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Agriculture Engineering-chptr 2
 

Agriculture Engineering-chptr 2

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    Agriculture Engineering-chptr 2 Agriculture Engineering-chptr 2 Presentation Transcript

    • ENGINE CONSTRUCTION
    • Basic parts of Internal Combustion Enginea) Cylinder head top of the engine which contain a hole for valves valves, intake and exhaust passages, cooling passagesb) Valves open and close to let fuel air mixture (petrol engine) or air only (diesel engine) exhaust gases out of each cylinderc) Camshaft rotates to open and close the valves by cam action
    • d) Cylinder block Main housing of the engine and supports other main parts Contain cylindrical vessels in which combustion takes place and piston makes a reciprocating motione) Cylinders Hollow tubes, piston moves back and forthf) Pistons Move in the cylinders and apply the force of combustion to crankshaftg) Piston rings A component that fitted into the slot around the piston which seal the combustion chamber and help transfer heat
    • h) Connecting rods A rod that interconnect the piston and the crankshaft and transmit the forces from the piston to crankshafti) Crankshaft Receives the force from pistons and transmit as rotary driving powerj) Main bearings Support crankshaft in cylinder blockk) Flywheel Attach to crankshaft at rear, provides momentum and help return pistons to the top of cylinders
    • l) Timing drives Link the crankshaft, camshaft and other parts together to assure each is doing its job at the right timem) Cams Integral part of camshaft design to open the valve at the correct timing and to keep them open for the necessary durationn) Gudgeon pin Forms the link between the small end of the connecting rod and the piston
    • Classification of TractorsAccording to the Power of Engine (horse power) – Small < 25 hp – Medium 25 – 50 hp – Large > 50 hp
    • Comparison Between Petrol and Diesel Enginea. Fuel Supply and Ignitionb. Compression Ratioc. Design of Engine Partsd. Grade and Type of Fuel Used
    • a) Fuel Supply and IgnitionPetrol Engine Fuel and air mixed outside the cylinders in the carburetor and intake manifold Mixture is forced into cylinders by partial vacuum created by intake stroke of piston Uses electric spark to ignite fuel air mixture Compression ratio 8 to 1 (8:1)Diesel Engine No premixing of air and fuel Air taken into cylinders through intake manifold and compressed Fuel is sprayed into cylinders and mixed with air as the piston nears the top of its compression stroke Use heat and compressed air for ignition Compression ratio 16 to 1 (16:1)
    • b) Compression RatioCompression ratio is a characteristic of an enginei.e. related to engine efficiency i.e. the ability of theengine to convert in the fuel to useful mechanicalenergyThe greater the compression ratio, the greater thepotential efficiency of the engineCompares volume in cylinder before compressionwith volume after compressionHigh compression ratio of diesel – cause hightemperature of air to ignite fuel without a sparkTherefore diesel engine more efficient becausehigher compression i.e greater expansion of gasesin cylinder therefore more powerful stroke
    • c) Design of Engine PartsEngine of diesel more sturdier parts to withstand greater forces
    • d) Grade and Type of Fuel Used• Diesel fuel -- more heat units (joule) per gallon• Therefore produces more power per gallon of fuel – fuel low cost but fuel injection equipment is more expensive than petrol equipment
    • Comparison between Engines Diesel Petrol1. Fuel efficiency Best Fair2. Time before maintenance Good Fair3. Weight per horse power High Low4. Cold weather starting Fair Good5. Acceleration Good Good6. Continuous Duty Good Fair7. Lubricating oil contamination Moderate Moderate
    • DIESEL ENGINE PETROL ENGINE1. Fuel System 1. Fuel System Use diesel Use petrol No carburetor Have carburetor Uses heat & compressed air Uses electric spark to ignite for ignition air‐fuel mixture2. Higher compression ratio 2.Lower compression ratio 14 – 16 : 1 7 – 10 : 13. Operation 3.Operation No pre‐mixing of air and fuel Fuel and air mixed outside the Air taken into cylinder cylinders in the carburetor through intake manifold and and intake manifold compressed Mixture is forced into Fuel is sprayed into cylinders cylinders by partial vacuum and mixed with air as the created by intake stroke of piston nears the top of its piston compression stroke
    • Engine Construction Functions1. Valves - Intake and Exhaust Valves The valves allow fuel-air in and exhaust gases out of each cylinder during combustion cycle by opening and closing the intake and exhaust parts of the cylinder.Intake Stroke Intake valve opens allowing fuel air mixture to enter combustion chamberCompression and Power Stroke Both valves are closed to seal in combustible mixtureExhaust Stroke Exhaust valve opens allowing gases to be exhaustedEnd of Exhaust Stroke Intake valves opens, beginning another cycle
