176
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE
Iv.
PRESS~RE-TI;JfPERATL~RE-COMPOSITIOP\T DATA FOR METHAXOL-BENZE~ E AZEOTROPE
Pressure, him. Hg 200 223
Azeotrope Boilin Point,
400
725.5 737 760 6000 11,000
08.
26 2; 42 40 56.7 56.7 58.3 57 124 149
Azeotrope Composition, Mole yo Me011 55.7 55.6 57.5 58.7 59.9 59.9 61.5 61.9 74.8 80.7
Ref el ence
- 1362/(t 7.89419 - 1478/(t
log P =
+ 230) + 230)
boiling point relationship for .riarious hydrocarbon-water heteroazeotropes. In the case of heteroazeotropes, there should be no nonazeotropic point. V7here this may appear to occur, the conditions are such that the system is in the critical range or in the solid phase. CONCLUSION
It has been shown that two accurately determined pressure-
zene azeotrope is shown in Figure 5. The equations for the azeotrope and for pure methanol are, respectively: log P = 7.62580
Vol. 43, No. 1
boiling point-composition data completely define an azeotropic system. Because many homoazeotropes become nonazeotropic a t either a low oi a high pressure (or a.t hoth), the pressure-temperature relationship permits the calculat,ion of that pressure. If this is known, then only one addit’ional point is needed coniplctcly to define an azeotropic syst,em.
(9)
LITERA’I‘URE CITED
(10)
The temperature above which the system is nonazeotropic is calculated from Equation 8 as 219’ C., and from Equations 9 and 10 as 202” C. This relativcly close check is significant, for it permits the determination of the composition-temperature relationship (Equation 7 ) from the pressure-temperature relationship and only a single composition-boiling point datum. Application of the relationships t o data of systems already reported in the literature a t once reveals those data which may be in error. This was done for the ethyl alcohol-water azeotrope and for the ethyl acetate-carbon tetrachloride azeotrope on the basis of the data of several investigators. $n inspection of Figure 6, in which the nonazeotropic points were calculated from the pressure-temperature relationship, reveals those data which obviously need rechecking. Figure 7 shows the composition-boiling point relationship for several maximum azeotropes and Figui e 8 shows the compoiition-
Coulson, E. A , , and Herington. E. F. G., J. Chem,.
Soc., 1947,
597.
Dreisbach, R. R.. a n d Spencer, R . S.,ISD. Esr:. C m x . , 4 1 , 176 (1949).
Horsley, L. H.. Anat. Chem.. 19, 603 ( 1 9 4 7 ) . Lecat, RI., Ann. SOC. sci. Bmselles, 49B,261-333 jlSSS!. Ibid., 55B,4 3 (1935). Lecat, M,, “L’A4zeotropisme,”Brussels, Lamertin, 1918. Lippincott, S. B., and L y m a n , M. A t . ,
[email protected] H E h f . , 38, 320 ( 1 9 4 6 ) .
Nutting, H. S.,and Horsley, I,. H.. Anal. Chent., 19, 002 (1947) Prieoeine. I.. Bull. snc. c h i m Belges. 52, 95 ( 1 9 4 3 ) . Redlich, O., and Sohutfi, P. TT., J . Am. Chem. Soc., 66, 1007 (1944).
Soday, F. J., and Bennett. G. IT., J . Chem. Education, 7, 1336 (1930).
RECEIVED J a n u a r y 26, 1950. Pie-ented before the chemical -,yniposinm, sponsored by tlie Delaware Section of the .k\IERICAN CHEVXCAI, sOCI8:TT i n collaboration with the Uniyersity of Delaware, Newark, Del., J a n u a r y 2 1 , 1950.
Temperature Gradients and Temperatures in Carbon Black Flame -~
F. W. JENSEN AND KERMIT ANDERSOY Agricultural a n d Mechanical College of Texas, College Stution, l e x .
T
HE voluminous literature which exists on production of fine
carbon pigments testifies to its importance to technology, and to the tremendous amount of effort which has been expended in this field. An examination of this literature, however, shows that tlie majority of the work has heen application research and process development. Few studiefi of a fundamental nature have been undertaken. Carbon black, in the restricted sense common in the industry, refers t o those pigments formed by impingement of small sootforming diffusion flames on heavy metallic surfaces ~ h i c hare in motion. The most common design of modern plants uses channel irons as the impingement surface and employs many small batwing shaped flames burning from slotted lave tips. -4photograph of one such flame is shown in Figure 1.
