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عالم المحركات .. شرح مبسط جدا بالصور المتحركه
منتدى كلية ينبع الصناعية > المنتديات التقنية و الهندسية > قسم الهندسة الميكانيكية التطبيقية
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May 14 2008, 12:25 PM
اخواني سوف نبدا هنا باذن الله عرض مجموعه من المحركات التي تستخدم
في مجال الطيران و في غير مجال الطيران

كبدايه سوف نبدا في شرح المحرك المكبسي اولا و من ثم ننتقل الي المحرك النفاث

Four Stroke Engine

كان اول عرض لهذا المحرك عن طريق العالم Nikolaus Otto عام 1876 , لذلك عرف المحرك باسم Otto cycle , و هو يعتبر اكثر الانواع شيوعا في الوقت الحاضر و يستخدم
في السيارات و الشاحنات .

(الكرات الخضراء تمثل الشحنه الجديده من الوقود + الهواء .. و الكرات الرماديه تمثل العادم ... و الون البرتقالي يمثل شعله الاحتراق)

شرح مبسط جداا لنظريه العمل و كيفيه الحصول علي الطاقه ..


1- Intake في هذه المرحله يتحرك المكبس الي اسفل في حين دخول شحنه جديده
من الوقود + الهواء .

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).


2- Compression يتم غلق الفتحتين المسؤلين عن دخول و خروج الهواء
مع الوقود بواسطه valves و يبدا المكبس في الصعود الي اعلي
لكي يضغط علي الهواء و يزيد من ضغطه داخل الاسطوانه

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.

3- Power بعد الانتهاء من المرحله السابقه و عندما يبدا المكبس في النزول
مره اخري فان شعله الاحتراق تنطلق spark plug لكي تشعل في الوقود مع
الهواء المضغوطين داخل الاسطوانه...و عند الاحتراق فان الوقود و الهواء معا
يضغطوا علي المكبس بقوه كبيره و تكون هذه هيا البارو التي ناخذها من المحرك

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.


4- Exhaust عند نزول المكبس الي اخر مشواره في المرحله السابقه يبدا
الvalve المسؤل عن خروج الخليط المحترق من الهواء و الوقود
في الانفراج لكي يخرج العادم.

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.
الحقوق ل ملتقى المهندسين العرب
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May 14 2008, 12:27 PM
Two Stroke Engine


- يستخدم هذا المحرك لانجاز كل ما كان يفعله stork 4 و لكن هنا مع stork 2 فقط


(الكرات الخضراءتمثل الشحنه الجديده من الوقود + الهواء .. والكرات الرماديهتمثلالعادم ... والون البرتقالييمثل شعله الاحتراق)



Intak

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
في البدايه .. فان شحنه الهواء و الوقود .. يتم ادخالها عن طريق valve ..
و يتم ادخالها عندما يكون المكبس في اعلي مشواره (كما هو موضح في الرسم)

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
اثناء هبوط المكبس .. فان قوه الضغط تذداد علي الvalve مما تودي الي اغلاقه
و في نفس الوقت يتم رفع الشحنه الي غرفه الاحتراق ليتم حرقها.



Compression

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
يبدا المكبس في كبس الهواء و الوقود لزياده ضغطهم ..
و في نفس الوقت يبدا عمليه دخول لشحنه هواء جديده (كما هو موضح بالرسم)


Power

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
بعد الانتهاء من عمليه كبس الهواء مباشره .. تبدا شعله الاحتراق spark plug في حرق الهواء و الوقود بعد وصولهم الي ضغط كبيير لكي يسهل احتراقهم..
و يتولد عن هذا الاحتراق انه يدفع المكبس بقوه كبيييره جداا الي الاسفل و هذه القوه الكبييره هي قوه المحرك التي نستفيد منها


a two stroke engine is usually more powerful than a four stroke engine of equivalent size

Transfer & Exhaust

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
اثناء هبوط المكبس .. فانه يسمح بخروج الشنحه المحترقه و في نفس الوقت يسمح
بدخول الشحنه الجديده لكي يتم احتراقها داخل غفه الاحتراق (كما موضح بالرسم)


يستخدم هذا المحرك في ...
( متسكلات البحر - درجات بخاريه خفيفه - نماذج الطائرات - درجات ناريه خفيفه - ...)

