Classic History Books

William J. Claxton - The Mastery of the Air

Dover, without once alighting.


CHAPTER XXI. The Internal-combustion Engine(Cont.)

I suppose many of my readers are quite familiar with the working of a steam-engine. Probably you have
owned models of steam-engines right from your earliest youth, and there are few boys who do not know

how the railway engine works.

But though you may be quite familiar with the mechanism of this engine, it does not follow that you
know how the petrol engine works, for the two are highly dissimilar. It is well, therefore, that we include

a short description of the internal-combustion engine such as is applied to motor-cars, for then we shall

be able to understand the principles of the aeroplane engine.

At present petrol is the chief fuel used for the motor engine. Numerous experiments have been tried with
other fuels, such as benzine, but petrol yields the best results.

Petrol is distilled from oil which comes from wells bored deep down in the ground in Pennsylvania, in
the south of Russia, in Burma, and elsewhere. Also it is distilled in Scotland from oil shale, from which

paraffin oil and wax and similar substances are produced. When the oil is brought to the surface it

contains many impurities, and in its native form is unsuitable for motor engines. The crude oil is

composed of a number of different kinds of oil; some being light and clear, others heavy and thick.

To purify the oil it is placed in a large metal vessel or "still". Steam is first passed over the oil in the still,
and this changes the lightest of the oils into vapours. These vapours are sent through a series of pipes

surrounded with cold water, where they are cooled and become liquid again. Petrol is a mixture of these

lighter products of the oil.

If petrol be placed in the air it readily turns into a vapour, and this vapour is extremely inflammable. For
this reason petrol is always kept in sealed tins, and very large quantities are not allowed to be stored near

large towns. The greatest care has to be exercised in the use of this "unsafe" spirit. For example, it is

most dangerous to smoke when filling a tank with petrol, or to use the spirit near a naked light. Many

motor-cars have been set on fire through the petrol leaking out of the tank in which it is carried.

The tank which contains the petrol is placed under one of the seats of the motor-car, or at the rear; if in
use on a motor-cycle it is arranged along the top bar of the frame, just in front of the driver. This tank is

connected to the "carburettor", a little vessel having a small nozzle projecting upwards in its centre. The

petrol trickles from the tank into the carburettor, and is kept at a constant level by means of a float which

acts in a very similar way to the ballcock of a water cistern.

The carburettor is connected to the cylinder of the engine by another pipe, and there is valve which is
opened by the engine itself and is closed by a spring. By an ingenious contrivance the valve is opened

when the piston moves out of the cylinder, and a vacuum is created behind it and in the carburettor. This

carries a fine spray of petrol to be sucked up through the nozzle. Air is also sucked into the carburettor,

and the mixture of air and petrol spray produces an inflammable vapour which is drawn straight into the

cylinder of the engine.

As soon as the piston moves back, the inlet valve is automatically closed and the vapour is compressed
into the top of the cylinder. This is exploded by an electric spatk, which is passed between two points

inside the cylinder, and the force of the explosion drives the piston outwards again. On its return the

"exhaust" or burnt gases are driven out through another valve, known as the "exhaust" valve.


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