1 Present address, N E P A Division, Fairchild Engine a n d Airplane Corp., Oak Ridge, Tenn.
This research has as its primary purpose the determination of the structure of the bat-wing t,ype of carbon black flame. I t s long range purpose is to furnish part of the information upon which a theory of the mechanism of soot production in diffusion flames burning hydrocarbon gases can be based. The long rango program includes measurement of boundaries of the flamc, temperature gradients within the flame, and true flame temperatures, as well as a delineation of regions of high soot density, and analyses of gaseous composition of nhe flame and of the gases above the unlit jet. The iniorination obtained in t,hiswork should be of general value to the carhon black technologist in practical work in the field. JViegand ( 6 ) has studied the structure of two typca of carbon black flames from the standpoint of operative variables and their eflect on yield of carbon. He introduced the concept of surfacevolume ratio of the flame and attempted to show that, this variable controlled the yield and type of carhon produced in the flame.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January 1951
The literature on diffusion flames is well covered in monographs by Lewis and Von Elbe (6) and by Bone and Townend (1 ). The work discussed herein deals with measurements of temperature gradient and true t e m p e r a t u r e of the flame. MEASUREMENT
OF
TEns-
PERATURE GRADIENTS
P
ff
The measurement of temperature gradients within the flame was carried out ,,y using fine noble metal couples coated lightly with magnesia to reduce shortil.g by deposited carbon. These measurements perlnit de-
T h e physical and chemical behavior of diffusion-type carbon black flames, inadequately known, at present, should be of interest to scientists working toward development of new types of fine carbon pigments and to engineers seeking to improve the channel process. The authors studied temperatures and mapped temperature gradients in a bat-wing type carbon black flame burning from a standard 0.044-inch slotted steatite tip. Temperatures as high as 1450' C. were observed using the Kurlbaum method for measuring true temperatures of luminous flames. Temperature gradients were observed with noble-metal couples, thinly coated with magnesia. The flame was found to be an ovoidal cylinder whose walls, composed of high temperature reacting gases, enclose a well defined region in which carbon forming reactions can take place. Gradients immediately within the flame wall are sharp, dropping from near 1400" to 1450"C. near the flame surface to temperatures near 500" to 900" C. in the interior zone of the flame. A t such temperatures hydrocarbon cracking, reforming, and oxidation reactions become im-
177 and so t h a t n o air passed into the burner box. Complete freedom of movement t h r o u g h t h r e e dimensions was retained. As an indicator for this couple, a Leeds & Northrup type HS galvanometer was c a l i b r a t e d against a standard electromotive force using a Type K potentiometer, and suitable resistances and batt e r i e s . T h e electromotive f o r c e - t e m ~ e r a t u r e tables furnished for platinum a g a i n s t 10 yo r h o d i u m for h d s h K ~ ~ thrup were used to convert g a l v a n o m e t e r readings to temperatures in degrees tigrade. The couple was mounted on a universal stand with micmneter dials permitting three perpendicular axes. The of the couple at a location datulll
lineation of the portant mechanisms leading to carbon production. position was carefully determined in relation t o the axis of the flame, by dividing i t of the burner tip. The couple into zones of low and high could then beinserted into the t e m p e r a t u r e and locating flame, and the indicated temperature read from the gahmometer. The position of t h e C O U P ~ the boundaries of these zones as regions of high temperature relative t o the tip in the region occupied by the flame could be gradient. read from the micrometer dials on the stand. EQUIPMENT AND METHODUSED. The measurements were carried out in a small single burner unit having a mica window through which the flame could be observed. The single burner used was a 0.044-inch lava tip of standard design. Forty-four cubic feet of gas per 24 hours was selected as a standard rate for this work. Ventilation was through a number of 0.5-inch drill holes in the bottom of the sheet metal housing. Air input could be decreased from the maximum by stopping up holes with properly sized corks. Top draft was through two slide-controlled slots in the lid of the burner box. The thermocouple was carried into the box through a standard 0.25-inch black iron pipe. The couple, insulated over the length enclosed in the metal with standard two-hold insulators held rigid b y glass tubing, was cemented into the pipe u ith litharge-glycerol cement.
