IATDCSTRI;ILA-lsD E.IW-IEERISG CHEMISTRY
1026
initial and final voluiiies of the reaction. The actual work accomplished by the transformation of a given charge is
w=c
(7’3
-
Y3)
146’1
aiid for unit charge,
Vol. 20, s o . 10
fuel. The rapid drrrease in the rate of the explosive reaction, however, due to a n increase in the fuel excess, quickly preYive revents the possibility of maintaining a zone of explo-‘ action in the mixture. Acknowledgment
In Figure 13 the ordinates of the curve slio~vnare values of 1); the abscissas represent partial pressures of the active gases. The figure shows that, although the rate of reaction
(2-
has been greatly reduced by a n excess of methane, the total energy liberated has not been so affected. I n fact, the nlnsin i u ~ nwork appears to be obtained with a ~111a11excess of the
V i t h gratitude and appreciation the writer would acknowledge here his indebtedness to the Sational Advisory Committee for Aeronautics for encouragement and $upport in a n investigation of gaseous explosive reactions that has been carried on for a number of years a t the U. S. Bureau of Standards.
The Wormal” Propagation of Flame in Gaseous Mixtures William Payman SAPSTY IS
l I I s E s RESEARCH BUARD,RESEARCH STATION, H
In this paper a preliminary attempt has been made to trace the relationships, where they exist, between the speeds of flame in mixtures of air with the constituents of the common industrial gases, hydrogen, carbon monoxide, methane (and other paraffin hydrocarbons), ethylene, and acetylene, inflamed under different conditions. It is hoped to extend these relationships as the result of work now in progress, and also to be able to examine systematically, and in somewhat greater detail, the exceptions to these relationships as they appear.
T
HE study of gaseous combustion has proved so com-
plex that the necessity of reducing the variable factors to a minimum in any one investigation has long been 1 ealized. Thus. notwithstanding the importance of the combustion of coal gas, for example, in industrial burners or in internal-combustion engines, experiments with coal gas under such practical conditions have not been largely favored by investigators in this field. The reasons for this are sound, and are bawd, firstly, on the fact that such industrial gases may vary considerably in composition, and results obtained with one particular gas may Iiot hold n i t h another gas. or even n i t h anotlier sample of the ‘;tine type of gas from a different source. Secondly. tlie results olitained in a burner or engine of one particular design may apply only to the special conditions under which they have been obtained. I n most of tlie systematic investigations whicli have been carried out on gaseous combustion, pure gases have been used and inflammation or explosion has been carried out under standard conditions usually much simpler than those obtaining in practice. Though the utility of such a procedure is obvious, and considerable information of both a practical and theoretical nature has been obtained, the diversity of choice of apparatus. materials, and conditions which has been made by different investigators raises the question of d i e t h e r some sort of connection cannot be found between the results thereby obtained, in order to be able to make the fuilest use of them. It is essential to know not only how far the results obtained by one investigator can apply t o and so supplement thoqe obtained by another, but also how far the results obtained under such simplified conditions can be applied to the complex conditions of the practical utilization of inflammable gases in industrial operations. The present paper describes a preliminary attempt to correlate some of the results obtained by diverse means.
IRPIJR
HILL,B ~ ~ X T ODERBYSHIRE, X, ENGLAND
The record of simple relationships will serve to indicate the direct effect of change of particular factors, while exceptions to rules which apply to a large number of gases or conditions will indicate the coming into play of other factors of importance whose study’ might be followed up with advantage. The study of gaseous combustion is divided into four main and distinct branches-the ignition of gaseous mixtures, surface combustion, “normal” inflammation,l#* and detonation. Though there can be no doubt that these branches are interconnected in many ways, it would be extremely difficult to trace any connection a t the present stage of our knowledge. Only the third branch, that concerned with the “normal” propagation of flame, will be discussed here, and consideration will be limited to the inflammable constituents of the common industrial gases-namely, hydrogen, carbon monoxide, methane (and other paraffin hydrocarbons), ethylene, and acetylene-in admixture with air. Inflammation of Different Gas Mixtures under Constant Conditions
If the rate of flame propagation is measured in a series of mixtures of any one inflammable gas with air under any one constant set of conditions, the variation in rate with concentration always follows the same sequence. Below R certain concentration of inflammable gas, known as the “Iower limit of inflammability,” continuous self-propagation of flame does not take place. As the percentage of inflammable gas is increased the speed of propagation of flame in the mixture increases above the speed in the limit mixture. This increase alnays continues until the concentration of inflammable gas is higher than that in the mixture for complete combustion. by a n amount which has been termed the “displacement” of the “maximum-speed mixture.” Further addition of inflammable gas causes a decrease in the speed of flame until the “upper limit of inflammability” is reached, aiid mixtures containing a higher concentration of inflammable gas than this are again incapable of supporting the continued propagation of flame. A number of speed-percentage curves showing the manner of this variation with the gases considered in this paperhydrogen,* carbon m ~ n o x i d emethane,4 ,~ pentane,4 ethylene,j and acetylenee-are given in Diagram 1. The speeds are those of the “uniform movement” of flame in a horizontal tube 2.5 cm. in diameter. The uniform movement7 i s the
* Numbers in text refer t o bibliography a t end of article.
