oil fuel is found to give better results than the coal previously used, and there is an accompanying saving in the cost of fuel of 40 to 60 per cent. Mr. Ropp gives the following reason for not employing oil in the blast-furnaces: " Solid carbon plays a very important rôle, especially in the upper level of the blast furnace shaft. Its function, especially with the fine ores, is largely to limber up the charge, and allow the flow of gas to penetrate the charge evenly; besides, incandescent carbon has certain functions to perform in the blast-furnace, which are of a chemical nature, and which need not be discussed. If coke or charcoal should be entirely replaced by oil in the blast-furnace, the blastfurnace charge would very likely become too dense to allow the combustion gases to escape freely."

In an article on the economic position of the oil-fuel question, published in The Engineer of 29th December 1911, Messrs. Sydney H. North and G. Maitland Edwards state that in the rolling mills of the Southern Pacific Railway works at Sacramento 40 gallons of crude petroleum are used to heat 2000 lbs. of scrap metal or pile, in place of 500 lbs. of bituminous coal formerly employed in a reverberatory furnace for the same purpose; that the output of the oilfired furnace is 20 per cent. higher than that of the coal furnace; and that there have been 50 per cent. less car-axles condemned since the adoption of oil fuel.

The earliest application of oil fuel for general heating purposes naturally was at the refineries where large quantities of residual heavy oils were available, and its application to petroleum distillation and steam-raising at the refineries and on local railways followed.

In Russia, where the petroleum industry has long since become mainly a great fuel industry, the development in the use of liquid fuel on the railways was mainly due to the initiative of Mr. Thomas Urquhart, who whilst locomotive superintendent on the Grazi-Tsaritsin railway demonstrated the merits of this fuel. Liquid fuel is not only employed as the source of heat in a large number of industrial establishments throughout Southern Russia, but is also used on the locomotives of the railway systems of that district and on the steamships on the Caspian Sea. It is also similarly employed in the Baku and Grozni oil-fields and refineries. Fig. 322 shows the details of an arrangement for burning liquid fuel, as applied to a steam-boiler for use in oil-fields, including the method of construction of the brick baffle in the combustionchamber.

In a paper read before the Institution of Mechanical Engineers by Mr. R. Godfrey Aston, the results of the working of oil-burning locomotives of the Baldwin consolidated type on the Tehuantepec National Railway of Mexico were given as follows:

Based on tests which have been made, the company reckoned that 31 barrels, or 147 United States gallons, of oil are equal to 1 short ton (2200 lbs.) of coal.

The fuel used by this railway company was purchased from the Texas Company of Port Arthur, Texas. The railway company stipulated in its contracts

with the Texas Company that the flash-point (closed) should not be under 110° F. The calorific value in British thermal units varied from 17,000 to 20,000.

In the Galician oil-fields, crude oil has largely replaced coal and wood for steam-raising purposes, and petroleum residuum and "blau " oil are used as fuel in several refineries and factories in Galicia. In Rumania a mixture of benzine and residuum was similarly employed. On the Arlberg railway in the Tyrol locomotives are being driven with liquid fuel.

In this country the principal exponent of the advantages of liquid fuel for

railway work has been Mr. James Holden, locomotive superintendent of the Great Eastern Railway, who commenced the use of fuel oil on this line in 1886, with a form of burner invented by him which is elsewhere described in this section.

In practice it has been found that one ton of oil is equal in thermal efficiency to about one ton and three-quarters of steam coal, and, although there is no doubt still room for improvement in the burning of liquid fuel, it does not seem reasonable to conclude that the steam-raising power of oil will ever much if at all exceed twice that of good steam coal. At present it may be taken that whereas 1 lb. of good steam coal will evaporate 9 lbs. of water, 1 lb. of liquid fuel will, under the best conditions, evaporate 16 lbs., and in locomotive practice from 13 to 14 lbs. In his evidence before the Coal Commission, Mr. Holden stated that, weight for weight, the liquid fuel had, according to his experience, approximately twice the evaporative efficiency of coal.

An elaborate investigation of the relative evaporative efficiencies of coal and liquid fuel under forced and natural draught has been conducted by the United States "Liquid Fuel" Board, and the exhaustive report issued in 1904 constitutes an important contribution to the literature of the subject. The coal used was Pocahontas and New River, the calorific value of which (in B.Th.U.) ranged from 14,067 to 14,992. The oil employed was chiefly Texas crude petroleum, from which the sulphur and some of the more volatile constituents had been removed, but Californian oil was also used in some of the tests. The calorific value of the Texas oil, calculated on the analysis of the United States chemist by Dulong's formula, was 19,481 B.Th.U. Seventeen distinct forms of liquid-fuel burners, some of which are described in the following pages, were tried, and it was found that they were " undoubtedly about equal in efficiency, and that there was but little difference in the value of the oil from the two localities as measured from the standpoint of weight." On the other hand, it was demonstrated" that the character of the installation was all-important."

In regard to the similarity of conditions attending the oil-fuel installations for locomotive and torpedo-boat work, it was found that the following advantages were practically obtainable in both cases :

(a) Economy of space reserved for carrying fuel.

(b) Ease in filling tanks.

(c) Rapidity of time in meeting a varying load on boiler.

(d) Ability to force boiler to extreme duty in case of emergency.

(e) Absence of smoke under light normal working conditions.

(f) Short height of stack.

(g) Superior personnel available for the operation of the burners.