* للاسف فان هذا المحرك اسوء بكثير من المحرك السابق
من حيث انه ملوث جدااا للبيئه بسبب هروب كميات كبيره
من الوقود الغير محترقه خارج اسطوانه الاحتراق.
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May 14 2008, 12:27 PM
Wankel Engine

هو محرك رائع و زكي جدا من حيث التصميم و يعتبر افضل من otto cycle
و تم بتطور العالم Felix Wankel في عام 1950


In the Wankel a triangular rotor incorporating a central ring gear is driven around a fixed pinion within an oblong chamber
الحركه الدورانيه تتولد من دورانه حول ترس كبييير متحرك ياخذ حركته من ترس اخر اصغر منه
في الحجم و ثابت لا يتحرك


The fuel/air mixture is drawn in the intake port during this phase of the rotation.


The mixture is compressed here.


The mixture burns here, driving the rotor around.


And the exhaust is expelled here.


The rotory motion is transferred to the drive shaft via an eccentric wheel (illustrated in blue) that rides in a matching bearing in the rotor. The drive shaft rotates once during every power stroke instead of twice as in the Otto cycle. ok
الحركه الدورانيه يتم نقلها الي العمود shaft via عن طريق حلقه دورانيه ليست في المركز
و الموضحه باللون الازرق.
The Wankel promised higher power output with fewer moving parts than the Otto cycle engine, however technical difficulties have apparently interfered with widespread adoption. In spite of valiant efforts by Mazda, the four stroke engine
remains much more popular
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May 14 2008, 12:28 PM
Atkinson Engine

The Atkinson engine is essentially an Otto-cycle engine with a different means of linking the piston to the crankshaft. It was originally designed to compete with the Otto engine, but without infringing on
any of Otto's patents

هو يعتبر مثل محرك Otto-cycle engine و لكن بطريقه مختلفه لربط الpiston مع ال crankshaft ..
و هو صمم خصيصا لكي ينافس محرك Otto-cycle في التصميم و لكن مع مراعاه حقوق
محرك Otto-cycle في براءه اختراعه .


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May 14 2008, 12:29 PM
Turbojet






.يعتمد هذا المحرك علي احتراق الاكسجين من الهواء الجوي

At the front of the engine, the turbine shaft drives a compressor. The compressor works a lot like the turbine only in reverse. Its purpose is to draw air into
the engine and pressurize it.
في البدايه فان الهواء يدخل علي الcompressorو الذي يقوم بدوره في ضغط الهواء بقوه


Fuel continuously burns inside a combustion chamber just like the rocket. The expanding gasses escape out the nozzle generating thrust in the opposite direction.

عند دخول الهواء المضغوط الي غرفه الاحتراق .. فانه يتم اشعاله بواسطه شعله للاحتراق فيتم بذلك
ارتفاع حرارته و ضغطته بصوره كبيره و من ثم عند خروجه من الغرفه فانه يولد قوه الدفع
التي يخرجها المحرك

Now the differences: On its way out the nozzle, some of the gas pressure is used to drive a turbine. A turbine is a series of rotors or fans connected to a single shaft. Between each pair of rotors is a stator -- something like a stationary fan. The stators realign the gas flow to most effectively direct it toward the blades of the next rotor

بعد اكتمال احتراق الهواء و الوقود و عند خروجه فاننا نستخدمه لكي نشغل التربينه و هيا مجموعه من الريش
متصله مع بعضها البعض علي محور واحد .. و لكي نتاكد من ان الهواء سيقوم بلف التربينه فاننا نضع stator
بين كل مروحتين من مراوح التربينه .. و فائدته انه يحدث توجيه للهواء المحترق
بحيث يعمل دوران جيد للتربينه
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May 14 2008, 12:29 PM
Steam Locomotive Engine




