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Chapter 7 - Heat

Chapter 7 - Heat. Science for X. Agenda. Heat Engines External combustion engine Internal combustion engine Petrol engine Diesel engine Efficiency of heat engine Advantages of Internal combustion engine. Application of Heat Engines.

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Chapter 7 - Heat

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  1. Chapter 7 - Heat Science for X

  2. Agenda • Heat Engines • External combustion engine • Internal combustion engine • Petrol engine • Diesel engine • Efficiency of heat engine • Advantages of Internal combustion engine

  3. Application of Heat Engines • It is customary to cool liquids such as fruit juice by adding a piece of ice. The required heat for melting of ice is taken from the juice • The high latent heat of steam is useful in working of a steam engine • Have you observed that water in an earthen pot gets cooled after sometime? So how does it happen? • The pot has number of poles in its wall. Water oozes out through these pores and evaporates by taking heat from water. Thus the water is cooled

  4. Heat Engines • Thomas Savery in 1698 patented an early steam engine • Use: His steam engine was extensively used for pumping water out of mines and also to lit water from wells

  5. Experiment • So How is heat is converted to mechanical energy? • Small Experiment • Take some water in test tube and close it with cork • Heat the test tube and when the water boils the cork flies off • The steam produced inside the test tube after some time exerts pressure on the cork and the cork flies off

  6. Heat Engine • Heat engine is a system that works on the principle of converting the thermal energy to mechanical energy • Types of Heat Engine Heat Engine External Combustion Engine Internal combustion Engine

  7. External Combustion Engine Steam Engine Parts Boiler Inlet Valve Crankshaft Piston Cylinder Connecting Rod Pump Outlet Valve Condenser

  8. External Combustion Engine • Operating Principle • The steam engine basically consists of two strokes of operation that is required to convert the heat energy to mechanical energy namely – • Expansion stroke • Exhaust stroke

  9. External Combustion Engine Expansion Stroke Steam • In this cycle, the water in the boiler is heated • The generated steam gets to the cylinder using the inlet valve • The expanding steam forces the piston to move outwards as shown • During this stroke, the outlet valve remains closed Boiler Inlet Valve Heat Crankshaft Piston Cylinder Connecting Rod Pump Outlet Valve Water Condenser

  10. External Combustion Engine Exhaust stroke Steam • As the piston moved inwards, the outlet valve opens • The used steam is pushed into the condenser • As such this cycle repeats • The inlet valve will be closed Boiler Heat Inlet Valve closes Crankshaft Piston Cylinder Connecting Rod Pump Outlet Valve opens Water Condenser

  11. External Combustion Engine De-merits • Steam engines are bulkier • Major portion of heat energy wasted • Engines cannot be started instantaneously as getting steam at high temperature is time consuming • Risk of accidents due to bursting of boiler very high

  12. Internal Combustion Engine • The limitations of the external combustion engine led to the development of internal combustion engine • As name suggests, the combustion of the fuel takes place inside the cylinder itself, hence named internal combustion engine • Internal Combustion engines – types: Internal combustion engine Petrol Engine Diesel Engine

  13. Internal Combustion Engine – Petrol Engine Intake Stroke Inlet Valve Opens Outlet Valve will be closed • The Piston moves away from the cylinder head • This results in low pressure inside the cylinder and the inlet valve opens • The fuel mixture from the carburetor enters the cylinder • The outlet valve remains closed during this stroke Fuel Mixture enters Piston Intake Stroke

  14. Internal Combustion Engine – Petrol Engine Compression Stroke Inlet Valve Closed Outlet Valve remains closed • The fuel mixture is compressed by the piston moving towards the head • Both the inlet and outlet valve remains closed Fuel mixture compressed Piston Compression Stroke

  15. Internal Combustion Engine – Petrol Engine Power Stroke Inlet Valve Closed Outlet Valve remains closed • The compressed mixture is ignited by the spark generated by the spark plug • The resulting product of combustion consisting of carbon dioxide (CO2) and water vapor expands suddenly • This causes the piston to be pushed outwards with greater forces • Even in this stroke both the valves remains closed v Fuel mixture Ignited by spark plug Piston pushed outwards Power Stroke

  16. Internal Combustion Engine – Petrol Engine Exhaust Stroke Inlet Valve remains Closed Outlet Valve opens • The exhaust valve opens • The piston moves upwards • The waste (burnt) gases are through the exhaust (outlet) valve • The inlet valve remains closed Exhaust gases Piston moves upwards Exhaust stroke

  17. Internal Combustion engine - Diesel • Diesel engine is similar to petrol engineexcept that the fuel injunction is fitted in place of spark plug • A carburetor is not required in a diesel engine • Working cycle of diesel engine also consists of four strokes • Intake stroke • Compression stroke • Power stroke • Exhaust stroke

  18. Internal Combustion Engine Petrol Vs Diesel Burnt fuel exits through the exhaust valve Spark plug ignites the fuel mixture Fuel mixture enters the valve Fuel mixture is compressed Petrol Engine Exhaust stroke Power stroke Compression stroke Intake stroke Air enters through the inlet valve Fuel is injected to the cylinder and hot air burns the fuel Air is compressed Burnt fuel exits through the exhaust valve Diesel Engine Exhaust stroke Power stroke Compression stroke Intake stroke

  19. Efficiency of Heat Engine • Efficiency of an engine is defined as the fraction of heat that is converted to useful mechanical work • It is usually represented as percentage • Efficiency of petrol engine is about 40% • Efficiency of steam is about 15 % WorkDone Efficiency = X 100 Heat Supplied

  20. Advantages of Internal Combustion Engine over External Combustion Engine • Efficiency of internal combustion engine is greater than external combustion engine • Internal combustion engine can be startedinstantaneously • Internal combustion engine can be manufactured in differentsizes and can be fitted to smallmachines • There is no risk of accidents due to storage of material in high pressure Used in

  21. Back Up slides

  22. External Combustion Engine Steam Engine –Expansion stroke Steam Boiler Inlet Valve Crankshaft Heat Piston Cylinder Connecting Rod Pump Outlet Valve Water Condenser

  23. External Combustion Engine Steam Engine Exhaust stroke Steam Boiler Inlet Valve Crankshaft Heat Piston Cylinder Connecting Rod Pump Outlet Valve Water Condenser

  24. Internal Combustion Engine

  25. Internal Combustion Engine Burnt fuel exits through the exhaust valve Spark plug ignites the fuel mixture Fuel mixture enters the valve Fuel mixture is compressed Petrol Engine Exhaust stroke Power stroke Compression stroke Intake stroke Air enters through the inlet valve Fuel is injected to the cylinder and hot air burns the fuel Air is compressed Burnt fuel exits through the exhaust valve Diesel Engine Exhaust stroke Power stroke Compression stroke Intake stroke

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