ic pp -unit ii

8/13/2019 IC PP -UNIT II

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Unit II

Internal Combustion(Diesel) PowerPlant

By

Mq. K. Obula ReddyAsst. Pqof. Dept. of Mech.Gitam Univeqsity Hydeqabad


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Diesel power plants produce power in the range of 2 to

50 MW.


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Classification of Engines

Engines can be classified in many different ways, asthey have many attributes, whereby making them

capable of meeting a variety of needs and

requirements.

vcylinder numbers & arrangement

vengine cycles

vvalve position & location

vmethod of air supply

vmethod of fuel supply

vcooling system


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Cylinder numbers & Arrangement


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Engine CyclesIn four-stroke engine the cycle of operation is completed in four strokes of the piston or

two revolution of the crank shaft.

In two-stroke engine the cycle is completed in two strokes, i.e. one revolution of the

crank shaft.The difference between two-stroke and four stroke engines is in the method of filling the

cylinder with the fresh charge and removing the products of combustion.


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valve position & location

A - valve in block (L)

B - valve in head (I)

C - one in head and

one in block (F)

D - on opposite sides


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Method of Air Supply

1. Naturally aspirated engine:Admission of charge at near atmospheric pressure

2. Supercharged engine:Admission of charge at a pressure above atmospheric


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Method of fuel supply

2.Multi-port fuel injection

consists of an injector for each cylinder

in the engine. This injector sprays fuel

directly through the intake valve or

valves into the combustion chamber.

Each injector is activated separately bywire

1. Direct and Indirect Injection

In an indirect injection (abbreviated

IDI) diesel engine, fuel is injected

into a small prechamber, which is

connected to the cylinder by a narrow

opening.2

1

3


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Cooling System

Liquid Cooling Air Cooling


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Layout of a Diesel power plant


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The essential components of a Diesel Electric Plant are:

(1) Engine

(2) Engine air intake system

(3) Engine fuel system

(4) Engine exhaust system

(5) Engine cooling system

(6) Engine lubrication system

(7) Engine starting system


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Diesel Engine

This is the main component of the plant which develops power.

Generally engine is coupled directly to the generator

Diesel engine may be a four stroke or a two stroke engine

Four stroke engine is generally preferred as it has higher efficiency,lower specific fuel consumption and more effective lubrication than a

two stroke engine

Other things which may be specified in diesel engines are: arrangement

and number of cylinders used, simple aspiration or supercharging,efficiency and economical fuel consumption


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Engine air intake systemThis includes air filters, ducts and supercharger (an integral part of the

engine). The system supplies the required quantity of air for combustion. Air

requirements for large diesel plants are considerable, around 4-8 m3 per kwh.

Air is drawn from outside the engine room and delivered to the intake

manifold through the air filters which remove the dust and other suspended

impurities from air.

The purpose of the filter is to catch any air borne dirt as it otherwise may

cause the wear and tear of the engine. The filter should be cleaned

periodically.

Filters may be of dry type (made up of cloth, felt, glass wool etc) or oil bathtype. In oil bath types filter the air is swept over or through a bath of oil in

order that the particles of dust get coated.

The supercharger increases the pressure of air supplied to the engine so that it

could develop an increased power output. Superchargers are generally driven

by the engine.


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Engine fuel system

This include fuel storage tanks, fuel transfer pumps, strainers, heaters

and connecting pipe work. Fuel transfer pumps are required totransfer fuel from delivery point to storage tanks and from storage

tanks to engine. Strainers (filters) are needed to ensure clean fuel.

Heaters for oil may be required especially during winter.


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Engine exhaust systemThe function of the exhaust system is to discharge the engine exhaust to the

atmosphere outside the building. This includes silencers (muffler) andconnecting ducts/ pipes. A good exhaust system should keep the noise at a

low level, exhaust well above the ground level to reduce the air pollution at

breathing level and should isolate the engine vibrations from the building

by using a flexible selection of exhaust pipe. The exhaust pipe is provided

with a muffler to reduce pressure in the exhaust line and reduces the noiselevel.

Engine cooling system


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Engine cooling system This includes coolant pumps, spray ponds, water treatment or

filtration plant and connecting pipe work. The purpose of the

cooling system is to carry heat from engine cylinder to keep thetemperature of the cylinder within safe limits.

There are three system for the re cooling of water for continuous

use:

1. Open system or direct evaporation.

2. Closed system including heat exchangers with a secondary

water circulation.

3. Radiators.



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Engine lubrication system

The life of the engine and the efficiency depend largely on the

lubrication system.

The main functions of the lubricating oil are: to lubricate the moving

parts, to remove the heat from the cylinders and the bearings, to help thepiston rings to seal the gases in the cylinder and to carry away the solid

dirt particles from the rubbing parts.

The parts of the engine, which need lubrication include piston and

cylinders, gears, crankshaft, and connecting rod, bearing etc. Piston andcylinder need special-lubricating oil.


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Engine Starting system.

Because of the high compression pressure, even a small diesel

engine in a power plant can not be started by hand cranking.

