lesson5_dieselengines.ppt

7/29/2019 Lesson5_Dieselengines.ppt

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Lesson 5


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Rudolf Diesel-1892-high-compression, self-ignition engine (intended to burn poweredcoal)

Herbert Akroyd Stuart-1888-oil fuel wasignited by compressing the mixture of oil+airin contact with a hot wall in the combustionchamber

the pressure was permanently increased hotsurfaces were not needed any more for theignition


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main or auxiliary propelling machinery

OPERATING CYCLE:

two-stroke cycle

four-stroke cycle

CYCLE a series of steps following each other

STROKE a single up or down movement


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single acting engines

double- acting engines

opposed piston engines

Single acting engine one end of the cylinder to develop power

Double-acting engine both ends of the cylinder / both piston faces

- complicated construction- low speed units

- pistons shorter than in single acting engine


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In-line cylinder arrangement

V arrangement of cylinders

Flat arrangement of cylinders

Radial arrangement of cylinders


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Low speed: > 200 rev/min

Medium speed: 200 600 rev/min

High speed: < 600 rev/min


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Trunk piston engine (piston directly connected tothe rod)

Crosshead type engine (piston indirectlyconnected to the rod = piston rod /

crosshead)


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Direct drive = direct coupled engines (coupleddirectly to the propeller shafting)

Geared engines = indirect drive (coupled to areduction gearing)


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Direct reversible engine

(clockwise & anticlockwise rotation)

Non-reversible engine

(unidirectional engines)


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1. INDUCTION: crankshaft rotates clockwise andthe piston moves down the cylinder, inlet valveis open and a fresh charge of air is drawn into

the cylinder.


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2. COMPRESSION: inlet valve has closed and thecharge of air is compressed by the piston as itmoves up the cylinder. Because energy is being

transferred into the air, its pressure andtemperature increase. By the time the piston isapproaching the TDC the pressure is over 100bar and the temperature over 500.


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3. POWER: Just before TDC fuel is injected intothe cylinder by the fuel injector. The fuel is"atomised" into tiny droplets. Because they are

very small these droplets heat up very quicklyand start to burn as the piston passes overTDC.


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4. EXHAUST: As the piston approaches the BDC,the exhaust valve starts to open. As the pistonnow moves up the cylinder, the hot gases are

expelled from the cylinder. As the Pistonapproaches TDC again the inlet valve starts toopen and the cycle is repeated.


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1. The crankshaft revolves clockwise and thepiston moves up the cylinder, compressing the

charge of air. Because energy is being

transferred into the air, its pressure andtemperature increase. By the time the piston isapproaching the TDC the pressure is

over 100 bar and the temperature

over 500C.


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2. Just before TDC fuel is injected into the cylinderby the fuel injector. The fuel is "atomised" intotiny droplets. Because they are very small these

droplets heat up very quickly and start to burnas the piston passes over TDC.


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The expanding gas from the fuel burning in theoxygen forces the piston down the cylinder,turning the crankshaft. It is during this stroke

that work energy is being put into the engine;during the upward stroke of the piston.


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3. As the piston moves down the cylinder, the

useful energy from the burning fuel is expended.

At about 110 after TDC the exhaust valve opens

and the hot exhaust gases begin to leave thecylinder.


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4. At about 140 after TDC the piston uncovers a

set of ports known as scavenge ports. Pressurised

air enters the cylinder via these ports and pushes

the remaining exhaust gas from the cylinder in a

process known as "scavenging".


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The piston now goes past Bottom Dead Centre

and starts moving up the cylinder, closing off the

scavenge ports. The exhaust valve then closes and

compression begins.


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http://www.youtube.com/watch?v=x9yS2xdPJSU&feature=related

http://www.youtube.com/watch?v=MW1jixDvUSY&feature=related

http://www.animatedengines.com/
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lesson5_dieselengines.ppt

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