Cylinder Head BoltsCylinder Head Bolts

Size of studsSize of studs

• Total force acting on the studs :Total force acting on the studs :

• This force is taken by 4 - 6 studs This force is taken by 4 - 6 studs nearest to the cylindernearest to the cylinder

• During engine assembly PRE-During engine assembly PRE-TENSIONNING force is applied to all TENSIONNING force is applied to all studsstuds

• For a single stud :For a single stud :

F D Pg 1 254

2. . max

FF

ng

b

F

A

x kN m

rootallowble

allowble 1 3 105 2.

CYLINDER HEADCYLINDER HEAD

• Design depends onDesign depends on– the shape of the combustion chamberthe shape of the combustion chamber– the arrangement of the valvesthe arrangement of the valves– the position of the spark plugs (SI the position of the spark plugs (SI engines)engines)

– the position of the injectors (CI the position of the injectors (CI engines)engines)

– the intake and exhaust ductsthe intake and exhaust ducts–external pipingexternal piping–direction of the cooling fluiddirection of the cooling fluid

SI ENGINESSI ENGINESWITH OVERHEAD VALVESWITH OVERHEAD VALVES

• Hemispherical chambers are used with 2 valvesHemispherical chambers are used with 2 valves• Pent - Roof chambers are used with 4 valvesPent - Roof chambers are used with 4 valves

Valve Head Diameters Valve Head Diameters

ShapeShape InletInlet ExhaustExhaust Vp (mean)Vp (mean)

Wedge or BathtubWedge or Bathtub 0.43-0.46D0.43-0.46D 0.35-0.35-0.37D0.37D 15 m/s15 m/s

Bowl-in-pistonBowl-in-piston 0.42-0.44D0.42-0.44D 0.34-0.37D0.34-0.37D14 m/s14 m/s

HemisphericalHemispherical 0.48-0.5D0.48-0.5D 0.41-0.43D0.41-0.43D 18 18 m/sm/s

Four valveFour valve

PentroofPentroof 0.35-0.37D0.35-0.37D 0.28-0.32D0.28-0.32D20 m/s20 m/s

SI Combustion Chamber SI Combustion Chamber ShapesShapes

SI Combustion ChamberSI Combustion ChamberParametersParameters

• Chamber compactnessChamber compactness• Port DesignPort Design• Surface/Volume RatioSurface/Volume Ratio• Flame Travel LengthFlame Travel Length• Squish and swirl type of mixture motionSquish and swirl type of mixture motion

Important Parameter in Modern DesignsImportant Parameter in Modern Designs• High rate of flame propagationHigh rate of flame propagation

– Better emission controlBetter emission control– Leaner mixturesLeaner mixtures– Less dissociationLess dissociation– Less Heat transferLess Heat transfer– Less Pumping workLess Pumping work

CI Combustion ChambersCI Combustion Chambers(Direct Injection)(Direct Injection)

CI Combustion ChambersCI Combustion Chambers(InDirect Injection)(InDirect Injection)

Wall ThicknessesWall Thicknessesof Combustion Chambersof Combustion Chambers

Cast Iron Cylinder Heads (Large CI engines)Cast Iron Cylinder Heads (Large CI engines)

Aluminium Alloy Cylinder Heads (SI engines)Aluminium Alloy Cylinder Heads (SI engines)

Conservative Conservative

ApproachApproach

t x D

t x D

h

wj

1 5 10 0 09

2 2 10 0 03

3

3

. .

. .80 150 D mm

t x D

t x D

h

wj

3 5 10 0 09

2 2 10 0 03

3

3

. .

. .

t DP

where Allowable bending stress

hb

b

0 434. max