1028
lSDCSTRIAL .4A3 BNGI NEERING CIIE.I.IIISTRY
usually not uniform, and the speed of any one flame may vary within quite wide limit.5, it. might be doubted whether any real comparison could be made betn-een the rate of propagation of flame in different gas mixtures when exploded under such conditions. A series of experiments is being carried out'4 in which careful photographic (moving-film) records are being made of the passage of flame from the center to the ends of 3 closed brass cylinder. 20 em. lonrr and 5 cm. in diameter. the nhotograph being t a k e n through a long, narrow nindoi? in one side of the explosion vessel. Though these experiments are not yet complete, some very interesting results have already been obtained, which indicate that the manner of flame propagation in such a vessel remains the same uith n IarKe - V 3 l l P t Y of gasFigure 3 Figure 4 eous mixtures, provided, of course, that the strength and position of the source of ignition, an electric spark, are unaltered. A typical photograph is reproduced in Figure 1, an explanatory diagram being giveii in Figure 2. In the diagrams a t the bottom of Figure 2, the position of tlie slit in the hrass vessel is indicated, and the direction of movement of the flame is shown Iiy the arrows. Tlie film moved upward. The mixtiire was of acetylene and air containing 6.5 per cent of inflamiiiable gas, and the initial pressure was 3 quarter of an at,snosplierc. It will he seen that tlie Anme appears the moment the spark passes, and it spreads out symmetrically toward each end of tlre explosion vessel. It accelerates froin the poiiit of ignition, but about t,wo-i.hirds of the way along the tube slows down rather suddenly and passes more slowly to the ends of the tube. I n tire present paper we are concerned mainly with the rate of propagation of the flame, and so the portion of this aiid similar photographs to be considered is the flame front only. The main feature of such photographs is t.he arrest of the flame. A flame armst has frequently heon noted by investigators examining the movements of flame in gaseous mixtures contained in closed vessels, and different explanais that the tions have been offered to account for it. arrest is due to the compression wave from ignition, moving at. the speed of sound in the unburnt gases and being reflected from the far end of the tube. The second explanationlo involves assumptions of gas surgiiig or gaseous movements en masse, it being held, in general, that tlie arrest marks 3 point. a t which pressure behind the flame becomes equal to the pressure in front. The following a.lteriiative explanation has been recently advanced:' When an inflammable gas mixture is igiiited at a point within 3 closed vessel, flame spreads simultaneously in all directions. During the first stage of propagation, before tlie flame touches the walls of the containing vessel, little heat will be lost by the flamc, save to unhurnt gases, except t.hat lost by radiation. When the flame touches tlie walls of the tube 3 second phase commences, heat being lost tu the walls by conduction as the flame trarels along in contact wilh them, bot11 by the flame and the hot gases behind the flame, and the flame speed is reduced. I n a cylinder the flame commences to spread spherically, but soon be~~
Val. 20, No. 10
comes egg-shaped, as in shown in the series of flame snapshots in Figure 3'8 (taken with a different gas mixture and in a similar vessel hiit of different dimensions), so that the most forward portion of the f a m e in each direction has traveled some distance along the tube before its equatorial belt has touched the walls. The distance hetween the two ends of the flame may be quite large compared with the diameter of the tube before the portion touching the walls first is extinguished hy them at that. point. This extinction a t the sides of the eggshaped flame will result in propagation being now carried on solely by the two ends-that is, by two separate flames moving in opposite directions. Retardation probably commences as soon as the flame touches the walls or comes close enough to lose an appreciable amount of lieat to them. The definite arrest of the flame would correspond to the moment of separat.ion of the flame into two portions, so that the arrest would necessarily be simult,aneous on each side of the point of ignition. The simultaneous arrest of the flame front