The Submarine Torpedo Boat
Its Characteristics And Modern Development

THE POWER PLANT 113 in actual practice and construction it is exceedingly far from being so. The theory of the Diesel principle is: that on the first down stroke of the piston the cylinder is filled with fresh air, which is then compressed by the following up stroke of the piston to a pressure of about 500 pounds per square inch. This compression of the air raises its temperature to about 1,000° F. At the instant the piston reaches the top dead center a small quantity of fuel oil is injected along with a fresh quantity of air under a pressure of about 900 pounds per square inch. This injection takes place usually through a period of one-tenth of the downward stroke of the piston. The fuel which is broken up into a fine spray by the pressure of the air enter- ing with it, immediately it comes in contact with the hot air within the cylinder starts up combustion due to the temperature of the contained air being much higher than the flash point of the oil. The combustion continues through part of the stroke, supposedly until all of the oil has been completely burned, and expansion takes place during the remainder of the stroke on account of the ex- pansive force of the pressure and temperature of the gas- eous products of combustion. During the first part of the stroke the aim is to have the combustion proceed at a rate which will cause the volume of the gas to increase in the same ratio as the volume of the cylinder during this combustion so as to keep the pressure constant until the fuel is completely consumed. At the end of the stroke the exhaust valves are opened and the burnt gases are pushed out by the next up stroke of the piston. The foregoing statements apply more particularly to the four stroke cycle Diesel, but the principle of the two stroke cycle is essentially the same. The chief difference