Solar Oil.—This is a trade name covering some of the lighter grade distillates and may vary over a wide range in gravity from 36 to 42° Baume. Like stove oil, it cannot be classed among the desirable fuels and should be used only where frequent starting and stopping arc usual, such as in a Diesel-engined tug. Serious preignitions are of frequent occurrence with this fuel. Its price is usually some 2 cents per gallon above fuel-oil quotations.
Fuel Oil.—This term covers all oil residue that remains after distillation has removed the gasolene, kerosene and light dis tillates. Dependent on the particular crude, the fuel oil may vary in gravity from 20 to 32° &time. In practically all cases it is black in color, though some of the Eastern oils have a light color, as also have certain North Texas fuel oils. When properly filtered, etc., it is the most desirable fuel that can be purchased. Since all the light volatile gases have been removed, there is no preignition danger. It is low in price in comparison with either crude or the light oils.
Gas Oil.—After the kerosene, gasolene, etc., have been re moved, if the distillation temperature is sufficiently increased, all the remainder of the crude will distil over, with the exception of a heavy tarry portion which is sold for road surfacing. These heavy distillations are called gas oils and are sold for Diesel consumption. They are superior to the fuel oils, being free from asphaltum residue, but their price, which is above that. of fuel oil, somewhat limits their application.
Diesel Oil.—This is a refinery trade name for a filtered fuel oil. It is sold at a slight advance over the unfiltered fuel and has a ready market in the Midwest. For small plants where no filtering apparatus is installed it is the fuel that should be purchased.
Desulphurized oil is, as its name indicates, a fuel oil which has been desulphurized. As customarily sold, the fuel contains a considerable percentage of distillates. Its use, in preference to fuel oil, cannot well be recommended since it is sold at a considerable advance in price.
Distillate Oil.—The distillate oils range in gravity from 30 to 39° Baum& They have a yellow-green tinge and are the products of a distillation, being vaporized at a higher temperature than is kerosene or stove oil. They are ideal fuels for hot-bulb engines, but the price is entirely too high to be attractive for Diesel use.
Tops.—Topped oil is the residue after the gasolene has been removed. It is not commercially offered in any but limited quantities and can be ignored in making a test of Diesel fuels.
Crude Oil.—Within this class fall all crude oils which have undergone no process of distillation and which are marketed as they come from the well. With the exception of some South Texas and Mexican crudes which do not justify distillation, no crude can be obtained save in limited quantities. In some locali ties the owners of small wells sell the raw crude to the local plants. Since the range in the character of oils forming the crude is great, it is not a desirable oil. The gasolene content becomes a fire hazard that cannot be ignored. The functioning of the engine on the crude is by no means perfect. The Mexican crudes do not carry such a range in hydrocarbons and perform fairly satis factorily if the engine's fuel nozzle and combustion chamber are designed to atomize and mix the air and fuel in an efficient man ner. It is essential that the heavy crudes be heated; a tempera ture of 150° can exist in the fuel line without a fire hazard, being present. The pump, however, must have its suction under a pressure head to avoid the creation of oil vapors during the 'pump suction stroke.
Specifications.—The following specifications are quite broad and cover all oils that can be successfully burned in the Diesel engine, A few plants may be using oils of a heavier character, but investigation ordinarily will prove that the operation is not entirely satisfactory.