Figure 2.
Apparatus Used in Measurement of Temperature Gradients
Figure 2 gives a diagram of the system and shows the couple su ported on its stand and inserted in the flame. b n c e the couple would pick up carbon and short itself out in regions of the flame where high carbon density existed, it was inserted into such regions as rapidly as possible and reitding of the maximum swing of the galvanometer was taken. The temperatures so measured were in no sense true flame temperatures, but were considered to be reasonably comparable for the purpose of determining regions of high temperature and high temperature gradient.
Figure 1. Carbon Black Flame
into the burner box was through a hole in an airtight sliding window which could move for an adequate distance through the two degrees of freedom of the front vertical plane of the box. The 0,25-inch pipe was turned dowTn in the lathe so that i t fitted into the hole in this sliding metal window
DATAON TEMPERATURE GRADIENTS. The bat-wing flame is a. flattened ovoidal cylinder in horizontal cross section. I t s appearance normal t o its horizontal major axis is t h a t of a n elongated kerosene lamp flame, with its top truncated by intrusion of the channel. T i p height distance was held in all flames at 2.75 inches. Temperatures were closely mapped in eleven horizontal planes, beginning 0.25 inch above the tip. The first ten such planes were at 0.25-inch intervals along the vertical axis of the flame, and the last One was o'2 inch above the highest Of the ten? placing this last p h e a t a height of 2.70 inches, or 0.05 inch below the channel.
Vol. 43, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
178
I
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00
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00
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075 INCHES ABOVE
'
012
'
04
06
08
FLAME WIDTH-INCHES
FLAME WIDTH -INCHES
TIP
100 INCHES ABOVE TIP
Figure 3. . I s o t h e r n ~ a Contour l Charts for I I o r i ~ o n t a lPlanes 0.25, 0.50, 0.75, and 1.00 Inch above Tip heat,ed tube. By some mechanism, as yet undetermined, carbon is formed in the upper zone of the flame and is deposited on the channel. The maximum temperatures observed by the thermocouple fall near 1300" C. and correspond to the maximum true temperatures near 1408" C. observed by the optical method discussed below. T h e t,einperatures observed in the interior region of the flame range from near 500" to above 1000" C. However, the junction of the couple, while being used t o observe these latter temperatures, TW,P enveloped by the intensely hot, luminous flame wall and was probably heated materially above the temperature of the gases with which it \?-asimmediately in contact by radiation from these malls. ITence the temperatures observed within the interior zone of the flame are probably considerably too high. As the temperatures determined by the couple are not true flame temperatures, no further conclusions will be drawn at this point.
Figure 3 shows isothermal lines mapped in planes 0.25, 0.50, 0.76, and 1.00 inch above the top of the tip. Figure 4 shows sin+ lar planes 1.25, 1.50, 1.76, and 2.00 inches above the tip. Figure 5 shows planes a t 2.25, 2.50, and 2.70 inches above the tip. If the idealized contour of maximum temperature of each of these figures is drawn, the horizontal trace of the flame boundary is shown to resemble a dlstorted ovold of Cassini. The temperature gradients are seen to be rather sharp, with the higher temperaturw being in the flame walls and increasing toward the top of the flame. The interior of the flame is a moving body of gases heated to gradually higher temperatures the farther they advance through the flame. Since a relatively high velocity component in the complex diffusional pattern must evist in the upward direction, the hydrocarbons existing within the flame walls may be considered t o be comparable to diluted hydrocarbon gases within a
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Figure 4.
00
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02
02 0.4 a6 r L A M E WIDTH - I N C H E S
0.0
08
2.00 INCHES ABOVE T I P
Isothermal Contour Charts for Horizontal Planes 1.23, 1.50, 1.75, and 2.00 Inches above Tip
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1951
119
MEASUREMENT O F TRUE FLAME TEMPERATURES
0.6
0.8
0.4
0.0
0.2
0.2 0.4 0.6 FLAME WIDTH -INCHES
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Figure 5. Isothermal Contour Charts for Horizontal Planes 2.25, 2.50, and 2.70 Inches above Tip
A
OPTICAL
/
PYROMETER ,GLASS
WINDOWS.
