Diesel power plant

Gas Turbine

Combustion and

Power Generation Dr. O.P. TIWARI

H.O.D, Mechanical Engg.

S.R.I.M.T

S.R.I.M.T

DEPARTMENT OF MECHANICAL ENGG. S.R.I.M.T,Lko

By-

DEPARTMENT OF MECHANICAL ENGG. S.R.I.M.T, Lko

Power Plant Engineering

Classification of Power Plants

Steam (Thermal) Power Plant

Hydro Electric Power plant

Nuclear power Plant

Gas Turbine Power Plant

Diesel Power Plant

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INTRODUCTION • A generating station in which diesel engine is used as

the prime mover for the generation of electrical energy is

known as diesel power station.

• The diesel burns inside the engine and the products of

this combustion act as the working fluid to produce

mechanical energy.

• The diesel engine drives alternator which converts

mechanical energy into electrical energy.

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• As the generation cost is considerable due to high price

of diesel, therefore, such power stations are only used to

produce small power.

• Diesel electric plants in the range of 2 to 50 MW

capacity are used as central stations for small supply

authorities and works and they are universally adapted

to supplement hydro-electric or thermal stations where

stand-by generating plants are essential for starting from

cold and under emergency conditions

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.

• Diesel engine power plants are installed where:-

1. Supply of coal and water is not available in desired

quantity.

2. Where power is to be generated in small quantity for

emergency services.

3. Standby sets are required for continuity of supply such

as in hospital, telephone exchange

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Working cycle(Diesel Cycle) Air-Standard Diesel Cycle

The air-standard Diesel cycle is the ideal cycle that approximates the Diesel

combustion engine

Process Description

1-2 Isentropic compression

2-3 Constant pressure heat addition

3-4 Isentropic expansion

4-1 Constant volume heat rejection

• The P-v and T-s diagrams are :---

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7

Thermal efficiency of the Diesel cycle

th Dieselnet

in

out

in

W

Q

Q

Q, 1

Now to find Qin and Qout.

Apply the first law closed system to process 2-3, P = constant.

Thus, for constant specific heats

Q U P V V

Q Q mC T T mR T T

Q mC T T

net

net in v

in p

,

,

( )

( ) ( )

( )

23 23 2 3 2

23 3 2 3 2

3 2

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8

Apply the first law closed system to process 4-1, V = constant (just as we did for the

Otto cycle)

Thus, for constant specific heats

Q U

Q Q mC T T

Q mC T T mC T T

net

net out v

out v v

,

, ( )

( ) ( )

41 41

41 1 4

1 4 4 1

The thermal efficiency becomes

th Dieselout

in

v

p

Q

Q

mC T T

mC T T

,

( )

( )

1

1 4 1

3 2

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9

th Dieselv

p

C T T

C T T

k

T T T

T T T

,

( )

( )

( / )

( / )

1

11 1

1

4 1

3 2

1 4 1

2 3 2

What is T3/T2 ?

PV

T

PV

TP P

T

T

V

Vrc

3 3

3

2 2

2

3 2

3

2

3

2

where

where rc is called the cutoff ratio, defined as V3 /V2, and is a measure of the duration

of the heat addition at constant pressure. Since the fuel is injected directly into the

cylinder, the cutoff ratio can be related to the number of degrees that the crank

rotated during the fuel injection into the cylinder.

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10

What is T4/T1 ? PV

T

PV

TV V

T

T

P

P

4 4

4

1 1

1

4 1

4

1

4

1

where

Recall processes 1-2 and 3-4 are isentropic,

so

PV PV PV PVk k k k

1 1 2 2 4 4 3 3 and

Since V4 = V1 and P3 = P2, we divide the second equation by the first equation and

obtain

Therefore,

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11

th Diesel

c

k

c

k

c

k

c

k

T T T

T T T

k

T

T

r

r

r

r

k r

,

( / )

( / )

( )

( )

11 1

1

11 1

1

11 1

1

1 4 1

2 3 2

1

2

1

What happens as rc goes to 1? Sketch the P-v diagram for the Diesel cycle and

show rc approaching 1 in the limit.

P

v

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TYPES OF DIESEL ENGINES USED FOR

DIESEL POWER PLANTS

• The diesel engines are generally classified as four-stroke engines

and two-stroke engines.

• The four-stroke engine develops power after every two revolutions

of crank shaft whereas two-stroke engine develops power with each

revolution of crank shaft.

• Generally, two-stroke engines are favored for diesel power plants for

the advantages described later.

• Duel Fuel Engines. In duel fuel engines, gas and oil both are used

as fuels for the engines. The gas is used as main fuel and oil is used

as helper for ignition.