Steam engines like this drove trains from the early 1800s to


the 1950s
( الكرات الحمراء تمثل شحنه الهواء الجديده ..الكرات الخضراء و تمثل الهواء المحترق مع الوقود )








In a steam engine, the boiler (fueled by wood, oil, or coal) continuously boils water in an enclosed chamber creating high-pressure steam
في المحركات التي تعمل بالبخار .. فان تسخين و غلي الماء يتم باستمرار داخل غرفه لتكوين
بخار الماء و يكون ضغطه مرتفع.





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

يتم دخول البخار الي الاسطوانه الاولي لكي يتم ضغطه .. و يدخل بواسطه
valve slide الموضح باللون الازرق ..






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


عند انتهاء المكبس من مشواره .. فان المحبس الازرق يسمح بخروج الهواء المحترق للاعطاء قوه الدفع ..و بما انه هواء علي ضغط عالي و يخرج بسرعه ايضا فان لخروجه صوت مميز

و هو صوت القطارات التي نسمعها






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
في نفس الوقت .. فان الvalve يسمح بمرور ضعط عالي في الاسطوانه الخلفيه ..
و هذا الضغط يساعد المكبس علي ضغط علي طرد الهواء المحترق.



At the end of the forward stroke, the steam is released from the
.(rear portion of the cylinder (another choo
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May 14 2008, 12:29 PM
Oscillating Steam Engine

This style steam engine employs the cylinder as the steam valve
It operates on the same principle as the locomotive steam engine
( الكرات الحمراء تمثل شحنه الهواء الجديده ..الكرات الخضراء و تمثل الهواء المحترق مع الوقود )


Steam from the boiler enters the power manifold and is and is admitted to the top end of the cylinder when the cylinder port aligns with the manifold port. The steam presses the piston downward, driving the flywheel around
one half turn


At the end of the stroke the cylinder shifts, exposing the top port to the
exhaust manifold. The expended steam is released


At the same time, the bottom cylinder port, aligns with the power manifold, admitting steam to the bottom end of the cylinder. This presses the piston
upward, driving the flywheel around another half turn


At the end of the stroke, the bottom port aligns with the exhaust manifold, releasing the expended steam


Due to its exceedingly simple construction, this type of engine is popular in working toy steam engines, including one I had as a kid. An even simpler type employs power in only one direction, relying on flywheel momentum to carry the piston around for the remainder of the cycle. This is called a single acting engine. The type illustrated here is a double acting engine

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May 14 2008, 12:30 PM
Coomber Rotary Engine



I first learned of this delightful engine while attending the PRIME show in Oregon. A most prolific modeler, Marlyn Hadley, had one on display. I referred to his excellent book6 to create this illustration
I have not illustrated the valve linkage, as I'm not exactly sure what it looks like! It appears to be a rotary type, incorporated into the main drive shaft. Steam would be admitted to one end of the cylinder at a time, just as in any other double-acting steam engine.
The inner dimension of the stationary ring is not circular, but is slightly elliptical. The main bearing is offset from the center of this ellipse by a one half the stroke length

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May 14 2008, 12:30 PM
CO2 Motor



This style engine could be powered by steam (I've heard of at least one) but is more commonly seen in small model airplane engines powered by compressed air or CO2 (carbon dioxide) gas. The popular Air Hogs toy airplanes are propelled by this style motor






At the top of the stroke, the pin on the cylinder presses the ball valve upward, admitting high pressure gas into the cylinder
عند ارتفاع المكبس الي اعلي مشواره فانه يضغط علي الكره الموضحه في الرسم .. مما يسمح
بمرور الغاز الي داخل غرفه الاحتراق




