FUEL OIL SPECIFICATIONS Heat Value.—Not less than 18,500 B.t.u. per pound. Contractor must give low heating value of the fuel supplied.
Gravity at 60° F.—With engines having closed fuel nozzles the oil shall not be heavier than 20° Baum& For engines having open nozzles the oil should not be heavier than 16° Baume. The oil should not be lighter than 36° Baum& Residue.—Not more than 10 per cent. The residue is that portion of the fuel remaining in the cup after being subjected to a temperature of 300° C. (572° F.) for 120 hours.
Flash Point.—From 125° to 250° F.—dependent on the engine.
Burning Point.—From 160° to 300° F.
Sulphur.—Not over 2.0 per cent.
Water.—Not over .3 per cent.
Ash.—Not over .05 per cent.
Heat Value of Fuel is self-evident that the oils having a higher heat value are more valuable than those oils with a low heating value. All other qualities being equal, the comparative values of two oils are in direct proportion with the ratio of their heating values. If oil of 36° Baume gravity having 18,000 B.t.u. per pound is quoted at $3.60 ppr 100 gallons or $5.12 per 1000 pounds, an oil containing 20,000 B:t.u. is equally attractive at $4.00 per 100 gallons or $5.69 per 1000 pounds. The policy of purchasing oil by the gallon is not to be recommended, although it is the custom to quote in this manner. Orders for oil should be placed on the pound basis since the heating value of oil is so com puted. Since the pounds per gallon of fuel •oil of 30° and 20° Baume are respectively 7.294 pounds and 7.777 pounds, it is apparent why the heavier oil is worth more per gallon.
usual method of indicating the weight of crude or fuel oil is by the Baume scale. The numbers of this scale are given by the formula: f 140 • Degrees Baume = 130 s.g.
where s.g. is the specific gravity, water being —1—. The specific gravity can be determined by a hydrometer. The gravity of a fuel, in itself, is of no vital importance; however, it can be generally employed as an indication of the oil's freedom from a large residue content and from a heavy percentage of the more complex hydrocarbons that are difficult to burn in a Diesel engine. Table V is a table of the relation of &tne gravity to
pounds per gallon.
Residue.—The residue that remains after an oil has been sub jected to a temperature of 572° Fahrenheit (300° Centigrade) consists of coke and dirt. The most serviceable oil is that oil which has the minimum percentage of residue. The coke will not burn at any temperature occurring in the cylinder. Pos sessing some of the characteristics of tar, it settles on the fuel and exhaust valve seats, resulting in leaks, and fouls the piston rings, freezing them in the grooves and thereby destroying the engine compression. Frequently the coke deposits on the cylinder walls, especially if there be any rough spots on the walls, with a scored piston as an immediate result.
The dirt also has a deleterious effect on the valves and piston. There is no excuse for any oil being dirty as filtering will remove all the dirt in suspension. While the upper limit of the dirt and coke is set at 10 per cent., a value of half this amount can well be adopted as the upper limit of the residue carried by the oil. For the purpose of removing any dirt, a filter such as is illustrated in Fig. 179 is quite satisfactory. This of a flanged tank carrying a brass cylindrical screen which is provided with a felt gasket at the base; the upper flange holds the screen against this gasket. Terry cloth is wrapped around this screen as indicated. The filter is fitted with a by-pass not shown. The large area of the terry cloth enables the filtering to be carried on at a slow rate. A 1000 h. p. filter, 12 X24 in. outside diameter, is required to filter gallon per hour per sq. inch of screen area; this gives a velocity of .4 inch per minute. The terry cloth screen may be of as many thicknesses as desired. Three folds ordinarily give ample filtering effect. To clean, the top flange is removed, the screen lifted out and new cloth wound on the screen while the dirty cloth is washed.