This document provides an overview of the design of internal combustion (I.C.) engine components. It discusses the classification of I.C. engines as either diesel or petrol, two-stroke or four-stroke. Key engine components are described, including the cylinder, piston, connecting rod, crankshaft, and valve gear system. Design considerations and equations for determining dimensions of each component based on factors like material properties, engine size, speed, and operating pressures are presented. Guidelines are provided for thickness of walls, liners, heads, studs, rings, pins, and bearings.

1. Design of I.C. Engine
Components
Prepared by:
Bhosale K.C.
Assistant Professor,
Department of Mechanical Engineering,
Sanjivani College of Engineering, Kopargaon
Savitribai Phule Pune University, Pune

4. I.C. Engine Classification
 Petrol Engine – Spark Ignition Engine
 Diesel Engine-Compression Ignition Engine
 Two Stroke Engine
 Four Stroke Engine

5. Diesel Engine
 High thermal efficiency
 More uniform torque
 Run at low speed, low maintenance cost
 Reliable And safe due to robust construction

6.  4 Stroke engine
- lower fuel consumption
- Higher efficiency
 2 Stroke Engine
- Light in weight
- Compact construction

7. I.C. Engine Components
 Cylinder & Cylinder liner
 Piston, Piston Pins & Piston Rings
 Connecting Rod
 Crank Shaft & Crank –Pin
 Valve gear system

8. I.C. Engine Components

9. Cylinder & Cylinder Liner
 Basic functions of Cylinder
-To retain working fluid
- to guide piston
 Cooling
- Air Cooled
- Water Cooled

10. Cylinder Liners

11. Materials
 Made of Gray C.I. with homogeneous and
closed structure.
 Centrifugally cast
 For heavy duty cylinder-Ni C.I. & Ni-Cr C.I.
 Cast steel & Al. Alloys

12. Bore & Length Of Cylinder
 Bore means I.D. of Cylinder
 Where,
 IP=Indicate power, W
 BP=Brake power, W,
 = mechanical efficiency ( in fraction) if not
specified assume 0.8

13.  Where,
 Pm= Indicated mean effective pressure (N/mm2)
 l = Length of Stroke (m)
 A= Cross Sectional Area of Cylinder (mm2),
 N= Engine speed (rpm)
 D= Dia. Of cylinder ( mm),
 n= No. of working strokes / min.
 For 2 Stroke engine n=N
 For 4 Stroke engine n=N/2
IP= PM LAN/60, Watts

14.  l/D ratio is assumed from 1.25 to 2. ( if not
specified assume 5)
 Length of cylinder is more than the length of
stroke. There is clearance on both the sides of
the stroke. Total clearance is taken as 15% of
the stroke.
 L= 1.15 l
 L= length of the cylinder.

15. Thickness of the cylinder Wall
 The engine cylinder is treated as Thin cylinder.
 t= Thickness of cylinder wall (mm)
 Pmax=Maximum gas pressure inside the cylinder (N/mm2)
 D= I.D. of Cylinder (mm)
 c=Permissible circumferential stress (N/mm2)
 C= Reboring allowance (mm)

16. Thickness of the cylinder Wall
 Max. Pressure is assumed 10
times mean effective pressure
 Permissible c=35 to 100N/mm2)
 Reboring allowance is taken from
table

17. Empirical Relations
 Thickness varies from 5-10 mm , Thickness=
 Thickness of dry liner =
 Thickness of water jacket wall = 1/3 t-3/4 t
 Thickness of water jacket wall =0.032D+ 1.6 ( mm)
 Water space = 9 mm for 75 mm to 75 for 750 mm of D
 Water space = 0.08 D + 6.5 mm
 Thickness of cylinder flange= 1.2 t -1.4 t
 Radial distance between O.D. of flange & PCD of studs=
(d+6) to 1.5 d
 d= nominal dia. Of bolt or stud

18. Cylinder Head
 A cylinder cover is provided for:
 Inlet & exhaust valves
 Air & gas ports
 Spark plug or atomiser
 In preliminary design, cylinder head is assumed
as flat circular head
 Where,
 th=thickness of cylinder head (mm),
 K=0.162
 Permissible c=35 to 50 N/mm2)

19.  Studs are used to connect cylinder, cylinder head
& gasket for leak proof joint.
 Initially studs are tightened by spanner to induce
preload, and
 In working condition they are subjected to
tensile stresses due to internal gas pressure
acting on cylinder head.

