Design of IC Engine Components

1. DESIGN OF IC ENGINE COMPONENTS
DR.MAHALINGAM COLLEGE OF ENGINEERING AND TECHNOLOGY, POLLACHI.
P.KARUPPUSAMY AP / AUTO
R.VISHNURAMESHKUMAR AP / AUTO
DEPARTMENT OF AUTOMOBILE ENGINEERING
Reference:
1. A text book of MACHINE DESIGN – R.S. KHURMI
2. Design of MACHINE ELEMENTS – V.B. BHANDARI
Year / Sem : III / VI
AY : 2018 – 19

2. UNIT – IV
DESIGN OF FLYWHEEL
2

3.  A flywheel is a heavy rotating body that acts as a reservoir of energy.
 The energy is stored in the flywheel in the form of kinetic energy.
 The flywheel acts as an energy-bank between the source of power and the driven
machinery.
FLYWHEEL

4.  Depending upon the source of power and type of driven machinery, there are two distinct
applications of the flywheel.
1. In certain cases, the power is supplied at a uniform rate, while the demand for power
from the driven machinery is variable, e.g. a punch press driven by an electric
motor.
2. In other applications, the power is supplied at variable rate, while the requirement of
the driven machinery is at a uniform rate, e.g. machinery driven by an internal
combustion engine. In I.C. engines, the power is generated at a variable rate.
APPLICATIONS OF THE FLYWHEEL

5.  The flywheel absorbs the excess energy during the expansion stroke, when the power
developed in the cylinder exceeds the demand.
 This energy is delivered during suction, compression and exhaust strokes.
 The flywheel, therefore, enables the engine to supply the power at practically uniform
rate.
WORKING OF THE FLYWHEEL
(i) To store and release energy when needed during the work cycle;
(ii) To reduce the power capacity of the electric motor;
(iii) To reduce the amplitude of speed fluctuations.
FUNCTIONS OF FLYWHEEL

6.  The arms have an elliptical cross-section.
 In small flywheels, the arms are replaced by a solid web.
 In large flywheels, stresses are induced in the arms during the casting process.
 There is a heavy concentration of mass at the rim and at the hub, which results in unequal
cooling rates for the rim, the hub and the arms.
 The resulting stresses, called cooling stresses, are sometimes of such a magnitude as to
cause the breakage of arms.
 Such cooling stresses can be avoided by using a split-type construction.
 In this case the rim and the hub are cut through the centre.
 The arms are, therefore, free to contract during the cooling process in the mould and
residual cooling stresses are avoided.
Solid one-piece flywheel Split-type flywheel
CONSTRUCTION OF THE FLYWHEEL

7. FLYWHEEL (vs) GOVERNOR
FLYWHEEL GOVERNOR
The flywheel limits the inevitable fluctuations of
speed during each cycle, which arise from
fluctuations of turning moment on the crankshaft.
The governor controls the mean speed of the
engine by varying the fuel supply to the engine
The flywheel has no influence on mean speed of
the engine. It does not maintain a constant speed.
The governor has no influence on cyclic speed
fluctuations.
If the load on the engine is constant, the mean
speed will be constant from cycle to cycle,
flywheel will always be acting.
If the load on the engine is constant, the mean
speed will be constant from cycle to cycle and the
governor will not operate
A flywheel may not be used if the cyclic
fluctuations of energy output are small or
negligible.
A governor is essential for all types of engines to
adjust the fuel supply as per the demand.
the kind of energy stored in flywheel is kinetic
energy. The kinetic energy is 100% convertible
into work without friction.
The governor mechanism involves frictional
losses.