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GENERAL LAYOUT OF

DIESEL POWER PLANT

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The layouts of diesel power plants for high

capacity (50 MW and above)

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MEDIUM CAPACITYDIESEL POWER PLANT

(25 to 50 MW)

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LOW CAPACITY

DIESEL PLANTPOWER(blow 25 MW)

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ESSENTIAL ELEMENTS OF DIESEL

POWER PLANT

1. Engine.

2.

Fuel Supply System.

3.

Air Intake

System

4.

Supply System

.

5.

Exhaust System.

6. Cooling System

7.

Lubricating

System.

8. Starting system.

9. Governing system.

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1.Air Intake System. • A large diesel engine power plant requires considerable amount of

air as 4 to 8 m3/kW-hr.

• This system supplies necessary air to the engine for fuel

combustion. It consists of pipes for the supply of fresh air to the

engine manifold.

• Filters are provided to remove dust particles from air which may act

as abrasive in the engine cylinder.

• the air is sucked or bubbled through a housing that holds a bath of

oil such that the dirt in the air is removed by the oil in the filter.

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• The air then flows through a screen-type material to

ensure any entrained oil is removed from the air.

• In a dry filter system, paper, cloth, or a metal screen

material is used to catch and trap dirt before it enters the

engine.

• In addition to cleaning the air, the intake system is

usually designed to intake fresh air from as far away

from the engine as practicable, usually just outside of the

engine’s building or enclosure.

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ESSENTIAL ELEMENTS OF DIESEL POWER PLANT(Cnti…)

Fig : Air Intake System

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2.Fuel Storage and Fuel Supply System.

• The fuel storage and supply arrangement generally depend on the

type of fuel, size of plant and type of engine used and so on.

• The supply system is generally classified as:-

(a) Simple suction system and

(b) Transfer system.

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• In a simple suction system, the oil is taken by a suction

pump driven by engines from service tank located a few

cm below the engine level. Such pump delivers constant

volume of fuel, therefore, an overflow line is required

back to the tank. This system is used for small capacity

plant.

• In transfer system, the motor driven pump takes the oil

from main storage and supply to the day storage tank.

The oil from day-storage tank flows under gravity to the

engine pump.

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Transfer system type fuel storage and

supply arrangement.

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3.FUEL INJECTION SYSTEM

• Fuel injection is a system for mixing fuel with air in an internal

combustion engine. A fuel injection system is designed and

calibrated specifically for the type of fuel it will handle.

• Most fuel injection systems are for diesel applications. With the

advent of electronic fuel injection (EFI), the diesel gasoline hardware

has become similar.

• The primary difference between carburetors and fuel injection is that

fuel injection atomizes the fuel by forcibly pumping it through a small

nozzle under high pressure, while a carburetor relies on low

pressure created by intake air rushing through it to add the fuel to

the air stream

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Typical EFI Components

Animated cut through diagram of a typical fuel injector

Injectors

Fuel Pump

Fuel Pressure Regulator

ECM – Engine Control Module; includes a digital computer and circuitry to communicate with

sensors and control outputs

Wiring Harness

Various Sensors (Some of the sensors required are listed here)

Crank/Cam Position (Hall effect sensor)

Airflow (MAF sensor)

Exhaust Gas Oxygen (Oxygen sensor, EGO sensor, UEGO sensor).

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Typical EFI

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VARIOUS INJECTION SCHEMES

• 3.1 Throttle Body Injection Systems

• Throttle body injection is a form of continuous injection-one or two

injectors delivering fuel to the engine from one central point in the

intake manifold.

Fig :Throttle Body Injection Fig :Throttle Body Injection Unit

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3.2 Continuous Fuel Injection Systems

• Continuous fuel injection systems provide a continuous spray of fuel

from each injector at a point before the intake valve. • They are used on gasoline engines only when more precise fuel

metering is desired.

• In the continuous system, fuel is delivered to the mixture control unit

by the fuel pump.

• The fuel pressure regulator maintains fuel line pressure by sending

excess fuel back to the gas tank.

• The mixture control unit regulates the amount of fuel that is sent to the

injectors, based on the amount of airflow through the intake and the engine

temperature.

• The mixture control unit on mechanical systems is operated by the

airflow sensing plate and the warm-up regulator.

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Fig :-Continuous Injection system

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3.3 Multi-point Fuel Injection

• Multi-point fuel injection injects fuel into the intake port just upstream

of the cylinder’s intake valve, rather than at a central point within an

intake manifold, referred to as SPFI, or single point fuel injection.

Stage 1 Stage 2

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MPFI Cnt..