t,akes place not only under tire conditions of t.ho present experiment, but also under conditions such that the flame moves a t appreciably differerit speeds toward the two ends of the tube.'g The sequence of affairs is shown in Figures 1 and 2. The flame may he regarded, before it breaks, as 3 luminous shell (like an eeeslielli enclosine a non-luminous snace. The outer ,, ~ , edges of the flame-that 'is, t,lie portions abvanciiig toward the ends of the tube--are in line with tile axis of the camera, which, therefore, records a considerable depth of flame and shows u p as 3 dark black line whose width gives some indication of t,lic (maximum probable) thicknessof tlie flame front. The portions near t.he side of t,he tube are at right angles to the camera axis, and the depth of flame recorded is much less, so that the sides of the flame do not appear so black. At any one instant tlie position of the flame behind the slit in the explosion vessel is indicated by 3 narrow horizontal section of the pliotograph. Three such secbioiis are shown in Figure 2. At the instant shown in the uppermost section the flame is 3 complete spherical or egg-shaped shell. From the moment of ignition t,o tlie instant corresponding to the middle sect.ion the flame front has been accelerating, and the shell has been unbroken. Kow, Iiowever, the flame is breaking and the break is rapidly increasing in size. At approxiI
0
*
e ?
CInPmetcir
9
"
9
.
.
,
I
. P
I
Fipure 5
Fibwe 6
Figure 7
mately the same instant the flame front begins to slow down. At the instant shown in the third section two distinct flames are observed, traveling in opposite directions. ( C o m p r c Figure 3) Having considered tlie mode of propagation of flame in one particular mixture in this vessel, we may proceed to examine the effect of change of coiiditions-initial pressure, for example-and of change of composition of the mixture, or
I;L'DCvSTRIdL A S D E,l;GIATEERISG CHE.WISTRY
October, 1928
1029
constructed by multiplying throughout by a factor 1.4 (93.0 : 66.6). This smooth curve is shown in Diagram 2, while the dots show the values actually obtained in a 5-cm. tube for the whole series of m i x t ~ r e s . ~ It~will be seen that, except close to the upper limit, the observed values lie on the calculated curve, The relationship here is therefore very close. A similar relationship is observed with the other hydrocarbons, as shown in Table 11,in which are given the observed values in the 5-cm. tube, and the values calculated from those obtained in the 2.5-cm. tube, for the maximum-speed mixtures in air, by multiplication by the same factor (1.4). Table 11-Speed DIAMETER OF
I f i t h a m per ced. Dogrom
2.
of'the type of inflammable gas. Figure 4 shows the result of a repeat experiment similar to that for Figure 1, except that the initial pressure was atmospheric instead of only one quarter of an atmosphere. The record of the flame front is identical in Figures 1 and 4, although the after-effects, the re-illumination noted in all the records, are far less pronounced a t the lower pressure, indicating that they have no effect on the speed of the flame. To proceed next to the effect of change of inflammable gas. we may note the effect of addition of hydrogen to the acetylene. Figure 5 shows the niode of spread of flame in an air mixture with an inflammable gas of the composition C2H2+H?. the particular mixture being chosen because the speed of flame is approximately the same in it as in the mixture of acetylene along with air shown in Figure 1. The records of theiflame front are almost identical. A record of a far different mixture, which shows a greatly increased re-illumination after the flame has passed but approximately the same flame-front record, is shown in Figure 6, the mixture in 02, a t an initial pressure of half this instance being 2CO an atmosphere and saturated with mater vapor a t 15' C. A complete series of determinations has been made with mixtures of ethylene and air in the same vessel and the point of arrest noted. It was found to be the same with all mixtures, whatever the speed, except a t the limits of inflammability, where convection currents apparently come into play. The same point of arrest was also noted when mixtures of methane, ethane, propane, pentane, and acetylene were inflamed with just sufficient air to allow of their complete combustion to carbon dioxide and steam.