The gas expands, driving the piston downward



when the piston advances past the exhaust port, the high-pressure gas is released




Flywheel (or propeller) momentum carries the piston upward to complete the cycle




This animation also illustrates the CO2 reservoir, or "fuel tank." Compressed CO2 is a liquid and becomes a gas as the pressure is released... Another way to state this is that the liquid CO2 boils at normal atmospheric temperature and pressure, so one might say this engine runs on "CO2 steam

Model engines of this type have been made to incredibly small dimensions. Stefan Gasparin produces one with a displacement of only 3.2 cubic millimeters!
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May 14 2008, 12:31 PM
Crank Substitute Engine

Like the Coomber, this engine also came from Marlyn Hadley's wonderful book.6 I can do no better than to quote him



This elaborate arrangement of gears and linkages enabled the builder to eliminate the crank as we know it. While this engine required more labor to construct, it did make a compact engine which did not require a heavy crosshead as the connecting rod connection on the bar between the two gears moves but a very small amount. This means the piston rod guides can be made of a lighter construction

I do not know who invented it, when, or what prompted the inventor to think this arrangement is better than a crank...
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May 14 2008, 12:31 PM
Revolving Cylinder Engine



This is yet another of Marlyn Hadley's6 model engines. The inventor is not known

The valve is not illustrated, but is apparently a rotary type, admitting steam to one end of the cylinder at a time
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May 14 2008, 12:32 PM
Watt Beam Engine





This illustration shows the general arrangement of a typical beam engine. Beam engines were used in many factories to drive machinery of all types and were sometimes built to enormous proportions. I have omitted the valve gear, as it was substantially the same as the locomotive engine.

It was important to restrict the motion of the piston and rod to a straight line in order to reduce friction and wear on the upper cylinder seal. The Watt linkage illustrated here is one of many contrivances for accomplishing this linear motion.
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May 14 2008, 12:32 PM
Grasshopper Beam Engine




The "Grasshopper" beam5 is another type of linear motion linkage, obviously named for the beam's resemblance to a grasshopper's hind leg
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May 14 2008, 12:33 PM
Another Beam Engine




This illustration shows a beam engine with yet another linear motion linkage. I found this linkage in Five Hundred and Seven Mechanical Movements. The book did not say who invented this linkage or what it is called
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May 14 2008, 12:34 PM
Newcomen Atmospheric Engine

This magnificent engine was patented in 1705 by Thomas Newcomen, and is generally regarded as the first 'modern' steam engine. Unlike later steam engines, the Newcomen works on the atmospheric principle.


The Newcomen was first used to pump water from mines in England. The pump rod at left is coupled to the driving piston by a large rocking beam.

Water is boiled continuously to produce steam. During the piston's upward stroke this low pressure steam (about 5 p.s.i.) is admitted to the cylinder.
The pressure is insufficient to lift the piston on its own -- the weight of the pump rod does most of the work



At the top of the stroke the steam valve is closed and a water jet is briefly turned on, cooling the steam in the cylinder.


The cool steam contracts, sucking the piston downward. ...Or stated another way: the higher atmospheric pressure drives the piston downward, hence the name atmospheric engine. At the end of the stroke, the cooling water is drained from the cylinder by an extra passage not illustrated here.


During the upward stroke, an auxiliary pump fills the cooling water reservoir.



Newcomen engines were successful in part because they were very safe to operate.. Since the steam was under such low pressure, there was no risk of a dangerous boiler explosion.
As near as I can tell, the earliest Newcomen engines featured manually operated valves, as illustrated here.
An operator apparently stood on a platform near the cylinder base and threw the valve levers on each stroke. (From the illustrations I have available, this engine seems to have stood at least 20 feet tall).
Later Newcomen engines featured automatic valves which were coupled to a pushrod attached to the main beam.
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May 14 2008, 12:36 PM
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).


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).

