The brothers' design is very simple by today's standards, so it is a good engine for students to study to learn the fundamentals of engine operation. This type of internal combustion engine is called a four-stroke engine because there are four movements, or strokes, of the piston before the entire engine firing sequence is repeated. The four strokes are described below with some still figures. In the animation and in all the figures, we have colored the fuel/air intake system red, the electrical system green, and the exhaust system blue. We also represent the fuel/air mixture and the exhaust gases by small colored ***** to show how these gases move through the engine.


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