COLLIMATOR /TUB'
-24 PYROMETER d
ABLE
POTENTIOMETER
Figure 6. Apparatus for Measurement of True Flame Temperature
The measurement of temperature in any system such as a diffusion flame raises the question of whether the system is in thermodynamic equilibrium, and whether a temperature meaeurement would have any meaning. The measurement of true temperatures in diffusion flames has been discussed by Hottel and Broughton ( 2 ) who conclude that since the time of redistribution of energy from an activated reaction product molecule is of the order of a tenth of a microsecond, the flame may be considered to be fairly close to thermodynamic equilibrium. These same writers define true temperature of a flame as the temperature of a test body, small compared to the dimensions of the flame but large compared to the individual molecules. Hottel and Broughton showed that the soot particle in the luminous flame fulfills these conditions, and that its temperature differs from that of the surrounding gases by less than 1O C. Hottel and Broughton (3') have discussed the various methods that have been proposed and used to measure the true tempeiature of flames. Two general classes of methods, one using thermocouples, the other using optical pyrometry, can be employed. The use of thermocouples, together with suitable means for compensating for heat losses, has the advantage of approaching the desirable case of measuring temperature a~ a point function of the space within the flame. Experimental difficulties involved in these methods, especially when used in soot-forming flames, led to the consideration of the optical methods. This step was taken in spite of the fact that optical measurements will represent an average value through the observed flame, and through a relatively large region, which may even contain portions having high temperature gradients. The most commonly used optical method for measuring t i u e temperatures of luminous flanies is that of Hottel and Broughton (8). This method involves the use of two different color acreens in the optical pyrometer, with the reading of a red and a green brightness temperature. The true temperature can then be obtained from these readings by use of equations relating these brightness temperatures to the true temperature of the flame. A second method, described by the same authors uses a standaid optical pyrometer together with a black screen and a mirror of calibrated or known reflectivity. Some experimental work VI as done with this method but the results were not reproducible, so the method way discarded. The method finally used was that of Kurlbaum (4). This method was selected because the measurements could be carried out with equipment already available, since equipment for the less laborious Hottel and Broughton ( 8 ) method was found to be unobtainable under wartime conditions. The Kurlbaum method uses a standard disappearing filament-type optical pyrometer calibrated for black body radiation and an auxiliary source of radiation which need not be a black body. The temperature of the auxiliary radiator is set a t some point and observed with and without interpoflition of the flame whose temperature is to be measured. The temperature of the radiator is then adjusted until the interposition of the flame causes no difference in its apparent temperature. Under these conditions the brightness temperature of the auxiliary radiator and of the soot particles in the flame must be the same. This, in effect, has measured the brightness temperature of the soot particles which have been shown to be suitable test bodies satisfying the definition of flame temperature given above, but it can be shown that the soot particles in the flame are effectively black bodies, so that their brightness temperature and their true temperature are identical. Hence the true temperature of the flame will have been measured,
EQUIPMENT AND EXPERIMENTAL PROCEDURES. Hottel and Broughton showed that greatest accuracy in measurement of tiue temperatures of small luminous flames could be secured when the optical pyrometer was sighted throu h a number of flames. This is especially true when using the Kurfbaum method on natural gas
INDUSTRIAL AND ENGINEERING CHEMISTRY
180
T.LBLC I. STIIIMARY
OB
--
Height aborc ,pip, Inches 0.260 0,500
:entral Axis O F . O C .
2474
0.730 1.000 1,260
2492 2522 2539 2556 2566 2582 2602 2608 2608 2609 2602
1.375
1.6W 1,626
1.750 2.ooO 2,125 2.230 2.500
2.700
.... 1397 .... 1367 1383 1393 1402 1408 1417 1428 1431 1431 1432 1428
TRUE F L A M E TEMPERATIJRE n.4r.4 T r u e Flame Teinueratures 0.25-Inch 0.?,75-Inoh
Odset
Offset, ' F . O C . 2442 1339 2480 1360 2500 1371 2526 1386 2546 1397
....
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.
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.
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.
