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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.
5
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.
8
Piston Rings The rings seal the
compression gases above the piston keep the oil below the piston rings.
9
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.
10
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.
12
Flywheel Carries the inertia
when there is no power stroke.
13
Lower End Action
14
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.
15
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.
22
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