INTERNAL COMBUSTION ENGINES

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If carbon and oxygen be made to combine chemically, the process is accompanied by the phenomenon called heat. If heat be applied to a liquid or gas in a confined space it causes a violent separation of its molecules, and power is developed. In the case of a steam-engine the fuel is coal (carbon in a more or less pure form), the fluid, water. By burning the fuel under a boiler, a gas is formed which, if confined, rapidly increases the pressure on the walls of the confining vessel. If allowed to pass into a cylinder, the molecules of steam, struggling to get as far as possible from one another, will do useful work on a piston connected by rods to a revolving crank. We here see the combustion of fuel external to the cylinder, i.e. under the boiler, and the fuel and fluid kept apart out of actual contact. In the gas or oil-vapour engine the fuel is brought into contact with the fluid which does the work, mixed with it, and burnt inside the cylinder. Therefore these engines are termed internal combustion engines. Supposing that a little gunpowder were placed in a cylinder, of which the piston had been pushed almost as far in as it would go, and that the powder were fired by electricity. The charcoal would unite with the oxygen contained in the saltpetre and form a large volume of gas. This gas, being heated by the ignition, would instantaneously expand and drive out the piston violently.