Design of I.C. Engine Parts

By:Er. Shankar Sehgal

Faculty of Mech. Engg., UIET,Panjab University, Chandigarh

Website: http://shankarsehgal.weebly.com

I.C. Engine

Design of Cylinder

• Types of stresses:– Stresses due to Gas Pressure

• Longitudinal Stresses

• Circumferential Stresses

– Stresses due to Piston Side Thrust

Design of Cylinder

• Bore and Length of Cylinder:

• Where, – ; I.P. = Indicated Power, B.P. = Brake Power

– pm is indicated mean effective pressure– l is length of stroke = 1.5 D– A is cross-sectional bore area of cylinder– n is number of working strokes per minute

• Length of Cylinder = 1.15 l

60.. lAnpPI m

mech

PBPI

....

Design of Cylinder

• Thickness of Cylinder Wall:

• Based upon thin cylinder formula

• Where C is allowance for reboring

CpDtc

2

Design of Cylinder Flange

• Cylinder flange thickness = 1.4 t• Considering tensile failure of cylinder flange

bolts:

• Use bolts of diameter greater than 16 mm only

2

2

4

4

cdn

pD

AF

Design of Cylinder Head

• Cylinder head thickness:

• Considering tensile failure of cylinder head bolts:

ch

pCDt.

2

2

4

4

cdn

pD

AF

Design of Piston

Piston of I.C. Engine

Design Considerations for Piston

• High strength to withstand the high gas pressure and inertia forces.

• Low weight density

• Low coefficient of thermal expansion

• High heat conductivity

Materials for Piston

• C.I.

• Cast Aluminium

• Cast Steel

• Forged Aluminium

• Forged Steel

Design of Piton Head

• Considering tensile strength requirement:– Using Grashoff’s Formula

tH

Dpt16.3 2

Design of Piton Head

• Considering heat dissipation requirement:

• Where, – H is heat flow rate

– k is coefficient of thermal conductivity

– TC is Temperature at centre of the piston

– TE is Temperature at edges of the piston

ECH TTk

Ht

56.12

Design of Piton Rings

• Compression Rings– Three to seven in number– Transfer heat from piston to cylinder liner– Absorb side thrust on piston– Cross-section is rectangular– Diameter is slightly larger than cylinder bore– Diagonal or step cut is provided

• Oil Control Rings– Help in lubrication of liner

Design of Piston Rings

ringsnDt

102 t

wpDt

31

Design of Piston Rings

• Width of top land

• Width of other ring landsHtb 1

22 tb

Design of Piston Barrel

9.4100

313 tDt

34 41 tt

Design of Piston Skirt

• Considering bearing failure of piston skirt:

skirtb Dl

Dpp

2

4101

Design of Piston Pin

• Considering bearing failure of piston pin:

• Where,

10

2

4ld

Dppb

Dl 45.01

Design of Piston Pin

• Considering bending failure of piston pin:

64

4222

2

44

12

ioo dd

lPlP

d

IM

y

Design of Connecting Rod

Connecting Rod

Ratio

• l = length of connecting rod

• r = radius of crank

• Small

– small and compact engines– large angular motion of connecting rod– large side thrust of connecting rod– rapid wear and tear of cylinder liner

5__4 torl

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