ELECTRICAL PROPERTIES OF FLAMES Burner Flames in Longitudinal Electric HARTWELL
F. CALCOTE’
Fields
ROBERT N. PEASE Princeton University, Princeton, N. 1. AND
A
I
N B previous paper ( 2 )it was demonstrated that the deflection
study of the effect of longitudinal electric fields on the blowoff limits, dead space, and flame pressure of Bunsen burner flames was undertaken to determine the nature of the effect and the significance of the abnormal concentrations of ions in flames. The results indicate t h a t the electric field has a strong influence on the flame stability, the direction depending on the field polarity. A mechanical model in which momentum is transferred from positive ions to the gas qualitatively explains most of the results. The change in flame pressure indicates that the product of the ion concentration in ions per cubic centimeter and the flame thickness in centimeters is approximately lO’O, in agreement with the value calculated for transverse electric fields. For high negative electric fields it is assumed that the electrons acquire sufficient energy to raise the gas to a n excited state. The large number of ions which must be present to produce these effects cannot be accounted for thermodynamically and are probably due to chemi-ionization. although they do not appear to play a significant role in the combustion process.
of Bunsen flames in transverse electric fields could be explained satisfactorily by a mechanical picture. The positive ions u-ere assumed t o transfer momentum t o the gas as in an electrical wind. The high concentration of ions deduced for the inner cone was taken as strong evidence for “chemi-ionization’’ in the flame front a s opposed to thermal ionization. The purpose of this paper is t o examine the effect of longitudinal electric fields (the electric field is parallel t o the mixture flow lines) on the inner cone of Bunsen burner flames. In addition to observing the appearance of the flame, blowoff, dead space, and flame pressure were measured. It is also desirable to examine further the quantitative relationships arrived at from the study of the effect of the transverse fields. Previous investigators have argued either that the ions play an active role in flame propagation or that the effect of electric fields on flame propagation is due t o a mechanical effect; unfortunately, fex quantitative data have been presented to support the various contentions. The work reported here and in the previous paper was undertaken in order t o resolve this problem. Other considerations also warrant such a study. Since there is the posclibility of utilizing the ionization phenomena as an analytical tool with which one might work back t o the elucidation of the combustion processes leading t o flame formation, it is important first to learn by what mechanism and t o what extent the various reported alterations of flame properties 16, 7, 14) in electric fields take place. From a more practical standpoint the possibility of employing electric fields as flame stabilizers is also of considerable interest. APPARATUS AND PROCEDURE
The gases, n-butane and air, were fed to the burner through regulating devices for maintaining constant flow-, capillary-type flowmeters for measuring the rate of feed, and then through a mixing chamber, The air was taken directly from the laboratory supply, and the n-butane from Matheson Co. cylinders graded C.P. (99.0% n-butane). The burner was a smooth seamless brass tube with an internal
P L A T I N U M RING O N O U T S I D E OF M A N T L E
6 \ J
1 l
E
e 0
c W
6 u-
6
: Figure I. Burner, Mantle, and Electrode Arrangement Quartz mantle: 2.5 cm. internal diameter 0.15 cm. wall thickness, brass burner: 0.660 cm. internal dihneter, 0.12 cm. wall thickness. electric field is positive when ring is positive with respect to burner and negative when this polarity is reversed 1
TOTAL
Figure 2.
RATE OF FLOW,
Blowoff
CC/SEC.
OF n-Butane-Air Flame
15-kv. positive longitudinal electric field
Present address, Experiment Inc.. Richmond. \’a.
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December 1951
I N D U S T R I A L A N D ENGINEEF!ING
CHEMISTRY
2727
tem, the values obtained can be accepted only as order-of-magnitude and relative readings. E X P E R I M E N T A L RESULTS
0 v.