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that their line of sight was parallel to the burner pipe axis, and the relationship between their optical axisand the line passing through the top center of the burner tips was determined. The tips were carefully adjusted so that their slots were parallel, with the wide face of the flame normal to the optical axis of the pj-rometer. The equipment was then ready for a temperat'ure determination. Figure 6 shows a diagram of the equipment. The burner box is shown as a rectangle, as are potentiometers. meters, and galvanometers. Temperatures were determined by setting the filament current of the T-24 lamp at a value which gave a brightness temperature obviously loxer than the apparent temperature of t h e flame. The brightness temperature of the filament was observed and recorded, together with the filament current of the T-24 lamp. The temperature of the T-23 lamp \VRS then progressively increased and read, through the flanies, until it was obviously brighter than the flanie through whieh it \vas read. 1.hch of these data was recorded together with t,he corresponding filament current, of the lamp. These data were then corrected foi, absorption by the glass window of t,he burner box and plotted on the same axes with the corrected calibration curve for the T-24 lamp. The intersection of these two curves gives the temperature at which no change occurs in the apparent temperature of the lamp filament due to interposition of the flame. As point,ed out above, this corresponds to the true temperature of the flame. A4nexample of this type of plot is shown in Figure 7 .
TRGETEMPERATURE l > a ~ a . The t,rue temperatures of -the flame weredetermined at, intervals along four vertical lines, cutting the flame. These lines n-ere the 'vertical geometric axis of the flame, and lines offset from thie axis by distances of 0.25 0.375, and 0.5 inch. Thc exact data are given in Table I and shown graphically in Figure 8.
OBSERVED TEMPERATURE
2
Vol, 43, No. 1
2500
39
35
40
CURRENT
- MILLIVOLTS
45 DROP
Figure 7. Typical Graphical Determination of True Flame Temperature
flames such as are produced by the standard slotted tips used in the channel black process. A special burner box was built for this work in which ten 0.044-inch tips, fed from a 1-inch standard black iron burner pipe, were placed between two glass Rindows in the opposite narrow ends of the box. The tip spacing was 6 inches, center to center. The burner pipe was equipped with Huber-t)rpe shields. Drafting from the bottom was through two r o w of 0.5inch drilled holes placed 0.75 inch from the bottom of opposite long walls of the box. Top drafts consisted of two slots 1 X 6 inches in length, equipped with sliding dampers cut in opposite ends of the 18 gage sheet metal lid of t,he box. An 8-inch channel supported on angle irons from brackets a t the sides of the box was so placed that the tip to channel distance was 2.75 inches. The gas was metered through a calibrated orifice-type flowmeter a t the riite of 44 cubic feet per tip per 24 hours. Yields of carbon black nwasured on these flames ran near 1.85 pounds per 1000 st'andard cubic feet. A General Electric type T-24 ribbon filament pyrometer lamp M W used as an auxiliary radiation source. The filament was heated by storage batteries, and the heating current was controlled by means of a rheostat. The current was measured by observing potential drop across a low resistance shunt with a Type I< potentiometer. The view of the filament through the windows of the burner house was restricted by a screen and collimator tube. The area observable was approximately 1/64 square inch. The lamp was supported on a stand with micrometer motion through two degrees of freedom parallel to the window of the burner box. The st,andard Leeds Br. Northrup optical pyrometer x a s supported on a similar stand a t the opposite end of the box. Light absorption a t 6500 A. by the glass window a t the end of the box next to the pyrometer was measured as a function of temperature. Calibration data for the T-24 lamp were then determined, in which brightness temperature of the lamp, as observed through the two windows of the box with the burners unlighted, at various filament currents was measured in millivolts drop acros~l the measuring shunt. These temperatures were then corrected for glass absorption and the h a 1 calibration curve was obtained. The pyrometer and the auxilia,ry lamp Kere next adjusted so
1300 0.0
'
'
I
0.50
1.00
I
I
I50
HEIGHT ABOVL TIP
-
'
2.00
'
"
2.50 2.70
INCHES
Figure 8. True Temperatures as Function of Position in the Flame RESULTS AND COKCLUSIONS
