Ih'D USTRIAL B N D BNGINEERING CHBMISTR Y
October, 1928
1013
can:be plainly seen at the sides is no longer continuous, and unburned carbon is escaping freely a t the top. Figure 12 is a luminous Rame of propane and oxygen (33.75
In Pig& 13 (33.40 per cent) the cone has.become a foursided figme, and the luminous zone has separated into four streams which rise from the dark ridges of t h e non-luminous miman zone. This view. fscinr one side. shows t h e dark iidges -from which no 1iaht is &in%, the figure cdsisting mcrely of four disconnected sides.
13
15
14
C16
Figures 12 to 17-Ropane-OrY*en
17
smaller, forming an apparently continuous nng at the base and extending upward like the sides of a cup.
The Flicker of Luminous Flames D. S . C b m b e r l i n a n d A. Rose' LES~OH
u~rvsnszrv.8 e m L * m s m . PA.
The vibratory motion of luminous flames has been studied by t h e photographic method. The rate of vibration, speed of flame, movement, a n d amplitude of vibration have been determined for various gases under differe n t conditions. The d a t a show t h a t the upper portion of the luminous zone rises to a maximum height ten times per second. This rate of vibration is not greatly affected by change in conditions. T h e lower portion of the flame has a continuous existence, b u t periodically gives off another flame, which rises above the main flame during its short period of existence.
BSERVATIOS of a luminous Bunsen flanie shows that the flame is not in a steady state at any time, but that there is considerable motion, especially in the upper part. This is apparently true of all flames burning w-ithout primary air, from any tip or opening. Although a large amount of work has been done on the phenomena of flames in general, there has been almost 110 study of this vibratory nature of most flames.z It has been noted in flame-speed studies that the flame does not travel wit21 uniform motion but with periodic increases and decreases of speed.s In some cases the flame travels alternately forward and backward, the backward movement being the slower. However, all such observations have been made in tubes having one end closed and which were completely filled with a mixture of combustible gas and oxygen or air a t tlie start of the experiment. These con-
0
I Columbian Carbon 9
Fdioa.
Cos Agr-KeCord. 67 (1926).
*Bone nnd Tobwoeod, "Plame and Combustion ill Gases," Longmanr.
Gr-
& company.
ditions are quite dificrent from those of a free flame burning from an orifice of any kind, and it is questionable whether the two sets of phenomena are related. Since no explanation of this behavior of free flames wm evident, a closer study was made. The photographic method was used, by means of which pictures were taken at the rate of 32 per second and developed and studied by projecting the image of the film. The results sliorved that the flicker CODsisted of a regular upand-down movement of the middle and upper portions of tlie flame while the lower portion remsined quite steady, and that the downward movement is extremely rapid if the flame exists at all during this stage. The upward movement is approximately that of the Bane speed of the gas mixture probably present iU the flame, and the rate of vibration for tlie flames of all t.he gases investigated is of the order of 10 per second. This rate is not greatly affected by the at,mosphere in which the flame bums or by the tip from which the gas issues, or by the rate of flow of the gas. Furthermore, there is only one way in wllich the flicker can be stopped and that is by inserting a plate or similar object into tlie flame a t or below 9 definite point in the flame structure. This destroys the upper part of the flame structure snd, therefore, eliminates the flicker. Materials The gases whose flames were studied were natural gas, hydrogen, carbm monoxide, ethylene, methyl chloride, hutane, ethane, and hydrogen sulfide. All cxcept carhon monoxide were obtained in cylinders under pressure and were practieally pure. The carbon monoxide was prepared by dropping formic acid into hot sulfuric acid, The natural gas had the
screen of coerdiriate paper. I n this way n series of Aame images such as those in F i y r e 1 was obtained. It can be seen xt once that successive pictures arc quite different in appearance, iiidicatiirg a distinct change in the Annie during the T h e apparatus used to uhtain flames suii.able for photo- dosed interval of the shutter of 0.0130 second. First of all, it will he noted that there is a distinct up-andi.r:iplric pnrjioses consisted of a gasomet,cr for supplying gas :it colist:tnt pressure, it wet meter, :ictive-carhon al.isorhing down motion to the flame. This can be shown also by a series towers. a flovrnieter, and a ~ J I ~ S S U Tgage. ~ The gas was < i f pictures in slow motion. I n general, every Miird picture biirtied in a cuhioal nshestos box irllich a a s provirlcd wit.h IL appears &out the same. It is also evident that the movelarge quartz window. Tlir buriier was without air ports and rnent is confined to