IN THE SUBMARINE "Q-4"
sene or gasoline, at a vast saving, and that instead of having the charges in the cylinders ignited by electric sparks, in the only way he had ever heard of, the engines produced their own heat for ignition by compression.
"It's like this," elaborated Clancy. "These are four cycle engines, do you see? That is, one of the pistons does four strokes to one explosion of the charge, two up and two down. Now take this fellow. When the piston in this cylinder goes down it draws a lot of air into the cylinder after it. When it goes up again it compresses that air something fierce; about five hundred pounds to the square inch. That heats the air, do you see, to something like a thousand degrees. Next oil is sprayed into the cylinder by compressed air, and when it hits that hot air already there it lights. That's what they call combustion, and that sends the piston down again and turns the shaft over. That's the third stroke. The fourth is the next up-stroke and that pushes the burnt gases out, and there you are!"
Nelson shook his head. "It sounds all right," he said, "but what makes the engine start first of all?"
"The storage batteries."
"And how fast will they, drive the boat?"
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