topic 8 physics
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8.1 Energy degradation power generation
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Definiton: It is not possible to transfer heatcontinuously without at the same timetransferring some heat from a warmer body to
colder body. No heat engine that works in a cycle
completely converts into work
When a cold body and a hot body are broughtinto contact with each other, heat always flowfrom hot body to the cold body
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What is thermodynamic engine?
A device that transform thermal energy tomechanical energy or mechanical energy to
thermal energy. Boyles Law
When volume of gas increase, the pressuredecrease
Two crucial features for engine: It must work in cycle to be useful
The cyclic engine must have more than one heatresevoir
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Isothermal process
Is a state change when there is no temperaturechange occurs.
Adiabatic process Is a state change when there is no transfer of heat to
or from the system during the process
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Otto invented the gasoline engine in 1876
The gasoline engine works on 4 principle
The four-stroke principles of the gasolineengine are
The intake stroke
The compression stroke
The power stroke (combustion stroke) The exhaust stroke
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Isothermal process
Is a state change when there is no temperaturechange occurs.
Adiabatic process Is a state change when there is no transfer of heat to
or from the system during the process
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1. The inlet valve open. The exhaust valve clossed.
2. Intake stroke: a mixture is drawn into the cylinder(through the inlet valve as the piston moves down
3. Compression stroke: the piston moves up,compressing the gas adiabatically. Thetemperature increases to about 300 degree celcius
4. Spark ignites the petrol
5. Exhaust stroke: the rest of the burnt gas isexpelled as the piston moves up.
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Diesel engine works on two stroke:
i. Power stroke
ii. Compression stroke
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How the diesel engine work:
1. The highly charged compressed air filled thepiston which is at the top of its travel. Then,
diesel fuel is sprayed in and it is quicklyignites. This is because of the pressure and heatcontained in the cylinder.
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2. The pressure (created by the combustion offuel) resulted the piston to move downwardand this is called the Power stroke.
3. The exhaust gas is drawn out as the exhaustvalve open when the piston nears the bottomrelieving the pressure.
4. The piston moves further down, it uncoveranother intake ports. This allow the intake of ofgases into the cylinder .
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. The piston moves up and pressurizethe air inside the cylinder and force theexhaust gases that remains out of thecylinder through the exhaust port. Thisis called the compression stroke
6. As the piston nears the top of thecylinder, the cycle repeats with step 1.
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