Lecture 2 fp lecture notes engine1

Roger C. Montepio

Engine-Review

Convert fuel chemical energy into mechanical powerCombustion of the fuel causes one or more reciprocating pistons, to turn a crankshaft

Transmission of power:Crankshaft via flywheel

Connecting rod

Piston Output shaft

Desired load

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Piston and Crankshaft

Reciprocating motion to rotary motion

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What happen inside the Piston?

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Engine Framework

Serves as an enclosureSupport all the component parts of the engine mechanisms and systemsFormed by a number of components that are rigidly held together

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Principal Engine parts?

1. Cylinder/cylinder block

2. Cylinder head3. Piston4. Piston rings5. Piston pin6. Connecting rod7. Crankshaft8. Flywheel

9. Valve system10. Fuel supply and carburetion system11. Ignition System12. Cooling system13. Lubrication System14. Governing System

Components of engine framework

Roger C. Montepio

Roger C. Montepio

Cutaway drawing of a 2.2Li displacement 4-cycle spark ignition engine

-Bore=87.5mm-stroke=92mm-compression ratio = 8.9-Power max= 65kW-5000rev/min

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Cylinder block

Cylinder block and crankcase – the main structural unit- monoblock construction

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Cylinder block and crankcase of a tractor

Liquid-cooled In-line type engine

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Liquid-cooled V- type engine


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Air-cooled type engine


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Components of engine block

- divides into two major compartment (cylinder block the upper half and crankcase the lower half-cylinder block specific component1. Surface2. Tappet inspection window3. Tappet guide4. Push rod hole, cylinder bore5. Crankcase, camshaft recess, oil

pump recess, water pump recess6. Main journal cap

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Function:- provide the space in which the piston

operates- hollow spaces in the block provide for

the circulation of the cooling medium- houses the cylinder liners

Cylinder block

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Cylinder liners

Removable cylinders - Cylinder liners or sleeves can be classified as:Dry type – serves as the inner lining and cylinder

wearing surface- usually much thinner and easier to replace

Wet type- serves as the entire cylinder wall and comes into direct contact with the coolant

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Roger C. Montepio

Cylinder head

Its function is to cover the upper end of the cylinderIs a part where the valves and rocker arms may be housedContains the pocket or space above the cylinder and piston called combustion chamber

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Component parts?

1. Surface – plane surface that presses the gasket against the surface of the block for purpose of sealing

2. Combustion space – part of cylinder head surface directly over the piston surface

3. Pre-combustion chamber – part where the fuel is first injected and burned

4. Valve guide – drilled hole above the valve ports where the valve stem is inserted

5. Valve cage – removable parts of cylinder head during/when servicing

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Component parts?

6. Water jacket – water compartment surrounding the cylinder for cooling water to be stored7. Push rod hole - hole at the cylinder head or block where the push rod is inserted8. Stud bolt hole9. Oil hole10. Nozzle hole and heater11. Water pump mounting recess12. Valve ports13. Water outlet spout recess, water hole14. Water jacket expansion plug

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Crankcase and oil pan

Crankcase – part of the engine w/c supports and encloses the crankshaft and camshaft

- serve as mounting for such accessories as oil pump, oil filter, generator, starter motor and ignition partOil pan – the lower part of the crankcase

- serve as reservoir for the lubricating oil- components are base, baffle plate, drain plug

and depth stick guide

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Piston

part of both the 2-stroke and 4-stroke engines that receives the energy from the combustiontransmit power to the crankshaft

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Piston

Piston moves (acceleration) from TDC to BDC or vise versa at 50mph (80kph) at the midpoint from stop, then decelerate to stop againPiston head subjected to pressure in excess of 1000psi (6895 kPa)Piston head is subjected to temperatures well over 600˚F (316˚C)

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Piston

Construction materials-weight is the primary consideration in designinga. gray cast iron – used in heavy duty engines and low

speed, more wear resistantb. Cast steel – used in heavy duty engines and low

speedc. Aluminum alloy- suitable for high operating speed,

best material for piston construction- disadvantage: high coefficient of expansion,

