ENGINE CONSTRUCTION

Basic parts of Internal Combustion Engine

a) Cylinder headtop of the engine which contain a hole for valvesvalves, intake and exhaust passages, cooling passages

b) Valvesopen and close to let fuel air mixture (petrol engine) or air only (diesel engine)exhaust gases out of each cylinder

c) Camshaftrotates to open and close the valves by cam action

d) Cylinder blockMain housing of the engine and supports other main partsContain cylindrical vessels in which combustion takes place and piston makes a reciprocating motion

e) CylindersHollow tubes, piston moves back and forth

f) PistonsMove in the cylinders and apply the force of combustion to crankshaft

g) Piston ringsA component that fitted into the slot around the piston which seal the combustion chamber and help transfer heat

h) Connecting rodsA rod that interconnect the piston and the crankshaft and transmit the forces from the piston to crankshaft

i) CrankshaftReceives the force from pistons and transmit as rotary driving power

j) Main bearingsSupport crankshaft in cylinder block

k) FlywheelAttach to crankshaft at rear, provides momentum and help return pistons to the top of cylinders

l) Timing drivesLink the crankshaft, camshaft and other parts together to assure each is doing its job at the right time

m) CamsIntegral part of camshaft design to open the valve at the correct timing and to keep them open for the necessary duration

n) Gudgeon pinForms the link between the small end of the connecting rod and the piston

Classification of Tractors

According to the Power of Engine (horse power)– Small < 25 hp– Medium 25 – 50 hp– Large > 50 hp

Comparison Between Petrol and Diesel Engine

a. Fuel Supply and Ignitionb. Compression Ratioc. Design of Engine Partsd. Grade and Type of Fuel Used

a) Fuel Supply and Ignition

Petrol EngineFuel and air mixed outside the cylinders in the carburetor andintake manifoldMixture is forced into cylinders by partial vacuum created byintake stroke of pistonUses electric spark to ignite fuel air mixtureCompression ratio 8 to 1 (8:1)

Diesel EngineNo premixing of air and fuelAir taken into cylinders through intake manifold and compressedFuel is sprayed into cylinders and mixed with air as the pistonnears the top of its compression strokeUse heat and compressed air for ignitionCompression ratio 16 to 1 (16:1)

b) Compression Ratio

Compression 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 Parts

Engine of diesel more sturdier parts to withstand greater forces

d) Grade and Type of Fuel Used

• Diesel fuel -- more heat units (joule) pergallon

• Therefore produces more power per gallon offuel– 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 Good 5. Acceleration Good Good6. Continuous Duty Good Fair7. Lubricating oil contamination Moderate Moderate

DIESEL ENGINE PETROL ENGINE

1. Fuel SystemUse dieselNo carburetorUses heat & compressed airfor ignition

1. Fuel SystemUse petrolHave carburetorUses electric spark to igniteair‐fuel mixture

2. Higher compression ratio14 – 16 : 1

2.Lower compression ratio7 – 10 : 1

3. OperationNo pre‐mixing of air and fuelAir taken into cylinderthrough intake manifold andcompressedFuel is sprayed into cylindersand mixed with air as thepiston nears the top of itscompression stroke

3.OperationFuel and air mixed outside thecylinders in the carburetorand intake manifoldMixture is forced intocylinders by partial vacuumcreated by intake stroke ofpiston

Engine Construction

1. Valves - Intake and Exhaust ValvesThe valves allow fuel-air in and exhaust gases out of eachcylinder during combustion cycle by opening and closing theintake and exhaust parts of the cylinder.

Intake StrokeIntake valve opens allowing fuel air mixture to entercombustion chamber

Compression and Power StrokeBoth valves are closed to seal in combustible mixture

Exhaust StrokeExhaust valve opens allowing gases to be exhausted

End of Exhaust StrokeIntake valves opens, beginning another cycle

Functions

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 lowside of the cam

• Cam movements are designed to open or close thevalves at the right moment

3. Engine Crankcase and Cylinder Block

• Made of iron casting and is an integral withcylinder block which houses cylinder liners

• Liners are said to be wet or dry according towhether they are or not in contact with coolingwater that circulate through engine block