Stage 3 Stage 4

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LUBRICATION SYSTEM • The system minimizes the wear of rubbing surfaces of the engine.

• It comprises of lubricating oil tank, pump, filter and oil cooler.

• The cost of the lubricating oil in the diesel plant is considerable

compared with other plants as the consumption is nearly 3 liters per

1000 kW-hr generated at full load conditions.

• Thus the lubricating oil consumption is nearly 1% of the fuel oil

consumption.

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LUBRICATION SYSTEM cnt….

• The lubrication oil is drawn from the lubricating oil tank by the pump

and is passed through filter to remove impurities .

• The clean lubrication oil is delivered to the points which require

lubrication.

• The oil coolers incorporated in the system keep the temperature of

the oil low.

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Methods of lubrication:-

• 1. Mechanical system – Splash lubrication

• 2. Pressure lubrication system.

a. Wet sump lubrication system

b. Dry sump lubrication system.

• 3. Semi pressure lubrication system.

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1.Splash lubrication:

• In the splash lubrication system, the oil retained in the oil

pan is churned and splashed up by the internal parts of

the engine.

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2.PRESSURE LUBRICATION SYSTEM

• In the pressure lubrication system, the lubricating oil is

pumped under pressure to the various engine bearings.

• The oil is delivered by an oil pump under a pressure of

1.30 to 1.40 kscm into an oil gallery or distributor duct.

• This gallery distributes oil to the various engine parts

and bearings.

• The oil pump is driven by the engine crankshaft or

camshaft.

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a). Wet sump lubrication • In the wet sump lubrication system, the main oil supply is kept in the

sump which is below the engine cylinder in the crankcase.

• The oil pump draws oil from the crankcase and forces it through the

lubricating oil filters to the various parts of the engine.

• This system is widely used incars and trucks.

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b).Dry sump lubrication • The dry sump lubrication is used in more expensive cars.

• In the dry sump pressure lubrication system, there is no oil sump in the

crankshaft chamber.

• In this system, the oil is kept either in a separate tank or reservoir, provided

with cooling fins.

• Two pumps are used in this system.

• One pump sucks the oil from the reservoir and forces it under pressure to

the various bearings of the engine, as in the wet sump system.

• The other pump (also called scavenger oil pump) is of large capacity. This

pump sucks oil which drains down to the bottom of the crankshaft

chamber, and returns it to the oil reservoir

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3.Semi pressure lubrication system

• The semi pressure lubrication system is a combination of

splash and pressure lubrication system.

• Most automotive engines use this system.

• This is more simple and less costly than the complete pressure

lubrication system.

• This system also enables bearing loads and engine speeds than

for the splash system.

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Fig : - Semi pressure lubrication system

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Lubricating System cant..

Figure : Lubricating System Layout of large power plant

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cooling system

• Necessity for cooling:- In an internal combustion

engine, the fuel is burned within the engine cylinder. During combustion,

high temperatures are reached within the cylinder , for example in a

compression ignition engine as high as 2000-25000C is reached.

• Effects of over heating of the engine components:

• Setting up of thermal stresses

• Sticking of piston rings in the ring grooves, due to carbonization of the oil.

• Burning of piston crown.

• Burning and warping of exhaust valves.

• Reduction in volumetric efficient i.e. reduced weight of charge retained in

the cylinder.

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Optimum cooling

• To avoid overheating, and the consequent ill effects mentioned

above, the heat transferred to an engine component (after a certain

level) must be removed as quickly as possible and be conveyed to

the atmosphere.

• It should be remembered that abstraction of heat from the working

medium by way of cooling the engine components is a direct

thermodynamic loss.

• Effects of excessive cooling:

• 1. Reduction in thermal efficiency.

• 2. Increased corrosion of engine parts.

• 3. Reduced mechanical efficiency.

• 4. Improper vaporization of fuel.

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TYPES OFCOOLING SYSTEM

• Air cooling

• Liquid Cooling:-

1. Thermo syphon cooling system:

2.Forced circulation cooling system (or Pump circulation

cooling system):

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1.Air cooling

• In air cooling, large quantities of air is circulated around the hot

engine components.

• where the engine is totally enclosed by the vehicle body, air is

forced by a fan or blower of generous capacity. The fan or blower is

fixed to the flywheel.

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Advantages of air cooling: 1. Cylinder and cylinder head casting are less complicated.

2. Engine weight is reduced, because engine jackets are not there.

3. Cheaper to manufacture- both labor and material.

4. Volume or size (overall) may be reduced, as no device such as

radiator is required for re-cooling the coolant.

