August 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY LITERATURE CITED
( 1 ) Barusch, M. R . , and Payhe, J. Q., IND.ENO.CHEM.,43, 2329
Barusch, M. R., Crandall, H. W., Neu, J. T., Payne, J. Q., and Thomas, J. R., Ibid., 43, 2761 (1951). (2) Burgoyne, J. H., Tang, T. L., and Newitt, D. M., Proc. Roy. Soc. (London),1 7 4 , 3 7 9 (1940). (3) Cullis, C. F., Hinshelwood, C. N., Mulcahy, M. F. R., and Partington, R. G., Discussions Faraday Soc., No. 2 , 1 1 1 (1947). (4) Hurn, R. W., and Smith, H. M., IND.ENG.CHEM.,43, 2788 (1951);
(5)
(6) (7)
(8) (9) (10)
(12)
Livengood, J. C., and Leary, W. A,, IND.ENG.CHEM.,43, 2797
(13)
Maccormac, M., and Townend, D. T. A,, J . Chem. Soc., 1938,
(14)
Milas, N. A,, and Surgenor, D. M., J . Am. Chem. Soc., 68, 205
(1951). p. 238. (1946).
Pastell, 0. L., S. A . E. Quart. Trans., 4 , 571 (1950). Petrov, A. D., “Dependence of the Antiknock Properties and Pour Points of Diesel Fuel Hydrocarbons upon Their Structure,” Translation 649, UOP survey of foreign petroleum lit(1951). erature (1946). Jentzsch, H., Brennstoff-Chem.,31, 255 (1950). (17) Spence, K., and Townend, D. T. A., ‘‘Third Symposium on ComJohnson, J. E., Blizzard, R, H,, and Carhart, H. w., J . Am. bustion, Flame, and Explosion Phenomena,” pp. 404-14, Chem. SOC.,7 0 , 3 6 6 4 (1948). Baltimore, The Williams and Wilkins Co., 1949. Johnson, J. E., Crellin, J. W., and Carhart, H. W., IND.ENG. (18) Townend,D. T.A., Chem. Revs.,21, 259 (1937). CHEM.,4 4 , 1 6 1 2 (1952). C., and Rifkin, E. B.,I N D . ENG. CHEM.7 439 2844 johnson, j. E., cre1lin, J. w,, and carhart, H. w., ~~~~l R ~ - (19) WalCutk (1951). search Laboratory, Rept. No. 3859 (Dee. 2 1 , 1 9 5 1 ) . (20) Walsh, A. D., Trans. Faraday SOC., 4 3 , 3 0 5 (1947). Jost, W., “Third Symposium on Combustion, Flame, and Explosion Phenomena,” pp. 424-32, Baltimore, The Williams and RECEIVED for review March 27, 1953. ACCEPTED May 20, 1953. Wilkins Co., 1949. Presented before the Division of Petroleum Chemistry at the 122nd Meeting, Levedahl, W. J., and Howard, F. L., IND.ENG.CHEM.,4 3 , 2 8 0 5 SOCIETY,Atlantic City, N. J. The opinions and asAMERICAN CHEMICAL (1951).
(11)
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Lewis, B., and von Elbe, G., “Combustion, Flames, and Explosions of Gases,” New York, Academic Press, Inc., 1951.
(15) (16)
sertions contained in this article are the private ones of the authors and are not to be construed as reflecting the views of the Navy Department or the Naval establishment at large.
Spontaneous Ignition of Lubricating Oils CHARLES E. FRANK’, ANGUS U. BLACBHAM2, AND DONALD E. SWARTS Applied Science Research Laboratory, University of Cincinnati, Cincinnati 21, Ohio
T
HIS paper summarizes a continuation of the study on spontaneous ignition phenomena previously reported (7).
