Other formats

    TEI XML file   ePub eBook file  


    mail icontwitter iconBlogspot iconrss icon

The New Zealand Railways Magazine, Volume 2, Issue 12 (April 1, 1928.)

The Brick Arch and its relation to Fuel Economy

The Brick Arch and its relation to Fuel Economy.

The advantages claimed for the use of the brick arch are:—(1) Fuel saving; (2) smoke abatement; (3) tube protection and reduction in tube repairs; (4) improvement of steaming qualities under demands for maximum power; (5) reduction of engine failures from leaking tubes and low steam pressure; (6) reduction in tube stoppage; (7) reduction in clinkering or honeycombing of the tube plate; and (8) the beneficial effect on the life of a set of tubes and of the tube plate.

Against these advantages can only be set the cost of maintenance of the brick arch. We have all of us got past that point where we questioned the advantages of the brick arch; we know, from practical experience, that the brick arch does give the results claimed for it. A large portion of the saving effected by the brick arch is due to the intimate mixing of the combustible gases and oxygen brought about by the arch. A thorough mixing of the gases in the firebox is impossible without a brick arch. Many of the fine fuel particles that break off the coal in the fuel bed are so light that they are often picked up by the draught and whirled page 37 out of the firebox (in company with the fine coal dust that never reaches the fuel bed) in a partly burned condition—unless they are “baffled” and thrown down again by striking the brick arch. In order to secure perfect combustion of the gases, all flame must be burnt out entirely before reaching the tube plate. Now this can only be accomplished by “baffling” them in such a manner that none can reach the tubes without passing around and over the brick arch. Under average working conditions (with the firebox equipped with an arch) the loss due to the escape of unburned gases may be between 2 and 10 per cent. The losses, however, are much greater without the arch, as the saving of 10 to 16 p.c. effected . by the arch, is largely due to the decrease in the amount of combustible material that escapes unburned in the form of gases, coal dust, sparks and cinders.

“Mere length of combustion chamber counts for little compared with some device for thoroughly mixing the gases of the flame stream (says Dr. Breck-enridge). One good mixing wall or ‘baffle’ is probably worth more than many feet of undisturbed flow.”

This is not said to discount the significance of the combustion chamber length, but to emphasise the importance of mechanically mixing the different strata of the gas stream.

In the Auckland Province.Photos. J. F. Davey Top: Rotorua express leaving Auckland—Ab. engines. Bottom: Suburban-train nearing Ellerslie—Wab. Engine.

In the Auckland Province.
Photos. J. F. Davey
Top: Rotorua express leaving Auckland—Ab. engines. Bottom: Suburban-train nearing Ellerslie—Wab. Engine.