8.  Traditionally, flywheels are made of cast iron.
 From design considerations, cast iron flywheels offer the following advantages:
i. Cast iron flywheels are the cheapest.
ii. Cast iron flywheel can be given any complex shape without involving machining
operations.
iii. Cast iron flywheel has an excellent ability to damp vibrations.
 Flywheels are made of high strength steels and composites in vehicle applications.
 Graphite-fiber reinforced polymer (GFRP) is considered as excellent choice for flywheels
fitted on modem car engines.
FLYWHEEL MATERIALS
 CI has a poor tensile strength compared to steel.
 The failure of cast-iron flywheel is sudden and total.
 The machinability of cast iron flywheel is poor compared to steel flywheel.
DISADAVANTAGES OF CI FLYWHEEL

9. COEFFICIENT OF FLUCTUATION OF SPEED
 The difference between the maximum and minimum speeds during a cycle is called the
maximum fluctuation of speed.
 The ratio of the maximum fluctuation of speed to the mean speed is called coefficient of
fluctuation of speed.
 The coefficient of fluctuation of speed is a limiting factor in the design of flywheel.
 It varies depending upon the nature of service to which the flywheel is employed

10. Permissible values for coefficient of fluctuation of speed for some machines.

11. COEFFICIENT OF STEADINESS
 The reciprocal of coefficient of fluctuation of speed is known as coefficient of
steadiness and it is denoted by m.

12. Fluctuation of Energy
 The fluctuation of energy may be determined by the turning moment diagram for one
complete cycle of operation.
 Consider a turning moment diagram for a single cylinder double acting steam
engine as shown.
 The vertical ordinate represents the turning moment and the horizontal ordinate
(abscissa) represents the crank angle.

13.  A little consideration will show that the turning moment is zero when the crank angle is
zero.
 It rises to a maximum value when crank angle reaches 90º and it is again zero when
crank angle is 180º.
 This is shown by the curve abc in Fig. and it represents the turning moment diagram for
outstroke.
 The curve cde is the turning moment diagram for instroke and is somewhat similar to the
curve abc.

14. TURNING MOMENT DIAGRAM for a four stroke internal combustion engine
 The variations of energy above and below the mean resisting torque line are called
fluctuation of energy.
 The difference between the maximum and the minimum energies is known as maximum
fluctuation of energy

15. MAXIMUM FLUCTUATION OF ENERGY
Turning moment diagram for a multi-cylinder engine
Let the energy in the flywheel at A = E, then from Fig.,
Energy at B = E + a1
Energy at C = E + a1 – a2
Energy at D = E + a1 – a2 + a3
Energy at E = E + a1 – a2 + a3 – a4
Energy at F = E + a1 – a2 + a3 – a4 + a5
Energy at G = E + a1 – a2 + a3 – a4 + a5 – a6 = Energy at A
The maximum of these energies is at B and minimum at E.
∴ Maximum energy in the flywheel = E + a1
& Minimum energy in the flywheel = E + a1 – a2 + a3 – a4
∴ Maximum fluctuation of energy, ΔE = Maximum energy – Minimum energy
= (E + a1) – (E + a1 – a2 + a3 – a4 ) = a2 – a3 + a4

16. COEFFICIENT OF FLUCTUATION OF ENERGY
It is defined as the ratio of the maximum fluctuation of energy to the work done per cycle.
It is usually denoted by CE. Mathematically, coefficient of fluctuation of energy,

18. Coefficient of fluctuation of energy (CE) for Steam and IC engines

19. Energy Stored in a Flywheel
m = Mass of the flywheel (kg)
k = Radius of gyration of the flywheel (m),
I = Mass moment of inertia of the flywheel about the axis of rotation
(kg-m2)= m.k2,
N1 and N2 = Maximum and minimum speeds during the cycle (r.p.m.)
ω1 and ω2 = Maximum and minimum angular speeds during the cycle (rad /
s)
N = Mean speed = (N1+N2)/2
ω = Mean angular speed = (ω1 +ω2)
CS = Coefficient of fluctuation of speed = (N1 − N2)/N or (ω1 - ω2)/ω

20. Mean kinetic energy of the flywheel
The maximum fluctuation of energy

21. Because of the thickness of rim is very small as compared to the diameter of rim.
The radius of gyration (k) = the mean radius of the rim (R)

