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PHYSICAL AND CHEMICAL PROPERTIES OF FUEL OIL
Crude petroleum in its raw or unrefined state varies considerably in character and appearance, according to the locality from which it is obtained. Petroleum is a very complex mixture of organic compounds which are chiefly hydrocarbons, that is, compounds composed of hydrogen and carbon. Although the hydrocarbons are the chief constituents of petroleum it also contains in small amounts, sulphur, oxygen, and nitrogen. While petroleums from various sections of the country differ considerably in character, they may, however, be divided into three main classes:
1. Those in which the residue is predominantly paraffin wax.
The paraffin petroleums of the United States occur chiefly in the eastern part of the country. The asphaltic petroleums are found in California and in the Gulf region and the compound paraffinasphalt base petroleum is found generally in the mid-continent field.
It is possible to burn crude petroleum itself as a fuel and nearly one-fifth of the domestic consumption is thus utilized, but while the evaporative efficiency of crude and refined oil is practically the same no matter from what locality the oil may come, the danger of using crude oil is much greater than that of using fuel oil. The most of the petroleum produced in the United States is refined into a series of products. The four main products obtained through the distillation of petroleum in refineries are gasoline, kerosene, fuel oil, and lubricating oil. There are, of course, a large number of by-products obtained in the process of refining of which benzine, vaseline, paraffin, road oil, asphalt and petroleum coke are well-known examples. Table 5 gives analyses of typical American oils used as fuels.
When crude petroleum is distilled, the most volatile products are given off first. Gasoline, as the term is commercially used, covers those products which are more volatile than kerosene and includes, therefore, some benzine and naphtha. The next most volatile constituent of crude petroleum is kerosene, which is the common type of illuminating oil and is heavier than gasoline, but lighter than distillate which is taken out immediately after kerosene and can be considered a high grade special fuel oil. Under the heading fuel oil are included all of those distillates which are heavier than illuminating oils and lighter than lubricating oils. Fuel oil, therefore, includes gas oil. Gas oil is nothing more than a high-grade fuel oil which is used in the manufacture of gas. The term fuel oil also includes the residuum left after gasoline and kerosene only have been extracted from petroleum.
Inasmuch as the crude oils from different sections of the country vary widely in chemical composition, it is only natural to expect that the fuel oils obtained as a result of the distillation of these crude petroleums will also vary widely in ultimate analyses.
In purchasing fuel oil it is sufficient to specify the desired viscosity, specific gravity, flash point, calorific value, water content, and sulphur content. The specifications of the U. S. Navy for fuel oil at Atlantic and Gulf ports are:
"(a) Fuel oil shall be a hydrocarbon oil free from grit, acid and fibrous or other foreign matter likely to clog or injure the burners or valves. If required by the Navy Department it shall be strained by being drawn through filters of wire gauge having 16 meshes to the inch. The clearance through the strainer shall be at least twice the area of the suction pipe and strainers shall be in duplicate.
(b) The unit of quantity to be the barrel of 42 gallons of 231 cu. in. at a standard temperature of 60° F. For every decrease or increase of temperature of 10° F. (or proportion thereof) from the standard, 0.4 of 1 per cent (or prorated percentage) shall be added or deducted from the measured or gauged quantity for correction.
(c) The flash point shall not be lower than 150° F. as a minimum (Abel or Pennsky-Marten's closed cup) or 175° F. Tagliabue open cup. In case of oils having a viscosity greater
than 8 Engler at 150° F. the flash point (closed cup) shall not be below the temperature at which the oil has a viscosity of 8 Engler.
(d) Viscosity shall not be greater than 40 Engler at 70° F. (e) Water and sediment not over 1 per cent. If in excess of 1 per cent the excess to be subtracted from the volume or the oil may be rejected.
(f) Sulphur not over 1.5 per cent.
NOTE: If the Engler viscometer is not available, the Saybolt standard universal viscosimeter may be used. Equivalent viscosities:
300 seconds Saybolt .1,500 seconds Saybolt"
VISCOSITY OF FUEL OIL
The viscosity of an oil is inversely proportional to its fluidity, and is a measure of the internal friction in the oil itself, that is. of its resistance to free flowing. Inasmuch as there are a number of different instruments for the purpose of measuring viscosity, and since there is no recognized standard instrument or method of measuring it, the term "viscosity" means nothing unless there are also stated the name of the instrument used, the temperature at which the viscosity was determined, and the amount of oil tested. The viscosity of an oil is generally stated as the time in seconds required for a given quantity of the oil in question to flow through a small orifice at the stated temperature. It can be stated as the ratio of the time of flow of the oil being tested to the time of flow of water or some oil chosen as a standard at a stated temperature. Common types of viscosimeters or instruments for measuring the viscosity of oil are the Engler, Saybolt and Tagliabue. In stating viscosity the name of the instrument used should always be given. Figure 4 shows a Saybolt viscosimeter. The tentative test for the viscosity of lubricants adopted by the American Society for Testing Materials is as follows:
1. Viscosity shall be determined by means of the Saybolt Standard Universal Viscosimeter.
2. (a) The Saybolt Standard Universal Viscosimeter is made entirely of metal. The standard oil tube J is fitted at the top with an overflow cup E and the tube is surrounded by a bath L. At the bottom of the standard oil tube is a small outlet tube through which the oil to be tested flows into a receiving flask R,
a. Reprinted by permission.