November, 1928
I N D L S T R I 9 L AA-D ENGINEERING CHEMISTRY
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1219
Auto-Ignition Temperatures of Liquid Fuels’)’ Oscar C. Bridgeman and Charles F. Marvin, Jr. BCREAUO F STANDARDS, WASHINGTON, D. C.
UTO-IGKITIOS temThe published data of more than thirty observers t u b e m e t h o d ; t h e bomb p e r a t u r e s of liquid on the ignition temperatures of liquid fuels by four method; and the method of fuels have been studied type methods are considered with respect to the followa d i a b a t i c compression, A b y n u m e r o u s investigators ing experimental variables: material and volume of classified s u m m a r y of t h e during the past fifteen years ignition chamber, concentration of oxygen in the inmethods used by the different with reference to one or more flammable mixture, time lag before ignition, pressure, i n v e s t i g a t o r s is shown in of thefollowingproblenis: (a) and composition of fuel. Certain trends are noted, Table 11. I n these methods determining the suitability of but in general the values reported depend on the t h r e e c r i t e r i a have, been specific method and apparatus used. Results on gasochosen for indicating the igfuel oils for use in Diesel lines obtained at the Bureau of Standards by a bomb n i t i o n point-namely, inengines, (b) estimating the method are no exception. Analysis of the mechanism flammation of the mixture, tendency of automotive fuels to pre-ignite in the engine, of ignition indicates that heats of reaction and heat the sound of an explosion, ( c ) evaluating the effect of transfer are of fundamental importance in the interand the rapid rise in pressure pretation of ignition temperatures. It is pointed out of the system. It seems reaknock-suppressing a n d knock-inducing agents on the that the usual methods of measuring ignition tempersonable to assume that these tendency of fuels to pre-ignite atures involve considerable time lag and that any such three phenomena may occur or detonate in the engine, and method, if standardized, would serve to indicate relaalmost simultaneously. (d) specifying temperatures tive fire hazard from spontaneous combustion. A Among the factors recogabove which various combus“true ignition temperature” which is a property of the nized as having a significant tibles will constitute a fire or fuel is defined and means for its experimental determieffect upon the ignition temexplosion hazard from the nation are suggested. This is believed to be the autoperatures measured are (1) s t a n d p o i n t of spontaneous ignition temperature of most interest in connection material of the igniting vessel combustion. with automotive fuels and their relative tendency to or igniting mechanism, (2) The investigation of these pre-ignite and detonate. volume of the ignition chamber, (3) concentration of oxyproblems has been conducted with such variety of apparatus and method that its chief gen in the inflammable mixtures, (4) time lag before ignition, contribution has been t o indicate the complexity and the (5) pressure, and (6) composition of fuel. Although the effect multitude of variables involved rather than to establish of one or more of these variables has been studied by most of definite ignition temperatures. The lack of agreement of the investigators, no one investigation has covered the effect of the experimental data is very marked, even for pure sub- all of them. Hence the value reported for the ignition temperstances, and’is well illustrated in Table I, where values are ature of any substance depends on the specific apparatus and given for the ignition temperature of benzene as reported by method used. This means that no common basis appears different investigator;. A review of the published data to have been established which will permit a quantitative concerning the effects of certain factors on experimentally comparison of either absolute or relative values found by determined ignition temperatures, together with a brief various observers for the ignition points of different subdescription of some preliminary measurements made a t the stances. Each of the six variables will be discussed in turn Bureau of Standards by the bomb method, are presented. on the basis of such experimental evidence as is found in the These are analyzed from the point of view of the phenomena literature. involved in the ignition process, and the significance and ap~ I A T E ROF I AIGNTIKG L VESSELOR IGNITING ~IECHANISMplication of ignition temperatures are discussed. A bibliog- The effect on the ignition temperature of the material conraphy of the literature is included a t the end of the paper. stituting the igniting vessel is inconclusive. Csing 24-1111. crucibles of various materials, lIoore4 found that the ignition Table I-Ignition Temperature of Benzene temperatures of a gasoline in oxygen were practically uninOBSERVER AIR OXYGEN OBSERVER *IR fluenced by the crucible material, diereas, on the other hand, c. c. c. c. 740 662 the Underwriters’ Laboratoriesl4 found an appreciable difHolm 520 Tausz and Schulte Moore 620 Masson and Hamilton 656 .. .. . ference for a gasoline in air when using 160-ml. conical flasks Wollers and Ehmcke 570 Egerton and Gates 700 Jentzsch . 