    • 2. Camshaft• is turned by the engine crankshaft.• A lobe (cam) on the camshaft causes the cam follower and push the rod to push the valve open• The spring closes the valve when the cam allows the push rod and cam follower to return to low side of the cam• Cam movements are designed to open or close the valves at the right moment
    • 3. Engine Crankcase and Cylinder Block• Made of iron casting and is an integral with cylinder block which houses cylinder liners• Liners are said to be wet or dry according to whether they are or not in contact with cooling water that circulate through engine block• Crankcase houses the crank gear and valve gear
    • 4. Engine Block• Houses the injection pump, oil pump, water pump and power generator• The front part carries the timing cover, rear end carries clutch bell housing on which the starter motor is mounted• Provided with oil filler cap and breather, oil dipstick and water connection to the radiator
    • 5. Cylinder Head Consists of fuel injectors , inlet and outlet valves, the rockers Cylinder head is in a single piece for engines up to 4 cylinders Between cylinder head and engine block – cylinder head gasket; to prevent gas, coolants and lubricating oil from escaping Also connected the inlet and exhaust manifolds water pipe from radiator6. Oil Sump Made of iron casting Seals the crankcase at the bottom Functions as a reservoir for the lubricating oil
    • 7. Piston, Connecting Rod & Cylinder Liners Piston move in the cylinders and apply the force of combustion to the crankshaft Combustion chamber machined in upper part known as piston head or crown ; lower part known as piston skirt Connecting rods Transmit the motion of the pistons to the crankshaft Cylinder Liners made of cast iron may be wet or dry; wet liners can be inserted and removed by hand; dry liner removal and installation with the use of a press (of a few tons capacity)
    • 8. Crankshaft Receive the force from the pistons and transmits it as rotary driving force Rear end carries the flywheel incorporating starter ring gear Front end carries crankshaft gear used to drive valve timing mechanism, oil pump9. Flywheel Attaches to crankshaft at rear & provides momentum to help return the pistons to the top of cylinders after each downward thrust10. Timing Drives Link the crankshaft, camshaft and other parts together so that each is doing its job at the right time
    • What is Internal and External Combustion Engines• Internal Combustion Engine – Form of heat engine because heat engine produced by the burning of fuel within the engine is changed into mechanical energy• External Combustion Engine – Heat energy is supplied from external source in the form of steam from boiler outside the engine
    • Adjusting Valve Clearance• Proper valve maintenance is necessary so that engine works efficiently and not be damaged• When valves are properly adjusted, there is a small clearance between valve stem and end of rocker arm• This clearance is referred to as Valve Clearance or tappet clearance
    • Valve Clearance• Allows for heat expansion of valve operating parts• Without clearance, “tehe” heated parts would cause the valves to stay partly open during operation & engine would lose compression & power• The valve clearance is small, approx: 0.15-0.75 mm. Valve clearance varies with different engine model; whether the engine should be hot or cold during adjustment
    • Effects of Too Small Valve Clearance• Caused the valve out of timing• Valves open too early & close too late• Valves stems may lengthen from heating & prevent valves from seating completely.• Hot combustion gases rushing past the valves cause overheating because the valves seat so poorly that normal heat transfer into the cooling system does not have time to take place• This causes Burned Valves
    • Effect of Too Big Valve Clearance• Causes a lag in valve timing which made the engine out of balance• Fuel air mixture is late in entering the cylinder during the intake stroke• Exhaust valve closes early & prevents waste gases from being completely removed• This causes Valve Damaged
    • Why Proper Valve Adjustment is Important• Engine will use fuel more efficiently• Engine will start more easily• Maximum power will be achieved• Valves will give longer service• Overheating of engine is less likely to occur
    • Adjusting Valve Tappet Clearance – Check valve tappet clearance every 500 hours of operation or at interval indicated in operator’s manualValve Timing – Opening and closing of both inlet and exhaust valves when the piston is at the exact top (TDC) or bottom (BDC) of its strokeValve Overlap – Both valves are open at once at the same period
    • WHAT IS ENGINE• Is a structure that converts chemical energy (fuel) to mechanical energy.• Usually made available on a rotating output shaft.• Normal engine that been used on road is known as Internal Combustion Engine (IC)• Is a reciprocating engines that have pistons that move back and forth in cylinders within the engine.
