Novemher, 1924
INDUSTRIAL AND ENGINEERING CHEMIXTRY
1163
Determination of Dilution of Crank-Case Oil' By H.H. Knoch, P. A. Crosby, and R. R. Matthews ROXANAPETROLEUM CO.,ST. Lours. M O .
HE question of dilution of automobile crank-case oils has grown to large proportions, especially in recent years, and its importance to the automotive engineer as well as to the lubrication engineer cannot be overestimated. This problem is present a t all times, but it is especially troublesome in cold weather. Some of this trouble is due to mechanical difficulties inherent in the motor itself after a certain mileage is attained; a large part to the excessive use of the choke, especially in extreme cold snaps; and possibly, as some authorities persist, to the oil itself. The problem, therefore, is of decided interest, not only to the automobile manufacturer, but also to the refiner who produces motor oil. Up to the present time no quick and accurate determination of crank-case dilution has been developed. The lowering of the flash point of the oil in the crank-case and the change in specific gravity are indications that have been used with a measure of success. The determining factor is the change in viscosity, which, if reduced too low, may cause excessive wear of the motor. Since change in viscosity is directly dependent on the dilution with the so-called heavy ends of the gasoline, a determination of the amount of dilution is of interest and importance. I n casting about for a method of determination of crankcase dilution, the use of a vacuum distillation seemed most likely to give accurate results, and this paper shows results of using it in two different ways.
T
APPARATUS AND OPERATION The general outline of the vacuum distillation apparatus for use in connection with the distillation of petroleum is shown in Bulletin 207 of the Bureau of Mines. Some slight changes have been made to adapt the apparatus to the particular purpose of dilution determinations. The most important change is the substitution of a straight tube for the coil condenser. The apparatus as used consists of a Hempel flask, an accurate thermometer, a condenser, a glass receiver, a container of sufficient size to maintain a steady vacuum, a manometer, a vacuum pump, and motor. The automatic vacuum control, described in the bulletin, is used for maintaining a constant vacuum. All connections are sealed with a litharge and glycerol mixture. The top of the glass jar is put on with a mixture of melted rubber and petroleum jelly. The charge of 100 cc. of oil is carefully measured into the Hempel flask before the joints are sealed. After the pump is started, a vacuum of 40 mm. is maintained for our particular use. If some other point is chosen, care must be exercised in maintaining that point constant. After the vacuum has become established, the oil in the flask is heated by means of a gas burner, electric heater, or any available source of heat which will bring the oil to its initial boiling point. The method in use a t this laboratory is to determine the initial boiling point a t the time when the first drop of oil falls from the end of the condenser. This method of determination of dilution requires a knowledge of the initial boiling point of the motor oil before use in the crank-case. It is, therefore, advisable to run the initial boiling point of all oils in which the refiner is interested and
to record them for future use. As long as one is sure that the process of manufacture remains the same, it is not necessary to obtain this preliminary reading at each determination, but checks should be run occasionally, or if there is any doubt in the matter.
FIRSTMETHOD For the used crank-case oil, two general methods have been used. The first method in use is to introduce the measured quantity of oil into the Hempel flask and proceed exactly as in the determination of the initial boiling point on a fresh oil. The vacuum is kept at the chosen point and distillation continued until a temperature has been reached equal to the initial boiling point of the oil before it was used in the crank-case. The residue is permitted to cool in the vacuum and finally the flask is brought to atmospheric pressure. The residue is carefully drained from the flask and measured a t the temperature a t which the oil was introduced. The difference gives the amount of dilution, which can then be readily calculated as percentage of dilution by volume. SECOND M E T H O D
The second method is to introduce into the glass receiver a tray of graduated test tubes, which can be turned to receive various fractions of the oil as they come from the condenser. A larger quantity of oil is desirable, however, when this method is used. The general procedure is identical with the previous determination, except that the distillate is caught and measured in fractions and heat is applied until a vapor temperature beyond the initial boiling point of the original oil has been reached. The residue in the flask is measured after cooling, its specific gravity read and adjusted with some of the last portions of distillate so that the specific gravity of the oil is the same as before use. Tests of the individual fractions or the total amount of diluent can be made if it is desired to know their characteristics. The percentage of gasoline present, as well as that of kerosene, can be determined. Such determinations would necessarily be made with a larger quantity of oil or by means of two or more distillations.
CHECKS I n order to check up on the accuracy of the first method, samples of lubricating oil were diluted with known quantities of gasoline and kerosene. The recovery in all cases was within an experimental error of 1 per cent, which is probably the best accuracy that could be expected with the method. It has been found that the two methods will check fairly well with each other, and owing to the simplicity of the first method it is generally used. However, if a very accurate result is wished, it may be best to use the second method. RESULTS The following results were obtained on motor oils made from Midcontinent crude oil: Sample of crank-case oil
Initial boiling point O F.
before the Division of Petroleum Chemistry at the 67th Meeting of the American Chemical Society, Washington, D. C.,April 21
500
to 26, 1924.
420
1 Preseoted
500 505
-PPR CENT DILUTIONFirst method Second method
8 15 20 15.4..
8.4 15.2 20.4 18.6
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