20. Design of Studs
 No. of Studs:
 Min. no. of studs =0.01 D+4,
 Max. no. of studs =0.02 D+4
 Dia. Of studs
 Gas force acting on cylinder head=
 Resisting force offered by all studs=

21. =
 Where,
 dc= core dia. Of studs (mm),
 z= no. of studs
 t=Permissible tensile stress for stud (N/mm2)=
 t=35-70 (N/mm2)
 Nominal dia=

22.  Pitch of Studs:
 PCD of Studs=
 Pitch of Studs=
 Min. Pitch= 19d max. pitch = 28.5d

23. Piston
 Piston is a reciprocating part of I.C. engine.
 Transmit force due to gas pressure to crankshaft
through connecting rod.
 Compresses the gas in compression stroke.
 Seals inside portion of cylinder from crankcase
by means of piston rings
 Takes side thrust resulting from obliquity of
connecting rod.
 Dissipates large amount of heat from
combustion chamber to cylinder wall.

25. Design requirements of Piston
 Should have sufficient strength
 Should have sufficient rigidity
 Adequate capacity to dissipate heat
 Should have minimum weight
 Form an efficient seal to prevent leakage
 Noiseless operation

26. Piston Materials
 Cast Iron,
 Cast Steel,
 Forged Steel,
 Cast Aluminum Alloy,
 Forged Aluminum Alloy

27. Thickness of Piston Head
 There are two types of piston heads:
 Flat head
 Cup type

28. Criteria for calculating piston head
thickness
 Strength
 Heat dissipation

29. Strength criteria
 Piston head is treated as flat circular plate of
uniform thickness.
 Where,
 th= thickness of Piston head (mm),
 D= Cylinder bore (mm),
 Pmax = Max. gas pressure (N/mm2)
 t=Permissible bending stress (N/mm2)

30.  Bending stress
 Bending stress- for C.I. (30-40 N/mm2) & for
Al. Alloy (50-90 N/mm2).
 Max. gas pressure may rise to 8 N/mm2. but
average value is taken as 4-5 N/mm2.
 Empirical formula to find out piston head
thickness

31. Heat dissipation criteria
 Thickness of piston head
 Where,
 Th= thickness of piston head (mm),
 H= amount of heat conducted through head (W)
 K= thermal conductivity factor (W/m/0C)
 Tc= temp. at center of piston head (0C)
 Te= temp. at edge of piston head (0C)

32.  K values
 C.I.=46.6 (W/m/0C)
 Al. alloy = 175 (W/m/0C)
 Permissible temp. difference( Tc-Te)
 C.I.=2200 C
 Al. alloy = 75 0C

33. Amount of heat conducted
 HCV= Higher Calorific Value (kJ/Kg)
 M= mass of fuel per power per second (kg/kW/s)
 BP=brake power of engine per cylinder (kW)
 C= ratio of heat absorbed by piston to heat
developed in cylinder=0.05

34.  HCV values
 For diesel = 44*103 kJ/kg
 For Petrol = 47*103 kJ/kg
 The Avg. consumption of fuel in diesel engine is
0.24 – 0.30 kg/kW/h

35. Piston ribs and cups
 Piston head is provided with a no. of ribs for:
 Strengthening piston head against gas pressure
 Ribs transmit large portion of heat from piston
head to piston rings.
 Side thrust created by obliquity of connecting
rod is transmitted to piston at piston pin.

36. Guidelines for ribs
 th < 6 mm – no ribs
 th > 6 mm – ribs required.
 No. of ribs = 4 – 6
 Thickness of rib is
 Where,
 tR=thickness of rib
 th= thickness of piston head

37. Piston Cup
 A cup provides additional space for combustion
of fuel.
 Depends upon volume of combustion chamber.
 And arrangement of valves.

38. Guidelines for cup
 l/D < 1.5 – cup required
 l/D > 1.5 – cup not required
 Radius of cup= 0.7 D

39. Piston Rings
 Compression ring
 Oil scrapper ring

40. Guidelines for design of rings
 Material– Gray C.I. & Alloy C.I.
 No. of piston rings—
 Compression rings for aircraft engine= 3 – 4
 For stationary engine= 5-7
 Oil scrapper rings= 1 – 3

41. Dimensions of c/s
 Rectangular c/s
 Where,
 b = radial width of ring
 Pw = allowable radial pressure on cylinder wall (N/mm2)
 t=Permissible tensile stress for ring material (N/mm2)
 Pw =0.025 – 0.042 (N/mm2)
 t = 85 – 110 (N/mm2)
 Axial thickness of ring h = (0.7 b ) to b