+
Comparison of Speed-Percentage Curves Obtained under Different Conditions
It is therefore possible to obtain conditions which should be comparable, even when the spread of flame is not uniform, and to examine how far comparisons made under one set of conditions agree with those made under different conditions. This will now be discussed with the assistance of a series of speed-percentage curves. UNIFORM MOVEMENT OF FLAME I N TUBESOF DIFFEREKT DIAMETER-The most accurate and Complete determinations of the speed of uniform movement of flame are those for mixtures of methane and air determined in horizontal tubes of 2.5- and 5-cm. diameter. The maximum speeds of flame in methane-air mixtures in these tubes are 66.64 and 93.07 em. per second, respectively. From the values obtained in the 2.5-cm. tube a smooth curve was
2c
g 4 Is
1
g ,c
$
$ g c. F=
TUBE
of Flame i n Tubes of Different Diameter CsHs C4Hll CIHir Cm. p e r sec. Cm. p e r sec. Cm. per sec. 85.6 82.1 82.6 83.0 116 120 115 115 113 127 114 113
CzHs Cm.aer sec.
Cm. 2.5 Obsd.4 5.0 Ohsd.20 5.0 Calcd.
Acetylene is the only other gas whose mixtures with air have been examined and the speed of uniform movement of flame determined in its mixtures with air in tubes of these dimen-
500
B
-
402-
$0-
e2 200'b
loo-
? 2
4 6 ErPy ene per cent
a Diogrom
IO
12
1~
3
sions. The calculated value for the uniform movement of flame in a 5-cm. tube using the same factor is 395, but the value found is only 312 cm. per second. As acetylene has also been found to be an exception to other relationships, the reason for its non-agreement should prove of interest. It is probably due to the endothermic nature of this gas. But it may also be noted that in an acetylene-air explosion the acetylene may combine not only with the oxygen but also with the nitrogen of the air.21J2 Both these factors may be influenced by the pressure effect of confinement.
INDCSTRIAL A S D ESGINEER1,VG C'HBJfISTRY
1030
Vol. 20, No. 10
The time of attainment of maximum prcssurc in the maximum-speed mixture of methane-air when ignited centrally in a 4-liter sphere is 0.067 second.'4 The maximum speed of the uniform movement of flame in a horizontal glass tube 2.5 em. in diameter is 66.7 cm. per second, from - which a constant 0.067 X 66.7 = 4.47 is obtained, a n d a s s u m i n g time (4-liter vessel) X speed (uniform movement) is constant, the times of attainment of maximum presure in other mixtures may be calculated. The results of such calcula- tions are given in Table 111, and are compared with the observed values. The agreement is shown to be quite good for maximum-speed mixtures. In order to find Is S IO whether the agreement is as good for the full range Methane per ceniof air mixtures of each gas, two sets of "smooth Diagram Z calculated curves'' have been drawn as before. The first set (Diagram 4) shows calculated and observed values for the gases methane, propane. and pentane, the second (Diagram 5 ) for H1. CO H2,and 3 CO H?. The two sets are not shown on the same scale, since the order of time is so vastly different. For the same reason a factor has been chosen for Diagram 5 calculated from the hydrogen resultsnamely, 485 X 0.007 = 3.4. The agreement is, in general, quite good, but it will be seen that the curves for propaga\ I tion of flame in the sphere are steeper than the uniform movement curyes. an important difference and possibly an effect of the difference in confinement.
- Cdculded -LZiYwd
~
I
F
I
I
I
m 2 5 a 3 5 Inflammable gas per cent Dugrum 5
4
0
+
lru
C
II
cH:\.-
..
IO Informace
+
-\
I
2C
1
I
33
Ai
50
oer cemi.
