Four Stroke Engine

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Four Stroke Engine Operation M.M.Palitha Mahinda Munasinghe Mechanical Instructor

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Four stroke cycle Intake stroke Piston moving down Intake valve open Exhaust valve closed 2009/10/05 2 mmpmm

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Compression stroke Piston moving up Intake valve closed Exhaust valve closed Four stroke cycle 2009/10/05 3 mmpmm

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Power stroke Piston moving down Intake valve closed Exhaust valve closed Four stroke cycle 2009/10/05 4 mmpmm

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Exhaust stroke Piston moving up Intake valve closed Exhaust valve open Four stroke cycle 2009/10/05 5 mmpmm

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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) 2009/10/05 6 mmpmm

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2009/10/05 mmpmm 7 Four stroke cycle (Diesel)

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2009/10/05 mmpmm 8 Fuel Injection System

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2009/10/05 mmpmm 9 Fuel Pump (Diesel) Rotary Type Pump Inline Type Pump

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2009/10/05 mmpmm 10 Fuel Feed Pump Draw fuel from tank and feed to injection pump

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2009/10/05 mmpmm 11 Engine Cooling System Engine heat is transferred through walls of the combustion chambers and through the walls of cylinders

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Piston Dwell Time Piston travel 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 2009/10/05 12 mmpmm

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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 2009/10/05 13 mmpmm

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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 2009/10/05 14 mmpmm

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Effects On Valve Timing 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 2009/10/05 15 mmpmm

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COMBUSTION Spark ignition Maximum cylinder pressure 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 2009/10/05 16 mmpmm

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Valve Mechanism OHV (overhead valve) Pushrod configuration Many reciprocating parts Higher valve spring pressure required Compact engine size compared to OHC 2009/10/05 17 mmpmm

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OHC (overhead cam) Fewer reciprocating parts Reduced valve spring pressure required Higher RPM capability Cylinder head assemblies are taller 2009/10/05 18 mmpmm Valve Mechanism

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Cam-in-head No pushrods Use rocker arms 2009/10/05 19 mmpmm Valve Mechanism

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Valve lash compensators Solid lifters No internal parts Periodic adjustment 2009/10/05 20 mmpmm

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Hydraulic lifters To maintain zero lash Quieter No periodic adjustment Anti-scuff additives are required in oils Valve lash compensators 2009/10/05 21 mmpmm

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Hydraulic lifter operation Valve closed Oil flows through lifter bore & past check valve Plunger return spring maintains zero lash 2009/10/05 22 mmpmm

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Valve open Check valve seats and limits the slippage Now operates as a solid lifter Hydraulic lifter operation 2009/10/05 23 mmpmm

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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) 2009/10/05 24 mmpmm

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Metering Device Metering valve meters the oil flow to the pushrod 2009/10/05 25 mmpmm

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Gear sets Cam and crank rotate in opposite directions Noisy if not free of burrs Helical and spur cut gears 2009/10/05 26 mmpmm Timing Gear Wheel sets

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Timing chains Single and double roller Tension Pulley 2009/10/05 27 mmpmm Timing Belt sets

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Timing belts Require maintenance Silent operation 2009/10/05 28 mmpmm Timing Chain Drive

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2009/10/05 mmpmm 29 Engine Lubricating System Lubrication with oil through pressure to every moving parts

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Splash and spray 2009/10/05 30 mmpmm Lubricating System

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Oil pan baffles To keep oil in sump during braking, accelerating, and cornering 2009/10/05 31 mmpmm Lubricating System

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Oil pan windage tray To prevent oil aeration in the sump 2009/10/05 32 mmpmm Lubricating System

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Oil pumps Driven by distributors, gear on camshaft, or crankshaft 2009/10/05 33 mmpmm Lubricating System

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Oil pumps with pressure relief valves Gear type pump Rotor type pump 2009/10/05 34 mmpmm Lubricating System

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Full flow oil filtering system Oil pump output flows through filter first Bypass circuit for restricted filters will allow oil to flow to engine 2009/10/05 35 mmpmm Lubricating System

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Diesel Engine Advantages Higher engine torque Better fuel economy Long engine life Disadvantages Engine noise Exhaust smell Hard start 2009/10/05 36 mmpmm