Thus the weight of oil produced in the United States is about 5 per cent. of the weight of coal, or say 7 per cent. of the calorific capacity. After the removal of the lighting and lubricating oils, the amount of fuel oil remaining will be quite small as compared with the coal output. It may be assumed that the total oil production of the world is not five per cent. of its coal production. Any idea of entirely displacing coal must be out of the question, unless the yield of oil be increased beyond any present prospects, and the use of fuel must therefore be undertaken with common sense caution, and not in any wholesale manner, to the expected exclusion of coal.

At the same time, when the limitations of the subject are recognized, it cannot be denied that liquid fuel lends itself to certain conditions as to steam raising which must render it extremely valuable and of great convenience. Marine work and electrical work are, par excellence, the two lines along which liquid fuel appears likely to advance most successfully, and in the Author's opinion steam-driven motor cars will eventually discard the dearer oils and employ the heavy oils and residuum as fuel by means of atomizers. According to present appearances the motor car or tractor offers one of the finest fields for the use of the heavy fuel oils as distinguished from the petrols or even the cheap lamp oils, such as are already used on steam cars and referred to in Chapter XXIII. Little has perhaps yet been done in this direction, but Chapter XXII. contains a slight reference to the use of heavy liquid fuels by means of the atomizing system, which alone appears likely to lead to success.

H

I

Chapter II

THE ECONOMIES OF LIQUID FUEL

N considering the application of liquid fuel every case must be taken by itself and the costs evaluated. In favour of oil there is, first, the ease and rapidity with which a liquid can be taken into store and delivered to the bunkers of a ship

be

almost nil in case of a single boiler with one attendant to the engine and boiler.

or it may be very great where there are many boilers.

The superior calorific power of oil must then be equated with the price, and the

cost per unit of evaporation found from this.

The removal of cinders and ash may or may not be a matter of cost according

to the demand for them locally.

Liquid fuel possesses great elasticity of use and fits well with sudden and varied demands for power. Hence its value in railroad work, electric light work.

and other power stations where loads vary greatly.

the mere question of economy, as based on the actual weight of fuel consumed. Where the mixed system is employed, as with the Great Eastern Railway

is to be found as follows:

with coal and oil, it is found to consume (M units of coal.

A locomotive consumes N units of coal per unit distance. When running

Then Ox

oil.

The price of coal is y; of oil a per unit.

x + M × y ≤ N X y

1000

1000

or x L

per ton at Baku costs 185 francs-£7 88. 6d. in France.

y

0

(N–M)

The difference of 182

The cost of oil is largely a matter of carriage. What costs three francs-2s. 6d. franes is made up of railway and sea carriage, handling, customs, warehousing. The customs stand for ninety francs, so that the same oil at an English port should

not cost over £3 16s.

MM. Colonner and Lordier, who give the above figures, dismiss oil as an economical American residues cost five to six francs more than Russian mazut, whence

fuel pending the reduction of the tariff.

365: 274 or 33 per cent. in favour of oil.

On the Southern Pacific Railroad the relative evaporation of oil and coal is

equal to a ton of coal, and at 12s. 6d. per ton and 2s. 4d. per barrel the economy On the International and Great Northern four barrels of oil proved more than oil was 13 to 14 per cent. including the economy of handling and storing. The

only application of liquid fuel in Austria, despite its proximity to oil fields, is in the Arlberg tunnel. But the Austrian Government are also coal owners, and so also are other Austrian railroads and steam navigation companies and possibly do not encourage oil fuel.

To produce 1,000 units of steam, coal gives out more carbonic acid than oil, though of course the oil destroys quite as much oxygen and reduces the life-supporting power of the air to probably equal extent. So long as combustion is perfect and no actual poisons are made there is not much to choose between the two fuels beyond their sulphur contents. As regards the safety of oil it has been shown that oil with 117°C. =239°F. flash-point did not ignite if fired at with shell, nor did dynamite exploded in a reservoir of this oil do more than throw up jets of oil which did not ignite.

Any danger with liquid fuels is with the oils which have not parted with their inflammable and volatile gases. This is a danger with oils when used absolutely crude. Purged of these portions, however, oil is safe, and, moreover, unlike coal, it contains no power of spontaneous combustion. Though it is claimed by some that oil does not deteriorate if kept in tanks, others do claim that a certain deterioration is produced which renders it difficult to atomize, the oil becoming more thick and viscid.

In Russia circular atomizers are often employed which give out a large hollow flame. The Béreznef atomizer, fig. 101, is one of these. They have the disadvantage of being out of reach in the middle of the fire of a locomotive, and they become burned also through being in such close contact with the flame.

Steam enters below the central disc and oil flows under a head of two to three metres on the upper side of the disc.

1

square metre 10.76 square feet. Kilograms per square metre÷ 5 =pounds per square foot

nearly.

The advantage of this form is said to be its constant output.

Too much mazut produces smoke, too much steam is wasteful. There is a certain fixed ratio of oil and steam to give the best result. The Issaief atomizer. which resembles the Béreznef, will feed 50 to 100 kilos. of oil per hour (110 to 22h, and it consumes nearly 0-4 kilos. =88 lb. of steam at 4 to 5 atmospheres pressure per kilo. of oil (2.2 lb.). The table, page 11, is given by M. Keller, of Moscow, s

the result of tests made with various atomizers.

