This document provides an overview of mechanical engineering elements, including thermal prime movers, heat engines, heat engine cycles, and the Otto and Diesel cycles. It defines a heat engine as a device that absorbs heat and uses it to do useful work in a cycle. The Otto cycle uses combustion and constant volume processes, while the Diesel cycle uses constant pressure combustion. Key aspects of both cycles like their stages and efficiencies are described.

2. Vadodara Institute Of
Engineering
Element Of Mechanical Engineering
-Mr.Tushar Kumbhani
 Bhosle Jaykumar [17mech013]
 Shethwala Mohd Shafi M.Shoeb [17mech014]
 Jayesh Nakiya [17mech015]

3. Contents…….
 Thermal Prime Movers
 Elementary Heat Engines
 Source Of Heat
 Working Substance
 Converting Machines
 Classification Of Heat Engines
 Heat Engine Cycle
 Otto Cycle
 Diesel Cycle

4. @ The Thermal Prime Mover Is A Prime Mover That Is Made
To Utility The Heat Energy For Conversion Into Mechanical Work.
@ Thermal Prime Mover Have Played Very Important Role In The
Field Of Transportation And Communication On Land, On Sea
And In The Space.
1) Internal Combustion Engines
2) Steam Turbines
3) Gas Turbines
4) Rockets
Thermal Prime Movers

5. Elementary Heat Engine
• A Heat Engine Is A Device That Absorbs Heat (Q) And
Uses It To Do Useful Work (W) On The Surroundings When
Operating In A Cycle.
• Sources Of Heat Include The Combustion Of Coal,
Petroleum Or Carbohydrates And Nuclear Reactions.
• Working Substance: The Matter Inside The Heat Engine
That Undergoes Addition Or Rejection Of Heat And That
Does Work On The Surroundings. Examples Include Air
And Water Vapour (Steam).
• In A Cycle, The Working Substance Is In The Same
Thermodynamic State At The End As At The Start.

6. HE2 Thermal Physics
E
Hot Body
(Source Of Heat)
Q1
Cold Body
(Absorbs Heat)
Q2
W

7.  Chemical Energy :- The Chemical Energy Of Solid, Liquid Or
Gaseous Fuels Is Converted Into Energy By Burning Of Fuel.
Fuel.
 Nuclear Energy(atomic Energy) :- Nuclear Energy Or Atomic
Energy Is Recent Development. Heat Production By The
Fission Or Fusion Of Atoms May Be Used To Produce Shaft
Power.
 Heat Energy :- Heat Energy May Be Obtained Directly From
The Various Natural Resources Such As Solar Radiation,
Geothermal Energy Etc.

8. Working Substance (Medium To Carry Heat):-
# When A Gas Or Mixture Of Gases Or A Vapour Is
Used In Engine For Transferring Heat, It Is Known As
Working Fluid Or Working Substance.
# Working Fluid Is Never Destroyed Or Reduces In
Quantity During The Process.

9. ØConverting Machines
 Converting Machine Convert Heat Energy Of Working
Fluid Into Mechanical Work.
 In Reciprocation, Machine Piston Reciprocates Inside
A Hollow Cylinder.
 In Rotary Machine, Blades Or Vanes Are Fitted On
Wheel.
 In Jet Machine Fluid Is Discharge With High Velocity
And Produce Thrust Which Causes The Motion

10. Classification Of Heat Engines…………
֍ Heat engines are classified into two broad classes……
1) External combustion engine:- Heat of combustion product
is transferred of working flied of the cycle.
Example:- steam engine, steam turbine
2) internal combustion engine:-In internal combustion engine
(I C engine),the product of combustion is directly used as
working fluid. In this engine, combustion take place inside
the cylinder of engine.
Example:- petrol, diesel, gas engine, open cycle gas
turbine, jet engine, etc.