580 Tizard and Pye 3iob . . of various materials. With a closed tube 4 em. in diameter, Underwriters’ LaboraMcDabid 1062 . . White and Pricez0 studied the effect of inserting various tories 500a Ormandy and Craven . 639 metal sleeves and found practically no difference in the iga Report on Propagation of Flame, October 1, 1919. nition temperatures of a 4.3 per cent mixture of ethyl ether b Quoted by Egerton and Gates. with air. I n opposition to this, Egerton and Gates” inserted various metal disks in the bottom of a 65-ml. silica Previous Work crucible and found considerable effect on the ignition temA study of the previous work shows that four types of peratures of a gasoline in air. These investigators also foulld methods have been employed, which may be designated as that insertion of glass wool around the sides of the silica the crucible method, both dynamic and static; the dynamic crucible raised the ignition temperatureof a gasoline in air 1 Presented as a Dart of the Svmuosium on Combustion before the from 405” to 5%” c. Of interest in this connection is the . joint meeting of the Divisions of Gas and Fuel Chemistry and Petroleum work of White slid Prices2 on the ignition of soap bubbles Chemistry a t the 76th Meeting of the American Chemical Society, Swampcontaining a 4.9 per cent mixture of ether with air by means Scott, Mass., September 10 t o 14, 1928. of an electricalb’ heated platinum Spiral which was Cali2 Publication authorized bq- the Director of the Bureau of Standards of the Department of Commerce. brated by means of molten salts. They found the following
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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
I220 ~NVESTIGATOR
Factory Mutual Underwriters' Laboratories
T a b l e 11-Methods Used for M e a s u r i n g Ignition T e m p e r a t u r e s of L i q u i d F u e l s MATERIAL VOLUME GAS TIME LAG CRUCIBLE METHOD, STATIC Steel 1270 ml. Air Tin 1270 ml. Air ... Glass Air 160 ml. Varying Glass Air 300 ml. Varying Iron Air 160 ml. Varying Copper Air 160 ml. Varying Quartz Air 160 ml. Varying Platinum Air 1 sec CRUCIBLE METHOD, DYNAMIC Porcelain ... Air Platinum ... 0 2 and air ... Xickel ... Air ... Porcelain Air ... Platinum 0 2 a n d air Max. ii'ml. Nickel Max. 9 ml. 0 2 Steel Max. ... 0 2 Silica Max. 0 2 Porcelain 0~. 9 Max. Steel ... 0 2 ...
...
Masson and Hamilton
...
Holm Constam and Schlapfer Moore
Wollers and Ehmcke Jentzsch Ormandy and Craven
...
...
Steel Iron Iron
White and Price
0 2
16 ml. 25 ml. 24 ml. 51 ml.
i
Soap bubble Soap bubble
hfason and Wheeler Tausz and Schulte Neumann
Quartz Iron Iron Steel
Tizard and Pye
Iron
...
effect of time: 20 minutes after calibration, 968" C.; 3 days afterwards, 985' C.; 3 weeks, 1040" C.; and 20 minutes after recalibration, 970" C. Any conclusions which might be drawn as to the-effect of material are largely vitiated by failure to maintain the same time lag before ignition in each case. A tabular summary of the results obtained by the above investigators is shown in Table 111. VOLUMEOF IGNITION CHAMBER-The investigations of Ormandy and Craveng with steel crucibles, of the Underwriters' Laboratorie~l~ with conical flasks, and of White and Pricez2with soap bubbles seem to be in agreement in indicating that increase in volume decreases the measured ignition temperature. On the other hand, in some experiments by White and Pricez0on ignition in closed glass tubes of various diameters, i t was found that with increasing diameter the temperature decreased a t first and then increased. The observed effects of volume are given in Table IV. I n the dynamic tube method change in diameter of the tube would introduce another effect, velocity of flow. With a single tube White and Pricez0found that increase in flow increased the observed ignition temperature of a 14 per cent ether-air mixture. OXYGENCONCENTRATION-Alarge amount of work by a considerable number of men has shown that ignition temperatures in air are in general very much higher than in oxygen. Moore4 studied the effect of adding carbon dioxide to oxygen, MOORE Platinum Nickel Silica Porcelain Steel
c. 284.5 282 279.5 284 281
Gasoline in oxygen Values for maximum time lag Crucible 24 ml. capacity Oxygen flowing
and air
0 2
Air Air Air
1 iS 'ml. TUBE METHOD, DYNAMIC 2 cm. diam. Air 4 cm. diam. Air 5 . 6 cm. diam. Air Air Air Air BOMB METHOD 3.7 cm. diam. Air 2.5 cm. diam. Air 3.7 cm. diam. Air 5 . 0 cm. diam. Air 85 ml. Air Air 25 ml. Air 10 ml. Air ADIABATIC COMPRESSION ... Air
Glass 1 Copper I Iron Lead Zinc J Galvanized iron
McDavid White and Price
0 2 0 2
PRESSURE Atm. Atm. Atm. Atm. Atm. Atm. .4tm. htm.
YEAR
190; 1927
IIILi
1013 1913
Atm. Atm. Atm. Atm. Atm. Atm.
1017
1!l20
...
0 2
38 'ml .
Steel Steel Iron
Tausr and Schulte Tanaka and Nagai General Electric Egerton and Gates Weerman
'
Vol. 20, No. 11
Max. Max. Max.
... ... ... ... 1919
Max. Max. Max. Max. Max. Max.
