ton's engine he used gasoline and oil. Air only was compressed in the compression tanks and just before it was passed into the cylinder of the engine it was

drawn across a sponge soaked in either gasoline or kerosene. See Fig. 7.

In the Brayton engine the inlet valve closed when the piston had traveled about one-half of its stroke and the expansion of the burning fuel mixture forced

it on to the end in precisely the same manner as does the latent heat in steam. Brayton built a large number of these engines, and they were the best that had been made up to that time.

1

The Four Stroke Cycle Gas Engine.-As far back as 1682 Beau de Roches, of France, conceived and patented the scheme of making a four stroke cycle 1 gas engine, that is, an engine in which the first stroke would suck in the fuel mixture; the second stroke would compress it; the third stroke would be the power stroke, in virtue of the fuel mixture exploding, and the fourth stroke would push out the burnt gases.

Nearly 200 years later, that is, in the year of 1861, Nicholas August Otto, a German engineer, built a gas engine on the identical principles laid down by De Roches, and used a flame igniter quite like the one devised by Barnett.

This engine, see Fig. 8, is known as the Otto four stroke cycle gas engine, and was shown for the first time in public at the World's Fair in Paris, in 1867. The improved Otto engine was exhibited at the Centennial Exposition in 1876, and it worked so nicely and efficiently that over 30,000 of them were built and sold during the first ten years.

It was soon found that the four stroke cycle engine could be adapted equally as well to the use of

1 The term four stroke cycle means four successive strokes of the piston in which each one performs a different operation and the continued repetition of which makes the engine develop power.

liquid fuels, such as gasoline and kerosene, provided the proper devices were used to break up these liquids into a spray and mix them with the right amount of air.

When these small but important improvements had been made there grew up the great industries of

building stationary, marine, motor car and, more recently, airplane engines.

The Diesel Self-Ignition Oil Engine.-When air is compressed sufficiently, its temperature is raised high enough so that it will fire kerosene or other fuel oils if these are allowed to come in contact with it, and hence neither a flame nor a spark is needed to ignite the fuel charge.

Working on this principle, Rudolf Diesel, a German inventor, began to experiment with high compression engines in 1892. In his engine the air is compressed in the engine cylinder and, when it is under a high pressure and hot enough, the fuel oil is

injected into it when the latter is fired and explodes. Diesel engines are made in all sizes from 3 horse power, which is suitable for farm use, on up to those developing 2,000 horsepower. A diagram of the first Diesel engine is shown in Fig. 9.

CHAPTER II

THE INTERNAL COMBUSTION ENGINE SIMPLY

EXPLAINED

To begin with, all engines in which the fuel is fired in the cylinders, or internal combustion engines, as gas, gasoline and oil engines are now generally called, work on the same fundamental principle, and that is by the expansive force of a gas acting on a piston in a cylinder.

How a Simple Gas Engine is Made.-To get a clear idea of how a gas engine works, let us start with a single cylinder engine and find out first how it is made.

Such a gas engine is shown in Fig. 10, and from this drawing you will see that it is built up of (1) a cylinder open at one end and which is fitted with (2) a piston that slides freely back and forth in it, (3) a connecting rod, one end of which is pivoted to the piston and the other end attached to the pin of (4) the crankshaft, and to the latter is fixed (5) the flywheel, which is not shown. Geared to the crankshaft is (6) a pair of camshafts with cams fixed on them so that they open the inlet and exhaust