extent as marine fuel, namely, the danger of carrying an inflammable oil, giving off volatile gases at a low temperature in bulk at sea. The use of petroleum for steam fuel is determined by its cost relative to other kinds of fuel. With the low price of petroleum at Baku and the absence of wood and coal on the steppes of Russia and the shores of the Caspian sea, there can be no question that petroleum is the cheapest and best fuel to be had in that region. In fact, the Baku oil fields have created the FIG. 235. DIL AIR Caspian fleet. But in the United States the question lies between petroleum and anthracite coal for ocean steamers, and bituminous coal on the western rivers, and while there may be circumstances under which the increased cost of firing with petroleum would not be a valid objection to its employment, a considerable increase in the use of petroleum for marine purposes in the United States cannot be looked for in the near future. Bidle's pan furnaces, figs. 235, 236 and 237 were constructed, in 1862, in North America, and designed especially for marine boilers. They consist of an iron box cast in one piece, and at the bottom. The latter slants slightly backwards and is provided with grooves radiating from the centre, see ground plan (Fig. 237), which ensures an equal distribution of the oil. A pump sucks the oil from storage-tanks in the bilge, and forces it into a box over the boilers. From this box it is conveyed through a pipe along the outside of the front wall of the boiler, and it then runs through branch-pipes into the separate furnaces. These branch-pipes enter in the centre of the firebox, and immediately below their mouths are surrounded by an iron basket filled with red hot coal or coke, which serves the purpose of igniting the oil. The oil that escapes ignition runs into the grooves, where it is burned. Small apertures (Fig. FIG. 236. 236) in the bottom of the fire-box, in the immediate vicinity of the entrance of the oil, were provided for the purpose of admit ting sufficient air for perfect combustion, but were found to be insufficient and large volumes of smoke were the result. FIG. 237. Bidle blew in more air by introducing fans and increasing the number of apertures. Combustion was thereby improved, but the entire arrangement became too complicated by the fans which required special steam engines. FIG. 238. Shaw and Linton's furnace, patented in 1862, in the United States, is designed for locomotive and machine boilers, and forms the transition from hearth furnaces to gas furnaces. As shown in Fig. 238, the crude oil passes from a holder placed at a higher level into a tank in the furnace, and flows on to the fire-plate A, previously heated by a wood or coal fire. The lighter oils vaporize and pass at B from the tank into the firebox, where they are consumed. The non-vaporized oil runs into the vessel C secured below A, which is heated to a greater temperature, and here the heavier oils are vaporized. The residue remaining non-vaporized passes through the opening D to the floor of the furnace, the grate of the latter having been removed and replaced by a cast-iron plate provided with depressions. The residue is burned upon this plate. Alongside the oil supply-pipe enters a pipe for the introduction of air. This mode of firing was defective in that the quantity of oil vapors evolved could not always be brought into accord with the amount which could be consumed, and to avoid explosions a safety-valve for the escape of the excess of hydrocarbons had to be placed upon the furnace. During the trials made by Shaw and Linton with a marine engine, the oil was forced by a pump from tanks in the bilge into a holder placed over the boiler. Draught was promoted by a jet of steam blown into the furnaces. To produce this jet of steam a subsidiary boiler was heated with anthracite coal before the generation of steam commenced in the main boiler, twenty-eight minutes being required for the latter purpose with crude oil or residuum, and sixty minutes with coal. 2.2 pounds of crude oil or residuum. evaporated 22.79 pounds of water, while the anthracite, it is claimed, did not evaporate more than 11.2 pounds of water. The temperature of combustion was so great that the chimney became red-hot about twelve inches from its base, which proved that the heating surface was too small for the perfect utilization of the heat. The introduction of this apparatus had to be given up on account of the large working expenses it entailed. Lenz's new slit sprinkler. To make this apparatus more suitable for locomotive and marine boilers, the straight slit-like mouth has been replaced by a circular aperture running round the cylindrical chamber, which insures a circular flow of the oil-spray. In order to obtain a flame spreading more upward and downward, as shown in Fig. 239, the tongue also had to be somewhat modified. FIG. 239. 1:20 In all other respects the sprinkler is arranged like that described on p. 618. By these improvements the usefulness of Lenz's sprinkler has been considerably extended; it is, however, also more expensive and less simple. Spakowski's nozzle-sprinkler. This apparatus, Figs. 240 and 241, was first used in 1870, for marine boilers. It has since been much improved, and its present simple form has been applied to four steamers built in 1879 and 1880, for the Caspian Sea trade. The liquid fuel, in this case illuminating oil residuum, flows out of the inner nozzle, which protrudes about one FIG. 240. OIL RESIDUES FIG. 241. millimeter into the mixing pipe (Fig. 241), while the steam issues from the annular aperture surrounding this nozzle. |