The complicated action and re-action met with in burning coal may be divided into three processes. First, the conversion of coal into gases; second, the burning of the gases; and third, the separation and disposal of the ash and refuse. None of these processes are easily carried out in the ordinary locomotive firebox where bituminous coal is used.

The conversion of coal into gases can be managed without difficulty if it were possible to hold all of the coal on the firebars until gasification was completed; but under ordinary working conditions from 5 to 15 per cent, of the coal is picked up by the draught (or blast) and ejected at the smoke stack as cinders or sparks. Under bad conditions as much as 25 per cent, can be lost in this manner.

The loss of solid coal through the firebars and drop-grates generally averages from 1 to 2 per cent., but my observations lead me to believe it is nearer the vicinity of 10 per cent.—not through a badly designed fire-grate, but owing to careless and indifferent firing.

Under the most favourable conditions and at low rates of combustion, about 94 per cent, of the solid combustible matter is converted to gases. At medium rates about 85 per cent, is so converted, and at high rates only 75 per cent.

The burning of the combustible gases in the spaces above the fire is also attended with difficulties—due to lack of air, imperfect mixing of the gases, and insufficient combustion chamber volume (that is, the firebox isn't big enough).

The amount of air supplied through the grates depends upon the air opening through the ashpan and finger bars, the thickness of the fuel bed, the nature of the coal (as to size and ash and clinker forming contents), and above all, to the skill of the fireman. But even if all these conditions are favourable there is a gradual decrease in the air supplied as the rate of combustion increases. At high rates of combustion the supply of air is generally deficient.

Under ordinary conditions, with the firebox fitted with a deflector plate and a brick arch, the loss due to the escape of unburned gases varies from 2 to 10 per cent. The losses are much greater without the brick arch, as the saving of from 10 to 16 per cent, effected by the arch is largely due to the decrease in the amount of combustible matter that escapes unburned in the form of gases, coal dust, sparks and cinders.

The separation and disposal of the ash and clinker forming impurities is an unsolved problem which is largely responsible for the low average daily mileage of our locomotives. The frequent necessity for cleaning fires, dropping fires through the drop-grate (which often causes the tubes to leak) is due largely to imperfection in firebox design and to methods of burning coal that our great designers are always endeavouring to overcome.

The foregoing remarks will convey some idea, of the complicated structure of coal and the complexities of the problems yet to be solved in this direction. I trust, too, that firemen may be encouraged to study the problem of combustion. The firebox with which they are working becomes vastly more efficient for its purpose when an intelligent hand guides the coal and air supply.

Remember

One pound of coal—good coal—is nearly one pound of carbon, and one pound of carbon properly burnt results in the liberation of 14,650 heat units or B.T.U's. (B.T.U. means British. Thermal Unit, the amount of heat required to raise one pound of water one degree Fahrenheit.) A unit of heat will raise the temperature of one pound of water one degree Fahrenheit.

In order that the importance of an ample and uniform air supply (and the necessity of intimately mixing the air and the coal gas by every possible means), may be grasped, the following; figures are given:—

One cubic inch of air contains 443 billion billion (443,000,000,000,000,000,000) molecules; 93 billion billion of these are oxygen molecules. One molecule of oxygen is required to burn one atom of carbon. One cubic inch of air, therefore, contains oxygen sufficient to burn 93 billion billions of carbon atoms—this number of atoms page 31 being contained in a piece of coal no larger than a pin's head.

Those wishing to study more widely the problem of combustion will find the works of Millikan, Lodge, Comstock and Troland, Crowther, Rislieu, Deeley, Jones, Roscoe and Schorlemmer, Thomson, Campbell, Gibson, the U.S.A. Bureau of Mines and Professors Goss, Cranford, Fry and Dr. Brislee, of considerable interest and importance.

Locomotive Fuel Economy.

The first comprehensive and thorough study of this subject was made by the “American Engineer” (news journal) and appeared in April, 1908.

On November 20th, 1908, the International Fuel Association (to bring about economy in the use of fuel) was organised at Chicago with a membership of 35. Since the formation of the Association every railway has taken up this most important subject. There are to-day some who think that fuel economy is a new-fangled idea and a fad, but it is time we all woke up to the fact that fuel economy is the most important factor in railway operation costs. When the cost of coal is high it often depends on the amount of coal saved or wasted whether or not there be dividends.

We must bring up the work of the fireman to a higher plane and teach the chemistry of the firebox. To obtain the best, results enginemen must understand the theory which underlies the combustion of coal, and they must combine this theory with practice. It must be remembered that drivers and firemen are, for the greater part of their time, beyond the limits of direct supervision. If rules and regulations for controlling the use of coal are laid down for their guidance the reasons should be thoroughly explained, so that such rules, etc., not only appeal to their intelligence, but inspire interest in carrying them into effect.

The system of imparting instruction by those in charge of locomotives is by means of lectures, by the personal help of the older and more experienced enginemen, and by the inspectors on the footplate.

The function of the supervising officers is to see that the best use is made of the coal. The basis of any efforts directed towards securing greater fuel economy is the recognition that the human element is by far the most important factor.

Lectures and verbal instructions supply the means whereby some men will take full advantage of any knowledge offering.

It will usually be found that those who scoff and jeer in this respect will (when they realise that the “sit still” attitude solves no problems) in the end fall into line and assist the men who are trying to improve methods in this vitally important matter.

I could write many pages illustrating the methods adopted in giving publicity to the fuel economy campaign on many railways in American and Great Britain. Figures, lectures, and pamphlets, photographs and pictures—in fact no system of moden publicity is left untried to keep up the interest in this subject, and I am confident that, were we paying £2 a ton for coal (as some railways do) instead of what we are paying, we should have to step quick and lively along this road of fuel economy. But because our coal is cheap, we should not be careless in its use. In a recent year we used (on the South African Railways) the enormous amount of 2,153,970 tons of coal. It is obvious, therefore, that we have a great oportunity of saving the country a considerable sum of money by the intelligent use of coal.

The man who economises in the use of pins, or who uses an envelope a second time, deserves well of his employer. Likewise in the use of coal, it is within the power of the locomotive section of the railways to make savings in the big things—coal, oil, etc.

Everyone and everything connected with the operation of a locomotive or the movement of a train has some effect, direct or indirect, in the fuel consumption.

Fuel economy and efficient operation, under ordinary conditions, are practically synonymous.

The basis of a successful fuel campaign is the fact that the average man is anxious to do his best and thus to protect his reputation and his home. To secure the best results from the enginemen there requires to be a painstaking page 32 and thorough campaign of education which, will reach each man and inspire him to the proper performance of his duties.

Significance of a Pound of Coal.