This document summarizes different types of heat engine cycles. It describes a heat engine as a device that absorbs heat (Q) and uses it to do useful work (W) when operating in a cycle. The document then discusses the Carnot, Rankine, Otto, and Diesel cycles - providing details on the processes involved in each cycle and equations for calculating their efficiencies. The Carnot cycle uses two reservoirs at fixed temperatures and is the most efficient possible. The Rankine cycle completely condenses vapor before pumping. The Otto and Diesel cycles differ in whether heat is supplied at constant volume or constant pressure.

1. L.D. COLLEGE OF
ENGINEERING

2. HEAT ENGINE

3. 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.

4. Heat Engine
E
Hot Body
(source of heat)
Q1
Cold Body
(absorbs heat)
Q2
W

5. Heat Engine cycles
Following are the various “ Heat Engine cycles “
(1) Carnot cycle
(2) Rankine cycle
(3) Otto cycle
(4) Diesel cycle

6.  Nicolas Leonard Sadi Carnot in 1824 first proposed
the concept of heat engine working on reversible
cycle called 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 condsideration with the efficiency
of a reversible cycle operating between the same
temperatures.
Carnot cycle

7. Carnot Cycle
Hot Reservoir
T1
Cold Reservoir
T2
C
Q1
Q2
W

8. Volume
Pressure
•
•
1
2
•
4
T1
Q1
Carnot Cycle
Q2
V
nRT
P 1
=

V
const
P
.
=
T2•3
Q=0
Q=0
V
nRT
P 2
=
W
Isothermal expansion
Adiabatic expansion
Isothermal compression
Adiabatic compression

9. Carnot Cycle?
Efficiency of carnot cycle =
(1) Heat is transferred 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.
1
2
1
T
T
C 

10. 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

11. 1
2
34
Pressure
Volume
Qs
QR
Adiabatic process
Diesel cycle
Constant volume process
Constant pressure process

12. Efficiency of diesel cycle =
here,
r = compression ratio
𝛼 = cut-off ratio
Above this equation that the efficiency of diesel cycle
depends upon compression ratio (r), ratio of specific heats
(𝛾) and cut-off ratio (𝛼).

13. Otto cycle
Nicholas-A-Otto, A German engineer
developed the first successful engine
working on this cycle in 1876.
This cycle is also known as constant
volume cycle because heat is
supplied and rejected at constant
volume.

15. Efficiency of otto cycle =
Here,
r = compression ratio
𝛾 = ratio of specific heats
Above this equation that the efficiency of otto cycle
depends upon compression ratio only.

16. Comparison of Otto and Diesel Cycles
combustion
Q=0
Q=0
Work per cycle =
Area inside

17. Rankine cycle
It is very difficult to pump mixture of vapour and liquid as
incase of carnot vapour cycle.
This difficulty is eliminated in rankine cycle by complete
condensation of vapour in condenser and then pumping
the water isentropically to the boiler at boiler pressure.

18. Rankine cycle