(h) Ability to secure and maintain higher speed with oil fuel than with coal. The report points out that for marine purposes it is desirable that burners should be installed capable of effecting vaporisation of oil without the aid of any intermediary of steam or compressed air, since the direct use of steam entails a corresponding loss of fresh water, whilst the introduction of aircompressors encroaches upon the weight and space allowed for installation of machinery, and requires considerable attention in the nature of upkeep and repairs. Mechanical spraying of the oil can be effected by forcing the oil under considerable pressure from a properly formed orifice, or by passing it through a rapidly-revolving burner-head whereby it is whirled or flung outwards. Of the mechanical burners it is stated that very few have achieved success, but with the Körting burner a test was carried out which showed an

evaporation of over 16 lbs. of water from and at 212° F. per pound of oil fuel consumed. The Board reported that "the impossibility of successfully operating burners designed on the principle of superheating the oil to a point bordering on gasification had been both theoretically and practically demonstrated." The importance of making provision for the removal from the oil of mechanically suspended earthy matter and water, and in some circumstances for the heating of the oil to facilitate its flow to the burner, are insisted upon, and two forms of oil-strainers are described. The very important question of furnace-construction in connection with the substitution of liquid fuel for coal is fully discussed, and the difficulty of securing smokeless combustion in the extremely limited furnace-space available in marine boilers, especially those of battleships, is emphasised; in fact, the Board report that in the tests made under strong forced-draught conditions dense smoke was freely emitted. On the subject of the effect of steam in modifying the character of the combustion of the oil, the Board express themselves as follows: "While it may be true that the presence of steam may change the character and sequence of the chemical reaction, and result in the production of a higher temperature at some part of the flame, such an advantage will be offset by lower temperatures elsewhere between the grate and the base of the stack. All steam that enters the furnace will, if combustion is complete, pass up the stack as steam, also carrying with it a certain quantity of waste heat. The amount of this waste heat will depend upon the amount of steam, and its temperature at entrance of the furnace. The quantity of available heat, measured in thermal units, is undoubtedly diminished by the introduction of steam." The Board report that the relative evaporative efficiency of oil and coal as a fuel, as determined by the extended series of comparative experiments, is practically in the proportion of 15 to 10, but that the actual superiority of oil will be considerably greater; for in the coal experiments unusual skill was exercised in the management of the fires, lump coal of superior quality was used, and as the tests were of comparatively short duration, there was much less loss in cleaning fires than would occur in practice; whilst, on the other hand, the oil experiments were carried out under conditions that more closely approximated to those that could be secured on board a sea-going vessel. The actual evaporative efficiency of a pound of oil as compared with a pound of coal is therefore reported to be in the ratio of 17 to 10, and the Board state that these figures may be regarded as substantially correct. In noting the comparative efficiency, for naval purposes, of oil and coal, the Board point out that there must also be taken into consideration the fact that a ton of oil can be stowed in somewhat less space than a ton of bituminous coal; also, that in the carrying of oil the compartments can be more completely filled. The relative efficiency of oil and good steaming coal, from the naval standpoint of fuel-supply in warships, may thus, they say, be regarded as in the ratio of 18 to 10. In relation to the evaporative efficiency secured, the Board point out that the experimental boiler used was designed for actual navy conditions, and that the limitations prescribed by the Department as to height, weight, and floor-space were of a severe nature. There was not only considerable radiation from the boiler, but the proportion of heatingto grate-surface was not as large as in the land boilers. Taking these facts into consideration, the efficiency results are regarded as exceedingly satisfactory. Until greater space is obtained for the installation of marine boilers, it will not, in the opinion of the Board, be possible to secure, in actual naval practice, an evaporation from and at 212° F. of over 14 lbs. of water per pound of oil fuel; but it is considered that increased efficiency may be secured by heating the air requisite for combustion, by the adoption of the Howden or some

similar system, whereby the heat of the escaping gases is utilised for raising the temperature of the entering air requisite for combustion.

Types of Burners.-For generating steam in stationary boilers, Mr. Ludwig Nobel suggested the employment of a very simple system, the arrangement consisting of a series of shallow troughs arranged in superimposed series at the door of the furnace in such a manner that the liquid fuel supplied to the top receptacle overflowed into the one beneath it, and thus travelled downwards through the whole series. The troughs were separated sufficiently to admit of the entrance of a current of air which swept over the surface of the burning oil, and carried the flames into the furnace. It was found that 1 lb. of ostatki, when thus burned, evaporated 14.5 lbs. of water, while it only evaporated 12 lbs. when consumed in a spray burner, and that coal evaporated only 7 to 8 lbs. of water per pound of fuel, in the same boiler.

It is, however, more common and convenient to burn the oil by means of an injector, the oil being thus driven by a jet of steam, or in some cases, of compressed air, into the combustion-chamber in the form of spray, together with the amount of air necessary for its combustion, or atomised by being forced at high pressure through a suitably constructed jet. Such a system was patented as early as 1865-7 by Aydon, Wise, and Field. In 1868, Donald of Glasgow patented a similar arrangement.

Figs. 323 to 325 represent the method of burning liquid fuel introduced by Mr. James Holden, and at one time employed on many locomotives on the Great Eastern and other railways at home and abroad. Fig. 323 gives a vertical view of the injector, showing a supplementary oil-feed down the sloping pipe, P. Fig. 324 shows a sectional plan of the injector. The main oil-feed is through the side pipe, the oil passing to the annular passage, A B. The main steam enters through S1 into the annular passage, CD, and passes to the nozzle through the space between the central air-tube and the oil space leading from A B to the nozzle. The steam thus draws in the oil, together with a certain amount of air, and breaks up the oil into a spray. The oil is 61

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