Figure
8 KV.
3. Effect of Positive Longitudinal Electric Field on Inner Cone of Bunsen Burner Flame
3.6% n-butane at total Row velocity of 345 cc./aec., in kilovolts
tobl applied field indicated
Positive Fields. When the ring was positive with respect t o the burner, the most striking deviation in the burning characteristics was the change in the blowoff limits-for example, a t a total flow of approximately 66 cc. per second the normal limits of flame stability were 2.58 t o 4.430/, n-butane in the total mixture, whereas with a total field of 8000 volts the limits were 2.10 to 5.40%. This represents an increase of roughly 80% in the limits over which a stable flame can be maintained under the particular experimental conditions. At a total flow rate of 150 cc. per second the increase in limits attained 200%. Figure 2 shows a graph of the composition of the mixture a t blowoff as a function of the total flow rate with and without a n electric field of 15,000 volts. I n addition to an increase in the limits of stability for a particular flow rate, the range of flow rates over which a stable flame can be maintained is greatly increased. The actual effect on the maximum flow rate for blowoff is difficult to ascertain-for example, in one experiment, as the flow rate was continuously increased, with an applied field of 15,000 volts, the burner flame became increasingly turbulent until, a t 1000 cc. per secpnd (Reynolds No. = 9800) and 2.75% n-butane, the quartz mantle was punctured and the electric field shut off. The flame continued t o burn in the mantle just above the burner port so that it was impossible to determine the transition point from a burner flame t o a mantle flame (a flame burning in the mantle but not on the burner port). In this type of experimental arrangement, with a mantled burner, a flame is usually stable in the mantle a t the higher flow rates, and as the flow rate is further increased the mantle flame approaches closer t o the burner port. This accounts for the apparent merger of the two stability regions in the present experiment. For 3.6% n-butane in the mixture a t 200 cc. per second total flow (Reynolds KO.= 2000) the mantle flame was considerably above the ring; a t 345 cc. per second (Reynolds No. = 3400) the mantle flame was between the burner port and electrode ring, as shown in Figure 3. Figure 3 also shows the same flame stabilized on the burner port with an electric
diameter of 0.860 cm., and of sufficient length to ensure regular flow conditions, both laminar and turbulent. A quartz mantle with an internal diameter of 2.5 cm. was placed over the burner port (Figure 1). The mantle separates the inner and outer cones so that only the inner cone is under consideration. A borosilicate glass mantle, which was first tried, was immediately punctured a t approximately 10,000 volts. The quartz mantle was punctured twice, but only when the mantle was extremely hot and a t the highest voltages and flow rates employed. A longitudinal electric field was obtained, as indicated in Figure 1, by placing a platinum foil ring, for one electrode, around the mantle and making the brass burner the other electrode. The ring may be made either positive or negative with respect to the burner by interchanging the output leads from the power supply. In the remainder of this paper the field is referred to as positive when the ring is positive with respect to the burner, and negative when the ring is negative. The quartz mantle separates the two electrodes. The output potential of the high-voltage direct current supply could be varied continuously from 0 to 18,000 volts. The current through the flame was of the order of 0 to 100 microamperes so that %he power dissipation was of the order of 0.1 calorie per second. The flame was always ignited a t relatively slow flow velocities (approximately 60 cc. per second) by holding a small torch over the mantle with no applied field. The field was then turned on, and the butane and air-flow rates increased simultaneously up to the total flow velocity in which the blowoff limit was to be determined. Blowoff points were obtained by maintaining constant either the n-butane or air-flow rate while varying the other flow rate until the flame left the burner port. E KV. The dead space was measured with a cathetometer. Photographs of the flame were taken with a Leica 35-mm. camera having an f/2.5 lens and a shutter speed of l / i ~second; ~ ~ the burner port was illuminated with a 150-watt light bulb mounted directly above the burner. Unfortunately, since it was necessary to photograph through the quartz mantle, the flaws in the quartz are sometimes evident in the photographs. The flame pressures were determined with a manometer filled with petroleum ether mounted a t an angle of 1’40’ to 2.0 3.6 4.4 4.8 5.4 % the horizontal. From the known angle 0 v. and the density of petroleum ether the Figure 4. Effect of Positive Longitudinal Electric Field on Inner Cone of Bunsen Burner readings were converted to equivalent Flame centimeters of water. Because of the difficulties encountered with such a sysVarious concentrations of n-butane) air-flow velocity, 6 4 cc./sec.
