Post on 12-Apr-2017
Four Stroke Engine Operation
Four stroke cycle
Intake stroke
Piston moving downIntake valve openExhaust valve closed
2009/10/05 mmpmm 2
Compression stroke
Piston moving upIntake valve closedExhaust valve closed
Four stroke cycle
2009/10/05 mmpmm 3
Power stroke
Piston moving downIntake valve closedExhaust valve closed
Four stroke cycle
2009/10/05 mmpmm 4
Exhaust stroke
Piston moving upIntake valve closedExhaust valve open
Four stroke cycle
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• Each stroke takes 180° of crankshaft rotation to complete
• All cylinders fire in 720° of crankshaft rotation
• 720 divided by number of cylinders = firing interval
• Odd fire V-6 engine (90° block with 120° rod journals)
Four stroke cycle(Petrol)
6
2009/10/05 7
Four stroke cycle(Diesel)
2009/10/05 mmpmm 8
Fuel Injection System
2009/10/05 9
Fuel Pump(Diesel)
Rotary Type Pump Inline Type Pump
2009/10/05 mmpmm 10
Fuel Feed Pump
Draw fuel from tank and feed to injection pump
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Engine Cooling System
Engine heat is transferred through walls of the combustion chambers and through the walls of cylinders
Piston Dwell TimePiston travel is at a minimum
TDC and BDCCrank moves horizontally
Piston velocityMaximum when rod is 90° to crank
AccelerationMaximum 30° earlier
Best VE is obtained by synchronizing valve opening with piston speeds
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Other Valve PositionOverlap
• Both valves are open• End of exhaust & start of intake• Low pressure in exhaust port
Blow down• Exhaust valve opens before BDC• To help evacuate cylinder before piston
reverses• Pumping losses at end of exhaust
stroke
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Valve Mechanism
• Intake valve opening BTDC Low pressure in cylinder Intake valve closing• Intake valve closing ABDC Cylinder pressure is effected by timing• Exhaust valve opening BBDC Residual pressure helps blow down• Exhaust valve closing ATDC Low pressure in exhaust port draws air in
mmpmm 14
Effects On Valve TimingIntake valve opening
Late – Reduced VEEarly – Dilution of intake with exhaust
Intake valve closingLate – Reduces cylinder pressureEarly – Increases cylinder pressure
Exhaust valve openingLate – Pumping lossesEarly – Power reduction
Exhaust valve closingLate – Reduces vacuumEarly – Reduces VE
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COMBUSTIONSpark ignition
Maximum cylinder pressure 15° ATDCTumble and swirlMotion reduces misfiresExcess motion inhibits flowAFR 14.7:1 at part throttle, 12.5:1 under load
Compression ignition18:1 direct injection23:1 pre-chambers for better startingCompression heats to 800-1200 °F
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Valve Mechanism
OHV (overhead valve)Pushrod configurationMany reciprocating partsHigher valve spring pressure requiredCompact engine size compared to OHC
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OHC (overhead cam)
Fewer reciprocating partsReduced valve spring pressure requiredHigher RPM capabilityCylinder head assemblies are taller
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Valve Mechanism
Cam-in-headNo pushrodsUse rocker arms
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Valve Mechanism
Valve lash compensators
Solid liftersNo internal partsPeriodic adjustment
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Hydraulic liftersTo maintain zero lashQuieter No periodic adjustmentAnti-scuff additives are required in oils
Valve lash compensators
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Hydraulic lifter operation
Valve closed• Oil flows through
lifter bore & past check valve
• Plunger return spring maintains zero lash 22
Valve open• Check valve seats
and limits the slippage
• Now operates as a solid lifter
Hydraulic lifter operation
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Hydraulic lifter operation
Return to valve closed• New oil enters the
lifter body• This oil replaces oil
that has leaked between plunger and body (predetermined leakage)
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Metering Device
Metering valve meters the oil flow to the pushrod
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Gear sets• Cam and crank rotate in opposite directions• Noisy if not free of burrs• Helical and spur cut gears
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Timing Gear Wheel sets
Timing chains• Single and double roller• Tension Pulley
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Timing Belt sets
Timing belts• Require maintenance• Silent operation
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Timing Chain Drive
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Engine Lubricating System
Lubrication with oil through pressure to every moving parts
Splash and spray
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Lubricating System
Oil pan baffles• To keep oil in sump during braking,
accelerating, and cornering
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Lubricating System
Oil pan windage tray
• To prevent oil aeration in the sump
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Lubricating System
Oil pumps• Driven by distributors,
gear on camshaft, or crankshaft
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Lubricating System
Oil pumps with pressure relief valves• Gear type pump• Rotor type pump
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Lubricating System
Full flow oil filtering system
• Oil pump output flows through filter first
• Bypass circuit for restricted filters will allow oil to flow to engine
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Lubricating System
Diesel EngineAdvantages
• Higher engine torque• Better fuel economy• Long engine life
Disadvantages
• Engine noise• Exhaust smell• Hard start
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