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University of Aden Faculty of Engineering Summer Training I Students -: Rafat Abdo Abdullah 101029 Mahmood Galal Obaid 101082

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University of Aden

Faculty of Engineering

Summer Training I

Students -:

Rafat Abdo Abdullah 101029

Mahmood Galal Obaid 101082

Internal Combustion Engine: 1.

This site gives an overview of all the techniques used to study combustion processes and a guide to aid the understanding of the

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combustion cycle as a whole. As shown in fig. (1) The internal combustion, engine converts chemical energy into useful mechanical energy by burning fuel.

FIG (1.) IC Engine

1. The four stokes of engine :

-Intake:as the piston starts down from top dead center on the Intake stroke, the intake valve opens and the fuel-air mixture in petrol engine or fresh air in diesel engine is drawn into the cylinder .When the piston reaches the bottom of the intake stroke, the intake valve closes, trapping the air-fuel mixture or heated air in the cylinder

Compression :-

The piston moves up from the bottom dead center and compresses the trapped air fuel mixture or the heated air that was brought in by the intake stroke. The amount that the mixture is compressed is

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determined by the compression ratio of the engine. And the distance that the piston reaches the top dead center at the compression stroke is varies according to the design of each

company .

-Power:The spark plug fires, igniting the compressed air-fuel mixture or high pressure and heat explodes the compressed diesel from nozzle of injector, which produces a powerful expansion of the vapor.  The combustion process pushes the piston down the cylinder with great force turning the crankshaft to provide the power to propel the vehicle. Each piston fires at a different time, determined by the engine firing order. By the time the crankshaft completes two revolutions, each cylinder in the engine will have gone through one power stroke.

- Exhaust:With the piston at the bottom dead center of the cylinder, the exhaust valve opens to allow the burned exhaust gas or diesel to

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be expelled to the exhaust system.   Since the cylinder contains so much pressure,

when the valve opens, the gas or diesel is expelled with a violent force (that is why a vehicle without a muffler sounds so loud.)    The piston travels up to the top dead center of the cylinder pushing all the exhaust out before closing the exhaust valve in preparation for starting the four stroke process over again.

FIG (1.1) Four stokes of IC engine

1.2 Main parts of engine :

Cylinder block-:

The cylinder block is generally a single unit made of cast iron ,it also supports for the crankshaft and camshaft bearings.

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Cylinder block FIG (1.2.)

Piston-:

The piston transforms the energy of the expanding gases into mechanical energy. It is commonly made of aluminum or cast iron alloy. The piston has a rings in order to keep the compression and to avoid oil leakage into the combustion chamber.

FIG (1.2.1) Piston

-Crankshaft:

The crankshaft transforms the linear motion of the pistons into rotational motion ,crankshaft is made of forged steel .the crank shaft lies on the cast iron block crankshaft supports ,but it lies on special bearings called main bearings. The crankshaft has a large weights called counter weights that balance the weight of the

connecting rods .

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Crankshaft FIG (1.2.2)

Camshaft-:

Camshaft is a long bar with egg-shaped eccentric lobes, as the camshaft rotates the follower is forced up and down as it follows the cam lobe , the followers are connected to the engine valves through various types of linkage called pushrods and rocker arms. the push

rods and the rocker arms transfer the motion generated by lobes of the camshaft to the valves, opening and closing as

needed .The valves are tightened by springs

.

Camshaft FIG (1.2.3)

Fly wheel-:

The flywheel is located on one end of the crankshaft and serves for example that it reduces the vibration by smoothing out the power stroke as each cylinder fires , and in some engines the flywheel has

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a gear teeth around its perimeter that allow the starter motors engage and crank the engine .

Cylinder head-:

A cylinder head is bolted to the top of the cylinder block and contain the combustion process that takes place inside the cylinder. The cylinder head contains at least one intake valve and one exhaust valve for each cylinder. This allows the air-fuel mixture or

the compressed

diesel to enter the cylinder

and the burned exhaust gas to

exit the cylinder .