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
2728
field of 8000 volts. With no field this particular mixture (3.6%) b l o m off a t 188 cc. per second. The series of photographs in Figure 4 demonstrates the effect of an 8000-volt field on the flame appearance for different feed-mixture compositions a t a total flow rate of 64 cc. per second. A comparison of the corresponding photographs with and without a field shows that in the region in which the flame is normally
I
,o~o-o
0
O-
!i
I
i
W
-1
Vol. 43, No. 12
mability (4.43% a t this flow rate). The cones for these flames became increasingly diffuse and the luminosity decreased. A strong unidentified odor was observed in such rich flames stabilized by an electric field. When the air rate was maintained constant and the blowoff point determined as a function of applied voltage, by increasing or decreasing the rate of flow of n-butane, the curves in Figure 5 were obtained. These curves Bhow that the effect of the electric field reaches a saturation point for blowoff for rather small electric fields. The limit compositions are approximately 2.10% on the lean side and 5.40% on the rich side. The saturation point is approached more rapidly with rich flames than with lean flames. Measurements of the flame pressure (Table I) indicate that it is increased by the electric field. The actual flame pressure with the mantle was not measurable because of difficulties encountered in determining the “true” pressure drop through the burner with n o flame. A smaller pressure drop existed when the flame wa5 burning with a mantle than Lvithout a mantle. For exaniple., without the mantle the pressure: was 0.0678 em. of water, and with the mantle it was 0.0576 em. of water. The interpretation is further complicated by the observation that when the flame was extinguished and the flow rates maintained, the pressure slo~vly increased as the mantle cooled. Therefore, to obtain some idea of the actual flame pressure, scveral observations were made in an open burner with no electric field. These results, presented in Table 11, compare favorably with an observation by BIache (10) on a mixture of illuminating gas and air. h comparison of the results in Tables I and I1 shows that the pressure increase due to the field is comparable to the normal flame pressure. The direction of the pressure change is that which would be predic,ted assuming a mechanical effect due to the positive ions (3, 6, 7 ) and can be considered as indicating an increase in flame stability wit,h incrpasing electric field.
1
0
8
12
FIELD,
KILOVOLTS
4
APPLIED
Figure 5.
BlowofF of n-Butane-Air Flame
Positive longitudinal electric field; cc./sec.
I
16
air flow constant at 63.7
.stable the field has very little effect on the flame appearance, other than to decrease the dead space. The variation of the dead space as a function of the applied voltage is presented in Table I for several compositions. Although dead space measurements are never more than a relative measurement, because of the difficulty in determining the position of the base. of the flame, they areadefi,nite indication of flame stability (4,18, 17). I n this case the variation of dead space argues for an increase in flame stability with increasing field strength. The flame a t 2.0% (Figure 4), which would normally be unstable since it is below the normal 1oFer limit (2.6% a t this air velocity), is stabilized by the electric field. The cone IS still sharply defined, and the base of the flame has an extremely large overhang. The photographs a t 4.8 and 5.4% are for rich flames beyond the normal upper limit of inflam-
0
5
Figure 6.
a IO 3 . 6 % n-butane at 180 cc./rec.
Table
I. Effect of Positive Lon itudinal Electric Fields on Dead Space and Fqame Pressure
n-Butane, % of ‘rota1
Total Flow
Electric Field,
c~./s&.
3 GO
66.1
2.60
65.4
13
KV.
0.0 5.2 7.8 10.4 13.0 15.6
Pressure Dead Total Due to Current, Space, Pressure Field hlicroamp. Cm. Cm. H ~ OCm. H;O 0.0 0.031 0.0598 0.0 14. 0.026 0.0612 0.0014 0 , 0 1 8 0.0633 0.0035 0 . 0 0 8 0.0644 0.0046 79 0.010 0.0655 0.0057 130 0.006 0.0670 0.0072
i3
0.0
2.6 5.5 7.8 10.4 13.0 15.6
‘
0.0 2 8 11 19 30 47
0.085
0.076 0.051 0.035 0.031 0,026 0.025
I 8 KV.