M. Bertin, in dealing with the efficiency of liquid fuels, points out that a fi containing 85 per cent. of carbon and 14 per cent. of hydrogen will consume the oxygen of 7-56 cubic metres of air to satisfy the carbon, and of 2-72 metres to satis the hydrogen, or 10-28 cubic metres in all. By adding 40 per cent. excess of air or 14-4 cubic metres=18-7 kilos. of air per kilo. of oil, then combustion will be perfect

and smokeless.

The Author's own figure for the weight of air chemically necessary for the above sample would be 14-7 nearly, and 40 per cent. excess would increase this to M. Bertin's figure of 18-7 appears to represent about 27 per cent. air excess The theoretical temperature of combustion will be

20-56.

300

2480

11000

(18-7+1) × 0-23

=2480°C. =4496°F.

If the gases leave the boiler at 300°C.-572°F. the loss of heat will le

-12-10 per cent. of the total, which is equivalent to an increased efficiency of 6-65 per cent. as compared with coal. He further estimates a gain of 1.9 per cent, over coal in the absence of ashes and their cooling (on board ships).

oil firing or 0-75 + 0-0665 +0·019=0·835.

The efficiency of a boiler estimated at 75 per cent. for coal becomes 0-835 for

-835

65

But good combustion and utilization still further favour oil in the ratio 1-28-m; m becoming then r=1-20 x 1.28-1.53; the figure 1-20 being the

chemical ratio of power of coal and oil.

than the

Bertin, however, only obtained m=1-11 and r=1-33. The causes of the difference are found in the nature of the flame of oil, which has less radiating power In Torpedo-boat No. 62 (French) M. flame of coal, and the powerful effect of the directly heated coal furnace is sacrificed. and to secure the same results an undesirable extension of heating surface would

be necessary.

burners.

the

Secondly, the flame of oil is long if care be not taken suitably to arrange t partly burned may even relight in the chimney. The chemical action and reactions of a burning spray of oil may be very much complicated by dissociation or even It may pass between the tubes and become extinguished, and the gases by exothermic formations which may delay heat production. Later when combustion becomes active as shown by the light giving power of the flames it will be timet, during which the jet, travelling at a high velocity, v, passes through a more or less rapid according to the perfection of air admixture and will last for a

distance Lvt which may be yards in length.

Thus the course of the gas must be long or it may escape too hot to the chimney. Hence arises the necessity of cutting short the flame by early admixture and high

temperature so as not to lose the benefit of the boiler-heating surface.

It is for this purpose that in most successful oil-burning furnaces the jet

of

atomized oil is directed upon a brick obstruction of some kind so as to spread the flames and cause them to fill the furnace space and lick round the plate surface. Locomotive fireboxes may be studied, as in fig. 25, to show how this effect is secured before the gases escape to the small tubes.

General Principles of Liquid Combustion.-A review of the whole subject, in the light of chemical knowledge, of the claims of manufacturers and of users of liquid fuel enables us to state that successfully to burn a liquid it must be finely pulverized, to do which it must be heated sufficiently to destroy its tenacity and enable the spraying agent, air or steam, to tear it up and disperse it in a fine spray intimately mixed with air. The correct amount of air must be admitted to burn the liquid, and this is one of the advantages of employing air as the atomizing agent. Where sufficient air cannot be introduced with the fuel it must be admitted from below as through grate bars covered with broken bricks. Steam, preferably superheated, is undoubtedly the most convenient to employ as the atomizing agent, but on the salt seas it has the disadvantage of wasting from 3 to 5 per cent. of the steam made by the boilers, and this loss must be made good by evaporators. As with bituminous coal, which, like oil, is a complex hydrocarbon, liquid fuel should be burned in furnaces more or less protected from immediate loss of heat to the boiler surfaces by means of linings or baffles of firebrick. Liquid fuel, however, is more easy to burn completely than is coal, because it can be more intimately mixed with the necessary air. The interior of a combustion chamber should show a clear white incandescence with little apparent flame and no smoke or unburned gases coming from the chimney. If looked into through a piece of violet-coloured glass, the interior of the combustion chamber with its brick linings should show a light lavender colour indicative of perfect combustion with the production of actinic rays indicative of high chemical action. A chilled fire, such as is produced where a boiler is placed close upon the furnace of a coal fire will show very little light indeed through a violet glass, its flames being cut down from several feet in length to a few inches only in many instances, the flames of yellow and reddish intensity being resolved into streams of dun-coloured gas which throw off no light of sufficient actinic power to penetrate the glass.

Much difference of opinion exists in regard to the flash-point of the oil to be used. Crude oil is so widely different a product according as it comes from one or another locality that no rule can be laid down as to its safety or otherwise. Those crude oils, which, like the Pennsylvania oil, give a large proportion of gasolene and other volatile compounds are not used in their crude form because they pay better to refine, the heavier residuum being used as fuel and being much safer. The use of volatile liquids is only undesirable on the score of safety. Some of the crude oils, as for example those of the Beaumont field of Texas, contain so little of the lighter oils that they are used as fuel in their crude form. The one thing to note is that the more highly volatile oils have an element of danger from which the heavy oils are free, and this danger intensifies the results of every possible accident that may occur, especially those which arise from rupture of an overhead tank and the gravitation of the oil to lower points. The whole question is really very simple, and resolves itself into exactly the same conditions as the coal question, namely an intimate mixture with air in sufficient quantity and a proper conservation of the temperature pending full combustion. Fortunately for liquid fuels, these items are not only easy to realize, but, failure, when they are not realized, is far more disastrous and complete than in the case of solid fuels. Hence the really