BÀI GIẢNG TRANG TRÍ hệ ĐỘNG lực CHƯƠNG 4(ENGLISH)

- Fuel pipe must not be arranged near exhaust pipe, silencer, electric panel, and cabin or through fresh water tanks.. Cooling lubricating oil at the lubricating oil cooler.While lubrica

Chapter 5 SYSTEM OF MARINE PROPULSION PLANT

Introduction

Marine propulsion plant is supported by many systems These systems have a closed relation to each other On board, they can be classified as follow:

Fuel oil system.

Lubricating oil system.

5.1 Fuel oil system

I Fuel for Diesel engine

Fuel for diesel engine is used in liquid form Depending on properties, fuel oil can be classified into two kinds: first one is diesel oil (or DO) and other one is heavy fuel oil (or FO) They are characterized by

Viscosity of fuel oil is unit for measure of resistance to flow of fuel oil.

3 Water and sediment

These impurities are obviously not useful to diesel engine operation Water is the primary cause of corrosion in fuel storage tanks and equipment especially cylinder liner Sediment causes a wear in plunger and clog filters, injection valve.

II Function of fuel oil system

- To receive fuel oil into the ship.

- To store fuel oil in tanks.

- To transfer fuel oil between tanks.

- To clean fuel oil.

- To supply fuel for the main diesel engine, diesel generators, aux boiler.

- To indicate fuel oil level in tanks, fuel oil consumption

III Requirements of the fuel oil system

1 General requirements of the fuel system:

- The system must ensure normal working of all engines even when the ship rolling 15o and pitching 5o

- Fuel pipe must not be arranged near exhaust pipe, silencer, electric panel, and cabin or through fresh water tanks

- Fuel is normally stored in double bottom tanks or wing tanks Capacity of all tanks must be enough for continuing operation of the ship in estimated time with some percentage of fuel for stand by

- There must be interconnection between tanks The valves should be arranged so that it is easy for operation, checking and repairing

- There must be separated pipes for receiving and delivering fuel on each tank Besides this, vent pipe, drainpipe, overflow pipe (with sight glass), sounding pipe (or sounding device), manhole for inspection and repairing must be installed.

- Diameter of vent pipe is normally equal to receiving pipe The upper end of vent pipe is placed on upper deck with a copper net to prevent dust and fire from falling into fuel tanks Diameter of vent pipe in any case must not be smaller than 50 mm

- The system must be provided with international flanges for receiving and discharging pipe and placed on both sides of the ship (Port & Starboard side)

- The system must be equipped with remote control device for emergency shut down of delivery valves of each fuel tank in case of fire or flooding in the engine room

- There must be indicators, alarm devices such as: pressure gauge, thermometer, viscometer, flow meter, and low-high level alarm to increase the safety of the system.

- In case of using FO, FO purifier must be provided in the system FO must be heated in storage tanks, settling tank, service tank before transferring and purifying Heating coil

of the tanks should be arranged about 25 cm from bottom

of the tanks If use steam for heating, steam pressure must

be smaller than 7 kg/cm2 Fuel pipe must be heated and insulated to maintain FO temperature The heating temperature of FO before entering the engine depends on kind of fuel and engine This temperature can be adjusted

Figure 5.1: Fuel oil tank and fitting

5

2

8 9

4

7 1

6

3

1- Receiving pipe 2- Delivery pipe 3- Venting pipe 4- Overflow pipe 5- Drain valve

6- Thermometer 7- Level indicator 8- Heating coil 9- Manhole

DO store tank DO store

tank

tank

FO service tank

purifier

FO heater

Figure 5.2: FO & DO purifier system of the marine engine practical room

2 Requirements of fuel injection system of diesel engine.

- Fuel must be injected to combustion chamber at proper timing The beginning time of injection in degrees of crankshaft before top dead center must be the same for all cylinders and can be adjusted.

- Amount of fuel delivered to each of the cylinders must be the same.

- There must be a suitable rate and pressure of injection The fuel mass per degree of crankshaft travel must be the same for all the fuel injection pumps.

- The fuel must be properly atomized.

- The fuel must be distributed over the volume of the combustion chamber.

For auxiliary boiler, fuel sprayed into combustion chamber must be in good atomization corresponding to the load of boiler.

IV The typical fuel oil system.