the upper part of the flame. The lower XIS fitted ut the top with a lava t i p Air vents at the top tliird of the Baine remains almost stationary while the exand br,ttom of the ;tsbt~stoshox were covered with wire gauze treme upper portion moves up and down, and the middle to preveiit irregular drafts. The toy opening could he arl- portion moves in and out. Furthermore, the upward movement of the flame is much jiisicd to ohtain the rffcct of a dnntper rind thus regulatc the rlrnft through tlm hox. .4n sneinoruoter wsi used to measure slower than the downward movement. The upward m o v e the air entering t,lie l)ox. Before a Hnme was photographed, rnent usually requires two pictiires, the downward movement 1irrcnutious m r e always takeir l o allow conditions in the iiever more than one. Further study shows that the downu-ard movement must he practicaliy inst,antaneous. With BOIIS(~ to become rrnifrirm. the camera used, each picture shows the position of the flame near t,he end of the period of exposure in upward movement, nnd at the hegiuning of the period in the backward or downm r d movement. If the flame reecdcd gradually, there would be images of intermediate size between the tallest and the shortest. Tliis is not the case, as a sinall picture nlways imrncdiately follows a tall one. 111 certain csses a double picture (So. 3, Figure 1) is obtained and this bears closer study. (in sonic cases t x o complete separated flames can be noticed on the i;me pict,ure.) -Here tiie slluttcr opened just before the Rnme reached its highest point, so that a fnint exposure of tlic higliest Hmie was ohtained. Tlteii, with the shutter s t i l l open, tho tall fiamne entirely disappeared and nnollier flame :rppcareii at a much lower poitit (8')and again began to rise. The fniut d,araeter of tile t d l flmne a i d t,he dist.inct The Flicker of Luminous Flames image of the sinall flaiuc clearly show a short exposure and a long exposore, respcct,ively,and completely eliminate the possiThe flanies w r e photograplied a t a distance of 2.29 meters bility of tiny gradiial downwird rriovemeiit uf thc t ~ l Amee. l ( 7 3 feet) with a nioving-picture camern. The focal length of the leiis was 2.54 em. (1 inch), the length of a single exQuantitative Investigation of Pictures posure was 0.0182 second, and the shutter remained closed 0.0130 second between exposure$. 'The interval was thereIn ur&?r to nieasurc quantitntively tile rate of flicker, the fore 0.0312 second, 1/0.0312 = 32 exposures per second. speed of the rising flame, arid the total ri A governor on the camera prevented the shutter from opening flnnie (amplitude of vibration), tlie flame ~niagcswere proiinless the correct speed was heing obtained. jected upon a piece of eo6rdinate paper. 'l'he height, of the The pictures wrrc t,akcn in seriixs of 60 t o 120 by allowing highest. point of the tip (it), Figure 1. wiis then read off from ltie camera to rirn several seconds. After a series I u d t i ~ m each picture and recorded in the proper order. Observations i)botoerai,hed. the comlilioiis were chiineed arid ailother sliowed that the hot,t,oins of the Aame irniiges (D)m r e aluiays ., . series obtained in a sirnihr ~ n i i i i tier. In order t,o distinguish one series Crorrr the next, air electric P light lying i,!front of tlic asbestos box wis flashed on just .$ $. a t the end of each series. ? With mct,liyl chloride the flame refused to born stt:adily of I I I I I I I I its own accord, This was remT;*a - znrcrk.a/ b e f r r e e n f,"'"fS POJ,ZJeCDrds f , p ri edied by constructing a special burner, the biirrel of whieli w i s vound with nickel-eiin,ini~irn projected in the same place for a given series. Since the only wire, so ilint it acted as R prcheater for the gas. m d t e r of inter& was the variriiltion in the higher point, an Tlx: flames of hydrogen, carbon monoxide, and hydrogrn arbitriirv base line was choson and all t h e flame heights sulfide are so nearly eolorless that they f d r d to iiffect t,lie were ~:nlculatedfrom this. Tilo flame heights were tlieli film under the conditions of short exposure that Vcere neces- plotted agninst the number of the pictures in the. series, and sary. Several attempts \\'ere made to illuminstc these Banies through the result,ing points a curve call be drawn as show,, ( ? j hy adding armmoniuiii ellloride io the gas and (2) by put- iii Figure 2. Froin double pictures such curves it is posting sodium chloride into the flame. However, no sucressful sible to determine tlie rate of flicker, flnrne speed, aird ampiifilms were ohtailled from these gases. tude of flicker.
following cornpositbin: methane 71 2, ethane 23.3, iiitrogeii 4.7, carbon dioxide 0.8 per cent. Apparatus and Procedure
,$
I
Qualitative Interpretation of Pictures
Calculation of Rate of Flicker
When the film had been developed, it was placed in the projector and the pictures were shown one at n time on a
In order to calculate t,he rate of flicker, it is necessary to linow t,he time elapsed during n definite number of vibrations.