    • ENGINE CLASSIFICATIONS1. Types of ignition a) Spark Ignition (SI) An engine starts the combustion process in each cycle by using spark plug. The spark plug gives high-voltage electrical discharge between two electrodes which ignites the air-fuel mixture. Before spark plug been used torch holes been used (external flame)
    • b) Compression ignition (CI) CI engine starts when the air-fuel mixture self-ignites due to high temperature in the combustion chamber due to high compression.2. Engine cycle a) Four stroke cycle A four-stroke cycle experiences four cycle movement over two engine revolutions for each cycle. b) Two stroke cycle A two-stroke cycle has two cycle movement over one revolution for each cycle.
    • 3. Valve location a) Valves in head (overhead valve), known as I head engine. b) Valves in block (flat head), known as L head engine. c) One valve in head (intake) and one in block, known as F head engine.
    • 4. Basic design a) Reciprocating Engine has one or more cylinders in which pistons move back and forth. The combustion chamber is located in the closed end of each cylinder. b) Rotary Engine is made of a block built around a large non- concentric rotor and crankshaft. Combustion chambers are built into the nonrotating block.
    • 5. Position and number of cylinders of reciprocating engines a) Single cylinder Engine has one cylinder and piston connected to the crankshaft. b) In-line Cylinders are positioned in a straight line. One behind the other along the length of the crankshaft. They can consist of 2 to 11 cylinders or more Common are four cylinders engine
    • c) V engine Two banks of cylinder at an angle with each other along a single crankshaft. The angle are 15⁰ to 120⁰, common are 60⁰ to 90⁰ 2 to 20 cylinders, normally V6s and V8s V12s and V16s for luxury and high performances vehicles.d) Opposed cylinder engine (crankshaft at middle) Two banks of cylinders opposite each other on a single crankshaft (a V engine with a 180⁰ V). Used for small aircraft, known as flat engine.
    • e) W engine Same as V engine except with three banks of cylinders on the same crankshaft. Normally developed for racing automobiles.f) Opposed piston engine Two pistons in each cylinder with the combustion chamber in the center between the piston. A single-combustion process causes two power strokes at the same time. Each piston pushed away from the center and delivering power to a separate crankshaft at each end of the cylinder.g) Radial engine Engine with pistons positioned in a circular plane around the central crankshaft. The connecting rods of the pistons are connected to a master rod which, in turn, is connected to the crankshaft.
    • ENGINE COMPONENTS LAB 21. Block 16. Glow plug2. Camshaft 17. Cylinder head3. Carburetor 18. Head gasket 19. Intake manifold4. Catalytic converter 20. Main bearing5. Combustion chamber 21. Oil pump6. Connecting rod 22. Piston7. Crankcase 23. Piston rings8. Crankshaft 24. Push rods9. cylinders 25. Radiator 26. Spark plug10. exhaust manifold 27. Speed control-cruise control11. exhaust system 28. Starter motor12. fan 29. Throttle13. flywheel 30. turbocharger14. fuel injector 31. Water jacket15. Fuel pump 32. Water pump
    • BASIC ENGINE CYCLESA) Four Stroke SI Engine CycleB) Two Stroke SI Engine Cycle
    • Four Stroke SI Engine Cycle Intake Valve Exhaust Valve 4 1 2 Exhaust 3 Intake Manifold Manifold Spark Cylinder Plug Piston Connecting Crank Rod Crankcase Power Stroke Exhaust Stroke Intake Stroke Compression Stroke Fuel-air mixture burns, Exhaust valve open, Intake valve opens, Both valves closed, increasing temperature exhaust products areadmitting fuel and air. Fuel/air mixture is and pressure, expansion displaced from cylinder.Exhaust valve closed compressed by rising of combustion gases Intake valve opens for most of stroke piston. Spark ignites drives piston down. Both near end of stroke. mixture near end of valves closed - exhaust stroke. valve opens near end of stroke
    • THANK YOU