ployed, there being an additional arch of fire-brick brought forward from the bridge to prevent too early a passage of the gases among the tubes. The author would extend this (and also the first arch) further than shown in fig. 33, it being impossible either with coal or oil to secure smokeless results where the hydrocarbon Fig. 33. WATER TUBE BOILER WITHOUT GRATE gases pass too quickly among cold tubes. Nor is there space and time for such complete combustion with a minimum of fuel as is desirable. In fig. 34 is given a section of an oil furnace arranged with It is found that the position of the atomizer is important. If too high the combustion is vibratory, and an intolerable humming sound is Fig. 34. LIQUID FUEL BURNING LOCOMOTIVE WITH produced by the many rapid explosions due to non-continuous combustion. Mr. Holden lays it down that the oil fire must for the best results, and not too high above it. an oil burning locomotive at an expenditure Fig. 28. MACALLAN VARI- be along the plane of the coal fire The Cromer express is worked by of 190 gallons of tar residues of specific gravity 1.10. This is equal to 144 pounds of liquid per mile, in addition to about 6 cwt. of coal or 5 pounds per mile. Some 5 to 6 cwt. of broken bricks are spread on the grate for this journey of 138 miles in 175 minutes, the train of 17 cars weighing 271 tons empty, exclusive of the locomotive, which weighs 51 tons 14 cwt. 2 qrs., and the tender, which weighs 35 tons 17 cwt., the total weight being nearly 360 tons unloaded. Owing to its large proportion of hydrogen, the production of carbon dioxide is less, and this is held to be an advantage of liquid fuel for working tunnels, and the Arlberg tunnel is so worked by 32 engines. It must not, however, be overlooked that hydrogen destroys three times as much oxygen as is destroyed by a pound of carbon, and produces but little more calorific effect per pound of oxygen consumed, so that it is equally destructive of the vital properties of the air and introduces an excess of nitrogen in place of an excess of carbon dioxide. The physiological effect of the carbon dioxide is less to be feared than the absence of oxygen which it implies. Too much, therefore, should not be made of this supposed advantage of liquid fuel, the danger being due to the absence of oxygen. Locomotive Boiler. Fig. 35 is the fire-box used for liquid fuel on the Southern Pacific Railroad. the oil being sprayed into the front of the fire-box below the mud ring and under the usual brick arch and directed against a sloping brick lining of the back plate. The sides of the box are cased in bricks, and there are openings for air in the brick Fig. 35. BURNER LOCOMOTIVE FIRE-BOX FOR OIL bottom to admit air under the flame. A central brick arch baffle is thrown across the middle of the fire-box, and an arch is thrown across just below the fire-door. The plates of the upper part of the box are bare, and the results are said to be satisfactory. According to Mr. Holden the fuel supply should be above the level of the atomizers. This is a point with which all do not agree, as some consider that the fuel ought always to be pumped to the atomizers, and that no oil should be able to flow by gravity with the attendant risks in case of rupture. Unless there is an independent source of steam available, steam should be raised in the boiler by an ordinary fire until a pressure of, say, 25 pounds per square inch is obtained, when the liquid fuel apparatus may be started. All cocks and valves being closed, the cocks of the steam fitting connected with the fuel injector are to be first opened. The main liquid fuel cock on the tank may now be opened and the fuel admitted to the injector by slowly opening the regulating valve. To start with a clear flame, the incandescent fuel on the bars must be moderately bright, and not dull red. If coal and oil are to be burned, a thin bright fire should be maintained on the bars free from holes, and the corners and sides of the grate are to be kept well covered. If oil only is to be used, the remains of the lighting up fire should be gradually covered with broken fire-brick (about 2 inch pieces) keeping the base thus formed thinnest under the lines of jets from the injector, or say, at the centre of the grate; the sides and corners being closed round with small pieces of firebrick. As the fire-brick bridge or arch attains a red heat more liquid can be injected and less steam used. To shut off the apparatus the liquid fuel cock on the tank is first closed, then the regulating valve on the injector, and finally the cocks on the steam fitting are shut off. The oil burners must not be started before ascertaining that there is a flame in the furnace; if doubtful, a few pieces of wood or some oily waste should be set alight in the furnace before applying the oil fuel. The above rules are equally applicable to all systems of oil burning. A common danger with oil is the risk of gases accumulating in the furnace and leading to explosion when the dampers are opened and flame produced. As with coal, the accumulation of gas may be prevented by drilling a two inch hole near the top of the damper, so that when the damper is closed there is always a vent through it which will stop any accumulation of gas. United States Navy Tests. Special attention may be directed to Appendices 1, 2, 3, extracted from Rear Admiral Melville's Report of 1902 of the Bureau of Steam Engineering. Though the water tube boiler does not appear to be of the best design, it appeared to be satisfactory in its freedom from overheated tubes, and the same boiler was used both for coal and oil tests, and the tests were carried out by a disciplined body of men, and are good comparative tests. The summary of both coal and oil tests are given in these appendices, and as they cover a wide range, they may be studied with advantage. It is to be noted that the percentage of CO, in the chimney gases ranged from 7.15 up to 13-77 for coal