topic 8 physics

8/7/2019 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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topic 8 physics

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