Dnpm 6
FO
1^
8s
I I
Table 111-Time INFLAMMABLE GAS
: L ,
CHI CzHs
GHs C4HlO CsHiz C2H4 H2
for Reaching Maximum Pressure FOUND CALCULATED Second Second 27 0.067 0,067
REFERENCE 27 27 27 27 28 29
0,050 0.055 0.054 0.056 0.027 0,007
0.052
0.054 0.054
0,054
0,027 0.009
UKIFORJIMOVEMENT OF FLAME AND HEIGHT OF BUNSEX DIFFERENTI N F L A ~ I M A B L EGASES-It is known that the height of the Bunsen cone with a given gas mixture, and the tendency of the flame in that mixture t o fire-back in the burner, depend upon the speed of propagation of flame in it. The height of the Bunsen cone has indeed been used as a means of measuring the speed of propa3 0 w 25 50 L IS Im o % &-? gation of flame.?8~29~30 I n one series of determinations by unfmn nwcmnl of b m e JnnDmmohcn n r b c d spherr this method a speed of 27.2 cm. per second was obtained as Diogrom 8 hya" 9 the maximum for methane-air mixtures. The method has UNIFORM MOVEMENT OF FLAME AND PROPAGATION OF FLAMEalso been used for hydrogen-air, acetylene-air, and ethyleneI N A CLOSED CYLINDEn-The maximum speed of uniform move- air mixtures, and the results30are shown in Diagram 6, where ment of flame in ethylene-air mixtures in a horizontal glass they are compared with corresponding curves calculated from tube, 2.5 cm. in diameter, is 166 em. per second.6 The maxi- the speeds of uniform movement of flame in a 2.5-cm. tube mum mean speed of propagation of flame in such mixtures from by multiplying throughout by a factor obtained from the the center to the ends of the brass cylinder in which the photo- maximum speeds of flame obtained by the tJr-0 methods with graphic records in Figure 1, etc., n-ere taken is 482 cm. per sec- methane-air mixtures. This factor is 0.408 (27.2 :66.6). The ~ n d From . ~ ~the values obtained for the uniform movement Bunsen method gives results for the speed of flame which are of flame a smooth speed-percentage curve has been obtained somewhat erratic, and the rough correspondence of the curves by multiplying throughout by a factor 2.9 (482 : 166). This in this diagram may be considered satisfactory. The relative curve is shown in Diagram 3, on which the black dots show the speeds are of the same order, though the observed speed speeds obtained in the closed cylinder for the whole series of air for ethylene is rather high. With an inflammable gas mixture H2 the maximum speed was found mixture^.^ The agreement is remarkably good over the of the composition CO to be 137 cm. per second. The value calculated for this whole of the determined range. mixture is 131 em. per second. UNIFORM nf0VEMENT O F F L A M E AND RATEO F RISEOF PRESThe calculated and observed maximum speeds for hySURE IN A CLOSED SPHERE-It has been shownz4that When a gas mixture is ignited centrally in a closed sphere the time drogen are approximately the same, but the curves are appretaken for attainment of maximum pressure is the same as for ciably displaced. It has been shown, however, that the the flame to reach the walls of the containing vessel, both be- important feature of the speed-percentage curves from the ing measured from the moment of ignition, except with slowly point of view of utilization of gaseous fuels in industrial burners31 is the slope of the curves on the upper-limit side, moving flames near the limits of inflammability. C O N E WITH
+
1QU
arid the two curves agree quite well in this respect. The significance of these measurements is t,h:it tlic height of the Bunsen cone is inversely proportional to the speed of propagation of flame with a given mixture. EFFECT OF SIZEOF VzssEL-‘l’lre effect of size of vessel on the speed of flame has only been cxiimined, with an apprcciable range of sizes, vith the iiniform movement of flame, and
speed increasing to n maximiim \vIien about. 6 per colt of water vapor hy volume is present. Tliis maximuin r:tlue has been termed the “effect.ivespeed” of carbon monoxide,8 and is the value carbon inonoxide may be presunied to have when fuel gases are used. All sue11 gases cont,ain hydrogen, a small quantity of which gives t,o ctirhon nionoside its mnximum speed of Aamc. This point is illiistratecl by Diagrams 8 and 0 in which are plotted the speeds of flame during (I) the iiniform movement^ sild (2) flame propagation in 3 sphere with cent.ra1 ignit,ion,’? for two series of maximuin-speed carbon moiroxideliydrogen mixtures.. The effective speed of carbon monoxide (with about G per cent of moisture) is shown in each diagram by a cross, and the observed vnlue with only 2 per cent moisture (saturated at, 15” C.) is shoxn by an open circle. Determination of Absolute Values of Speed of Flame
“ J p m IO.
