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Four Stroke Engine

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    الصورة الرمزية م.مجدي عليان
    م.مجدي عليان
    م.مجدي عليان غير متواجد حالياً

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    تاريخ التسجيل: Jan 2005
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    Four Stroke Engine

    Four Stroke Engine
    The four stroke engine was first demonstrated by Nikolaus Otto in 18761, 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. The illustrated engine features a 'poppet' intake valve which is drawn open by the vacuum produced by the intake stroke. Some early engines worked this way, however most modern engines incorporate an extra cam/lifter arrangement as seen on the exhaust valve. The exhaust valve is held shut by a spring (not illustrated here).

    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.

    This animation also illustrates a simple ignition system using breaker points, coil, condenser, and battery.

    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]
    م.مجدي عليان
    م.مجدي عليان غير متواجد حالياً
    عضو تحرير المجلة
    الصورة الرمزية م.مجدي عليان


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    وهذا هو الرابط للذي يريد الاستفادة اكثر
    http://www.keveney.com/Engines.html

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  3. [3]
    م.مجدي عليان
    م.مجدي عليان غير متواجد حالياً
    عضو تحرير المجلة
    الصورة الرمزية م.مجدي عليان


    تاريخ التسجيل: Jan 2005
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    Steam Locomotive Engine

    Steam engines like this drove trains from the early 1800s to the 1950s.1 Though the engines varied in size and complexity, their fundamental operation remained essentially as illustrated here.

    In a steam engine, the boiler (fueled by wood, oil, or coal) continuously boils water in an enclosed chamber creating high-pressure steam.

    Steam from the boiler enters the steam chest and is admitted to the front end of the cylinder by the valve slide (illustrated in blue). The high pressure steam presses the piston backward, driving the engine wheels around one half turn.

    At the end of the piston stroke the valve shifts, allowing the expended steam to escape through the exhaust port (underneath the blue valve slide). The high pressure steam escapes in a quick burst giving the engine its characteristic choo choo sound.

    At the same time, the valve slide begins admitting high pressure steam to the back end of the cylinder. This presses the piston forward, pulling the engine wheels around another half turn.
    At the end of the forward stroke, the steam is released from the rear portion of the cylinder (another choo).
    The steam engine has a 'dead' spot at the extreme end of each stroke while the valve is transitioning from power to exhaust. For this reason, most engines had a cylinder on each side of the engine, arranged 90 degrees out of phase, so the engine could start from any position. This illustration only shows one side of the engine.
    Though not a scale represenation of any particular engine, these illustrations draw heavily from the many excellent illustrations in Modern Locomotive Construction.

    Home Engines Bibliography
    Copyright 2000, Matt Keveney. All rights reserved.

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  4. [4]
    م.مجدي عليان
    م.مجدي عليان غير متواجد حالياً
    عضو تحرير المجلة
    الصورة الرمزية م.مجدي عليان


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    Two Stroke Engine


    The two stroke engine employs the crankcase as well as the cylinder to achieve all the elements of the Otto cycle in only two strokes of the piston.
    Intake. The fuel/air mixture is first drawn into the crankcase by the vacuum created during the upward stroke of the piston. The illustrated engine features a poppet intake valve, however many engines use a rotary value incorporated into the crankshaft.

    During the downward stroke the poppet valve is forced closed by the increased crankcase pressure. The fuel mixture is then compressed in the crankcase during the remainder of the stroke.

    Transfer/Exhaust. Toward the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder. Unfortunately, some of the fresh fuel mixture is usually expelled as well.
    Compression. The piston then rises, driven by flywheel momentum, and compresses the fuel mixture. (At the same time, another intake stroke is happening beneath the piston).

    Power. At the top of the stroke the spark plug ignites the fuel mixture. The burning fuel expands, driving the piston downward, to complete the cycle.

    Since the two stroke engine fires on every revolution of the crankshaft, a two stroke engine is usually more powerful than a four stroke engine of equivalent size. This, coupled with their lighter, simpler construction, makes two stroke engines popular in chainsaws, line trimmers, outboard motors, snowmobiles, jet-skis, light motorcycles, and model airplanes. Unfortunately most two stroke engines are inefficient and are terrible polluters due to the amount of unspent fuel that escapes through the exhaust port.

    Home Engines Bibliography
    Copyright 2000, Matt Keveney. All rights reserved.

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  5. [5]
    م.مجدي عليان
    م.مجدي عليان غير متواجد حالياً
    عضو تحرير المجلة
    الصورة الرمزية م.مجدي عليان


    تاريخ التسجيل: Jan 2005
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    Two Cylinder Stirling Engine
    The Stirling engine is one of my favorites. It was invented in 1816 by Rev. Robert Stirling of Scotland. The Stirling is a very simple engine, and was often billed as a safe alternative to steam (since there's no boiler to explode). It enjoyed some success in industrial applications, and in small appliances like fans and water pumps, but was eclipsed by the advent of inexpensive electric motors.3 Since it can run on any source of heat, it now holds promise for alternative fuel engines, solar power, geothermal power, etc.

    Stirling engines feature a completely closed system in which the working gas (usually air but sometimes helium or hydrogen) is alternately heated and cooled by shifting the gas to different temperature locations within the system.

    In the two-cylinder or alpha configured3 Stirling, one cylinder is kept hot while the other is kept cool. In the illustration the lower-left cylinder is heated by burning fuel. The other cylinder is kept cool by an air cooled heat sink (a.k.a. cooling fins).

    The Stirling cycle may be thought of as four different phases: expansion, transfer, contraction, and transfer.

    Expansion. At this point, most of the gas in the system has just been driven into the hot cylinder. The gas heats and expands driving both pistons inward.

    Transfer. At this point, the gas has expanded (about 3 times in this example). Most of the gas (about 2/3rds) is still located in the hot cylinder. Flywheel momentum carries the crankshaft the next 90 degrees, transferring the bulk of the gas to the cool cylinder.

    Contraction. Now the majority of the expanded gas has been shifted to the cool cylinder. It cools and contracts, drawing both pistons outward.

    Transfer. The now contracted gas is still located in the cool cylinder. Flywheel momentum carries the crank another 90 degrees, transferring the gas to back to the hot cylinder to complete the cycle.

    This engine also features a regenerator, illustrated by the chamber containing the green hatch lines. The regenerator is constructed of material that readily conducts heat and has a high surface area (a mesh of closely spaced thin metal plates for example). When hot gas is transferred to the cool cylinder, it is first driven through the regenerator, where a portion of the heat is deposited. When the cool gas is transferred back, this heat is reclaimed; thus the regenerator "pre heats" and "pre cools" the working gas, dramatically improving efficiency.3

    Home Engines Bibliography
    Copyright 2000, Matt Keveney. All rights reserved.

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  6. [6]
    speed99a
    speed99a غير متواجد حالياً
    عضو فعال جداً


    تاريخ التسجيل: Jun 2007
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  7. [7]
    medo911111
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    عضو


    تاريخ التسجيل: Nov 2006
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    شكرا جزيلا

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