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How a Four Stroke Engine Works

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  • RX951
    Here is another good link comprised by NASA

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  • RX951
    started a topic How a Four Stroke Engine Works

    How a Four Stroke Engine Works

    For those newbies out there that was still learning about internal combustion engines, here is information on how a four-stroke engine works.

    The four stroke engine was first demonstrated by Nikolaus Otto in 1876, hence it is also known as the Otto cycle.
    The technically correct term is actually four stroke cycle.
    The four stroke engine is probably the most common engine type nowadays. It powers almost all cars and trucks.

    The four strokes of the cycle are intake, compression, power, and exhaust. Each corresponds to one full stroke of the piston, therefore the complete cycle requires two revolutions of the crankshaft to complete.

    Intake. During the intake stroke, the piston moves downward, drawing a fresh charge of vaporized fuel/air mixture.

    Compression. As the piston rises the poppet valve is forced shut by the increased cylinder pressure. Flywheel momentum drives the piston upward, compressing the fuel/air mixture

    Power. At the top of the compression stroke the spark plug fires, igniting the compressed fuel. As the fuel burns it expands, driving the piston downward.

    Exhaust. At the bottom of the power stroke, the exhaust valve is opened by the cam/lifter mechanism. The upward stroke of the piston drives the exhausted fuel out of the cylinder.

    Larger four stroke engines usually include more than one cylinder, have various arrangements for the camshaft (dual, overhead, etc.), sometimes feature fuel injection, turbochargers, multiple valves, etc. None of these enhancements changes the basic operation of the engine.