QUESTIONS AND PROBLEMS

1. How does the temperature of the steam within a locomotive boiler compare with its temperature at the moment of exhaust? Explain.

2. On the drive wheels of locomotives there is a mass of iron opposite the point of attachment of the drive shaft. Why is this necessary?

3. Why does not the water in a locomotive boil at 100° C.?

4. When the steam gauge of a locomotive records 250 lb. per square inch, the steam is at a temperature of 406° F. Explain how the steam produces this great pressure.

5. What pull does a 1000 H.P. locomotive exert when it is running at 25 mi. per hour and exerting its full horse power?

6. If the average pressure in the cylinder of a steam engine is 10 kilos to the square centimeter, and the area of the piston is 427 sq. cm., how much work is done by the piston in a stroke of length 50 cm.? How many calories did the steam lose in this operation?

INTERNAL-COMBUSTION ENGINES

243. Principle of the internal-combustion engine. Let two iron or steel wires be pushed through a cork stopper and their ends s brought near together (32 in. will do) (Fig. 183). By displacement of water introduce into the inverted bottle enough illuminating gas to fill it about one-fifth, allowing the remainder of the water to run out, or with an atomizer spray into the bottle a small amount of benzine or gasoline (the amount to use can be determined by trial), insert the stopper, and bring the tips of the heavily insulated wires leading from an induction coil to the under side of the wires a, b. A spark will pass at s; and, if the mixture is not too "rich" or too "lean," a violent explosion will occur, throwing the stopper as high as the ceiling. (A heavy round bottle must be used for safety. Wrap it well in wire gauze.)

FIG. 183. A mixture of gasoline vapor and air will explode

SECTION OF A MODERN AUTOMOBILE, SHOWING THE PRINCIPAL MECHANICAL PARTS

1, radiator; 2, timing gears to operate valves in proper relation to position of pistons; 3, pistons; 4, crank shaft; 5, valve
stems and push rods operated by cams on the cam shaft; 6, oil reservoir; 7, gasoline tank; 8, flywheel; 9, main rear bearing;
10, cooling fan; 11, clutch for connecting the crank shaft of the engine to the transmission; 12, transmission; 13, universal
joints; 14, gear-shift lever; 15, main driving gear and pinion; 16, electric control switch; 17, emergency-brake lever;
18, service-brake foot lever; 19, storage battery; 20, vacuum feed system; 21, muffler; 22, steering wheel

A BATTERY IGNITION SYSTEM USING A NON-VIBRATING INDUCTION

COIL, A BREAKER, AND A ROTATING DISTRIBUTOR

Within the last two decades gas engines have become quite as important a factor in modern life as steam engines (see opposite pages 89, 210, and 217.) Such engines are driven by properly timed explosions of a mixture of gas and air occurring within the cylinder.

Fig. 184 is a diagram illustrating the four stages into which it is convenient to divide the complete cycle of operations which goes on within each cylinder of such an engine.

FIG. 184. Principle of the gas engine

Suppose that the engine has already been set in motion. As the piston P moves down in the first stroke (see (1)) the intake valve D is forced open by a cam on the rotating cam shaft (see opposite page 210) and an explosive mixture of gas and air is drawn into the cylinder through D. As the piston rises (see (2)), valve D is forced shut by a spiral spring and the mixture of gas and air is compressed into a small space in the upper end of the cylinder. An electric spark ignites the explosive mixture, and the force of the explosion drives the piston violently down (see (3)). At the beginning of the return stroke (see (4)) the exhaust valve E is forced open, and as the

piston moves up, the spent gaseous products of the explosion are forced out of the cylinder. The initial condition is thus restored and the cycle represented by the four strokes begins over again.

Since it is only during the third stroke that the engine is receiving energy from the exploding gas, the flywheel is always made very heavy, so that the energy stored up in it in the third stroke may keep the machine running with little loss of speed during the other three parts of the cycle.

The efficiency of the gas engine is often as high as 30 per cent, or greatly in excess of that of the best steam engines. Furthermore, it is free from smoke, is very compact, and may be started at a moment's notice. On the other hand, the fuel (gas or gasoline) is comparatively expensive. Most automobiles are run by gasoline engines, chiefly because the lightness of the engine and of the fuel to be carried are here considerations of great importance.

It has been the development of the light and efficient gas engine which has made possible man's recent conquest of the air through the use of the airplane and airship.

244. The automobile. The plate opposite page 210 shows the principal mechanical features of the automobile in their relation to one another. It will be seen that the cylinders of the engine are surrounded by water jackets which form part of a circulating system. The heat of the engine is carried by convection currents in this water to the radiator, where it is lost to the atmosphere through the air currents produced in part by a revolving fan (10). Unless some means were provided for cooling a gas engine, it would become so overheated that the pistons would stick fast. The power of the engine is transmitted to the rear axle through the clutch (11), the transmission (12), and the differential gearing.

245. The clutch and the transmission. Since a gas engine develops its power by a series of violent explosions within the cylinders, it is clear that it cannot start with a load as does the steam engine. In starting an automobile it is necessary first that the engine acquire a reasonable speed and that the power be ap