5. Engine warms up more quickly, and delivers its full power in

lesser time than the liquid cooled engines.

6. Quick starting of the engine is possible even in frosty weather.

7. Rate of coolant frost (ice) damage of the engine (jackets) is not

there.

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Disadvantages of air cooling:

• Greater mechanical noise, particularly because of the

fan.

• Not suitable for multi-cylinder engines, unless a fan

(which absorbs some power) and suitable cowling are

used.

• Not suitable for engines to be mounted on vehicles

meant for agricultural and construction applications.

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2.Liquid Cooling:

• 1. Thermo syphon cooling system:

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2. Forced circulation cooling system (or Pump

circulation cooling system):

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Water-cooling system in large power plant. • If the engines are not properly cooled, the temperature existing

inside engine would disintegrate the film of lubricating oil on the

liners and wrapping of valves and pistons takes place.

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Starting system

• It is difficult to start even smallest diesel engine by hand cranking as

the compression pressures are extremely high.

• Therefore, some mechanical system must be used to start the

engine. Generally, compressed air, electric motors and auxiliary

gasoline engines are used 'for starting purposes. Compressed air

system is commonly used in big diesel power plants. Air starting

system uses valve arrangement to admit pressurized air at about 20

bar to a few of the

• cylinders, making them to act as reciprocating air motors to turn the

engine shaft. Admitting fuel oil to the remaining engine cylinder

helps the engine to start under its own power.

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PERFORMANCE OF DIESEL POWER PLANT

• Diesel plants also run at part load conditions like other plants.

• Therefore, it is necessary to study the effect of part load running on

the characteristics of an engine like specific fuel consumption, brake

thermal efficiency, and mechanical efficiency.

• The effects of part loads on the engine characteristics are shown in

Fig.

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SUPERCHARGING SYSTEM OF DIESEL

POWER PLANT

• The purpose of supercharging is to raise the volumetric

efficiency above that value which can be obtained by

normal aspiration.

• Since the I.H.P. produced by an I.C. engine is directly

proportional to the air consumed by the engine.

• greater quantities of fuel to be added by increasing the

air consumption permit and result in greater power

produced by the engine.

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• So, it is, therefore, desirable that the engine

should take in the greatest possible mass of air.

• The supply of air is pumped into the cylinder at a

pressure greater than the atmospheric pressure

and is called supercharging.

• When greater quantity of air is supplied to an I.C. engine

it would be able to develop more power for the same

size and conversely a small size engine fed with extra air

would produce the same power as a larger engine

supplied with its normal air feed

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TYPES OF SUPERCHARGER- • Supercharging is done by means of compressor; there are two types

of compressors that may be used as super chargers.

They are as follows:-

1. Positive displacement type surchargers.

(a) Piston Cylinder type

(b) Roots blowers

(c) Vane blower

• 2. Centrifugal type super chargers or turbo type.

• 3. Turbo type super chargers.

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ADVANTAGE OF SUPERCHARGING

1.

Power Increase.

2.

Fuel Economy.

3. Mechanical Efficiency.

4.

Fuel Knock.

5. Volumetric Efficiency.

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TURBOCHARGERS

• Turbocharger is a turbine driven air

compressor powered by exhaust gases from

the internal combustion engine.

The turbine basically expands the gas mixture,

which is at high temperature, and transfers

some of the energy into useful work.

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ADVANTAGE OF TURBOCHAGING:-

no gearing require.

Suitable for high speed engine.

Low maintenance.

Utilization of exhaust gas.

• DISADVANTAGE OF TURBOCHAGING:-

• Increase fuel consumption at low power o/p.

• Total cost unit increases

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• The part load increases the specific fuel consumption,

decreases the thermal and mechanical efficiency. But the effect

is not as predominant as in thermal plants.

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Comparative study of diesel power plant

with steam power plant

ADVANTAGES OF DIESEL PLANTS OVER THERMAL PLANTS

1.The diesel power plants are more efficient than steam power plants in

the range of 150 MW capacity. They maintain high operating

efficiency in the load range of 50% to 100% of full load.

2.Diesel plants are cheaper in first cost than steam plants ; plant units

up to about 7 kW. Above this capacity, the diesel cost rises rapidly

while that of steam plants continues to fall.

3.It has no standby losses.

4.It can burn fairly wide range of fuels.

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5. It can be quickly started up and brought into service (within one minute).

6 .Manufacturing periods are short, therefore, a diesel station may be rapidly

extended to keep pace with load growth by just adding the generating units

of suitable sizes.

7. The space required for diesel plant is considerably less than thermal plant

and, therefore, cost of foundation and buildings is less.

