DIESEL ENGINE POWER PLANT&MISCELLANEOUS TOPICS

Introduction Good for medium and small outputs Used where price comparison and

availability is made to coal power plants

Main element is a diesel engine

Classification of Engines Method of Ignition

– Spark Ignition– Compression Ignition

Cycles of Operation– Two Stroke– Four Stroke

On basis of fuel– Petrol– Diesel

4

Physical Principles related to Engine

Operation Energy conversion Vacuum Pressure The relationship between temperature,

pressure and volume. The three states of matter.

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Basic Parts of the Gasoline Engine

Cylinder block Piston Piston rings Piston pin Connecting rod Crankshaft

Cylinder head Intake valve Exhaust valve Camshaft Timing gears Spark plug

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Cylinder Block

Basic frame of gasoline engine.

Contains the cylinder.

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Piston

A sliding plug that harnesses the force of the burning gases in the cylinder.

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Piston Rings The rings seal the

compression gases above the piston keep the oil below the piston rings.

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Piston Pins

Also known as the wrist pin, it connects the piston to the small end of the connecting rod.

It transfers the force and allows the rod to swing back and forth.

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Connecting Rod

Connects the piston and piston pin to the crankshaft.

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Crankshaft

Along the the piston pin and connecting rod it converts the up and down motion (reciprocating) of the engine to spinning (rotary) motion.

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Flywheel Carries the inertia

when there is no power stroke.

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Lower End Action

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Cylinder Head

Forms the top of the combustion chamber.

Contains the valves, the passageways for the fuel mixture to move in and out of the engine.

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Intake and Exhaust Valves

Doorway that lets the gases in and out of the engine.

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Camshaft

Through the use of an eccentric the cam lobes push the valves open.

The valve springs close them.

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Spark Plug

Electric match used to begin the combustion process of burning air and gasoline to create heat.

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Engine Related Terms TDC (top dead center) BDC (bottom dead center) Stroke Bore Revolution Compression Ratio Displacement Cycle

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Four Stroke Cycle Intake Compression Power Exhaust

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Intake Stroke

Intake valve opens. Piston moves down, ½

turn of crankshaft. A vacuum is created in

the cylinder. Atmospheric pressure

pushes the air/fuel mixture into the cylinder.

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Compression Stroke

Valves close. Piston moves up, ½

turn of crankshaft. Air/fuel mixture is

compressed. Fuel starts to

vaporize and heat begins to build.

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Power Stroke

Valves remain closed.

Spark plug fires igniting fuel mixture.

Piston moves down, ½ turn of crankshaft.

Heat is converted to mechanical energy.

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Exhaust Stroke

Exhaust valve opens.

Piston move up, crankshaft makes ½ turn.

Exhaust gases are pushed out polluting the atmosphere.

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Four Stroke Cycle Animation

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Two Stroke Animation

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Diesel Animation

Diesel Engine

Intake Stroke:

•Piston moves from TDC to BDC creating vacuum in the cylinder

•Intake valve opens allowing only air to enter the cylinder and exhaust valve remains closed

Diesel EngineCompression Stroke

•Both valves stay closed

•Piston moves from BDC to TDC, compressing air to 22:1

•Compressing the air to this extent increases the temperature inside the cylinder to above 1000 degree F.

Diesel EnginePower Stroke

•Both valves stay closed

•When the piston is at the end of compression stroke(TDC) the injector sprays a mist of diesel fuel into the cylinder.

•When hot air mixes with diesel fuel an explosion takes place in the cylinder.

•Expanding gases push the piston from TDC to BDC

Diesel EngineExhaust Stroke

•Piston moves from BDC to TDC

•Exhaust valve opens and the exhaust gases escape

•Intake valve remains closed

Diesel EngineFour Strokes of Diesel Engine

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Diesel 2 stroke

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Diesel

Diesel Engine

The only difference between diesel engine and a four-strokegasoline engine is:•No sparkplug on Diesel engine.•Has a higher compression ratio. (14:1 to 25:1)•Better fuel mileage.

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Why not diesel?1. Diesel engines, because they have

much higher compression ratios (20:1 for a typical diesel vs. 8:1 for a typical gasoline engine), tend to be heavier than an equivalent gasoline engine.

2. Diesel engines also tend to be more expensive.

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Why not diesel?3. Diesel engines, because of the weight and

compression ratio, tend to have lower maximum RPM ranges than gasoline engines (see Question 381 for details). This makes diesel engines high torque rather than high horsepower, and that tends to make diesel cars slow in terms of acceleration.

4. Diesel engines must be fuel injected, and in the past fuel injection was expensive and less reliable

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Why not diesel?5. Diesel engines tend to produce more smoke

and "smell funny". 6. Diesel engines are harder to start in cold

weather, and if they contain glow plugs, diesel engines can require you to wait before starting the engine so the glow plugs can heat up.

7. Diesel engines are much noisier and tend to vibrate.

8. Diesel fuel is less readily available than gasoline

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Advantages The two things working in favor of diesel

engines are better fuel economy and longer engine life. Both of these advantages mean that, over the life of the engine, you will tend to save money with a diesel.

However, you also have to take the initial high cost of the engine into account. You have to own and operate a diesel engine for a fairly long time before the fuel economy overcomes the increased purchase price of the engine.

