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  1. #1
    Moderator RX951's Avatar
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    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.






  2. #2
    tomgtv's Avatar
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    great graphic!

    I have a 14yro son who has a tendency to not care how things work. This is very helpful! You need to know this basic stuff to come up with at least an informed opinion as to what might be going on!

  3. #3
    Moderator RX951's Avatar
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    I have a 14yro son who has a tendency to not care how things work. This is very helpful! You need to know this basic stuff to come up with at least an informed opinion as to what might be going on!

    Right. Some people are more "visual" than others in their learning process and seeing something like this may help them fully understand how it actually works.

  4. #4
    Top banana's Avatar
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    suck squeez bang blow = four stroke hehe

  5. +1 by:


  6. #5
    captain obvious Lurker's Avatar
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    4 stroke is easy, I'm still pretty lost on the 2 stroke, that is one of the reasons I own two 4 stroke skis.

  7. #6
    Moderator RX951's Avatar
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    suck squeez bang blow

  8. #7
    Moderator RX951's Avatar
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    How a Two Stroke Engine Works !

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

    The two-stroke engine consists of only three mobile parts: Piston, connecting rod and crankshaft

    The first two-stroke engine was a gas engine invented and built by Etienne Lenoir in 1860.
    A two-stroke diesel engine was built by Dugald Clark in 1878


    Mode of operation of the Two-Stroke engine

    1st Stroke
    At the point where the spark plug fires, fuel and air in the cylinder have been compressed, and when the spark plug fires the mixture ignites.
    The resulting forces drives the piston downward. As the piston moves downward, it is compressing the air/fuel mixture in the crankcase.
    As the piston approaches the bottom of its stroke, the exhaust port is uncovered. The pressure in the cylinder drives most of the exhaust gases (but not all) out of cylinder.


    note:
    As the piston finally bottoms out, the intake port is uncovered. The piston's movement has pressurized the mixture in the crankcase, so it rushes into the cylinder, displacing the remaining exhaust gases and filling the cylinder with a fresh charge of fuel.


    2nd stroke
    Now the momentum in the crankshaft starts driving the piston back toward the spark plug for the compression stroke.
    As the air/fuel mixture in the piston is compressed, a vacuum is created in the crankcase. This vacuum opens the reed valve and sucks air/fuel/oil in from the carburetor. Once the piston makes it to the end of the compression stroke, the spark plug fires again to repeat the cycle.






    http://www.southernskies.net/page_in...okeengine.html

    http://www.vf750fd.com/blurbs/stroke.html
    Last edited by RX951; 12-27-2008 at 01:28 PM.

  9. #8
    951: Damn bro, that is freakin cool illustration!...PR...

  10. #9
    951: and again, very cool illustration!...PR...

  11. #10
    Moderator RX951's Avatar
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    Here is another good link comprised by NASA

    http://www.grc.nasa.gov/WWW/K-12/airplane/engopt.html

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