42.  Gap between free ends
 3.5 b – 4 b
 Width of top land and
ring lands
 h1 = th – 1.2 th
 h2 = 0.75 h -h

43. Piston barrel
 t3 = (0.03 D + b + 4.9
 t3 = thickness of piston barrel at
top end ( mm)
 b= radial width of ring ( mm)
 t4 = thickness of piston barrel at
open end ( mm)
 t4 = 0.25 t3 – 0.35 t3

44. Piston skirt
 Acts as bearing
surface for side thrust

45.  Max. gas pressure on piston head=
 Side thrust =
 Where, µ= coefficient of friction = 0.1
 Side thrust=
 Where, Pb= allowable bearing pressure (Mpa)
 ls =length of skirt (mm)
 Equating above eqns.
 From this length of skirt is obtained

46. Piston pin
 To connect piston and
connecting rod.
 It is hollow circular.
 End movement is
restricted by circlips.
 Two criteria's
 Bearing
 bending

47. Bearing considerations
 Length of pin in small end of connecting rod l1=0.45 D
 O.D. of pin
 Force on piston=
 Resisting fore =
 (Pb)1 = brg. Pr. At bushing of small end of
connecting rod (Mpa)
 do = O.D.of piston pin

48. Bending considerations
 B.M. at section XX
 Also,
 Bending stress
 b = 84 (N/mm2) for case hardened steel
 b = 140 (N/mm2) for heat treated alloy steel

49. Connecting Rod
 Consists of an eye at small end to accommodate
the piston pin, a long shank and big end opening
split into two parts to accommodate crank pin.
 Basic function is to transmit push and pull forces
from piston pin to crank pin.
 Connecting rod transmits the reciprocating
motion of the piston to the rotary motion of the
crankshaft.
 Splash oil lubrication.

50. Connecting rod

51.  Subjected to gas pressure and inertia force due to
reciprocating parts
 Material medium carbon steel or alloy steel.
 Lubrication – splash & pressure feed
 Length
 When length is small compared to crank radius, it
has greater angular swing resulting in greater side
thrust on the piston.
 Normally

52. Buckling of connecting rod
 Subjected to compressive stress
 Designed as column or strut

53.  Buckling about XX axis, ends are hinged in
crank pin and piston pin. So, end fixity
coefficient is one.
 Buckling about YY axis, ends are fixed due to
constraining effect of bearings at crank pin and
piston pin. So, end fixity coefficient is four.
 Therefore, connecting rod is 4 times stronger
for buckling about YY axis as compared to XX
axis.

54.  If a connecting rod is designed in such a way
that it is equally resistant to buckling in either
plane then,
 Where, I = moment of inertia ( mm4)
 Substitute I = Ak2,
 k= radius of gyration (mm)

55. C/S for connecting rod
 P= force acting on piston due to
gas pressure (N)
 Ps = side thrust on side wall (N)
 Pc=force acting on connecting
rod (N),
 =angle of inclination of
connecting rod with line of
stroke
 =angle of inclination from TDC

56.  P = Pc cos 
 Max gas load occurs at = 3.30
 Max. force acing on the piston due to gas pressure =
 Dimensions are calculated by Rankin’s formula
 Pcr= critical buckling load
 c=compressive yield stress = 330 (N/mm2)
 A= c/s area of connecting rod mm2
 a = constant = 1/7500
 L= length of connecting rod (mm)
 Pcr = Pc (fs)

57. Procedure
 Calculate force acing on connecting rod
 Calculate critical buckling load Pcr = Pc (fs), fs=5 – 6
 By Rankine's formula
 Substitute,
 A=11t2
 Kxx= 1.78 t
 a= 1/7500
 c=330 (N/mm2)

58. Big and small end bearing
 Force acting on piston pin
bearing
 Also,
 dp= dia. Of piston pin
 lp= length of piston pin.
 (Pb)p= allowable bearing
pressure = 10 – 12.5 MPa
 l/d ratio for piston pin bush
= 1.5 – 2.

59. Big end cap & bolts
 Inertia acting on bolts
 Where,
 Pi= inertia force on cap or bolts (N)
 mr= mass of reciprocating parts (kg)
 r = crank radius (mm)
 n1= ratio of length of connecting rod to crank radius
 L= length of connecting rod

60.  Mass of reciprocating parts
 mr = mass of piston assembly+ 1/3 mass of
connecting rod
 The inertia is max at TDC when =0, cos =1