TỰ ĐỘNG HÓA HỆ THỐNG LẠNH

1.1 History of engine development .• Application of the internal combustion engines: • The internal combustion engines, especially diesel engines, have a wide use in stationary, marine

Marine Diesel Engines

• Theory: 90 periods (in class)

CHAPTER 1: Operational Principle of Diesel engines

• 1.1 Introduction and development history of diesel

engine.

• 1.2 The operational principles of four stroke engine

• 1.3 The operational principles of two stroke engine

• 1.4 Classification of internal combustion engine.

• 1.5 The symbol of diesel engine of some firms.

• 1.6 Nomenclature of internal engine

1.1 History of engine development

• In the 19th century and early 20th century, steam engines

were strongly developed in Europe as propulsion plants for trains, pumps, and steam ships

• In these engines, potential energy of the steam is converted

into mechanical work of a piston that moves in a cylinder.

1.1 History of engine development

• The steam is provided to the cylinder by a boiler The

steam engines can be called as the external-combustion engines.

• In 1778, the first internal combustion engine was

designed by a German engineer, Mr Otto This engine was called spark-ignition engine.

1.1 History of engine development

• In 1892, a German engineer, Rudolf Diesel designed a

new type of high compression engine that was constructed in 1897.

• This engine was operated on kerosene and hereafter

called a diesel engine.

• To memory its designer, the compression-ignition

engines were called Diesel engines.

1.1 History of engine development

• Application of the internal combustion engines:

• The internal combustion engines, especially diesel

engines, have a wide use in stationary, marine and transport applications compared to other heat engines

• Due to their advantages of:

 compact design,

small weight,

ability of high power creation,

the ability of operating with cheap fuel oils (heavy oil

products).

1.1 History of engine development

The tendency of engine development

• Nowadays, the diesel engines have been being more and

more used for marine applications, especially as main engines on board ships.

Market share

Type of engines Percentage %

Low speed diesel engines 75.5%

Medium, High speed engines 23.0

Steam, Gas Turbines 1.5%

Maker MAN-B&W SULZER Mitsubishi Others

1.1 History of engine development

The tendency of engine development

• Increasing the power rate

• Decreasing the fuel consumption

•  Moderating propeller revolution

•  Settling the counter-measures for the degraded fuel

oil

• Increasing the reliability and durability and

• Obtaining the easy handling and maintenance

• Reduction of environment pollution

1.2 The operational principle of four stroke engine

• By cycle performance, the internal combustion engine

is classified into:

1) Two-stroke engine

2) Four-stroke cycle engines.

•  The four-stroke cycle is completed in four strokes of

the piston, or two revolutions of the crankshaft.

1.2 The operational principle of four stroke engine

• To simplify this operation, we can suppose that the

principle operation of a 4-stroke diesel engines consists

of 4 basic processes as follows:

– Suction stroke

– Compression stroke

– Firing (combustion) and expansion stroke and,

– Exhaustion stroke.

1.2 The operational principle of four stroke engine

• TDC: Top dead center

• BDC: Bottom dead center

TDC BDC

Piston Cylinder liner

Connecting rod

Crank

Fresh air

1.2 The operational principle of four stroke engine

Suction stroke:

• The piston is moving downward

from TDC to BDC.

• The suction valve has been

opened and the fresh air is

drawn into cylinder.

• (The suction valve has been

usually opened before TDC

equivalent to an crank angle of

about 10 to 15 degree This

early timing is called Advanced

opening angle of suction valve )

• At the end of this stroke,

the fresh air is fully drawn into

cylinder

Fresh air Fuel injection valve

Exhaust valve

Suction valve

TDC BDC

Piston Cylinder liner

Connecting rod

Crank

1.2 The operational principle of four stroke engine

Compression stroke: Compression stroke:

• The piston is moving

upward from BDC to TDC.

• Both suction and

exhaust valves are closed

and the fresh air inside the

cylinder is compressed into

valve

TDC BDC

Piston Cylinder liner

Connecting rod

Crank

1.2 The operational principle of four stroke engine

Compression stroke: Compression stroke:

• About 10 0 –2020 0 before

TDC, the fuel is injected

into cylinder in a fine mist,

preparing chemical and

physical conditions for the

combustion process.

