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Joules cycle It consist of two constant pressure and two adiabatic processes as shown on p-v and t-s diagram

in figure

Now let us consider the four stages of the joule cycle let the engine cylinder contain m kg of air at

its original condition represented by point 1 on p-v and t-s diagram At this point let T1 and V1 by

the temperature and the volume of the air

(1) FIRST STAGE

The air is heated at a constant pressure from the initial temperature to temperature T2 represented

by the graph 1-2 in fig 5.7(a) and (b)

Heat supplied to the air

(2) SECOND STAGE

The air is allowed to expand Adiabatically from V1 to V2the adiabatic expansion is represented

by the graph 2-3 in fig 5.7 a and b the temperature of the air falls from t2 to t3 in this process no

heat is absorbed or rejected by the air

(3)THIRD STAGE

The air is now cooled at constant pressure from temperature t3 to t4 represented by 3.4(a) and (b)

Heat rejected by air

(4) FOURTH STAGE

The air now compressed adiabatically from v4 to v1.the adiabatic compression as represented by

the graph. The temperature of the air increases from t4 to t1.again no heat is absorbed or rejected

by air.

We see from above that there is no interchange of heat during the two adiabatic

processes. The only interchange of heat takes place during constant pressure processes.

NOTES:

(1).The efficiency of Joules cycle is lower than Carnot cycle efficiency

(2).cycle is not thermodynamically reversible because there is no regenerator to provide a

constant temperature during heating and cooling at constant pressure

(3). the reverse joules cycle is known asBell-colmans cycle and is applied tio the refigrators

where air is used refrigerant

OTTO CYCLE

The first successful engine working on this cycle was built by A.Otto. these days , many

gas,petrol and many of the oil engines run on this cycle.. it is also known as constant volume

cycle, as the heat is received and rejected at constant volume.

Thiscycle is taken as standard of comparison for internal combustion engines. For the purpose

of comparison with other cycles ,air is assumed to be working substance .

The engine conceived by Otto has air enclosed in a cylinder, whose walls are perfectly

non conductor of heat. But bottom is perfect conductor of heat .there is also a hot body and cold

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body and an insulating cap, which are alternately brought in contact with the bottom of cylinder

(i-e. a cylinder similar to that of carnot)

The ideal Otto cycle consists of two constant volume and adiabatic processes as shown in

P-V and T-S diagrams.

Let the engine cylinder contain m kg of air at point 1.at this point let p1,t1 and v1 be the pressure

,temperature and volume of the air respectively. Following are the four stages of the ideal cycle

(1)FIRST STAGE

The air is expanded adiabatically fro initial temperature t1 to a temperature t2 as shown by the

graph and figure. in this process no air is absorbed or rejected by the air.

(2)SECON STAGE

The air is cooled at constant volume from temperature t2 to t3 as shown by the figure and

graph. We know that heated rejected by air during this process

(3)THIRD STAGE

The air is compressed adiabatically from a temperature t3 to t4.as shown by the graph. In this

process no heat is absorbed or rejected by air

(4)FOURTH STAGE

The air is now heated at constant volume form temperature t4 to t1 as shown by the graph and fig.

we know that heat absorbed by air in this process ,

We see that air has been brought back to its original condition of pressure, volume and

temperature, thus completing the cycle

DIESEL CYCLE:

This cycle was devised by doctor Rudolph diesel in 1893,with an idea to attain a higher thermal

efficiency with a compression ratio. it is also known as constant pressure cycle .

The engine imagined by diesel has air enclosed in the cylinder whose walls are perfectly

non conductor of heat but bottom is a perfect conductor of heat again there is hot and cold body

and an insulating cap, which are alternately brought in contact with cylinder

The diesel cycle consists of two adiabatic, a constant pressure and a constant volume

crosses.

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Let the engine cylinder contain m kg of air at point 1 at this point p1.t1 and v1 be

pressure,temperature and volume of the air .

(1)FIRST STAGE;

The air is heated at constant pressure from initial temperature t1 to t2.

Heat supplied to the air ,

(2)SECOND STAGE

The air is expanded adiabatically from t2 to t3

In this process no heat is rejected or absorbed by the air

(3)THIRD STAGE

The air is now cooled at constant volume from t3 to t4

Heat rejected by air

(4)FOURTH STAGE

The air is compressed adiabatically form t4 to t1 in this process no heat rejected or absorbed by

air

We see that air has been brought back ti its original conditions of pressure, volume and

temperature, thus completing the cycle

Wok done=heat absorbed-heat rejected