Such information is of particular importance because ignition of lubricants by hot metal surfaces is considered to contribute materially t o the initiation of fires i n aircraft. Earlier work was concerned with the spontaneous ignition temperatures of pure compounds and the factors influencing these values. The present paper describes the investigation of various types of lubricants and potential lubricants, and gives further observations regarding the effects of structure, additives, and metal surfaces on spontaneous ignition temperatures (8).
slight shift i n the fuel-air ratio may bring about a relatively large shift in the observed ignition temperature. Accordingly, various charge sizes were tested at several air-flow rates to obtain as nearly as possible optimum conditions for ignition. I n this manner, good correlation between structure and spontaneous ignition temperature was obtained with pure compounds. This
APPARATUS AND PROCEDURE
The same crucible apparatus ( 7 ) was employed in the present investigation. This comprised a stainless steel block heated in an electric furnace, and containing a cavity into which ignition chambers prepared from various metals and alloys could be inserted; a stainless steel chamber was employed unless otherwise indicated. The procedure with the simple, volatile compounds involved heating the block to well above the ignition temperature then adding the material dropwise to the ignition chamber as the block slowly cooled. Throughout this earlier work, the size of charge was varied over a wide range to obtain the minimum spontaneous ignition temperature. The reason for this is apparent from a consideration of the general ignition curve shown in Figure 1. This curve represents the change in spontaneous ignition temperature with change in fuel-air ratio at a single pressure. With spontaneous ignition determinations which employ a single charge size for different compounds, it is difficult to obtain comparable results, as a 1 Present address, Research Division, National Distillers Products Corp., Cincinnati, Ohio. 2 Present address, Brigham Young Univeraity, Provo, Utah
1
w E
3
t
a
a W
n
I w
I-
FUEL/AIR ’
RATIO-
Figure 1. Typical Ignition Curve (1)
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correlation is substantially the same as that observed between structure and antiknock ratings, indicating the dependence of spontaneous ignition and knock on the same fundamental factors. COMPARISON O F DROPWISE- AND SPRAY-ADDITION PROCEDURES
PVhen attention was turned to the less volatile compounds of the lubricant class, it immediately became apparent that the determination of spontaneous ignition temperatures with these materials was not so simple or precise. This is, of course, the result of the higher molecular weights involved, and the correspondingly reduced vapor pressures. The effect of reduced vapor pressure had been noted in determining the spontaneous ignition
Vol. 45, No. 8
tion temperatures, as determined by dropwise addition, frequently fail to correlate with actual performance tests. It was hoped that the spray injection procedure might largely eliminate this difficulty. As the authors wished t c use the same ignition chamber as i n previous work and also to be able to test small experimental samples of material, the simple spray injector illustrated in Figures 2 and 3 was prepared. A hand-operated piston ejects the liquid through an opening 0.008 inch in diameter from a cylinder 0.125 inch in diameter. The piston is accurately machined to fit the cylinder well. The most critical part of the design is that of the nozzle, as it is somewhat difficult to obtain the desired spray with a small quantity of viscous oil. The nozzle illustrated performed well with as little as 5-mg. portions of a n SAE-30 oil. Results with liquids of higher viscosity were not satisfactory. As in the case of dropwise addition, the charge size in the spray injection was varied over a wide range to obtain the minimum spontaneous ignition temperature. If the effect of spray injection is simply that of overcoming vapor pressure limitations, then the dropwise and spray procedures should give identical results with readily vaporized compounds. It was important to check this situation before proceeding to the less volatile lubricants. These results are summarized in Table I. TT'hile the corresponding values are not identical, they are close enough to demonstrate the validity of the assumption. The slightly lower values obtained by the spray-injection procedure are consistent with the fact that all these compounds lie near the upper limit of precision for dropwise addition.
4-
S C A L E , INCHES
FRONT V l E W
Figure 2.
SIDE
VIEW
Assembly of Spray Injector Apparatus A. B.