and from 5.5 to 10-1 for oil. Oil was thus apparently inferior in respect of the proportion of excess air requi:ed, but it was also, as it ought to have been under such circumstances, superior in showing a less ratio of CO. This inferiority of oil is apparent only as shown later. Probably the combustion was more perfect in the furnace and the temperature higher with oil, for on the whole the chimney temperature was less with oil, as though the transmission of heat were more perfect, and the final boiler efficiency in terms of the percentage of fuel heat absorbed was thus about equal in each case. The furnace arrangements as shown by fig. 3, appendix 3, show that a large opening is provided for air in the front wall below the burning oil, and it may be suggested that the admission of air in large streams is equally undesirable as the same method with coal. Indeed, in the author's opinion, there is much to be said for the admission of air through a grate, well covered with sharply broken firebrick as in the Holden system of mixed coal burners. The air would become heated by its passage upwards through the broken fragments and finely divided. The area of this under grate need not be excessive. Probably it would be best kept short so as to admit air near the front of the furnace and so allow it the opportunity of mixing better with the burning gases above it. The furnace should be made. to secure the same sweeping action of all the gases in the furnace so as thoroughly to intermix them. In the detailed tables, which are too voluminous to reproduce, the proportion of air appears to be given at a lower figure than in the summary, some of the coal tests showing as little as 12-8, 13-2 and 14.4 pounds of dry air per pound of carbon, amounts which would point to absolute insufficiency when the hydrogen of the coal is taken into account. The discrepancy, of course, is due to the condensation and removal of the hydrogen, which leaves as a load upon the carbon that portion of the nitrogen which came in with the oxygen that disappeared in forming steam. As liquid fuel contains so large a percentage of hydrogen, the dry chimney gas from liquid fuel will contain an undue proportion of nitrogen, and the percentage of CO, in the chimney gases as shown in the summarized tables is made smaller in the case of both coal and oil, but the oil is the more affected, and columns 56 to 60 of the coal summary must not be compared with columns 44 to 48 of the oil tests summary. Pocahontas coal only averages about 4 per cent. of hydrogen and the New River coal under 5 per cent., these coals resembling Welsh smokeless to some extent. The oil, however, contains 12.41 per cent. of hydrogen as well as less oxygen. Calculation of Air. If the air for this fuel be calculated, it will be found as follows— Air required 317-44 × 4.32 = 1,371-34, or say, 14 pounds per pound of oil. The actual dry chimney gas per pound of oil is (2.22 × 4-32) + (0-9544 x 3-32) = 12.76 pounds. This cuts out the hydrogen and the oxygen it consumes, but leaves the nitrogen as a load on the carbon. The total dry gas per pound of carbon is thus 12-76÷ 0.8326 = 15-33, to which the pound of carbon itself being added gives 16-33 pounds of dry chimney gas, which may be laid down as the chemical minimum per pound of the carbon. The summary of the oil tests shows from 50 to 100 per cent. in excess of this in column 48. As, however, some of the nitrogen has come in with the air to satisfy the oxygen, column 50 gives a more favourable appearance to this point. To the weight in column 50, however, we should require to add the water 3.83 formed from the hydrogen or (12.41- x09 1.07 pounds per pound of oil. = and this added to column 50, would give the total chimney gases per pound of fuel. Thus the analysis of chimney gas for CO, in the case of oil is deceptive unless account be taken of the hydrogen. We have found above that 13.71 pounds of air is the chemical minimum per pound of fuel of the order given. If to this we add 1 pound for the fuel itself and 0-266 to satisfy the sulphur, we find practically that 15 pounds of air is the chemical minimum for oil fuel. Column 50, if increased by the 1 pound for water formed, would vary between 21 and nearly 37 pounds of total products, the former representing an addition of 33 per cent. of excess air and the latter of no less than 133 per cent; but this was exceptional, and for No. 9 the test of a burner that was admittedly not perfected. Throughout all the tests a good deal of smoke was formed. This seems to point to too direct escape of the products of combustion, and there can be little doubt that a longer distance is required between the burners and the first contact with the cold boiler surfaces. Regarding the conclusions drawn, it is to be noted that the atomizing agent, whether steam or air, should be hot, and that high pressure steam is better than low pressure steam; also that the tendency is to force the oil forward at a considerable pressure to the burners and compel it to escape, by a fine opening, thereby probably tending to atomize itself somewhat. The practice in America generally is towards pumping the oil to the burners rather than allowing it to flow by gravity. It will also be noticed that air at a moderate pressure appears to be as competent to atomize oil as steam at a high pressure. No explanation of this is given. but it is partially due to the greater density of air and probably in part to the fact that air is a supporter of combustion and induces earlier combustion or ignition. The Meyer System: This is shown in fig. 36, and is a modification of the Körting system. Oil is supplied by the Körting system and air is admitted through specially placed blades in an extension of the furnace front, the air being heated in a surrounding jacket, which is arranged with spiral divisions. The air is delivered to the surface in a whirling manner, and the system has been two years at work on several Dutch |