The major parts of diesel engines

The major parts of diesel engines Content of chapter 2 consist of: 2.1 Classification rules on diesel engine construction 2.2 Static parts 2.3 Moving parts 2.4 Driving mechanisms 2.5

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06/01/24 Editor: Nguyen Trung Cuong 1

Chapter 2 The major

parts of diesel engines

Content of chapter 2 consist of:

2.1 Classification rules on diesel engine construction

2.2 Static parts

2.3 Moving parts

2.4 Driving mechanisms

2.5 Indicate components

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2.1 Classification rules on diesel engine construction.

The construction of diesel

engine can be classified as follows:

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The main static parts of the diesel

engines consist of the following

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a Bedplate

• Main bearings serve

as supports for the

crankshaft

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a Bedplate

• Each Each bearing bearing

comprises a housing

cap and two

cylindrical shells

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a Bedplate

• The bedplate serves

to fasten an engine to

the body, to support

the entire weight of

fixed parts,

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a Bedplate

• To receive the forces

transmitted from the

moving parts;

• And to form the oil

basin for circulating

oil

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b Engine frame

• The boxlike framework connects

the cylinder block with the

bedplate and forms the oil-tight

crankcase.

• It It is is subjected subjected to to the the

compressive force caused by the

weight of the cylinder,

• Supports the tensile force exerted

by the cylinder at the time of

explosion and

• The thrust due to tilting of the

connecting rod.

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c Cylinder block.

• The high speed marine diesels

engine are built on the

"mono-block" principle,

• Their major static component is a

single piece cast block,

• Which are cast and bored with

individual cylinders

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• The structure of cylinder

blocks of two stroke engines

is more complicated than

that of four stroke engines

• Because they must have

passage for scavenging air

and exhaust gases.

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d cylinder covers.

• The cylinder covers,

which forms a part of

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• The design of a cylinder

cover depends upon such

factors as:

• the size of the valves,

• The size of fuel injection

valve,

• the size of cylinder, and

• the the shape shape of of the the

combustion chamber

•

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14 Editor: Nguyen Trung Cuong

06/01/24

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• The cylinder cover of

two stroke engine with

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06/01/24

• The cylinder covers of

return loop scavenge

two-stroke engines are

provided with sleeves

only for the injection

and starting valves

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• The cylinder cover is

cooled with water,

• Usually fresh water,

which is fed into the

cooling space through

the outer pipe.

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• For For preventing preventing air air

pocket forming inside

the cooling space

• The The air air pocket pocket

probably causes local

overheating that may

lead to cracks .

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2.3 Moving parts

The main moving parts of the diesel

engines consist of the following

ones:

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2.3.1 Piston and it's components

a Piston

There are two types of

pistons: trunk type and

cross-head type:

• The trunk piston is

used in engines where

the connecting rod

goes directly from the

piston to the

crankshaft.

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a Piston

• The The cross-head cross-head type type

piston has guides to

absorb the thrust of the

connecting rod

• And And their their sufficient sufficient

lubrication decrease the

mechanical friction

• Thus, the uneven wear of

the liner is avoided

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b

b Piston pins:

• The piston pin withstands, in spite of its sliding speed,

the highest bearing pressure within an internal

combustion engine and receives heat transmitted from the piston.

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b

b Piston pins

• Fixed type piston pin

• One end is bolted and

another is keyed

• Installation is by force

fit and for this the pin is

made larger than the

bore of boss by 2/100

mm

Key Piston pin

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Floating type of piston

 Medium, large and high

speed engine are mostly

used this type

 During operation, piston

pin is allowed to rotate

slowly.

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c Piston rings:

and oil ring:

• Gas-tight Gas-tight the the combustion combustion

chamber (top ring and piston

ring).

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c Piston rings:

The function of the piston ring

and oil ring:

• Transfers heat from piston.

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c Piston rings:

• Lubricate the piston

and liner

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c Piston rings:

• There are two type of

piston rings:

 Top ring and compression

rings, against leakage of

compressed air or

combustion gas.

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c Piston rings:

 Oil rings,

• Oil can pass through the ring to the ring back face and drain through the piston to the crankcase.

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c Piston rings:

• Scraper edges remove the excess oil on the downward stroke and distribute the oil on the upward stroke

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2.3.2 Connecting rods and cross-heads

a Connecting rods.

• The connecting rods converts

the rectilinear motion of the

trunk piston or cross-head in

to the rotary motion of the

crankshaft

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2.3.2 Connecting rods and

cross-heads

• Lubricating oil to the smaller

end is fed from the larger end

through the copper tube or a

hole provided along the trunk

of the connecting rods.

L.O from main pipe

piston pin

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b Cross-heads

 The cross-head often found in

large, low speed engines

 The piston and piston rod

moves only in the vertical

direction,

 There is no side thrust, so the

piston need not have an

extended trunk area to absorb

the thrust

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b Cross-heads

 There are, however,

cross-head guides to take the side

thrust, which results from the

angularity of the connecting

rod to crankshaft motion

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b Cross-heads

 The cross-head guides are

supported by the framework

of the engine.

 The structure consists of a

guide shoe and a slide guide

The lower end of the piston

rod is fastened to the

cross-head with nut

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2.3.3 Crankshaft.

a Acting force and materials:

 The The crankshafts crankshafts are are

subjected to bending and

torsional action during

engine operation and

 These alternately changing

forces exert complex and

repetitive stress.

 Forged steel is normally used

to make crankshafts and

nick-chrome steel is used for

high-speed engine to ensure

speed engine to ensure

durability

Position of crankshaft.

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2.3.3 Crankshaft.

b Arrangement:

in the multi-cylinder engine are arranged so that the backward movement is uniform by compensating for centrifugal force and irregular movement of moving parts.

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2.3.3 Crankshaft.

C Supply lubricating oil to the crankshaft

the main pipe to the main

piston pin

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2.3.3 Crankshaft.

crankshaft of the multi-cylinder engine

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2.3.3 Crankshaft.

d Counter weight (counter-balance):

Counter weights are designed to minimize engine

vibration by balancing the centrifugal force of the webs and pins, produced by the rotation of the crankshaft

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2.3.3 Crankshaft.

d Counter weight (counter-balance):

Also, due to the inertia effect of counter weights the

size of the flywheel can be reduced.

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2.4 Driving machanism.

 The camshaft is driven

by vertical shaft, chain

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1) What is function of the piston ring and oil

ring.

2) Why is the cross-head type piston longer

than trunk type piston.

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