 

FIG (1.2.4) Cylinder head

1.3 Petrol engine :

Chemical energy is released when the fuel-air mixture is ignited by the spark in the combustion chamber . The gas produced in this reaction rapidly expands forcing the piston down the cylinder on the power stroke. The basic components for a combustion cycle in a four stroke engine are the combustion chamber (cylinder), piston, intake port and outlet or exhaust port.

The piston reciprocates inside the cylinder, exhaust and intake ports open and close during various stages of the cycle. The movement of the piston up or down the cylinder makes up one stroke of the four stroke cycle. The linear motion is then converted to rotary motion by the crankshaft. The crankshaft is shaped to balance the pistons which are fired in a particular order to reduce engine vibration ,The flywheel then helps smooth out the linear movement of the pistons.

- Ignition Systems:

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The purpose of the ignition system is to create a spark that will ignite the fuel-air mixture in the cylinder of an engine.  It must do this at exactly the right instant and do it at the rate of up to several thousand times per minute for each cylinder in the engine.  If the timing of that spark is off by a small fraction of a second, the engine will run poorly or not run at all. The ignition system sends an extremely high voltage to the spark plug in each cylinder when the piston is at the top of its compression stroke. 

The tip of each spark plug contains a gap that the voltage must jump across in order to reach ground. The voltage that is available to the spark plug is somewhere between 20,000 volts and 50,000 volts or better.  The job of the ignition system is to produce that high voltage from a 12 volt source and get it to each cylinder in a specific order, at exactly the right time. 

Ignition System FIG (1.3.)

Petrol engine depends on the Distributer that is also called (Delco) which distributes the spark to each cylinder according to timing ,the Delco receives the voltage from the coil that is connected to the battery , which is responsible for magnifying the voltage that is

required to maintain the appropriate spark for the combustion

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Distributer FIG (1.3.1)

chamber .In petrol engine there is one spark plug for each cylinder that is connected to the Delco through an electric wire

Spark Plug FIG (1.3.2)

also in petrol engine the cylinder head is not aligned but is elliptical shaped in order to increase the combustion chamber, and the piston is aligned with no hole on its top surface. In petrol engine supplying the fuel to the cylinders across the carburetor that is provided with

the fuel from the main tank .

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Carburetor FIG (1.3.3)

1.4 Diesel engine :

Diesel engine four strokes are similar to the petrol engine ,but the main difference is that the diesel engine is ignited by a system having heater, fuel pump and injector which contains the nozzle , when the heater which is connected to the combustion chamber starts to heat then at the power stroke the injector injects a compressed diesel, then the explosion is maintained that pushes the piston down to the bottom dead center. and the fuel pump is the

responsible for providing the injector with fuel

Also another difference between the petrol and diesel engine is that the head cover in petrol elliptical shaped in order to increase the combustion chamber, and the piston is aligned with no hole on its top surface ,but in diesel engine the head cover is aligned and the top surface of the piston has a hole in order to increase the

combustion chamber

Injecting Systems-

In diesel engine the injecting system depends on the injector that is shown in figure below, that is used to mix the fuel with air in order

for the combustion is maintained .

Injector FIG (1.4)

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1.5 Gear box :

Gearbox is one of the most important parts of cars and boats. Because we know that the engine rotates continuously with no control, here comes the advantage of gearbox .As the car moves its heavy weight needs a strong push so we use gear1 where its size is

big it means that it takes short turns from big turns coming from

the engine.When the car moves we change to gear2 that is smaller than gear1 in order to increase the speed of the car, also for gear3-4-5.As the shaft that comes from engine rotates its gear rotates too and it turns the rest of gears ,when we change any gear we have to separate the motion of the engine gear pressing clutch then

freely gears are changed .

Gear box FIG (1.5)

Changing Gears is performed at the beginning of the car movement where it is recommended to press the clutch in order to separate the movement that comes from the engine .Because it is difficult to

stop the engine while the car is moving .

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Reverse motion of the car is in a need for an idler gear that is connected between the two gear in order to rotate in opposite

direction

reverse motion Gear box FIG (1.5.1)