11. Heat Engine Cycles
Θ Following are the various heat engine cycle will be
discusses in details.
1) Carnot Cycle
2) Otto Cycle
3) Diesel Cycle
4) Rankine Cycle **

12. Hot Reservoir
T1
Cold Reservoir
T2
C
Q1
Q2
W

13. Volume
Pressure
•
•
a
b
•
d
T1
Q1
Q2
V
nRT
P 1
=

V
const
P
.
=
T2•c
Q=0
Q=0
V
nRT
P 2
=

14. Volume
Pressure
•
•
a
b
•
d
T1
Q1
Q2
V
nRT
P 1
=

V
const
P
.
=
T2•c
Q=0
Q=0
V
nRT
P 2
=
W

15. From a to b: isothermal, so that DU = 0 and Q = - W
Thus, Q1 = +nRT1ln(Vb/Va) (+ve quantity)
Similarly, from c to d: isothermal, so that DU = 0 and Q = - W
Thus, Q2 = +nRT2ln(Vd/Vc) = -nRT2ln(Vc/Vd) (-ve)
From b to c: adiabatic, Q = 0, so that TV-1 is constant.
Thus, T1Vb
-1 = T2Vc
-1 or 1
2
1









b
c
V
V
T
T
Similarly, d to a: adiabatic, Q = 0, so that TV-1 is constant.
Thus, T2Vd
-1 = T1Va
-1 or 1
2
1









a
d
V
V
T
T

16. We see that:
11
2
1















a
d
b
c
V
V
V
V
T
T
a
b
d
c
V
V
V
V

Which means that
Now also:
)/ln(
)/ln(
)/ln(
)/ln(
2
1
2
1
2
1
dc
ab
dc
ab
VVT
VVT
VVnRT
VVnRT
Q
Q

This is an important result. Temperature can be defined (on the
absolute (Kelvin) scale) in terms of the heat flows in a Carnot Cycle.
But as the
volume ratios are
equal:
2
1
2
1
T
T
Q
Q


17. What’s Special about a Carnot Cycle??
(1) Heat is transferred to/from only two reservoirs at fixed
temperatures, T1 and T2 - not at a variety of temperatures.
(2) Heat transfer is the most efficient possible because the
temperature of the working substance equals the temperature of the
reservoirs. No heat is wasted in flowing from hot to cold.
(3) The cycle uses an adiabatic process to raise and lower the
temperature of the working substance. No heat is wasted in heating
up the working substance.
(4) Carnot cycles are reversible. Not all cycles are!

18. (5) The Carnot Theorem States That The Carnot Cycle (Or Any Reversible
Cycle) Is The Most Efficient Cycle Possible. The Carnot Cycle Defines An
Upper Limit To The Efficiency Of A Cycle.
• Where T1 And T2 Are The Temperatures Of The Hot And Cold
Reservoirs, Respectively, In Degrees Kelvin.
 As T2 > 0, Hc Is Always <1.
• Recall That For Any Cycle, The Efficiency Of A Heat Engine Is Given
As:
1
2
1
1==
Q
Q
Q
W
E
• For An Engine Using A Carnot Cycle, The Efficiency Is Also Equal
To:
1
2
1=
T
T
C
What’s Special about a Carnot Cycle??

19. Diesel Cycle (Constant Pressure Cycle)
This Cycle was discovered by a German engineer Dr. Rudolph Diesel.
Cycle is also known as Constant Pressure Heat addition cycle.
Example Were Diesel Engine is used:- Cars, Motors, Submarine,
Locomotives
It Comprises of 4 Stage:
☻ Intake: Inlet valve opens, Exhaust closed.
☻ Compression: Both valve closed. Piston compresses air upwards.
Fuel injected.
☻ Power: Fuel ignites. Gas forces piston downwards.
☻ Exhaust: Inlet valve closed. Exhaust valve opens. Piston travels
upward.

20. Diesel Cycle

21. Key-futures Of Diesel Engine
• The Diesel engine takes in JUST air.
• The compression ratio is higher, thus higher
efficiency.
• Diesel engines use direct fuel injection.
• No spark plug required.

22. Otto cycle (Constant Volume cycle)
Nicholas-A-Otta, a German engineer developed
the first successful engine working on this cycle in
1876.
Mainly this cycle is used in petrol and gas engines.
Air standard efficiency:- The efficiency of engine
in which air is used as working substance is knoen
as air standard efficacy. the air stander efficiency is
always greater than the actual efficacy of a cycle.

23. Ideal Otto Cycle

24. Reference
 http://auto.howstuffworks.com/diesel1.htm
 http://en.wikipedia.org/wiki/Diesel_cycle
 http://hyperphysics.phy-
astr.gsu.edu/hbase/thermo/diesel.html
 http://qph.ec.quorcdn.net/min/qimer-11fc44678a6gho
 http://google.co.in?serch?clicnt=ucweb-bookmark7EI.