8. There is no problem of ash handling as there is practically no refuse.

9. They can be employed in all climatic zones.

10. Machine sets are readily available as standard sets in the range of 500

kW to 40 MW.

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DISADVANTAGES OF DIESEL PLANTS OVER THERMAL PLANTS

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

thermal unit.

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

for steam plants. These costs are more or less fixed in case of

steam plants and more or less are proportional to output in the

case of diesel 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 diesel plants are not guaranteed for continuous operation

under overloads whereas steam plants can work under 25%

overload continuously.

8. The lubrication cost is high.

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Performance Testing of

Diesel Engine Power Plant

• The performance of the diesel engine focuses on the power and

efficiency.

• The engine performance varies with parameters of the engine like

piston speed, air-fuel ratio, compression ratio inlet air-pressure and

temperature.

.

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• A series of tests are carried out on the engine to determine its

performance characteristics, such as : -

indicated power (I.P.), Brake power (B.P.),

Frictional Power (F.P.),

Mechanical efficiency (ηm),

thermal efficiency,

• fuel consumption and also specific fuel consumption etc The two usual

conditions under which I.C. engines are operated are:

(1) constant speed with variable load, and

(2) variable speed with variable load

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1.Mean Effective Pressure and Torque

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2.Indicated Horse Power (IHP)

The indicated horse power (IHP) of the engine can be calculated as

follows :

• where Pm = LM.E.P. in kg/cm2

• L = Length of stroke in metres

• A = Piston areas in cm2

• N = Speed in R.P.M.

• n = Number of cylinders

• k = 1 for two stroke engine

• = 2 for four stroke engine.

IHP = Pm. L. A. N. n

4500 × k

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3.Brake Horse Power (BHP)

Brake horse power is defined as the net power available at the

crankshaft.

It is found by measuring the output torque with a dynamometer.

• T = Torque in kg.-m.

• N = Speed in R.P.NT..

4.Frictional Horse Power (FHP) :-

• The difference of IHP and BHP is called FHP. It is

utilized in overcoming frictional resistance of rotating and

sliding parts of the engine.

FHP = IHP – BHP

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5.Indicated Thermal Efficiency (ηi)

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Mechanical Efficiency (ηm)

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HEAT BALANCE SHEET • It is a useful method to watch the performance of the diesel power

plant. Among all the heat supplied to an engine only part of it is

converted into useful work, the remaining goes as waste.

• The heat balance of an engine depends on a number of factors

among which load is primary importance.

• Heat balance sheet is a useful method to watch the performance of

the plant.

• In order to draw the heat balance sheet of Diesel engine, the engine

is run at constant load and constant speed and the indicator diagram

is drawn with the help of indicator

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• The following quantities are noted:

1. The quantity of fuel consumed during a given period.

2. Quantity of cooling water and its outlet and inlet temperatures.

3. Weight of exhaust gases.

4. Temperature of exhausts gases.

5. Temperature of flue gases supplied

To calculate the heat in various items proceed as follows:-

Let-

W = Weight of fuel consumed per minute in kg.

G = Lower calorific value of fuel, kcal per kg.

Then heat in fuel supplied per minute = WCV kcal.

• The energy supplied to Diesel engine in the form of fuel input is usually

broken into following items:

(A) Heat Energy Absorbed in I.H.P. The heat energy absorbed in indicated

horsepower, I.H.P. is found by the following expression:-

Heat in L.H.P. per minute

(I.H.P. × 4500)/J kcal

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(B) Heat Rejected to Colling in Water:-

Let

W1 = Weight of cooling water supplied per minute (kg)

T1 = Inlet temperature of cooling water in °C

T2 = Output temperature of cooling water in °C

Then heat rejected to cooling water = W1(T2 – T1)

(C) Heat Carried Away by Exhaust Gases:-

Let W2 = Weight of exhaust gases leaving per minute in kg.

(sum of weight of air and fuel supplied)

T3 = Temperature of flue gases supplied per minute °C.

T4 = Temperature °C of exhaust gases.

KP = Mean specific heat at constant pressure of exhaust.

The heat carried away by exhaust gases = W2 × KP × (T4 – T3) kg cal.

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(D) Heat Unaccounted for (Heat Lost Due to Friction, Radiation etc):-

The heat balance sheet is drawn as follows:-

A typical heat balance sheet at full load for Diesel cycle (compression ignition) is

as follows:

(1) Useful work = 30%

(2) Heat rejected to cooling water = 30%

(3) Heat carried away by exhaust gases = 26%

(4) Heat unaccounted (Heat lost due to friction, radiation etc.) = 10%.

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