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
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May 14 2008, 12:36 PM
Single Cylinder Stirling Engine

This type of Stirling engine, known as the beta configuration3, features just one cylinder with a hot end and a cool end.
The working gas is transferred from one end of the cylinder to the other by a device called a displacer (here illustrated in blue).
The displacer resembles a large piston, except that it has a smaller diameter than the cylinder, thus its motion does not change the volume of gas in the cylinder - it merely transfers the gas around within the cylinder.


Expansion.
At this point, most of the gas in the system has just been driven to the hot end of the cylinder. The gas heats and expands driving the piston outward.


Transfer
At this point, the gas has expanded. Most of the gas is still located in the hot end of the cylinder. Flywheel momentum carries the crankshaft the next quarter turn. The bulk of the gas is transferred around the displacer to the cool end of the cylinder.


Contraction
Now the majority of the expanded gas has been shifted to the cool end. It contracts, drawing the piston inward.


Transfer
The contracted gas is still located near the cool end of the cylinder. Flywheel momentum carries the crank another quarter turn, moving the displacer and transferring the bulk of the gas back to the hot end of the cylinder
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May 14 2008, 12:37 PM
Stirling Engine with Ross yoke



Andy Ross
, a prominent Stirling engine experimenter, invented the linkage illustrated here.3
The engine is identical in operation to the two cylinder Stirling. In this illustration, the left cylinder is the hot cylinder

The linkage allows the engine to be more compact and reduces side loads
on the pistons and connecting rods (since their travel is almost linear


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May 14 2008, 12:38 PM
Gnome

The Gnome was one of several rotary engines popular on fighter planes during World War I.
In this type of engine, the crankshaft is mounted on the airplane, while the crankcase and cylinders rotate with the propeller

The Gnome was unique in that the intake valves were located within the pistons. Otherwise, this engine used the familiar Otto four stroke cycle. At any given point, each of the cylinders is in a different phase of the cycle
In the following discussion, follow the master cylinder with the green connecting rod

Intak
During this portion of the stroke, a vacuum forms in the cylinder, forcing the intake valve open and drawing the fuel-air mixture in from the crankcase

Compression
The mixture is compressed during this phase. The spark plug fires toward the end of the compression stroke, slightly before top dead
center

Power
The power stroke happens here. Note that the exhaust valve opens early -- well before bottom dead center

Exhaust
This engine has a fairly long exhaust stroke. In order to improve power or efficiency, engine valve timing often varies from what one might expect

Nonetheless, a number of engines were designed this way, including the Gnome, Gnome Monosoupape, LeRhone, Clerget, and Bentley to name a few. It turns out there were some good reasons for the configuration

Balance... Note that the crankcase and cylinders revolve in one circle, while the pistons revolve in another, offset circle. Relative to the engine mounting point, there are no reciprocating parts. This means there's no need for a heavy counterbalance

Air Cooling... Keeping an engine cool was an ongoing challenge for early engine designers. Many resorted to heavy water cooling systems. Air cooling was quite adequate on rotary engines, since the cylinders are always in motion

No flywheel... The crankcase and cylinders provided more than adequate momentum to smooth out the power pulses, eliminating the
need for a heavy flywheel


All these factors gave rotary engines the best power-to-weight ratio of any configuration at the time, making them ideal for use in fighter planes. Of course, there were disadvantages as well

Gyroscopic effect... A heavy spinning object resists efforts to disturb its orientation (A toy gyroscope demonstrates the effect nicely). This made the aircraft difficult to maneuver.

Total Loss Oil system. .. Centrifugal force throws lubricating oil out after its first trip through the engine. It was usually castor oil that could be readily combined with the fuel. (The romantic-looking scarf the pilot wore was actually a towel used to wipe the slimy stuff off his goggles


The aircraft's range was thus limited by the amount of oil it could carry as well as fuel. Most conventional engines continuously re-circulate a relatively small supply of oil
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May 14 2008, 12:39 PM
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