Effect of Negative Longitudinal Electric Fields on Inner Cone of Bunsen Burner Flame
0,0555 0.0661 0.0571 0.0588 0,0616 0,0634 0.0644
0.0 0.0006 0.0016 0.0033 0.0061
0.0079 0.0089
8 KV. 3 . 6 % n-butane at 940 cc./rec.
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
December 1951
Table
0
4 APPLIED
Figure
0 -PERMANENT
BLOW-OFF,
0 -TEMPORARY
BLOW-OFF
8
12
FIELD,
KILOVOLTS
16
7. Blowoff of n-Butane-Air Flame
Nesative longitudinal electric field; air flow conrtsnt at 63.7
cc./rec.
Negative Fields. When the ring was negative with respect to the burner, the results were not nearly so definitive nor so reproducible as with the positive field. For example, a t a total flow of 180 cc. per second and 3.6% n-butane (see Figure 2 for location with respect to the stable flame region without the field) the series of photographs in Figure 6 were obtained with increasing electric field. The dead space first increases as the electric field is increased, until the flame begins t o jump “off” and “on” the burner at .approximately 13,000 volts. At 18,000 volts a discharge is observable a t the burner port. In contrast to this apparent decrease in stability with the field, at a still higher total flow rate-namely, 240 cc. per second and 3.6% n-butane-an applied field of 8000 volts stabilizes a hanging flame on the burner port. At 15,000 volts this flame jumps “up” and “down,” but with no field a mantle flame above the ring is normally obtained. If the composition of the mixture a t blowoff is determined as a function of applied voltage, for a given air flow, as was done for a positive field, somewhat complex results are obtained. Although there is a stabilizing effect of the field with respect to blowoff on both the rich and lean sides (Figure 7), there is also an indication of a decrease in stability for both limits as the field strength is increased. On the rich side, as blowoff is approached, the polyhedral flame begins t o twitch and then t o rotate a t a somewhat lower composition (4.38%) than that at which the flame blows off mith no field (4.43%). At the higher field strengths the flame starts to lift on one side for still somewhat lower percentages of 12butane. This is to be compared with a blowoff with no field from a nonrotating polyhedral flame. On the lean side, when no field is applied, the flame blows off t o become a mantle flame. As the electric field is increased the extinction of the mantle flame (permanent blowoff) takes place a t increasingly higher percentages of n-butane, indicating a decrease in flame stability with increasing fields, up to approximately 8000 volts. As the mixture becomes leaner, below 8000 volts, the mantle flame jumps on and off the burner, spending increasingly more time off the burner. The incipient point is indicated in the figure as “temporary blowoff.” Above 8000 volts “blowoff” and “extinction” take place simultaneously a t progressively lower concentrations of butane, indicating an increase in flame stability. There thus seems to be a decrease in stability at low field strengths and an increase in stability a t the higher field strengths
II.
2729
Flame Pressure of n-Butane-Air Flames
(Flame open to atmosphere, no mantle; air flow rate constant = 63.7 oc /sec.) Total Flame n-Butane, Flow Pressure, Cm. HzO Pressure. % of Total Cc./Sek N o flame Flame Cm. H10 2 68 65.5 0 0662 0 0675 0 0013 2 91 65 6 0 0077 0 0702 0 0025 3 18 65 8 0 0691 0 0737 0 0046 3 60 66 1 0 0685 0 0737 0 0051 3 75 66.2 0 0687 0 0740 0 0053
The variation of dead space with field strengths (Figure 8) shows a similar decrease in stability-i e., a n increase in dead space with increasing field, and then a t a particular field strength, a sudden increase in stability as indicated by a decrease in the dead space. On some occasions this decrease in dead space took place a t somewhat lower voltages, and then at the highest voltages the flame would give way to a strong vibration followed by a sudden change into the “derby” shaped flame reproduced in Figure 9. It was under these conditions that the data on flame pressures in Table I11 were obtained. With increasing electric field the flame pressures show a genertil decrease correlating with an increase in dead space. This is followed a t higher voltages by an increase in flame pressure correlating a i t h the decreased dead space. Often a t the maximum dead space the flame would jump off the burner. The flame of maximum stability, 3.6% n-butane (Figure 2), shows a continual increase in the dead space and decrease in flame pressure as the field strength is intensified. The dead space and flame pressure, as well as the composition limits of stability, seem to indicate a reduction in stability with increasing fields and then an increase in stability a t the higher field strengths. Two series of photographs (Figure 9) show the effect on the flame appearance of changing the field strength for both a lean and a rich mixture. On the lean side (2.6%) the field has little in-
0
4 APPLIED
Figure
8
12
FIELD,
KILOVOLTS
18
8. Dead Space Variation
Negative longitudinal electric field) air Row constant at 63.7 cc./rec.