Important Terms Direct and Indirect Ignition Glow Plugs Engine Performance Parameters

DIESEL ENGINESIndirect and Direct 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.

The initial combustion takes place in this prechamber.

This has the effect of slowing the rate of combustion, which tends to reduce noise.

FIGURE 4-3 An indirect injection diesel engine uses a prechamber and a glow plug.

DIESEL ENGINESIndirect and Direct Injection

FIGURE 4-4 A direct injection diesel engine injects the fuel directly into the combustion chamber. Many designs do not use a glow plug.

GLOW PLUGS Glow plugs are always used in diesel engines

equipped with a precombustion chamber and may be used in direct injection diesel engines to aid starting.

A glow plug is a heating element that uses 12 volts from the battery and aids in the starting of a cold engine.

As the temperature of the glow plug increases, the resistance of the heating element inside increases, thereby reducing the current in amperes needed by the glow plugs.

Engine Performance Parameters

IMEP IHP BHP ITE BTE ME

Indicated Mean Effective Pressure (IMEP)

Indicator Diagram

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

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

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 output of the shaft

where N is speed in rpm

T is torque

2

4500

NTBHP

Frictional Horse Power (FHP)

It is the difference between IHP and BHP

FHP = IHP - FHP

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 fuel

J is the joules equivalent = 427

4500i

IHP

W CV J

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 fuel

J is the joules equivalent = 427

4500b

BHP

W CV J

Mechanical Efficiency It is the ratio of BHP to IHP

m

BHP

IHP

Example 4.4 A diesel power station has a supply power demand of

30kW. If the overall efficiency of generating station is 40%, (a) Calculate the diesel required per hour and also (b) calculate the electrical energy generated per ton of fuel

Efficiency = Output/ Input 0.4 =30/Input Input = 0.4*30 = 75kW Energy per hour = 75kWh = 75*860 kcal = 64500kcal Fuel Required = 64500 / 12000 = 5.37kg

Example 4.4 contd. (b) calculate the electrical energy generated per ton of fuel

Input per ton = 1000 kg= 1000 * 12000 kcal

= 1000 * 12000 / 860 KWh

= 13954 kWh

Efficency = Output/Input

Output = Efficiency * Input

= 0.4 * 13954

= 5581 kWh

Miscellaneous Topics Instrumentation

– Barometer– Manometer– Pyrometer

Running Alternators in Parallel Advantages of AC transmission Stability of Power Systems

AC or DC Brief History Available standards AC 220 or 110 ? 50Hz or 60 Hz

Running Alternators in Parallel What is synchronizing

– Connecting of two or more alternators

Conditions– Frequency of the systems should be identical– Phases of the incoming alternator should be

identical to that of the bus bar– Voltage of the incoming alternator should be

approximately same as that of the bus bar

Advantages of AC Tx Possible to generate voltage as high

as 33kV as compared to 11kV max in DC

Stepping up of voltage is much easier in AC as compared to DC

Easier to maintain AC substation Efficiency is much higher than DC

Torricelli Barometer

The mercury in the tube pushes down with its weight.

The bottom of the tube is open to the atmosphere.

The air pushes on the open surface of the mercury.

On an average day, the pressure of the air equals the pressure exerted by a column of mercury 760 mm high.

Above 760 mm, there is a vacuum in the tube.

Weight of mercury

Barometer DetailWhy doesn’t the diameter of the

column of Hg make a difference?Recall that Pressure = force/area.The “force” is the weight of the

mercury, but the pressure that results is that weight divided by the area of the column. So … a bigger column weighs more but also has a proportionally bigger area, and the two factors cancel one another out.

The pressure caused by the column of mercury pressing down is independent of the diameter of the column.

Manometer

A manometer is comprised of a bulb containing a gas and a U-shaped tube.

The U-shaped tube is partially filled with mercury. The weight of the mercury puts pressure on the gas.

If the U-tube is OPEN there is also air pressure acting on the gas.

The gas molecules put pressure on the mercury.

PHg

Manometer– measures contained gas pressure

U-tube Manometer Bourdon-tube gauge

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

lowerpressurehigher

pressure

Manometer

P1

Pa

height

750 mm Hg

130 mm

higher

pressure 880 mm Hg

Pa =

h =+-lower

pressure 620 mm Hg

P1 = Pa

P1 < Pa

Manometer

Pb

Pa

750 mm HgPa =

lowerpressure

ManometerPa

height

750 mm Hg

130 mm

lower

pressure 620 mm Hg

Pa =

h =-

880 mm Hghigher

pressure

higherpressure

ManometerPa

height

750 mm Hg

130 mm

Pa =

h =+

PYROMETERY

Pyrometery is the art and science of measurement of high temperatures. Pyrometery makes use of radiation emitted by the surface to determine its temperature

Temperature measuring devices invented are called pyrometers

PYROMETERS

Pyrometer is a device capable of measuring temperatures of objects above incandescence i.e. objects bright to the human eye).

It is a non contact device A device that measures thermal radiation in any temperature range.

PRINCIPLE

A pyrometer has optical system detector

It is based upon “Stephan Boltzmann law”

E=σ AT4

Basic Pyrometer