ill metliane-air mixtures.3’ Diagram 7 slioms the siiniiarity of the curves obtained witli tubcs of different diameter. Experiments with closed vessels have been mainly limit,cd to low capacities, and little information is available as to tlie effect of considerable increase in size of explosion vessel. It has been shown that. when metfia,nc-air nrixtiires a.re ignited centrally in a elused sphere the mean speed of the flame is thc? same when t.lie ciipacity is 4, 16, or 32 liters.24 A photographic investigation of the spread of flame in large cylinders is being carried out at present,as and two of the photogra.plis obtained with methane-air mixtures, in a cylinder 50 cm. loiig and 10 cm. in diamater, are shown in Figures 7 and 8. Figure 7: in which igiiition was ceiitral, may be compared ivith the earlier ~)hotographsin this paper, obtnirred by using an explosion cylinder only 20 ern. long and 5 em. in diameter. yi ccotiwm10 Figure 8 shows the I , ! ! , , ’ movement of flame in the large vessel when ignition is a t one end. Figure 9 shows a s i m i l a r pliotograph of the spread of flame in the small cylinder with ignition at one end.z3 The similarity is m a r k e d . A specd-percent.age ciirve is not available for the l a r g e r * vessel. When the _ _ _ _ ~ I 3 lerigtli of t.~iovessel FlSure 8 Figure 9 is increased still further, vibrat’ions are set up and the character of the fimie propagation is then nltered.
c
.
Combustion of Carbon Monoxide
Carbon monoxide is an import,aiit eonsbituent of many industrial fuel gases, but attempts to compare the speeds of flame in carbon monoxide-sir mixtures nuder different conditions are hindered by the fact that the speed of propagation of flame in a given mixtiire of carbon monoxide with air is dependent on tlie degree of saturatioii wit,h water vapor,3 the
The deduction of the absolute value of the speed of flame is obviously a matter of considerable difficulty. The speed of flame in a mixture of air with one corrcentration of inflammable gas cannot as yet be calcnlated from that, with another concent,ration of t h ine gas, nor can the factors used in the i:alculat,ions earlier in this paper be deduced, but the correlation of tlie vahics carried out liere may possibly he suggestive arid of assistance in formulatiiig a method of so doing. A still more difficult task would be the determination of the relationship between the maximum-speed, say, Of one inflammable gas and that of mother. It is not easy, for r?xample, to explain the great difference in the maximum Zpeed of flame in hydrogeii-air R J I ~ embon monoxideair mixtures, botli iiiflain~iablegases haviiig t,he s:me oxygeu requirements for complet,ecoinbustion :iiid the same calorific value.
With tlic hydrocarhorr gases tlie relationship is possibly simpler. One method of t.r:icing this relat,ionship is to compare the spceds of flriine in airmixtmes of a given inflammable jqns and a mixtiire of t r o other infla~nrnslile gases equivalent to the first in density and carbon-1iydroge.cn ratio. Thus the mixtiire CJf6 C91fz is equivalent t o ethylene (C&) aird either CjIIi2 CHr or 3 C& 2 15, is equivalent to propane (CiIU. It niust he noted that C2& -t 133 is not equivaleirt to ethylene, becarise t h o u ~ ht.hc carbon-liydrogen ratio of this gas is tlie sairie its density is only half that of et11yleiio. In Diagram 10 tlic continuous curve shows tlie speeds of propiigatittion of finme from okcrvcd vahies in the closed while t.he cylirider 20 cm. loiig with ethyleue-air
+ +
+
INDUSTRIAL AND ENGINEERING CHEMISTRY
1032
1
i m
10
lnflmnab'e
9"
ce-l
I
I
CO
)5
D/ogrom
%
62
12
dots show experimentally determined values for the equivaCzHs. There is a close correspondence. lent mixture CzHz In Diagram 11 the continuous curve shows the speeds of uniform movement of flame in a tube 2.5 cm. in diameter for pr~pane-air,'~ while the dotted curves show the speeds in CH, and 3 C5Hi2 2 Hz. the equivalent mixtures C5Hl2 Though the agreement with the mixture containing hydrogen is not so good as with the hydrocarbon mixture, it still seems close when the great differences in the maximum speeds and the ranges of inflammability, of the constituent gases, pentane and hydrogen, are compared (see Diagram 1).
