1. UNIT –III(B) POWER PLANTS
Introduction to EC and IC engines
Hydro
Thermal
Nuclear
Power plants and their layouts
Related numerical s
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ME Unit-3 Lecture -1

2. Power is produced in a unit other than where heat is generated.
EC engines
IC engines
Power is produced in a unit other than where heat is generated.
Working fluid is heated by external heat source.
Requires heat exchangers
Most of the components are subjected to maximum temperature of working fluid.
Moderately higher operating temperature.
More weight for same power.
Occupies more space
Heat is generated within the power producing unit.
Products of combustion itself is the working fluid.
No need of heat exchangers
Most of the components are subjected to lesser temperature.
So higher operating temperature can be used
Lighter weight for same power
Compact.

3. IC engines
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4. Classification of IC engines
Based on number of strokes
Two stroke
Four stroke
Based on Ignition
Spark Ignition
Compressed ignition
Based on cooling
Water cooled
Oil cooled
Air cooled
Based on Fuel used
Volatile liquid and gaseous fuel
Low volatile liquid fuel
Based on orientation of cylinder
Inline engine
Radial engine
Horizontal
V shaped engines
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5. Components and nomenclature
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8. Components
Cylinder block is the main part which is cast as a single unit. It carries cavities of large diameter called cylinders.
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9. Cylinder head is mounted on top of block which has provisions to accommodate valves, spark plug, fuel injector etc. it is held tight to the block by studs.
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10. Crank case is generally integral with the cylinder block
Crank case is generally integral with the cylinder block. It accommodates crank shaft.
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11. Piston fits in to the cylinder
Piston fits in to the cylinder. It moves between TDC and BDC within cylinder. Its function is to transmit the force created by combustion to connecting rod. Generally made of light weight metals like aluminium.
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12. Cam controls the opening and closing of valves and introduction of spark. The cam shaft will be coupled to crank shaft by gears or chain.
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13. Crank shaft is the component where we are getting useful mechanical power. It will be coupled to the mechanism to be driven by the engine.
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14. Oil pan is pressed steel or alloy cast iron component assembled to bottom of cylinder block and serves as reservoir for lubricating oil.
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15. Piston rings : upper ring is compression ring and lower ring is oil control ring which remove surplus oil from cylinder wall.
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16. Connecting rod connects piston to crank shaft
Connecting rod connects piston to crank shaft. This helps in converting reciprocating motion of piston to rotation of crank shaft.
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17. Inlet valve allows induction of fresh charge during suction stroke and
Exhaust valve allows removal of combustion products during compression stroke.
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18. Swept volume and compression ratio
The volume swept by the piston movement in between the TDC and BDC
The ratio of max volume formed in the cylinder to the clearance volume
Given by r = V(max) /V(min)
=V(tdc) /V(bdc)
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19. Mean effective pressure (MEP)
It is a fictitious force acting on the cylinder head during the entire power stroke.
Equals to the work done during the operation during the complete actual cycle
Wnet = MEP * piston area *Stroke
= MEP*Displacement volume
MEP = Wnet /(Vmax-Vmin)
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20. Four stroke Petrol engine
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21. Four stroke Diesel engine
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22. Cycle of Four stroke engine
Suction stroke
Compression stroke
Expansion/power stroke
Exhaust stroke
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23. Piston at TDC and move towards BDC IV is open and EV is closed
SUCTION STROKE
Piston at TDC and move towards BDC
IV is open and EV is closed
Suction is created which draws fresh charge in to the cylinder ( air in CI engine and A/F mixture in SI engine
Ends when piston reaches BDC.
IV gets closed at the end of suction stroke
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24. The charge is compressed by the return of piston
2. COMPRESSION STROKE
The charge is compressed by the return of piston
Both valves remain closed during this stroke
The volume of charge which was VT is compressed to Vc. At the end of compression stroke, combustion takes place.
In SI engine the mixture is ignited by using spark plug and burning takes place instantaneously so that volume remains constant during combustion. Pressure and temperature increases.
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25. 3. EXPANSION STROKE (POWER STROKE) starts with piston at TDC
In CI engine, fuel injection is started nearly at the end of compression stroke. Combustion will take place in such a way that the increase in pressure due to combustion is compensated by the increase in area during the expansion stroke.
3. EXPANSION STROKE (POWER STROKE)
starts with piston at TDC
The high pressure gas pushes the piston towards BDC and forces the crank to rotate
Power is generated
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26. After expansion, piston reaches BDC
4. Exhaust stroke
After expansion, piston reaches BDC
EV is opened and upward movement of the piston pushes the exhaust out of the cylinder.
Piston reaches TDC again and some gases are trapped in clearance volume.
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29. Two stroke engine
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30. Two stroke engine cycles
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31. Ignition happens at end of compression stroke.
In the compression stroke, piston moves upwards from BDC. Initially there is no compression as both TP and EP are open.
As the piston moves upwards, TP is closed first, then EP is closed and compression is begun.
Due to the upward movement of piston, the pressure in the crank case is reduced, the spring loaded inlet valve is opened and fresh charge enters to the crank case through inlet port.
Ignition happens at end of compression stroke.
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32. 2. Expansion stroke
The increase in pressure caused by the combustion pushes the piston downwards.
This compresses the charge in the crank case and it is moved towards TP.
Towards the end of expansion stroke, piston uncovers EP and the exhaust gas starts leaving the cylinder.
Further movement of piston uncovers TP and slightly compressed charge enters the cylinder. This further pushes the exhaust out.
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33. Two unproductive strokes are eliminated. Valves are replaced by ports
ADVANTAGES
Two unproductive strokes are eliminated.
Valves are replaced by ports
Suction and exhaust gas emission are achieved by some alternate arrangement
One power stroke for each revolution of crank shaft
The power output is theoretically doubled
Filling process is accomplished by charge compressed in the crank case.
The induction of fresh charge moves out products of combustion.
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34. Lubrication system Need:
Reduces the frictional forces that acts on the system parts.
Prevents corrosion by forming a layer on all the parts where its been circulated.
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35. Working
Oil from the sump is pumped through tubing arrangements where ever required.
Due to the property of the type of selected oil forms layers on the area where ever its is sprinkled , causes sliding of layers. Intern causes reduction of friction.
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37. Cooling system
Need:
Compact size makes the engines to under go more heat.
If dissipation doesn't occur causes engine break down.
Comfort or Ease while using the equipment.
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38. Types
Based on the Heat dissipation cooling systems are classified into
Air cooled systems
Liquid cooled systems
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39. Air cooled systems Air plays a major role in heat transfer
Contact area of the engine outer surface will be subjected to air
Special modification of outer surface area of the engine block is called ‘Fins’.
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40. Air cooled systems (fins)
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41. Fins structure (sectional view)
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42. Liquid cooled systems Need :
When ever there exist larger area that need to be cooled at regular intervals.
Multi cylinder engines where heat needs to be dissipated quickly and uniformly.
Where complex structure of the engine needs a cooling.
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43. Illustration of Liquid cooled system
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44. Types of liquid cooling
Most liquid-cooled engines use a mixture of water and chemicals such as antifreeze and rust inhibitors.
De-mineralized water
Heavy water
Mineral oil or synthetic oil
Liquid Nitro coolant
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ME Unit-3 Lecture -1