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ACTIVE LEARNING PROCESS. Branch: Computer Engineering. Guided By : Prof.Jugal panchal. Prepared By : Tejas Parmar -13BECEG125. Introduction:.

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Branch: Computer Engineering

Guided By :


Prepared By :

TejasParmar -13BECEG125

  • Heat engine is the device which converts chemical energy of fuel into heat energy and this heat energy is utilized converting it to mechanical work.
  • Heat engine mainly consists of a source of heat, a medium to carry the heat energy, and a converting machine.

Heat is continuosly supplied to the medium from the combustion chamber for conversion into mechanical work.

  • In addition to the above three elements, there is one cold body, at a lower temperature than the source known as heat sink.

Fig 5.1 illustrates the basic principle of an elementry heat engine.

  • The working fluid takes heat from heat source and flows to the converting machine E where heat energy converts into mechanical work. After this conversion it is discharged into the sink where it is cooled and comes to the original state. From the heat sink working fluid is supplied to heat source by the pump P, where it is heated again and cycle is repeated.
sources of heat
Sources of Heat:
  • Following are the various sources of heat, used for conversion into mechanical work.

① Chemical Energy

② Nuclear Energy

③ Heat Energy

classification of heat engines
Classification of Heat Engines:
  • Heat engine are classfied into two broad classes:

① External Combustion Engine:- In this engine, heat of combustion product is transferred to working fluid of the cycle. Ex: Steam engine, Steam turbine, Closed cycle gas turbine etc..

② Internal Combustion Engine:- In this cycle, the product of combustion is directly used as working fluid. Ex: Petrol, Diesel, Open cycle gas turbine etc..

heat engine cycles
Heat Engine Cycles:
  • Following are the various heat engine cycles which will be discussed in detail in this chapter.

① Carnot Cycle

② Rankine Cycle

③ Otto Cycle

④ Diesel Cycle

carnot cycle
Carnot Cycle:
  • According to carnot theorem “no cycle can be more efficient than a reversible cycle operating between the same temperature limits.
  • Carnot cycle is useful to compare the efficiency of any cycle under consideration with the efficiency of a reversible cycle operating between the same two temperatures.

Carnot Cycle Processes:

① Isothermal expansion

② Adiabatic expansion

③ Isothermal compression

④ Adiabatic compression

efficiency of carnot cycle
Efficiency Of Carnot cycle:
  • Heat supplied during isothermal process
  • Q₁=p₁V₂ loge V₂/V₁

=RT₁ loge V₂/V₁

  • Heat rejected during isothermal compression
  • Q ₂ =p₃V₃ loge V₄/V₃

=RT loge V₄/V₃

  • During adiabatic expansion and adiabatic compression,
  • Let r=ratio of expansion for process

= ratio of compression for process

  • By substituting the value of r ,

Q₁= RT₁ loge r

Q₂=RT₂ loge r

  • Workdone=RT₁ loge r - RT₂ loge r
  • Workdone= Rloge r(T₁ - T₂ )

Thermal efficiency= Q₁ - Q₂ / Q₁

  • ή= R loge r(T₁ - T₂ ) / RT₁ loge r
  • ή= T₁ - T₂/ T₁
  • Where T₁= Max Temperature of cycle

T₂ = Min Temperature of cycle

rankine cycle
Rankine Cycle:
  • It is very difficult to pump mixture of vapour and liquid as incase of carnotvapour cycle. This difficulty is eliminated in Rankine cycle by complete condensation of vapour in condenser and then putting the water isentropically to the boiler at boiler pressure.
  • The main for components cycle are:

① Boiler ③ Condenser

② Turbine ④ Feed pump

efficiency of rankine cycle
Efficiency Of Rankine cycle:
  • Heat supplied in boiler, Qs=h1-h2
  • Work developed by turbine,


  • Heat rejected to cooling water


  • Work supplied to feed pump,


  • Net work output , Wnet =(h1-h2)-(h4-h3)

Rankine cycle efficiency = network output /Heat supplied in boiler

  • ήR = (h1-h4)-(h2-h3) / (h1-h4)
  • ήR= 1-h2-h3/h1-h4
  • Usually pump work is very small, hence it is neglected

ήR= h1-h2/h1-h4

otto cycle
Otto cycle:
  • Nicholas-a-otto, a german engineer developed the first successful engine working on this cycle. This cycle is known as Constant volume cycle because heat is supplied and rejected at constant volume. Mainly this cycle is used in petrol and gas engines.
  • The efficiency of engine in which air is used as working substance is known as air standard efficiency.
efficiency of otto cycle
Efficiency Of Otto cycle:
  • Network done Wnet = mCv(T3-T1)-mCv(T4-T1)
  • Air standard efficiency,

ή=mCv(T3-T1)-mCv(T4-T1) / mCv(T3-T2)

= 1-(T4-T1)/(T3-T2)

  • Compression ratio defined as r=Vc+Vs/ Vc
  • ή = 1-1/r^y-1
diesel cycle
Diesel Cycle:
  • This cycle was discovered by a German engineer Dr.Rudolph diesel.
  • Diesel cycle is also known as constant pressure heat addition cycle.
  • The ideal diesel cycle consists of two reversible adiabatic process a constant pressure process and constant volume process. P-V diagram of this cycle is shown in fig.
efficiency of diesel cycle
Efficiency Of Diesel cycle:
  • Network done , Wnet = mCp(T3-T2)-mCv(T4-T1)
  • Air standard efficiency,

ή= mCp(T3-T2)-mCv(T4-T1) / mCp(T3-T2)

  • ή= 1-(T4-T1)/ y(T3-T4)
  • Let, compression ratio, r=V1/V2

cut-off ratio, p=V3/V2

Expansion ratio = V4/V3= r/p


For process (1-2):

T2=T1 (r)^y-1

  • For process (2-3):

T3=[T1 (r)^y-1].p

  • For process (3-4):

T4=T3 (p)^y-1/ (r)^y-1

  • By substitude the value of T3,



By substitude the values of T2,T3,T4 in eq.

ή=1-1/y[ T1p^y-T1/ T1.p.r^y-1-T1.r^y-1]

ή=1-1/(r)^y-1[ p^y-1/y(p-1)]

  • From the eq. it is clear that the effciency of Diesel cycle increases with the increase of compression ratio and with the decrease of cut off ratio.