+
+
+
Law of Flame Speeds These few results are instructive, and should prove of value as an aid to the law of flame speeds in further investigations. The law of flame speeds is a simple additive relationship for calculating the speed-percentage curves for complex inflammable gases from the curves with the simple constituent gases. This relationship has been developed in and will not detail in a number of papers12,4,3,11,34,35,27,36,37
VOl. 20, KO. 10
be discussed here, but a comparison of calculated and observed speed percentages will be of interest from the point of view of the present paper, and such a comparison is made in Diagram 12 for equimolecular mixtures of methane, hydrogen, and carbon monoxide, and will indicate the utility of the speed law. Bibliography 1-Payman, Proc. Roy. SOC.(London). 120, 90 (1928). . 2-Haward and Otagawa, J. Chem. SOC.(London),109,83 (1926). 3-Payman, Ibid., 115, 1454 (1919). 4-Payman, Ibid., 116, 1446 (1919). 5-Hartwell and Georgeson, Unpublished results. 6-Mason and Wheeler, J . Chem. SOC.(London), 115, 578 (1919). 7-Wheeler, Ibid., 111, 1044 (1917). 8-Mallard and LeChatelier, Ann. mines, 4, 274 (1883). 9-Tizard and Pye, Empire Motor Fuels Report, London, 1919. 10-Maxwell and Wheeler, J . Chem. SOC.(London), 1927, 2069. 11-Coward and Jones, J . A m . Chem. Soc.,49, 386 (1927). J . Chem. SOC.(London), 117, 48 (1920). 12-Payman, 13-Payma11, Ibid., 116, 1436 (1919). 14--Shepherd, Unpublished results. 15-Dixon, J. SOC.Automotive Eng., 9, 239 (1921). 16-Woodbury, Lewis, and Canby, Ibid., 8, 209 (1921). 17--Payman, Proc. Roy. SOC.(London), 1998. 18-Ellis and Wheeler, J . Chem. SOC.(London), 1927, 310. 19-Ellis, Ibid., 123, 1440 (1923). ZD-Mason, Ibid., 123, 210 (1923). Ibid., 191, 1729 (1922). 21-Garner, 22-Payman, Faraday Society Discussion, 1926. 23-Shepherd, Unpublished results. 24-Wheeler, J . Chem. SOC.(London), 113, 840 (1918). 25-Maxwell and Wheeler, Ibid., 1927, 2069. 26-Maxwell, Unpublished results. 37--Maxwell, Payman, and Wheeler, J. Chem. SOC.(London), 1927,297. 28-Gouy, Ann. chim. phys., 18, 1 (1879). 29-Michelson, Ibid., 37, 1 (1889). 30-Ubbelohde and Hofsdss, J. Gasbel., 16, 1225 (1913). 31-Payman and Wheeler, Fuel, 1, 183 (1922). 32-Mason and Wheeler, J . Chem. SOC.(London), ill, 1044 (1917). 33--Kirkby, Unpublished results. 34-Payman and Wheeler, J. Chem. SOC.(London),191,363 (1922). 35-Payman and Wheeler, Ibid., 123, 1251 (1923). 36--Payman, Ibid., 123,412 (1923). 37-Coward and Greenwald, Bur. Mines, Tech.Paper 427 (1928).
Gaseous Explosions VI-Flame
and Pressure Propagation1
J. V. Hunn and George Granger Brown UNIVERSITY OF MICHIGAN, ANNARBOR,MICH.
This investigation was undertaken in order to obtain experimental d a t a concerning the relation between flame propagation and the pressure changes resulting therefrom. The apparatus used a n d its method of operation are described in detail a n d the experimental d a t a are interpreted a n d discussed.
LTHOUGH many investigators have photographed the movement of the flame in gaseous explosions, and some have recorded the rise in pressure a t one point in the explosion chamber while photographing the flame, practically all conclusions concerning the pressure effects accompanying the flame are entirely speculative, as no experimental data have been reported giving the pressures developed by and accompanying the flame as it progresses through the explosive mixture. Many investigators have observed a halt in the advance of the flame front as it progresses through the explosive mixture.
A
1 P a r t of a thesis submitted by J. V. Hunn in partial fulfilment of the requirements for the degree of doctor of philosophy in the University of Michigan.
The cause of this halt has been explained in various manners. Dixon? believes it to be due to a reflected pressure wave set up by the igniting spark and traveling through the unburned gases ahead of the flame. After being reflected from the far end of the explosion chamber it meets the flame front before the flame front reaches the end of the explosion chamber. Woodbury, Lewis, and Canby3 observed this halt in the flame front when photographing the flame and recording the pressures developed a t the end of the explosion chamber opposite the point of ignition, and explained it in the following manner : It has been previously shown that the flame front is pushed forward by the expansion of the burned gases and that the unburned gases are compressed to a high density at the same time. Obviously a point can be reached a t which the pressure due to the temperature behind the flame is equaled by the pressure due to the density ahead of the flame. At that point the flame front is no longer pushed forward; the propagation is arrested.
* J . SOC.Automotive Eng., 9, 237 8
Ibid., 9, 209 (1921).
(1921).
