fuel gas in current use m = plane of maximum static pressure within b u r n e ~ tube None = plane of burner ports o = plane of fuel gas orifice x = substitute fuel gas B = blowoff F = flashback LITERATURE CITED
(’) Am. Gas Assoc., Research Rept. 1106A,Project TL-1 (October 1948) (2) Am. Gas Assoc., Testing Lab. BUZZ. 10 (March 1940). (3) Ibid., 26 (May 1944). (4) Ibid., 37 (September 1945). (5) lhid., 36 (February 1946). ( 6 ) Anthes, J. F., “Am. Gas Assoc. Progress Report on Mixed Gas Research,” Project TL-1 (May 1948). (7) Berry, W. M., Brumbaugh, I. V., Moulton, G . F., and Shawn, G. B., Natl. Bur. Standards, Tech. Paper 193 (September 1921). (8) Bollinger, L. M., and Williams, D. T., Natl. Advisory Coin. Aeronautics, Tech. Note 1234 (June 1947). (9) Garside, J. E.,Forsyth, J S., and Townend, D. T. A., J . I n s t . Fuel, 18, 175 (1945). (10) Harris, M. E., Grumer, J., von Elbe, G., and Lewis, B., “Third Symposium on Combustion and Flame and Explosion Phenomena,” p. 18, Baltimore, Williams & Wilkins Co., 1949. (11) Kowallre, 0.L.,and Ceaglske, N. H., Am. Gas Assoc. Proc., 1929,662. (12) Lewis, B.,and yon Elbe, G., J . Chem. Phys., 11, 76 (1943). (13) Shnidman, L., “Gaseous Fuels,” pp. 157, 158, Easton, Pa., Mack Printing Co., 1948. (14) Von Elbe, G.,and Grumer, J., IND. ENO.CHEM., 40,1123 (1948). (15) Von Elbe, G., and Mentser, M., J . Chem. Phys., 13 89 (1945). (16) Wohl, K.,Kapp, N. M., and Gazley, C . , Meteor Report UAC-26, United Aircraft Corp. (September 1948).
.
RECEIVED June 1, 1949. Presented before the Division of Gas and Fuel Chemistry, AMERICAN CHEMICAL SOCIETY,M a y 0 and 10, 1949, Pittsburgh, Pa.