22. The turning moment diagram for a petrol engine is drawn to the following scales:
Turning moment, 1 mm = 5 N-m;
Crank angle, 1 mm = 1º.
The turning moment diagram repeats itself at every half revolution of the engine and the
areas above and below the mean turning moment line, taken in order are 295, 685, 40,
340, 960, 270 mm2.
Determine the mass of 300 mm diameter flywheel rim when the coefficient of fluctuation
of speed is 0.3% and the engine runs at 1800 r.p.m.
Also determine the cross-section of the rim when the width of the rim is twice of
thickness.
Assume density of rim material as 7250 kg / m3.
Tutorial:

23. Given :
D = 300 mm or R = 150 mm = 0.15 m ;
CS = 0.3% = 0.003 ;
N = 1800 r.p.m. or ω = 2 π × 1800 / 60 = 188.5 rad/s ;
ρ = 7250 kg / m3

24. Mass of the flywheel
m = Mass of the flywheel in kg.
The turning moment diagram is shown in Fig.
scale of turning moment is 1 mm = 5 N-m,
scale of the crank angle is 1 mm = 1° = π / 180 rad
1 mm2 on the turning moment diagram
= 5 × π / 180 =

25. Let the total energy at A = E.
Therefore from Fig.
Energy at B =
Energy at C =
Energy at D =
Energy at E =
Energy at F =
Energy at G =
From above we see that the energy is maximum at B and minimum at E.
Maximum energy =
Minimum energy =
Maximum fluctuation of energy,
Δ E = Maximum energy — Minimum energy
=
=

26. Maximum fluctuation of energy (Δ E),
Δ E = m.R2.ω2.CS
m =
Cross-section of the flywheel rim
t = Thickness of rim in metres, and
b = Width of rim in metres = 2 t
∴ Cross-sectional area of rim, A = b × t = 2 t × t = 2 t2
Mass of the flywheel rim (m),
m= (A × 2πR) × ρ
t2 =
b = 2 t

27. The areas of the turning moment diagram for one revolution of a multi-cylinder engine with
reference to the mean turning moment, below and above the line, are – 32, + 408, – 267, +
333, – 310, + 226, – 374, + 260 and – 244 mm2.
The scale for abscissa and ordinate are: 1 mm = 2.4° and 1 mm = 650 N-m respectively.
The mean speed is 300 r.p.m. with a percentage speed fluctuation of ± 1.5%.
If the hoop stress in the material of the rim is not to exceed 5.6 MPa, determine the suitable
diameter and cross-section for the flywheel, assuming that the width is equal to 4 times the
thickness.
The density of the material may be taken as 7200 kg / m3.
Neglect the effect of the boss and arms.
Tutorial:

28. Given :
N = 300 r.p.m. or ω = 2 π × 300/60 = 31.42 rad/s ;
σt = 5.6 MPa = 5.6 × 106 N/m2 ;
ρ = 7200 kg/m 3

29. Diameter of the flywheel
D = Diameter of the flywheel (m)
Peripheral velocity of the flywheel
Hoop stress
σt = ρ × v2 =
D2 =
D =

30. The turning moment diagram
scale of crank angle is 1 mm = 2.4º = rad
scale of the turning moment is 1 mm = 650 N-m
1 mm2 on the turning moment diagram
= crank angle (rad) x turning moment (N-m)
=

31. Total energy at A = E.
Energy at B =
Energy at C =
Energy at D =
Energy at E =
Energy at F =
Energy at G =
Energy at H =
Energy at I =
Energy at J = = E = Energy at A
The energy is maximum at E and minimum at B.
Maximum energy =
Minimum energy =

32. Maximum fluctuation of energy
Δ E = Maximum energy – Minimum energy
=
=
The fluctuation of speed is ± 1.5% of the mean speed,
Total fluctuation of speed,
ω1 – ω2 = 3% of mean speed = 0.03 ω
Coefficient of fluctuation of speed,
CS = (ω1 − ω2)/ω =
Maximum fluctuation of energy (ΔE),
ΔE = m.R2.ω2.CS

33. Cross-section of the flywheel
t = Thickness of the flywheel rim
b = Width of the flywheel rim = 4 t
Cross-sectional area of the rim,
A = b × t =
mass of the flywheel rim (m),
m = A × π D × ρ
t =
b = 4 t =