1 The typical diesel oil system (DO system).

DO system is used on small ships, for high-speed diesel engines

or generator engines Because viscosity of DO is low, a heater of DO

is not required However, DO may be heated before separating A diesel oil system is illustrated in Figure 5.3

2 The typical heavy fuel oil system (FO system).

FO system is mostly used on ships When a heavy fuel oil system

is used, a diesel oil system is also required This is called “a two fuel system” When the ship is in running up condition, FO is used for the main engine On the other hand, when the ship is maneuvering, the main engine is switched over to DO

Today, on some modern ships only FO is used To maintain a proper temperature of FO in the fuel injection valves, FO must be continuously heated and circulated through the fuel injection valves even when the engine is stopping.

8

6 7

9 10 11

12

13 14

5

DIESEL OIL SYSTEM

1- Storage tank 2- Settling tank 3- Service tank 4- Sludge tank 5- Strainer 6- Transfer pump 7- Heater

8- Purifier 9- Rough filter 10- Supply pump (Booster pump) 11- Fine filter 12- Fuel injection pump

13- Fuel injection valve

14- Pressure regulating valve 15- Drain tank

13 14

1- DO settling tank 2- DO service tank 3- FO settling tank 4- FO service tank 5- Heater

6- DO purifier 7- FO purifier 8- Venting tank 9- Strainer

10- DO burner pump 11- FO burner pump 12- Flow meter

13- Rough filter 14- Supply pump 15- Circulating pump 16- Fine filter

17- Pressure regulating valve

V The main components of the fuel oil system.

A fuel oil system consists of following main components:

1 Fuel oil tanks: Storage tanks, settling tank, service tank,

dirty oil tank, spill oil tank (overflow tank), sludge tank

2 Transfer pumps.

A transfer pump is used to transfer fuel oil between tanks and supply fuel oil to the engines

3 Fuel injection pumps.

They create a high pressure of fuel oil before supplying to fuel injection valves

4 Fuel injection valves.

Their duty is to atomize and distribute fuel oil over combustion chambers of the engines

5 Filters.

The are two kinds of filter in the system, they are rough filter (strainer) and fine filter

6 Heaters

Their function is to maintain proper viscosity of fuel oil

Either electric heaters or steam heaters are used in the system

7 Purifiers.

They are used to separate water and sludge from fuel oil

8 Pipe lines: Both high pressure and low-pressure pipes

are used in the system

9 Indicators, alarm devices.

LO TK

FO SETTL

FO SERV

DO TK FWT

Heater

Fine filter

To serv TK

To serv TK

M/E 6NVD26 -A2

To FO tank

F

Figure 5.5:

Fuel oil system of the

marine engine practical room

5.3 COOLING SYSTEM

I Functions of cooling system

1 Cooling diesel engine (ME and DG).

It reduces the temperature of the diesel engine parts

to the suitable temperatures During the operation of the diesel engine, the fuel-air mixture is burned in the combustion chamber so its temperature is very high With such a high temperature, the parts of the diesel engine (such as cylinders, cylinder covers, piston crowns ) are heated Therefore, these parts need to

be cooled to prevent cracking due to heat.

2 Cooling lubricating oil at the lubricating oil cooler.

While lubricating the working surfaces of the diesel engine, the lubricating oil gets the heat that is created by friction at the working surfaces so its temperature is raised and its viscosity is reduced This is not beneficial for the diesel engine That is why the lubricating oil must be cooled

3 Cooling supercharged air at the air cooler.

When compressed to a high pressure, the temperature of the supercharged air is very high and its specific gravity is decreased So the supercharged air needs to be cooled before entering to the cylinders The purpose of this cooling is to increase the mass of fresh air entering to the cylinders

4 Cooling other machinery: such as air

compressors, hydraulic oil system, stern tube and stern bearings, intermediate bearings and thrust bearing, condensers of provision refrigerating system, air conditioner and auxiliary boiler

Depending on the parts that are cooled, many different kinds of cooling substance can be used in the cooling system such as fresh water, seawater, lubricating oil, and fuel oil;

Piston crowns may be cooled by water or lubricating oil.

Fuel injection valves can be cooled by fresh water

or fuel oil.

Other parts almost are cooled by water (fresh water or seawater).

II Classification of cooling system.

There are two kinds of cooling system on the ship They are:

1 The open cooling system

2 losed cooling system.