• Crankcase houses the crank gear and valve gear

4. Engine Block

• Houses the injection pump, oil pump, water pumpand power generator

• The front part carries the timing cover, rear endcarries clutch bell housing on which the startermotor is mounted

• Provided with oil filler cap and breather, oildipstick and water connection to the radiator

5. Cylinder Head

Consists of fuel injectors , inlet and outlet valves, the rockersCylinder head is in a single piece for engines up to 4 cylindersBetween cylinder head and engine block – cylinder head gasket; to prevent gas, coolants and lubricating oil from escapingAlso connected the inlet and exhaust manifolds water pipe from radiator

6. Oil Sump

Made of iron castingSeals the crankcase at the bottomFunctions 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 crankshaftCombustion chamber machined in upper part known as piston head or crown ; lower part known as piston skirt

Connecting rodsTransmit the motion of the pistons to the crankshaft

Cylinder Linersmade of cast ironmay 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 drivingforceRear end carries the flywheel incorporating starter ring gearFront end carries crankshaft gear used to drive valve timingmechanism, oil pump

9. Flywheel

Attaches to crankshaft at rear & provides momentum to help returnthe pistons to the top of cylinders after each downward thrust

10. Timing Drives

Link the crankshaft, camshaft and other parts together so that eachis doing its job at the right time

What is Internal and ExternalCombustion 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 duringoperation & engine would lose compression &power

• The valve clearance is small, approx: 0.15-0.75mm. Valve clearance varies with different enginemodel; whether the engine should be hot or coldduring 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 thatnormal heat transfer into the cooling system does nothave time to take place

• This causes Burned Valves

Effect of Too Big Valve Clearance

• Causes a lag in valve timing which made the engineout of balance

• Fuel air mixture is late in entering the cylinder duringthe intake stroke

• Exhaust valve closes early & prevents waste gasesfrom 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 manual

Valve Timing– Opening and closing of both inlet and exhaust

valves when the piston is at the exact top (TDC) or bottom (BDC) of its stroke

Valve 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 CLASSIFICATIONS

1. Types of ignitiona) 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 cyclea) Four stroke cycle

A four-stroke cycle experiences four cycle movement over two engine revolutions for each cycle.

b) Two stroke cycleA two-stroke cycle has two cycle movement over one revolution for each cycle.

3. Valve locationa) 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) RotaryEngine 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 enginesa) Single cylinder

Engine has one cylinder and piston connected to the crankshaft.

b) In-lineCylinders 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 moreCommon are four cylinders engine

c) V engineTwo banks of cylinder at an angle with each other along a single crankshaft.The angle are 15⁰ to 120⁰, common are 60⁰ to 90⁰2 to 20 cylinders, normally V6s and V8sV12s 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 engineSame as V engine except with three banks of cylinders on the same crankshaft.Normally developed for racing automobiles.

f) Opposed piston engineTwo 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 engineEngine 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 2

1. Block2. Camshaft3. Carburetor4. Catalytic converter5. Combustion chamber6. Connecting rod7. Crankcase8. Crankshaft9. cylinders10. exhaust manifold11. exhaust system12. fan 13. flywheel14. fuel injector15. Fuel pump

16. Glow plug17. Cylinder head18. Head gasket19. Intake manifold20. Main bearing 21. Oil pump22. Piston23. Piston rings24. Push rods 25. Radiator26. Spark plug27. Speed control-cruise control28. Starter motor29. Throttle30. turbocharger31. Water jacket32. Water pump

BASIC ENGINE CYCLES

A) Four Stroke SI Engine CycleB) Two Stroke SI Engine Cycle

Four Stroke SI Engine Cycle

Intake StrokeIntake valve opens,

admitting fuel and air.Exhaust valve closed

for most of stroke

Compression StrokeBoth valves closed,Fuel/air mixture is

compressed by rising piston. Spark ignitesmixture near end of

stroke.

IntakeManifold

Spark PlugCylinder

Piston

Connecting Rod Crank

Power StrokeFuel-air mixture burns,increasing temperatureand pressure, expansion

of combustion gases drives piston down. Bothvalves closed - exhaust valve opens near end

of stroke

1 2 3 4

Exhaust StrokeExhaust valve open,exhaust products are

displaced from cylinder.Intake valve opens near end of stroke.

Crankcase

ExhaustManifold

Exhaust ValveIntake Valve

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