4.2.5 Principle of Operation of Internal Combustion Engine
A four-stroke engine is called so, because the entire workflow is divided into four intervals - strokes. Of these cycles, only one is operating. That is, the one during which the piston moves under the action of gases that are released during the combustion of the fuel-air mixture. Each stroke falls on (approximately) one half turn of the crankshaft.
Note
Top dead center (TDC) - the extreme position of the piston in the upper part of the cylinder. Bottom dead center (BDC) - the extreme position of the piston in the bottom of the cylinder. The distance from TDC to BDC is called the piston stroke.
Surely everyone had a bicycle in their childhood. And if any tire was flat, then it had to be pumped up using a pump. So, albeit remotely, this tire inflation pump reminds us of a single-cylinder engine. There are also valves inside the cylindrical pump casing and the piston moves in the same way.
When you pull the piston handle towards you, air is sucked in through the valve in the casing. When you push the piston down - the valve at the intake closes and air goes out through it into the tube, getting into the tire of the bicycle wheel. Now let's mentally imagine an inverted pump, inside of which we began to move the piston downward, while drawing air inside the casing. Then we also mentally close the outlet, for example with a finger, and begin to move the pump piston upwards - the air will begin to compress, since it has nowhere to go. Upon bringing the pump piston to the stop, we took and set fire to the gunpowder in the housing, filled up before the start of this action. While burning, this gunpowder will emit a large amount of gas, which, in turn, will increase the pressure inside the body and begin to move the piston, only without our participation - on its own. Once the gunpowder is completely burnt out, and the piston reaches the lowest point, we will open the outlet and begin to move the piston up again, pushing the exhaust gases out of the pump housing. Having pushed the combustion products out, we again close the pump outlet with our finger and begin to repeat all of the above in the same sequence. Any four-stroke gasoline engine works in much the same way. Place the pump casing inside the block, install the valves inside the head, which is also mounted on the block, and connect the piston via the connecting rod to the crankshaft and get the simplest single-cylinder engine.
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