“But the Diesel engine,” he continued, “doesn’t need any carburetor or spark-plug. When the piston makes its first upward or compression-stroke, there is nothing in the cylinder but pure air. This is compressed to a pressure of about 500 pounds a square inch--and when you squeeze anything as hard as that, you make it mighty hot--”
“Like a blacksmith pounding a piece of cold iron to a red heat?” I suggested. The engineer nodded again.
“That compressed air is so hot that the oil which has been spurted in through an injection-valve is exploded, and drives the piston down on the power-stroke. The waste gases are then blown out by compressed air. There are an air-compressor and a storage tank just for scavenging, or blowing the waste gases out of every three power-cylinders.”
“What are the advantages of the Diesel over the gasoline engine?”
Auxiliary Switchboard and Electric Cook-stove, in a U. S. Submarine.]
“In the first place, it gives more power. You see, three out of every four strokes made by the piston of a gasoline engine--suction-stroke, compression-stroke, and scavenging-stroke--waste power instead of producing it. But the Diesel is what we call a two-cycle engine; its piston makes only two trips for each power-stroke. In the second place, it is cheaper, because instead of gasoline it uses heavy, low-price oil. And this makes it much safer, for the heavy oil does not vaporize so easily. The air in some of the old submarines that used gasoline motors would get so that it was like trying to breathe inside a carburetor, and there was always the chance of a spark from the electric motors exploding the whole business, and your waking up to find the trained nurse changing your bandages. The German navy refused to build a submarine as long as there was nothing better than gasoline to propel it on the surface. They didn’t launch their _U-1_ till 1906, after Dr. Diesel had got his motor into practicable shape. It cost him twenty years of hard work, but without his motor we couldn’t have the modern submarine. And they’re using it more and more in ocean freighters. There’s a line of motor-ships running to-day between Scandinavia and San Francisco, through the Panama Canal.