• (The suction valve still

opens after BDC equivalent

to an crank angle of about

20 degree This delay

timing is called Delay

closing angle of suction

valve)

Fuel injection valve Exhaust valve Suction

valve

TDC BDC

Piston Cylinder liner

Connecting rod

Crank

1.2 The operational principle of four stroke engine

Working stroke:

• The piston is moving

downward from TDC to

BDC

• Both suction and exhaust

valves are still closed.

• The combustion gases

inside cylinder expand

and cause a strong force

on the piston crown,

driving it downward.

Fuel injection valve Exhaust valve Suction

valve

TDC BDC

Piston Cylinder liner

Connecting rod

Crank

1.2 The operational principle of four stroke engine

degrees This timing is

called Advanced opening

angle of exhaust valve )

Fuel injection valve Exhaust valve Suction

valve

TDC BDC

Piston Cylinder liner

Connecting rod

Crank

1.2 The operational principle of four stroke engine

Exhaust stroke:

• The piston is moving upwards

from BDC to TDC

• The exhaust valve has been

opened and the burnt gases

are expelled by the piston

movement.

• Before piston reaches TDC,

the suction valve has been

usually opened about 10 to 20

degree This early timing is

called Advanced opening angle

TDC BDC

Piston Cylinder liner

Connecting rod

Crank

-

1.2 The operational principle of four stroke engine

Notes:

• Work against an external load (propeller or

generator) is only done in the expansion stroke

• The suction, compression and exhaustion stroke work

must be obtained from that stored in the flywheel or other cylinder, which is the loss.

• There is significant time lapse between the

commencement of the opening of a valve and its arrivals of full open position.

1.2 The operational principle of four stroke engine

• Notes:

• There is a valve overlap at

TDC where both the suction

valve and exhaust valve are

opened.

• This overlap period allows

the inlet air to sweep out the

burnt gases from the engine

clearance volume.

Operational principle of the 4-stroke diesel engines

1.3 The operational principle of two stroke engine

• The two-stroke cycle is

completed in two strokes of

the piston or one revolution

of the crankshaft

• First, the fresh air must be

forced in under pressure

• The incoming air is used to

clean out or scavenge the

exhaust gases and then to

fill or charge the space with

fresh air

TDC

BDC

1.3 The operational principle of two stroke engine

• Instead of valves holes, known

as 'ports', are used which are

opened and closed by the sides

of the piston as it moves.

a First stroke

• Consider the piston at the top of

its stroke where fuel injection

and combustion have just taken

place

• The piston is forced down on its

working stroke until it uncovers

the exhaust port

TDC

BDC

1.3 The operational principle of two stroke engine

• The burnt gases then begin to

exhaust and

• The piston continues down until it

opens the inlet or scavenge port

• Pressured air then enters and

drives out the remaining exhaust

gas

b Second troke

• The piston, on its return stroke,

closes the inlet and exhaust ports

TDC

BDC

1.3 The operational principle of two stroke engine

• The air is then compressed

as the piston moves to the

top of its stroke to complete

the cycle

TDC

BDC

1.3 The operational principle of two stroke engine

Opposed piston diesel engine

• The opposed piston diesel engine is a special case of the

two-stroke cycle

• Beginning at the moment of fuel injection, both pistons are

forced apart-one up, one down-by the expanding gases

1.3 The operational principle of two stroke engine

Opposed piston diesel engine

• The upper piston opens the exhaust ports as it reaches the end

of its travel

• The lower piston, a moment or two later, opens the scavenge

ports to charge the cylinder with fresh air and remove the final traces of exhaust gas.

1.3 The operational principle of two stroke engine

Opposed piston diesel engine

• Once the pistons reach their extreme points they both begin to

move inward.

• This closes off the scavenge and exhaust ports for the

compression stroke to take place prior to fuel injection and combustion

1.3 The operational principle of two stroke engine

Opposed piston diesel engine

• This cycle is used in the Doxford engine, which is no

longer manufactured although many are still in operation.