INDUSTRIAL AND ENG INEERING CHEMISTRY
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10
4.3
Vol. 43, No. 12
16KV.
15.8
70 n-butane at 6 1 cc./rec. cules present so that the field will exei t it force on the ionized combustion zone. If the surface area of the cone is A and the thickness of the ionized region is L , the foire due, to S ion3 per cubic centimeter u 111 be:
F , = AXe.VL 0
Figure 9.
8 15 2 . 6 % n-butane at 67 cc./rec.
1 6 KV.
(1)
The flame pressuic due to the field should then be
p =
Effect of Negative Longitudinal Electric Fields on Inner Cone of Bunsen Burner Flame
b
-5 =
A
Xel%-L
(2)
or since p is known to be -5 X cm. of rater, or -5 per square em., n-e can calculate ‘YL: fluence except at the high voltages where the flame becomes peculiarly round and then derby shaped. On the rich side (4.3%) the field decreases the number of sides of the polyhedron, until, at the highest voltages, the same peculiar derby-type flame is obtained. DISCUSSION O F RESULTS
Xost of the results, Tvith the exception of those a t large negative fields, might conceivably be explained by a mechanical model ( 2 ) or by ascribing an active role to some positive ion. The changes a t first appear somewhat large for a mechanical picture, but before any decision can be made a quantitative comparison must be made betlveen the experimental results and a reasonable quantitative picture. To do this let us assume a mechanical effect such as that encountered in the Chattock electrical wind ( 2 , I S ) , and for simplicity let us assume that all the force of the field acts normal to the flame surface. Only positive ions are considered because previQUS investigations (18)have demonstrated that the negative ions are electrons which, because of their small size, nil1 be uniniportant in momentum transfer. The field, X, everts a force = X e on each ion, where e is the electronic charge. In its many collisions the ion ~villcommunicate its momeiituni to all the gas niole-
Table 111.
Electric Field, K r .
Effect of Negative Longitudinal Electric Fields on Flame Pressure Current, Microamp.
Total Pressure, Cm. HzO
Pressure from Field, Cm. 1110
Reinarka
3,60% n-butane at 6G.1 c c . i s e c
,
0 2.6 6.2 6.8 7.8 7.8 10.4 11.7 13.0 14.3 l5,6
2.60% n-butane a t 0.0466 0.0466 0.0458 0.0481 0.0441 0.0476 0 0464 0.0468 0 0493 0.0493 M’2’ 0 0493 0 2 8 16 28 9 42 39 45
65.4 cc./sec. 0 0 0.0 -0 000s -0 0015 -0.0025 0.0010 -0.0012 -0.0006
+
f0.0027
+0.0027 +0.0027
Hanging flame Bouncing off burner Close t o burner CloEe t o burner One side pulls off Vibrating flame Derby-shaped flame
i\:L
2L > Xe
5 8 X 4.8 X
-
1.3
x
109
dyne3
(3)
X b ill be considerably less than 4___ lo~ooo X 300 -8 volts (electrostatic unitsj/cin. because most of the potential drop ~villoccur at the cathode (18) or through the quartz mantle. If X were roughly one tenth of that used, S L would be -lolo which agrees with the value previously obtained for transverse electric fields ( 2 ) . Such a crude calculation can only be of value in that it gives results consist’ent viith previous work (1, 2). T h e significant point is that the thermal considerations cannot account for the assuming a flame thickness large number of ions present of lo-* cm. ( g ) , nor can thermodynamics account for the fact that the ion concentration is greater in the inner cone or raact,ion zone than in the burned gases ( 3 , 8;16, 16). Thus “chemi-ioiiiaation” or some processes such as those discussed by Gaydon and Wolfhard (6)and Laidler and Shuler (11), in considering the abnormally high electronic excitation in flames, must be important. The change in flame stability and dead space would be accounted for by assuming an alterat’ion of the boundary velocity gradient (12, 17) due t o the mechanical gas movement caused by momentum transfer from ionic movement in the