8/18/2019 Design of IC Engine Cylinder

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1.  DESIGN OF ENGINE CYLINDER

In designing of Engine cylinder, following parameters have to be determined

1.  Bore (D) and length of cylinder (Lc)2.  Thickness of cylinder liner (t)

3.  Thickness of cylinder head (t h)4.  Size (d) , number (z) of studs

1.1 Bore (D) and length of cylinder ():The dimensions of cylinder are calculated by using the following equations: = ..  

. =  Where

 = Mechanical Efficiency;B.P = Brake Power i.e. power available at crankshaft

I.P = Indicated Power i.e. power produced inside the cylinder;

 = Mean effective pressure;L = stroke length; N = Engine speed in rpmn = no. of working stroke per minute = N for 2 stroke engine

= N/2 for 4 stroke engine

Note:

•  If mechanical efficiency is not given, assume as 80 %.

•  For an IC Engine, stroke to bore ratio (

) lies between 0.9 to1.9. (From Mahadevan

DDB, page no. 364, table 18.2) In design problem its avg. value can be assumed i.e. 1.4.

•  Length of cylinder is taken as 15 % more than the stroke length due to clearance providedon both sides i.e.

Lc = 1.15 L 1.2 Thickness of cylinder liner (t):

The engine cylinder liner is assumed as thin cylinder and its thickness is calculated by the

following equation

t =pmax D

2σc+ C 

C = Reboring allowance (to compensate for reboring at intervals during the lifetime ofcylinder)

σc  = Permissible Hoop stress = Allowable tensile stress for the cylinder material ()pmax  = Maximum gas pressure inside the cylinder

Note:

If pmax  is not given, it is assumed as 10 times of mean effective pressure. 

The cylinder liner is made of brittle material (generally Grey cast Iron). If FOS andmaterial is specified then permissible hoop stress is calculated as below 

8/18/2019 Design of IC Engine Cylinder

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( ) =  Otherwise select suitable value for allowable tensile stress from Design data book (pageno 359, after equation number 18.14)

1.3 Thickness of cylinder head (t h): A separate cylinder head (or cover) is provided in most of the IC engines to accommodate

following parts:

•  Inlet and exhaust valves

• 

Spark plug / injector

•  Air and gas ports

The thickness of cylinder head is obtained it by the following relation assuming it as flat

circular plate

= .  �    ( From DDB , page no 359, equation no 18.14)  Note:

The cylinder head is made of brittle material. If FOS and material is specified then

Permissible tensile stress () is calculated as below 

= Otherwise select suitable value for allowable tensile stress from Design data book (page no

359, after equation number 18.14)

1.4 Design of Studs:

Studs are used to make the leak proof assembly of cylinder, cylinder head and gasket.

In design of studs, following parameters are important 

 Number of studs (Z): Z = 0.015 D + 4 (From Design Data book, page no 359, equation no 18.15)

Size of studs:

Let the core diameter = dc   Nominal diameter = d

• 

Core (or root ) diameter is obtained by equating the gas force on cylinder head tothe resisting force offered by all studs.

Gas Force =42   ; Resisting force = 4 2 

After equating the above two expressions

= �    (From DDB, page no 358, equation no 18.8)•  Relation between core diameter and nominal diameter is = .  

Pitch of studs: Pitch circle diameter Dp  is expressed as  [ = D + 3d]Pitch of studs =

      =

  Note:

The studs are made of ductile material. If FOS and material is specified then

Permissible tensile stress () is calculated as below  =  

Otherwise it is taken as 35 to 70 MPa. Its avg. value 50 MPa (approximate) can be usedin design problems.