Octoher. 1928
IAVDC;s'TRIdLA;VD E,VGIAVEERINGCHE-UISTRY
The time factor is easily obtained from the number of pictures being considered and the fact that the time for a single picture is 0.0132 second. The number of vibrations corresponding to a given number of pictures is more difficult t o obtain accurately, because the given number of pictures rarely, if ever, corresponds to a whole number of vibrations, and there is no way of determining just what fractional part of a vibration has been neglected. Of course, if a large number of pictures are considered, the error is relatively sinall, but the time consumed in obtaining the data from the film is too great t o make such a method practicable. The error can be reduced to negligibla size if care is taken in choosing the first ~ n laqt d pictures of the serie. used for calculation. I
1
i
I
I
1015
Most of the data need no explanation, but before discussing and correlating the various facts it is well to point out certain significant features. I n accordance with the previous work of Chamberlin and T h r i ~ nthe . ~ wide-slotted tip gave different results from the narrow slotted tip. The latter gave a curve very much like that obtained2with similar tips in a previous study. From a study of the flame-speed data, it appears that the speed of the rising flame increases as it rises. Figure 3 represents graphically the correlation of the data obtained, in which time is plotted against height of flame. The solid line ilil represents the upper flame boundary, the dotted line BB and the line CC the lower flame boundary. The curvature of the line A A represents the increase in speed of the upper flame boundary as it rises. The base line TT represents the height of tip. The area between the lines TT and DD represents the non-luminous lower portion of the flame, which consists of unburned gases issuing from the tip. The next higher region between DD and BB represents a hotter zone, where combustion is taking place and n-here the existence of carbon monoxide is indicated by the blue color of the flame. The next region (between BB and Table I-Data on Flame Flicker h I A X - RATEOF GAS I ~ A U SPEED E AMPLISERIES r r m s IMA FLICKER RATE Lower Upper TUDE J'ibrafions Liters/ p e r min. hour Cm./sec. Cm./ser Cm. PIC-
NATURALGAS 61
B?
a
b c I33 a
The first and last pictures must be ones in which the time of closing the shutter (end of exposure period) coincided as closely as possible with the instant when the flame reached its maxirnum height. The points of the curre in Figure 2 show that wccessive maxima gradually decrease until a double picture is reached, and in this case the maximum height is much greater, and then the following maxima decreases gradually again. Any double picture is very nearly the picture desired for the beginning or end of a series, since here we know that the shutter closed shortly after (less than 0.0182 qecond) the flame reached its highest point. Then, in the following maximum the shutter must have opened ju,t before the flame reached its maximum height. I n the calculations of rate of flickebr, the first and last pictures were a l w a y of the above type, so that the error involved in the cnlciilation was a minimum.
b c
€2 a b
Bs
The speed of the upward inovement was calculated from the difference in poqition of the flame between two pictures and the time interval between the two pictures. The actual distance traveled by the flame was calculated from the differences shown on the curves by use of the constants of the camera and the projector and the distances used in filming and projecting. The amplitude was calculated in the same manner from the lowest and highest points of the curve for a given series. Data and Discussion
The curves themselves are not given in the data, but only the results of the calculations. (Tables I and 11) The data for hydrogen, carbon monoxide, and hydrogen sulfide have been omitted. Visible observation of these flames shows that hydrogen and hydrogen sulfide flicker, while carbon monoxide probably does although not in a pronounced manner.
b c
13; a b c 6s a b c
Bs a b C
BG a b
I h
a
b c
EN a b Iil3
Calculation of Flame Speed and Amplitude
a
a
b
BH a 0 c
Tip Width, 0.089 cm. 13 610 16.43 32.9
6s 29 44 24 45 27 44 61
56.2 607 609 23.51 53.1 68.5 608 8 591 13 594 67.90 19.5 63.1 18 596 12 607 16 603 87.82 45.7 39.6 i 560 12 562 79.32 36.0 41.1 17 563 10 564 16 568 107.65 39.0 40.3 21 568 11 571 16 568 99.16 35.2 42,s 22 571 T i p Width, 0.026 crn. 5 686 16 668 10.48 12.4 14.0 24 66s 14 656 19.26 35.0 41.7 23 660 14 7n7 21 707 39.66 27.1 37.1 25 706 795 73.66 Irregular 12 18 is5 10 812 62.32 Irregular 19 so0 11 783 50.99 38.7 27.9 18 785 25 788
49 62 36 52 45 71 35
Tip Xl-idth, 0.089 cm. 15 588 19 589 22.66 34.5 11 587 39.66 46.6 16 591 14 598 56.66 35.1 22 595 11 603 73.66 25.1
39 19 41 60 26 42 58 3s 51 24 41 58 34 54 71 37 54 74
14 46 69 41 67 38
57
6 13 19
3 24 5 73
5.4s 4.48
3 74 4.23 3 99
1.74 3.99 2.74 1.74 L74 1 ,O!)
ETHYLESZ
a
:1:3
b .41r a b