In each type of cooling system, we will study

about:

It’s feature

Advantages

Disadvantages

1 The open cooling system

a Feature:

• Figure 5.8 is an illustration of an open cooling system In this system, seawater outside of the ship is taken in through the seachest valve and is pumped to cool the lubricating oil, the supercharged air, the diesel engines, the compressors and so on

• After carrying out its duty, the seawater goes out to overboard In this case the seawater contacts directly with the diesel engine and surfaces of the parts that need to be cooled

• To regulate the seawater temperature in the system, a three ways-valve is used Three ways-valve can be set in auto or manual mode

b Advantage

The system is simple and very cheap The seawater is available

c Disadvantages

- The seawater contains many scale components, so it is easy

to precipitate the scale on the cooling surfaces Because of this, it reduces ability of the heat exchange therefore, the parts of the diesel engine cooled by the seawater are easily cracked

- Because the seawater contains many scale and salt, it will cause erosion and electrolytic corrosion

- The temperature of the sea water going out of the engine is very low (It is limited to about 45  50o C) this lead to:

+ Thermal stress of the cylinders, cylinder covers and piston crowns are very high

+ Waste energy for cooling water is high.

+ The operators cannot reuse the thermal energy of the cooling water.

- Effect of the cooling depends on the environment condition that the ship is operating

• 1- High sea chest

• 2- Low sea chest

4 5

6

LO CLR

D/G No2 K161

Strainer

From sea chest

2 The closed cooling system

• The seawater is taken into the ship to cool the fresh water, the lubricating oil, the supercharged air and other machinery and then is discharged overboard

• The temperature of the fresh water can be regulated by a thermostatic control valve.

• Steam generated in the system will go up to the expansion tank The fresh water in the system will be replenished from the expansion tank to the suction pipe of the fresh water pump.

b Advantages:

- Reduce waste energy for cooling water

- Reduce rust, scale on the cooling surfaces of the engine

- Due to high quality of the fresh water (in comparison with seawater), the engine can be operated with a high temperature of the cooling water (60  85oC) This reduces thermal stress of the cylinders and piston crowns

In addition, the thermal energy of the cooling water can be reused so the efficiency of the propulsion plant will be increased

- The cooling water temperature can be automatically regulated

- Effect of the cooling mostly does not depend on the environment condition

c Disadvantages:

- The system is complex and expensive

l.o clr Air clr

Expansion tank

f.w clr

C.FW pump

C.SW pump

To auxiliary machineries

TK

FW

Cooler Outletpipe

III The main components of the cooling system.

There are following main components in the cooling system:

1 Sea chests

2 Cooling fresh water pumps

3 Cooling seawater pumps

4 Expansion tank

5 Thermostatic control valve

6 Fresh water cooler

7 Strainers

8 Pipe line and fitting

9.Indicators (thermometer, pressure gauges, level indicator )

IV Requirements of the cooling system

2- Strainer 3- Main valve (Low and high seachest valve)

4- Air vent pipe 5- Steam or compressed air valve

6- Mesh

2 Cooling water pump.

There must be two main pumps in the system, one is cooling fresh water pump, and other one is cooling seawater pump Besides these, the system must also have two emergency cooling water pumps: one for fresh water, other one for seawater In addition, there may be auxiliary machinery cooling water pumps Centrifugal pumps are widely used in the cooling system and

it is designed so as velocity of water in the delivery pipe is about 3 5 (m/s).

3 Thermostatic control valve.

Its function is to maintain the temperature of the cooling water at the constant value The principle operation of this valve is to regulate the fresh water temperature by passing the fresh water cooler according to the temperature of the cooling water going out of the engine

The flowing requirements are required for this valve:

- When load of the engine changes, the difference of the cooling water temperature in comparison with the preset value must be lower than 5o C

- When load of the engine is static, the difference of the cooling water temperature in comparison with the preset value is about 12o C

- When load of the engine changes, the control time of the cooling water temperature to preset value must be short

4 Pipe line and fitting

When designing the pipeline we must pay attention to following requirements:

- Expansion of water in the system is smallest

- Evaporation of water is smallest

- The expansion tank must be arranged in the system for expanding of the fresh water

- Steam is not existed in the system, if air or steam appears in the system, it needs to be quickly purged For this purpose, air purge valves must be arranged at high positions in the system

- The leakage of the system is smallest

- The hunting of pressure in the system is smallest

5.4 compressed air system

I Function of the compressed air system

The compressed air system supplies compressed air to carry out different purposes:

- To start and reverse the main engine.

- To start the diesel generators.

- To supply compressed air for the remote control system and other automatic control equipment.

- To supply compressed air for air whistle (air horn).

- To clean sea chest.

- To clean and dry parts of machinery when repairing, tighten and loosen bolts and nuts