1.3 The operational principle of two stroke engine

Graphic indication working.

• The piston moves downwards

from TDC to BDC

• When the crank is about

40-60 0 before BDC (point b), the

piston uncovers the exhaust

ports, and blow down the

exhaust gas to a manifold.

• The speed of opening the

exhaust ports is very rapid

and the pressure of the gases

in side cylinder falls quickly

1.3 The operational principle of two stroke engine

Graphic indication working.

• By the time the pressure of the

gases has fallen slightly below the

scavenging air pressure, the piston

uncovers the scavenging ports (d);

• The scavenging air blows in to the

cylinder, forcing out the remaining

gases

• The scavenging ports begins to be

uncovered by the piston movement

when the crankshaft is about 35 –20

55 0 before BDC.

1.3 The operational principle of two stroke engine

• Timing diagram of two stroke diesel engine

•The scavenging ports

begins to be uncovered

by the piston movement

when the crankshaft is

about 35 –20 55 0 before

BDC.

Definition

Comparison of two-stroke and four-stroke cycles

Four stroke engine

• The four stroke cycle

engine, with one

working or power stroke

every two revolution

Two stroke engine

engine, with one working

or power stroke every revolution

twice the power of a stroke engine of the same swept volume.

however and other losses,

Comparison of two-stroke and four-stroke cycles

Four stroke engine

• The four stroke engine

require the intake, exhaust

valves and complicated

valves and complicated

valve operating mechanism

Two stroke engine

• The The two two stroke stroke loop loop

scavenging engine does not require the intake, exhaust valves and complicated

valves and complicated

valve operating mechanism

Comparison of two-stroke and four-stroke cycles

Four stroke engine

• The four stroke engine

require the intake, exhaust

valves and complicated

valves and complicated

valve operating mechanism

Two stroke engine

• The The two-stroke two-stroke cycle cycle

Uniflow scavenging engine, require the exhaust valves and valve operating

and valve operating

mechanism only.

Comparison of two-stroke and four-stroke cycles

Four stroke engine

• The four stroke engine

require the intake, exhaust

valves and complicated

valves and complicated

valve operating mechanism

Two stroke engine

• Ports are arranged in the cylinder

liner for air inlet and a valve in the cylinder head enables the release of exhaust gases.( two stroke cycle Uniflow scavenging engine), or for air inlet and exhaust gas outlet (two stroke cycle lop scavenging engine)

1.4 Classification of internal combustion engines

1.4.1 By cycle performance:

• 4-stroke engines, 2-stroke engines

1.4.2 By kind of fuel used:

• Light liquid fuel (Petrol, kerosene)

• Gaseous fuel

• Heavy liquid fuel:(FO, DO, HFO)

• Mixed fuel (gas and liquid fuel) and

• Multi-fuel (petrol, kerosene, DO, FO, etc.)

1.4.3 By method of mixture formation

• Internal mixture formation

• External mixture formation

1.4 Classification of internal combustion engines

1.4.4 By type of combustion chambers

• Pre-combustion chamber

• Direct injection chamber

• Vortex chamber (Swirl chamber)

1.4.5 By method of igniting the working mixture

1.4 Classification of internal combustion engines

1.4.7 By the method of charging air

• Non-supercharged engine

• Supercharge engine

1.4.8 By the engine construction

a/ By the number of cylinders

1.4 Classification of internal combustion engines

1.4.9 By the reversibility of the crankshaft

• Irreversible (Non-reversible) engines

• Reversible engines

1.4.10 By cylinder action

• single acting

• double acting

1.4.11 By mean engine speed

•    Low speed engine : n < 250 rpm

•   Medium speed engine: n = 251750rpm

•   High speed engine: n >7 50rpm

1.4 Classification of internal combustion engines

1.4.12 By applications of the engine

• Stationary engines: power plants, pumping units etc.

• Marine engines: main engines, generators etc.

• Locomotives

• Vehicle engines

• Airplane engines and

• Engines for other machinery used in agriculture,

construction,

• road building etc.