Oxygen and Atmosphere.—The atmosphere is not oxygen. Only one-fifth of common air is oxygen, the residue being, principally, nitrogen, which is not a fuel. To produce the proper aëration, therefore, at least fifteen parts of air must be mixed with one part of hydro-carbon gas.
The term hydro-carbon is applied to petroleum, and its products, because the elements carbon and hydrogen make up the largest part of the oil, whereas this is not the case with most of the other oils.
We are now dealing with a fuel such as is needed in Internal Combustion Engines, and it is well to know some of the problems involved in the use of the fuel, as this will give a better understanding of the structure of the devices which handle and evolve the gases, and properly burn them within the engine.
Vaporizing Fuel.—As the pure liquid will not burn in that state the first essential is to put it into a gaseous form, or to generate a vapor from it. The vapor thus made is not a gas, in the true sense of that term, but it is composed of minute globules of finely-divided particles of oil.
Nearly all liquids will vaporize if permitted to come into contact with air. The greater the surface exposed to air the more rapidly will it turn into a vapor.
By forcibly ejecting the liquid from a pipe or spraying device, and mingling air with it, evaporation is facilitated, and at the same time the proper admixture of air is provided to make a combustible substance the moment sufficient heat is brought into contact with it.
This is what actually takes place in a gasoline engine, and all the mechanism is built with this end in view.
It has been the universal practice to make an explosive mixture of this character, and then ignite it by means of an electric spark, but it is now known that such a fuel can be exploded by pressure, and this needs some explanation.
Explosion by Compression.—The study of the compressibility of gases is an interesting one. As we have previously stated, the atoms, comprising the gases, are constantly moving among themselves with great rapidity, so that they bombard the sides of the receiver in which they are confined, and also contact with each other in their restless movements.
When compression takes place the speed of the movements of the atoms is greatly accelerated, the friction of their movements is increased, and heat is evolved. As the pressure becomes greater the heat increases until it is of such intensity that the gas ignites, and an explosion follows.