C. D. E.
Handles Plunger Nozzle Graduations See Figure 3 for detail
temperatures of the n-paraffins in the C16 to Czorange ( 7 ) . These compounds gave a reversal in the trend of spontaneous ignition temperature vs. molecular weight a t about 16 carbon atoms and a n air-flow rate of 126 cc. per minute. The reversal there, hornyever, was very slight; similarly, with a n SAE-IO oil, the dropwise procedure also is fairly effective. With still higher viscosities-Le., molecular weights-the limitation of the dropwise procedure becomes much more apparent. Thus, a series of four conventional automobile oils of SAE-IO, -20, -30, and -40 viscosities had spontaneous ignition temperatures (dropwise addition) of 262', 372", 386", and 402"C., respectively. Here the values obtained appear largely as a function of viscosity, and apparently are meaningless in so far as any structural features are concerned. Similar results were obtained with other lubricants examined, including the polyethers and the polyethylenes (8). It was extremely significant, however, that the polyisobutylenes and their hydrogenation products gave high spontaneous ignition temperatures (mainly above 400" C.) throughout the complete molecular weight range investigated. From both a theoretical and a practical viewpoint, it appeared desirable t o employ a spray injection as a means of overcoming in so far as possible the physical limitations of the dropwise addition. Thus, by enhancing the effective vapor pressure, such a procedure should extend the correlation of spontaneous ignition temperature with structure to these compounds of higher molecular weight; furthermore, i t should more nearly duplicate an actual flying hazard-i.e., the spraying of oil from a punctured oil line onto a hot metal surface. It is known that spontaneous igni-
H--
L
-
0
Figure 3.
1/2 S C A L E , INCHES
DISC 2 __
1
Detail of Spray Injector Apparatus
Main housing for plunger and insert Plunger piston c. Insert D . Piston cylinder, 0.125 inch i n diameter E . Disk-retaining nut F. Teflon washers G. Asbestos packing H . Concave channel J . 7/18 inch i n diameter K . 1/18 inch thick L . Nozzle opening, approximately 0.008 inch in diameter A. B.
EFFECTS O F STRUCTURE ON SPONTAIVEOUS IGNITION TEMPERATURE
Figure 4 shows the spontaneous ignition temperatures obtained with the group of motor oils mentioned previously. Substantially the same values were obtained by both dropwise and spray procedures for the SAE-10 oil; a t a 125-cc. air-flow rate, however, the dropwise procedure gives a nonignition zone between 290' and 335". The values for the SBE-20 and -30 oils both were lowered about 100" C. by the spray injection. The
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butylene structure contains no tertiary hydrogens and only about
TABLEI. COMPARISON OF DROPWISE-ADDITION AND SPRAY25% secondary. All the other structures listed contain from 50% INJECTION PROCEDURES FOR DETERMINING SPONTANEOUSto substantially 100% secondary and tertiary hydrogens. As IGNITION TEMPERATURES Soontaneous Ignition
Compound Hexadecane I-Dodecanol Bi~(2-ethylhexyl)adipate Di-n-octyl ether
232 283 262 210
230 278 260 208
TABLE 11. SPOXTANEOUS IGNITION TEMPERATURES OF VARIOUS LUBRICANTS
Lubricant Paraffin and naphthene mixture (-CHz-)n Polyethylene
Approx. Primary C-H Bonds,
%
10 30
Ignition Residue Heavy lacquer Heavy lacquer
ca. 300
400
Lacquer burns away Lacquer burns away
ca. 350
1°. At a highair-
The values previouslj. reported bj. J;ickson ( I O ) fall in the same order as the authors, but in a much Ion-er temperature range. The major difference between the two procedures is Jackson's use of a 125-cc. quartz flask and the author's use of a 43-cc. stainless ' steel cup. The authors' higher values must arise partly from tht: larger surface-volume ratios in their apparatus and the resultant increase in chain-breaking reactions; the metal surface also would be expected to have a more pronouncedchain-breaking action than quartz ( 2 ) . It is significant, that t,he differences here are the largest found in comparing the spontaneous ignition temperatures obtained by these two different procedures; thus, results obtained with compounds igniting in t,he low t'emperature range (
