Unit IV -IC Engines-PDF

7/27/2019 Unit IV -IC Engines-PDF

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it is a device used to convert heat energy into

.

Heat energy is obtained by combustion of.

. .

External Combustion en ine E.C En ine .


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eng ne:

w ere com us on o ue pe ro ese

with air takes place inside the engine cylinder.

EX: Petrol & Diesel engine.

u u u

the cylinder.


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IC engine Terminology

Bore: inside dia of the cylinder.

position of reached by the piston at thetop of the cylinder is called TDC.

Bottom Dead Centre: The extreme

position reached by the piston at thebottom of the cylinder is called BDC.

Stroke (L):the nominal distance travelledby the piston in the cylinder bn theextreme upper 7 lower position of the

p ston s terme as stro e.


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IC en ine Terminolo Cont...

Compression ratio( r) :

. .

Cylinder volume.

Swept volume.

Clearance volume.


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Major parts of IC engine Cont..

9Cylinder head: it is fitted at the top of

9Material: Cast iron, aluminum.


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9


A piston is a cylindrical piece of metalthat moves up and down inside thecy n er.

9Material : Cast iron, Al alloy , Ni alloy & cast steel

Piston rings provide a sliding seal

between the outer edge of the pistonan t e inner e ge o t e cy in er. T erings serve two purposes:

9 Material : alloy CI, plated with chromium


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The connecting rod connects the piston to the

.

its angle can change as the piston moves and.

Material : Plain carbon steel, Al alloy,Ni alloy.


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CrankshaftThe crankshaft turns the piston's up and down motion into

.

Material : Alloy steel .


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The Four Stroke En ine


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Th f r tr k f th l r

Intake or suction,

compression,

exhaust.


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Engine pulls piston outof cylinder

Low ressure insidecylinder

pushes fuel and air

Engine does work on the


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Engine pushes piston into

.

Mixture is compressed tohigh pressure and

temperature. Engine does work on the

ases durin this stroke.


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after compression stroke:Pressure = High


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3. Power Stroke

Mixture burns to form hot

Gases push piston out ofcy n er

Gases expand to lowerpressure and temperature

iduring this stroke


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Pressure = Very highTemperature = Very hot


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Burned gases after power stroke:

Temperature = High


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.

ng ne pu e p oninto cylinder

g pressure ns e

cylinder ressure pus es urnegases out of cylinder

ng ne oes wor on egases during this stroke


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Burned gases after

i :Pressure = Atmospheric

e era ure = o era e


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Burned gases after even

i :Pressure = Below atmospheric

e era ure = e


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Intake

The fuel/air mixture is first drawn into thecrankcase by the vacuum created during theupwar s ro e o e p s on. e us ra e

engine features a poppet intake valve, however

into the crankshaft.

the fuel/ air mixture is compressed

n e cy n er o g pressure

and temperature.


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Power stroke:

electric spark to ignite the fuel to start the combustion process.(fuel injector sprays the fuel in the case of diesel engine)

tends to move the piston downwards.

Exhaust stroke: At the bottom of the power stroke,

the exhaust port is opened .

the exhausted fuel out of the cylinder


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Two stroke engine


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Com arison of four stroke & two stroke en ines

FOUR STROKE 1. For ever two revolution

TWO STROKE 1. For every one revolution

of the crank shaft, there is

one power stroke.

o t e cran s a t, t ere s

one power stroke.

2. Because of the above,turning moment is not souniform and hence heavier

2. Because of the above,turning moment is more

uniform and hence a lighterflywheel is needed.

3. For the same ower

.

more space is required. 3. For the same power lessspace is required.


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4. Because of one power 4. Because of one power stroke

,

lesser cooling and lubrication

requires. Lower rate of wear

,

cooling and lubrication

requirements. Higher rate of

and tear. wear and tear.

.

and exhaust valves.

.

cylinder walls inlet, exhaust,

and transfer port.

6. Because of heavy weight,

complicated valve mechanism 6. Simple in design, light

,complicated design and

difficult to maintain.

to maintain.


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7. The airfuel mixture is 7. As inlet and exhaust port

efficiency is higher.

times fresh charges mayescape with exhaust gases. The

ex aus gases are no a ways

completely removed. Thiscause lower efficiency.

8. Volumetric efficiency is

8. Volumetric efficiency is low

induction.ue o esser me or

induction.

9. Lower fuel consumption

per horse power. 9. The fuel consumption per

horse power is more because

o ue ut on y t e ex austgas.


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CO SO O S C G S


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COMPARISON OF S.I. AND C.I. ENGINES

S.I ENGINES C.I ENGINES

1. The fuel used is gasoline(Petrol).

1. Fuel used is Diesel.

2. Air + Fuel mixture is takenduring suction.

2. Only air taken duringsuction.

3. For mixing air and fuel a 3. No need of carburetor.carburettor is required.

4. Since homogeneousmixture is produced incarburettor, no need of

.the fuel inside the cylinder,fuel injector is necessary.

injector.


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5. Pressure at the end of

compression is about 10

5. Pressure at the end of

compression is about 35

bar. bar.

6. A spark plug is used to

ignite the air fuel mixture.

6. Spark plug is not

necessary.

7. Self ignition temperature

of fuel is not attained. In

7. The fuel get ignited due

to the high temperature ofother words, the fuel is not

self ignited.

compressed air.

8. S.I. Engines works on otto

cycle (i.e) combustion takes

. . .diesel cycle (i.e) combustion

takes place at constant

place at constant volume. pressure.


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9. Compression ratio is

around 6 to 10.

9. Compression ratio is

around 15 to 25.

10. Cold starting of engine is 10. Cold starting of engine is

easy. difficult.

. .

12. Cost is com arativel

. .

low. 12. Cost is high.

13. Running cost is high.

13. Running cost is not high.


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14. Less maintenance. 14. High maintenance is

15. thermal efficiency is

about 25%.

.

15. thermal efficiency is

about 35 to 45%.

16. Over heating trouble is 16. Over heating trouble is

more. ess.

. par p ug nee s

frequent maintenance.

.

maintenance.

18. These are high speed

engines.

These are medium or slow

speed engines.

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Unit IV -IC Engines-PDF

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