Fuel fuels that are available for use in the Diesel engines fall into three groups. The first includes those hydrocarbons of the paraffine, olefiant and acetylene series, such as are familiarly known as the petroleum oils, the principal family being the paraffine series The second group covers the liquids known as benzol derivatives, such as coal tars. The third group is composed of the many vegetable oils containing hydrocarbons, such as peanut oil, palm oil, cocoanut oil and oils from other tropical and sub-tropical vegetation. The last group, up to the present time, has not been used commercially since their cost has been far above that of the petroleums. The coal tars are employed to a considerable degree in Europe; Germany, especially, has given much attention to the adaptation of the Diesel to these oils. The increasing favor of the tar oils has been largely induced by the low cost of these oils and by the import duty laid on the petroleum oil's; in Germany the import duty is equal to the cost of the fuel delivered at the wharf.
In the United States no fuel other than the petroleum oils has found favor; this is attributable to the low price and convenience of these oils. Some speculation has been indulged in as to the advisability of using the American tar oils. However, this will be unnecessary for many years to come. Table IV gives the production of crude petroleum for the years 1916 and 1917. Approximately 40 per cent., or 150,000,000 barrels, of this oil remains after the gasolene, kerosene and light distillates have been distilled off. These heavy residual oils are marketable as road surfacers, boiler fuel and Diesel fuel oils. Since the Diesel plant can offer a higher price than is justified by the boiler plant, all this oil may be regarded as a potential Diesel supply. The total of 150,000,000 barrels would furnish fuel for more than 10,000,000 h.p. on a 24-hour service. This is many times the total Diesel installation in America.
Furthermore, the Mexican oil fields are of vast productive possibilities. The many internal disturbances in Mexico have served to limit the output; this will be overcome in the near future, and vast quantities of Mexican crudes will be on the market. These oils offer but small inducements to the refiner since they carry very low percentages of the lighter distillates. The Mexican oils are marketable only as boiler fuels and Diesel oils. Their employment in a Diesel entails more attention from the engine operator than do the higher gravity oils of the United States. There is no constructional grounds for ignoring the
Mexican fuels when the supply of the American oils is depleted.
Of the petroleum oils of the United States those of the Eastern and Midcontinental fields prove the most satisfactory in Diesel operation. This is a generality, however, and oils from wells in the Southern Texas fields, where the fuel is somewhat similar to Mexican crudes, give excellent results. The Diesel plant can purchase oils covered by rigid specifications, but the only positive way to determine the suitability of an oil is to run a test. It is of no advantage to test a single barrel since no engine will reveal the objectionable features of a fuel on a one-barrel test. The lowest quantity to experiment with is at least ten barrels.
The petroleum oils on the market as Diesel fuels range from South Texas and Mexican crudes, which contain too small a percentage of gasolene to justify distillation, up to 40° dis tillate, which is actually a low-grade kerosene. Most Diesels are burning fuel oil from 20 to 30° Baume, which is a residue left after the gasolene and kerosene constituents have been distilled out of the crude and which has been filtered to remove the dirt. -This oil ordinarily is desulphurized, which process eliminates practically all the sulphuric acid which was introduced in the distillation. This fuel oil has a varied color, ranging from light yellow to a deep black. The color is no criterion of the gravity of the oil, the crudes of various fields diffeiing widely in color.
The Diesel fuels fall under the following grades: Stove Oil, Solar Oil, Gas Oil, Distillate, Fuel Oil, Diesel Oil, Desulphurized Fuel Oil, Crude Oil, Tops.
Stove a trade name attached to a low-grade kerosene from 39 to 44° Baume gravity. The oil is ordinarily of a yellow-white color having a dirty appearance. It is quite serviceable for a low-compression engine but cannot be termed a desirable Diesel oil since it flows very readily and will pass the injection atomizer disks without being broken up. Blowing into the cylinder ahead of the air, it produces severe preignitions. It is of advantage only as a starting oil that can be used in cold weather for the purpose of warming the engine before the heavier fuel oil is introduced. It constitutes a serious fire hazard if any large quantity is kept on hand. Its price, which averages 2 to 4 cents above fuel oil, would make its adoption inadvisable even if it were an otherwise desirable fuel.