The various methods used for starting are:

(1) Compressed air starting for medium and large capacitystationary and mobile units

(2) Electric-motor starting for small high-speed gasoline and

diesel engine

(3) Auxiliary-engine starting for medium capacity mobile units

SUPERCHARGING OF DIESEL ENGINES


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It is a known fact that the power output of the engine increases with an increase in amount of air

in the cylinder at the beginning of compression stroke because it allows to burn more quantity of

fuel.

Supercharging is a term used to a process which helps to increase the suction pressure of the

engine above atmospheric pressure and the equipment used for this purpose is known as

supercharge

Supercharging an engine performs the same function as turbo charging an engine. The difference

is the source of power used to drive the device that compresses the incoming fresh air. In a

supercharged engine, the air is commonly compressed in a device called a blower.

The blower is driven through gears directly from the engines crankshaft. The most common typeof blower uses two rotating rotors to compress the air.


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Supercharger Vs Turbocharger

The advantages of supercharged engines are listed below :


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The advantages of supercharged engines are listed below :

1. Power increase. By supercharging the engine, the engine output can be increased

by 30 to 50%at the same speed of the engine.

2. Fuel Economy. The combustion in supercharged engine is better as it provides

better mixing of the air and fuel than unsupercharged engine. Therefore, the specific fuel

consumption of a supercharged engine in less than natural aspirated engine. The thermal

efficiency of supercharged engine is also higher.

3. Mechanical efficiency. The mechanical efficiency of a supercharged engine is betterthan natural aspirated engine at the same speed. This is because, the power increase due

to supercharging increases faster than the rate of increase in friction losses.

4. Scavenging. The scavenging action is better in two-stroke supercharged engines

than naturally aspirated engines because the quantity of residual gases is reduced with the

increase in supercharged pressure.

5. Knocking. Supercharging reduces the possibility of knocking in diesel engines

because delay period is reduced with an increase in supercharged pressure. It has been

found that four-stroke engines are more easily adaptable to supercharging than two-stroke

engines.

Advantages(Merits) of DPP


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Advantages(Merits) of DPP1. The design and installation of diesel power plants are very simple These plants can be

located at any place any occupy lesser space. Requires less space for fuel storage and are

free from ash handling problems unlike thermal plants.

2. Diesel plants occupy lesser space because of the minimum auxiliaries

3. Diesel plants can respond to varying loads without any difficulty

4. Diesel plants have no standby losses

5. The quantity of the water required for these plants for cooling are limited

6. Diesel plants can be started from cold condition and can take up the load very quickly.

7. Diesel plants are mostly used for peak load condition in the power system

8. Diesel plants have the overall capital cost including installation per unit of the installed

capacity is lesser than that of steam power plants

8. In diesel plants, variety of fuels such as residual fuel oil, low sulphur heavy stock etc can

be used

10. These plants being simpler in operation requires less operating and supervising staff ascompared to that of steam power plants


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Disadvantages(Demerits) of Diesel Power plant

1. The unit capacity of diesel engine is considerably low than the thermal unit. The cost

of unit increases with an increase in unit capacity for diesel plant whereas the cost of

the unit goes on decreasing in case of thermal plant with an increase in unit capacity.

2. The repair and maintenance costs are generally much higher than for steam plants.

3. Life of 25 to 30 years is normal for thermal plant whereas the life of diesel plant is

hardly 2 to 5 years or less.

4. The diesel plants are not economical where fuel has to be imported.

5. The noise is a serious problem in diesel plant.

6. Selected types of fuels are required in diesel engines whereas there is more mobility in

case of thermal plant.

7. The lubrication cost is high.

8. The diesel plants are not guaranteed for continuous operation under overloads whereas

steam plants can work under 25% overload continuously.


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Engine Performance Parameters

IMEP

IHP

BHP ITE

BTE

ME


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Indicated Mean Effective Pressure

(IMEP)

Indicator Diagram


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Indicated Mean Effective Pressure

(IMEP)

In order to determine the power developed by the

engine indicator diagram should be available

Area of the indicator diagram shows power But it can also calculate average gas pressure on

piston in any stroke

This pressure is called IMEP


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Indicated Horse Power (IHP)

It can be calculated as

Pm is the IMPE in kg/cm2 L is length of stroke in m

A is area of piston

N is speed in rpm

n is number of cylinders

k is for stroke count of engine

. . . .

4500.

mP L A N n

IHPk


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Brake Horse Power (BHP)

It is defined as the net output power available at

the crank shaft.

It is found by using a dynamometer at the outputof the shaft

where N is speed in rpm

T is torque

2

4500

NTBHP


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Frictional Horse Power (FHP)

It is the difference between IHP and BHP

FHP = IHP - BHP


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Indicated Thermal Efficiency (ITE)

It is defined as the ratio of indicated work to

thermal input

Where W is the weight of the fuel

CV is the calorific value of the fuelJ is the joules equivalent = 427

4500i

IHP

W CV J


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Brake Thermal Efficiency

It is defined as the ratio of indicated work to

thermal input

Where W is the weight of the fuel

CV is the calorific value of the fuelJ is the joules equivalent = 427

4500b

BHP

W CV J


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Mechanical Efficiency

It is the ratio of BHP to IHP

m

BHP

IHP

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