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4 stroke engine
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- 2. Four stroke cycle Intakestroke Piston moving down Intake valve open Exhaust valve closed 2009/10/05 mmpmm 2
- 3. Compression stroke Piston movingup Intake valve closed Exhaust valve closed Four stroke cycle 2009/10/05 mmpmm 3
- 4. Power stroke Piston movingdown Intake valve closed Exhaust valve closed Four stroke cycle 2009/10/05 mmpmm 4
- 5. Exhaust stroke Piston movingup Intake valve closed Exhaust valve open Four stroke cycle 5
- 6. • Each stroketakes 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
- 7. 2009/10/05 7 Four strokecycle (Diesel)
- 8. 2009/10/05 mmpmm 8 FuelInjection System
- 9. 2009/10/05 9 Fuel Pump (Diesel) RotaryType Pump Inline Type Pump
- 10. 2009/10/05 mmpmm 10 FuelFeed Pump Draw fuel from tank and feed to injection pump
- 11. 11 Engine Cooling System Engineheat is transferred through walls of the combustion chambers and through the walls of cylinders
- 12. Piston Dwell Time Pistontravel is at a minimum TDC and BDC Crank moves horizontally Piston velocity Maximum when rod is 90° to crank Acceleration Maximum 30° earlier Best VE is obtained by synchronizing valve opening with piston speeds 12
- 13. Other Valve Position Overlap •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 13
- 14. Valve Mechanism • Intakevalve 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
- 15. Effects On ValveTiming Intake valve opening Late – Reduced VE Early – Dilution of intake with exhaust Intake valve closing Late – Reduces cylinder pressure Early – Increases cylinder pressure Exhaust valve opening Late – Pumping losses Early – Power reduction Exhaust valve closing Late – Reduces vacuum Early – Reduces VE 15
- 16. COMBUSTION Spark ignition Maximum cylinderpressure 15° ATDC Tumble and swirl Motion reduces misfires Excess motion inhibits flow AFR 14.7:1 at part throttle, 12.5:1 under load Compression ignition 18:1 direct injection 23:1 pre-chambers for better starting Compression heats to 800-1200 °F 16
- 17. Valve Mechanism OHV (overheadvalve) Pushrod configuration Many reciprocating parts Higher valve spring pressure required Compact engine size compared to OHC 17
- 18. OHC (overhead cam) Fewerreciprocating parts Reduced valve spring pressure required Higher RPM capability Cylinder head assemblies are taller 18 Valve Mechanism
- 19. Cam-in-head No pushrods Use rockerarms 19 Valve Mechanism
- 20. Valve lash compensators Solidlifters No internal parts Periodic adjustment 20
- 21. Hydraulic lifters To maintainzero lash Quieter No periodic adjustment Anti-scuff additives are required in oils Valve lash compensators 21
- 22. Hydraulic lifter operation Valveclosed • Oil flows through lifter bore & past check valve • Plunger return spring maintains zero lash 22
- 23. Valve open • Checkvalve seats and limits the slippage • Now operates as a solid lifter Hydraulic lifter operation 23
- 24. Hydraulic lifter operation Returnto valve closed • New oil enters the lifter body • This oil replaces oil that has leaked between plunger and body (predetermined leakage) 24
- 25. Metering Device Metering valvemeters the oil flow to the pushrod 25
- 26. Gear sets • Camand crank rotate in opposite directions • Noisy if not free of burrs • Helical and spur cut gears 26 Timing Gear Wheel sets
- 27. Timing chains • Singleand double roller • Tension Pulley 27 Timing Belt sets
- 28. Timing belts • Requiremaintenance • Silent operation 28 Timing Chain Drive
- 29. 29 Engine Lubricating System Lubricationwith oil through pressure to every moving parts
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- 31. Oil pan baffles •To keep oil in sump during braking, accelerating, and cornering 31 Lubricating System
- 32. Oil pan windagetray • To prevent oil aeration in the sump 32 Lubricating System
- 33. Oil pumps • Drivenby distributors, gear on camshaft, or crankshaft 33 Lubricating System
- 34. Oil pumps withpressure relief valves • Gear type pump • Rotor type pump 34 Lubricating System
- 35. Full flow oilfiltering system • Oil pump output flows through filter first • Bypass circuit for restricted filters will allow oil to flow to engine 35 Lubricating System
- 36. Diesel Engine Advantages • Higherengine torque • Better fuel economy • Long engine life Disadvantages • Engine noise • Exhaust smell • Hard start 36