electric field. The effect of the negative fields-namely, that of decreasing the flame stability and then increasing it at higher field strengthsis best explained by assuming that for lorr fields the mechanical effect discussed will be operative, whereas a t higher voltages the electrons will acquire sufficient energy t o excite or even ionize the gases present. (It is also assumed that by exciting the gases their burning velocity is increased.) Several theoretical considerations, as well as some experimental evidence, indicat,e that this is a reasonable view, although from an elementary analysis it would be concluded that the electron did not gain the necessary energy in its mean free path. First, a large part of the voltage drop, other than that lost a t the cathode and through the quartz mantle, nil1 be a t the burner port rvhere the flame is stabilized so that a t this critical position the electrons will have their maximum energy. Secondly, the energy that an electron acquires in the field ~villbe larger than that of the ions present. This is true because of the longer mean free path and the ]OK value for t,he fractional loss of energy by the electron on impact (13). A low value for the energy loss of the electron on impact would similarly explain the high electron temperatures found by Heumann (9) in a n ordinary Bunsen flame.
December 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
Heumann found, by applying Langmuir probe theory, that the electron temperatures were approximately 3200’ K. while the flame temperature was only 2000” K. His experimental evidence is in turn further verification of the proposal that the electrons may acquire sufficiently high energies t o excite the gases present. A third argument is obtained from Tufts (16)in 1906 who found t h a t for voltages between 100 and 400 volts per em. applied between electrodes in a flame, the current increase was greater than linear; for still higher potentials there was unmistakable evidence of ionization by impact, such as a sudden increase-in the current, a decrease in the potential gradient, and a marked increase in the temperature of the electrodes. Such considerations as these would probably explain much of the previously reported results of electric fields on flames and particularly those that allege to prove the important role played by the negative ion in flame propagation. SUMMARY AND CONCLUSIONS
For the experimental arrangement of a mantled burner flame with a field applied between the metal burner and an exterior ring on the mantle several centimeters above the burner port, the following have been demonstrated: For a positive field (ring positive) up to 16 kv: 1. The composition limits of flame stability can be increased by as much as 200%. 2. The composition limits of flame stability reach a saturation point a t very low voltages, of the order of 2 kv. 3. The range of flow rates over which a burner flame is stable can be increased by roughly 100%. 4. The dead space can be decreased by roughly 30%. 5 . The flame pressure can be increased by more than 100%.
For a negative field (ring negative) up to 16 kv: 1. The composition limits of flame stability can be increased a t high field strengths by ap roximately the same amount as with positive fields, although for Power fields there is an indication of a decrease in limits. 2. The range of flow rates over which a burner flame is stable can be increased, although in a rather capricious manner. 3. The dead space is increased and then suddenly decreased with increasing electric field; a t the highest fields the flame vibrates rapidly and then becomes derby shaped. 4. The flame pressure can be decreased by approximately loo%, and then as the field is increased to the point where the decrease in dead space is observed, the flame pressure is enhanced.