The true flame t,emperaturesobtained by t,heKurlbaum method show a maximum near 1450" C. This agrees with data obtained by Kurlbaum and others on similar flames, but is probably lower than the true maximum temperature in the flame. This is undoubtedly true since t,he optical path through the flame includes carbon particles which are a t much lower temperatures, as shown by the work on temperature gradients. FIoviever, other work indicates that the interior of the flame is poor in carbon and hence the majority of the elementary radiators may be within the
January 1951
c
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
thin laminar flame wall which would not diverge too greatly from the maximum flame temperature. I n conclusion, the carbon black flame is a region of ovoidal cross section, bounded by walls of high temperature flaming gases, whose interior is a preheating and cracking zone for hydrocarbon gases, diluted by products of combustion and hydrogen. The flame, used in this research, burning 44 standard cubic feet per tip per 24 hours through a 0.044-inch slot a t a tip height distance of 2.75 inches ranges in thickness from 0.25 t o 0.48 inch and in width, from 0.85 inch a t a height of 0.25 inch above the tip, through 1.20 inches a t 1.25 inches to a width of 1.50 inches at a point of 0.05 inch below the channel. The temperature gradient data together with visual observation show that the flame may be divided into three more or less diffusely defined regions. T h e bottom part of the flame, near the tip and the interior of the flame generally, consists of a lower temperature region wherein little carbon exists and in which gas phase primary reactions of the hydrocarbons may be taking
181
place. The temperatures in this region range from near 500“ to near 1000’ C., the higher temperatures being nearer the channel. The second zone, that of incipient carbon formation, surrounds this inner portion, being rather thin toward the bottom outer edges of the flame. This secondary portion blends into the bright reddish yellow top portion of the flame whose temperatures range around 1450’ C., in which the soot density is quite high and in which, evidently, the majority of the carbon-forming reactions occur. LITERATURE CITED
(1) Bone, W.A.,and Townend, D. T. A., “Flame and Combustion in Gases,” London, Longmans, Green & Co., Inc., 1927.
(2) Hottel. H., and Broughton, H. F., IND. ENQ.CHEM.,ANAL.ED.,4,
166 (1932). (3) Ihid., p. 167. (4) Kurlbaum, F., Physik. Z.,3, 187 (1902). (5) Lewis, B.,and Von Elbe, G., “Combustion, Flames and Explosions of Gases,” Cambridge, Cambridge Press, 1938. (6) Wiegand, W. B., IND.ENG.CHIM., 23, 178 (1931). RECEIVEDJuly 3, 1950.
Evaluation of Fuels Using the Jentzsch Ignition Tester
I
RUTH B. GILMER AND HARTWELL F. CALCOTE Experiment Incorporated, Richmond, Vu. I n the search for a small scale laboratory method for Otto cycle fuel evaluation, the German Jentzsch ignition tester was examined with respect to pure fuels, mixtures, and additives. The results of these tests were then correlated with the critical compression ratios found in the literature. In general, the variation in engine conditions has a greater effect on the correlation than the difference aooredited to the Jentzsch tester. The observations may be rationalized by comparing them with a pressure-temperature ignition diagram where in this instrument the pressure is simulated by oxygen flow. As a means of attaching a single number to a fuel to indicate its tendency to knock, the Jentzsch ignition tester is as adequate as any single engine test. I t therefore offers a simple and inexpensive means of evaluating the knocking tendency of fuels.
equation with “bubbles per minute plus one”-the “plus one” allows for the diffusion of air into the unit. After demonstrating the usefulness of wizardry, i t is possible, to a limited extent, to rationalize the principles involved with autoignition phenomena.
T
HE possibility of evaluating Otto cycle engine fuels without
*
h
actual engine tests has intrigued scientists for many yeare ( 3 ) . A simple test which could be carried out with small quantities of material would be especially valuable in research to appraise the usefulness of scarce new compounds and in routine control or testing of fuel quality. Such a test was invented in Germany by Jentzsch as early as 1926 (2) and used extensively by the Germans during the last war (7). This is attested by the large number of directives on the subject to the German navy and by the fact that the unit was evidently manufactured on a commercial scale. Nevertheless, fuel evaluation in this country is still carried out almost exclusively in standard test engines ( 5 ) . Although i t must be admitted a t the outset that any final conclusion as to a fuel’s utility must come from performance tests in the engine in which i t is t o be used, the advantages of the Jentzsch ignition tester as a practical tool cannot be ignored. Probably the greatest impedance to applying the Jentzsch ignition tester in this country is the apparent witchcraft involved in a method which plots bubbles per minute against temperature and then uses an
Figure 1. Jentzsch Ignition Tester
