The New Zealand Railways Magazine, Volume 3, Issue 4 (August 1, 1928)
Theory of Combustion
The interesting series of articles, on the Theory of Combustion, which have been appearing in the Magazine since January last, concludes with this instalment. In an early issue we hope to commence printing a further series of articles by Mr. Bishop, on “Derailments and Their Causes”— a subject of general interest to railwaymen.
Things for Enginemen to Remember
The nitrogen which is mixed with the oxygen in the air carries away much heat without serving any useful purpose; this is unavoidable.
10. The object of the damper is to supply air under the fire, which is necessary to make it burn. It is not possible to supply all the air required in this way, because air must be introduced to the top side of the fire to mix with the monoxide and thus produce combustion. The damper, however, is of the greatest possible use in regulating the fire. If the damper was kept absolutely closed and no air allowed to pass through it, the fire would burn very imperfectly—from the top only.
When running down banks standing at stations and signals—in all cases where steam is not being used as rapidly as produced, the damper serves a most useful purpose. If properly used in these cases it should be nearly closed. It thus prevents the fire from being burnt faster than is necessary. (The firehole door also should be closed if this can be done without smoke being given off.) The damper should always be used in connection with the firehole door as the means of regulating the amount of steam produced.
11. The correct position of the firehold door (when not open for firing) is that which allows the smallest amount of smoke to be given off. This is determined by observation, and it may be taken for granted that if the firehole door is operated according to this principle the coal is being used economically. When little steam is required the firehole door should be nearly or wholly closed, only sufficient air being admitted to allow of the gases given off by the fire being consumed.
12. The firehole door should never be opened to check the generation of steam. It is quite unnecessary to open the firehole door for this purpose, and it is one of the worst practices which can be indulged in. This is because it leads to waste by causing a large quantity of unnecessary air to be admitted into the firebox, air which is heated up and carried away without serving any useful purpose. Indeed, a sudden inrush of air, by cooling down the tube plate, may start the tubes leaking.
13. Other aids to combustion are the brick arch and deflector plates. These tend to throw together and mix the gases given off by the coal and the air admitted through the firehole door.
14. There is no definite rule for the proper firing of a boiler. It depends on several points that may vary with different locomotives. But general points which should be aimed at are: Regularity of firing, and the importance of keeping the fire as thin as possible.
15. The occasion when a fire should not be kept as thin as possible is when the grate is small and the blast somewhat sharp.page 25
If a very thin fire was kept under these conditions, the sharpness of the blast would draw in, through the grate and firehole door, more air than was required. The excess air would have to be heated up, and heat would thus be wasted. The fire would also tend to burn through in holes, through which excess air would be drawn causing sparks to be ejected from the chimney. In such a case the fire should be thickened. With a gentle blast and a large grate the fire should be kept as thin as possible without allowing it to burn into holes.
No. 1 Locomotive Ambulance Division (1927–1928), Dunedin.
Back row: B. F. Keating, A. E. Robinson (Treasurer), J. H. McCracken, J. Hall, W. W. N. Worth. Third row: J. Robb, R. H. McCurdy, T. F. McLennan, C. R. Tuck, W. J. Stackhouse, J. P. McEneany. Second row: A. Westfield (Corporal), G. R. Syder (1st Officer), A. G. Foster (Supt.), Dr. C. M. Greenslade (Div. Surgeon), J. Dickson (Sergt.), P. Cull (Hon. Sec.), J. Shaw. In front: D. J. N. McFie, R. A. Bramley.