2731
By assuming a mechanical picture for the effect of the electric field on the positive ions, a calculation from the pressure change gives a value of NL-101O ( N is the number of ions in the inner cone and L is the thickness of the inner cone) in agreement with N L calculated for transverse fields. The influence of a high voltage negative electric field is explained by assuming that the electrons acquire sufficient energy t o raise the gas to an excited state. LITERATURE CITED
(1) Calcote, H. F., review article, “Electrical Properties of Flames,” unpublished. (2) Calcote, H. F., ”Third Symposium on Combustion, Flame, and Explosion Phenomena,” p. 245, Baltimore, hld , Williams & Wilkins Co., 1949. (3) Davidson, J. F., Physik Z.,7, 108 (1906). (4) Garside, J. E., Forsyth, J. E., and Townend, D. T. A., Inst. FueE (London),Bull. 175 (1945). (5) Gaydon, A. G., and Wolfhard, W. G., Proc. Roy. Soc. ( L o n d o n ) , A201,561,570 (1950); A205, 118 (1951). (6) Guenault, E. N., and Wheeler, R. V., J . Chpm. SOC., 1931, 195; 1932,2788. (7) Haber, F., Sitzber. preuss, Akad. Wiss., P h y s i k . Math., 11, 162 (1929). (8) Haber, F;, and Lacy, B. S.,2.Phzlsik Chem., 68,726 (1909). (9) Heumann, T., Spectrochim. Acta, 1,293 (1940). (10) Jost, W. (trans by H. 0. Croft), “Explosions and Combustion Processes in Gases,’’ P. 80, New York, McGraw-Hill Book Go., 1946. (11) Laidler,K. J., and Shuler, K. E., Chem. Revs.,48, 153 (1951). (12) Lewis, B., and von Elbe, G., J . Chem. Phys., 11,75 (1943). (13) Loeb, L. B., “Fundamental Processes of Electrical Discharges in Gases,” New York, John Wiley & Sons, 1939. (14) Malinovskii, A. E., and coworkers, Physik 2. Sowjetunion (1932-36). (15) Tufts, F. L., Phys. Rev., 22, 193 (1906). (16) Vogt, K., Ann Physik, 12,433 (1932). (17) van Elbe, G., and Menteer, M., J . Chem. P h y s . , 13,89 (1948). (18) Wilson, H. A., Rec. M o d . Phys., 3, 156 (1931). RECEIVED June 21,1951. The work described in this paper was done in connection with Contract NOrd 7920 for the U. S. Navy Bureau of Ordnance 88 part of Project Bumblebee, Applied Physics Laboratory, The Johns Hopkins University, and Contract X6-ori-105 with the Office of Naval Research, U. S. Navy, as part of Project Squid, Princeton University. Acknowledgment is due Dean H. 9. Taylor, who has general supervision of this work. This report was abstracted in part from a thesis by H. F. Calcote submitted in partial fulfillment of the requirements for the degree of doctor of philosophy a t Princeton University.
COMBUSTION IN BUNSENFLAMES FRANK R. CALDWELL, HERBERT P. BROIDA, AND JEROME J. DOVER National Bureau of Standards, Washington, D. C.
Fj
Apparatus has been assembled, as a part of a continuing program of research on combustion chambers, for investigating mechanisms of the combustion process. Studies are being made of effects of fuel-oxidant ratio, pressure, and temperature upon burning velocity of laminar flames above a nozzle, temperatures attained in the flames, and the nature and concentrations of free radicals that play important roles in the reactions. Apparent flame speeds and line-reversal temperatures of methane-air mixtures have been measured at atmospheric pressure, and effects of water vapor, gas velocity, and nozzle temperature on flame speeds have been determined. A brief description is given of spectroscopic equipment for determination of rotational temperatures and concentration of radicals, and some preliminary observations on an acetylene flame are presented.
Preliminary results with this apparatus are sufficiently promising to encourage continued exploration of its potentialities in the search for fundamental information on flames. Suph information may aid in a better understanding of the mechanism by which flame travels through a combustible mixture, and in the solution of some of the practical problems of combustion.
A
PART of a continuing program of research on combustion chambers, sponsored at the Xational Bureau of Standards by the Bureau of Aeronautics, apparatus has been constructed for the purpose of obtaining detailed information on the combustion process as it occurs in laminar Bunsen-type flames burning above nozzles. Sufficient preliminary results have been obtained to warrant prrsentation a t this time of a description of the new equipment and its apparent capabilities and limitations.
