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Technical - Heat and Combustion |
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Heat may be regarded as a form of energy which can to some extent be converted into useful mechanical work. Heat is usually produced by the combustion of fuel, and in the case of the steam locomotive the fuels normally used are coal, oil and wood. On the SAR coal was the only fuel of any importance, and it consists essentially of carbon, a number of complicated chemical compounds of hydrogen and carbon (known as hydrocarbons), and incombustible ash.
When substances combine with oxygen, heat is produced, and when the production of heat is very rapid the reaction is usually called "combustion", and the substance is said to "burn". While coals from different areas vary widely in composition, the general conditions of combustion of coal in a locomotive firebox are the same. The carbon burns on the grate, liberating great heat, and driving off the hydrocarbons as volatile or gassy matter, which burns with luminous flames above the grate. The oxygen necessary to support combustion comes from the air, which consists approximately of one-fifth oxygen and four-fifths other gases, mainly nitrogen, which play no part in combustion.
The result of supplying insufficient air will be to cause smoke, which consists mostly of unburnt hydrocarbons, while if too much air is supplied, some of the heat of the fire will be uselessly absorbed in heating that portion of the air which is additional to that required for complete combustion.
One
of the most convenient ways of converting heat into mechanical work,
is to use the heat to change water into steam, which in turn can be
used in an engine. The water and steam are thus the means of transmitting
the heat energy liberated by the combustion of the fuel to the engine,
where useful work is produced. |
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