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Piston

Piston- has built-in features to help them control expansiona. Piston crown – is machined

to a diameter approx. 0.03-0.04 in (0.762-1.106mm) smaller than skirt area

b. skirt area – has slot cut up on the side

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Piston

c. Skirt area has T-slot, an additional horizontal slot to retard heat transferd. Piston aluminum has steel braces cast into the piston

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Types of Piston

1. Trunk or standard – (strut, skirt, plain) 2. Crosshead -

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Types of standard

Strut-type aluminum alloy – has struts embed made of steel or invar to control piston expansion and strengthen the piston

Split skirt aluminum alloy - the purpose of piston skirt is to keep the piston from rocking in the cylinder

Plain cast iron

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Purpose of partial skirt

Lightens the pistonReduces the contact area with the cylinder wallAllows the piston to be brought down closer to crankshaft

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Piston structure

Ways of making piston strong and lighter:

a. Piston heads are made as thin, to keep strong, additional ribs are cast into underside

b. Piston pin is reinforced called pin bossing

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Treatment applied to the piston to add strength and more wear resistant

Piston is coated with tin w/c will work into the cylinder wallPiston is anodized to produce harder outside surface… making the metal surface to aluminum oxide

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Terminologies

Anodizing – is the process that produces a coating on the surface by electrolysisPiston clearance – is the space between the piston wall and cylinder wall (0.0005 inch when cold)-aluminum alloy requires about twice as much clearance as cast iron-Too much clearance will cause loss of compression, oil pumping, and piston slap-Too little clearance will cause piston to stick when hot

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Piston Rings

What is its functions? To retain compression, or provide sealReduce the cylinder wall and piston wall contact area Control of the oil and cylinder lubrication, or prevent lubricating oil from bypassing the pistonControl of transmission of heat away from the piston and the cylinder wall or provide solid bridge to conduct heat from the piston to the cylinder wall

One-third of the heat absorbed by the piston passes to the cylinder wall through piston rings

Ring-like part inserted around the groove of piston

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Roger C. Montepio

Classed of piston rings

Compression ring – usually plain one-piece ring- always placed in the grooves nearest the piston headOil ring – grooved or slotted- Located either in the lowest groove above piston pin or in a groove near the piston skirt

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Types of Compression ring?

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Purpose of Compression ring?

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Roger C. Montepio


Roger C. Montepio

Configuration of Piston rings

Number of rings varies from 3 to 5Ordinary engines have 3 rings per pistonDiesel engines have 5 rings per piston

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Purpose of 2nd compression ring?

To hold back any blow by that may have occurred at the top ringAssembled in 60 degrees offset

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Configuration and operation of oil rings

1. Channelled 2. flexiflex

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Inner rings or expander – special, flexible, spring-steel bands placed in the ring grooves under regular rings – purpose of creating better contact between ring and wall

Piston ring clearance – space at the joint of the ring

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Piston ring End clearance

Cylinder diameter (inch)

End Clearance (inch)

1-1 31/322-2 31/323-3 31/324-4 31/325-6 31/327-8

0.005-0.0130.007-0.0170.010-0.0200.013-0.0250.017-0.0320.023-0.040

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Piston pin

Made of casehardened alloy steelFunction is to join the connecting rod to the pistonKept the piston from axial movement by internal spring lock ring or circlipsLubricated by splash from crankcase or by pressure

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Methods of anchoring Piston pin

The pin is clamp to the connecting rod by means of a clamp screw or setscrewThe pin is anchored to the piston by means of setscrew and the bearing is in the connecting rodThe pin is allowed to float and is held in place by means of snap rings at each end of the pin

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Connecting rod

Made of drop-forged steelRod like part of the engine that connects the piston with the crankshaft

Type are:conventional type – one having a halve cap for crankshaft crankpincrosshead type – design to minimize eccentricity of the crankshaft, usually used in diesel engine

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Parts of connecting rod (I-beam type)

1.Wrist pin boss2.Bushing3.Body4.Oil hole5.Cap bolt6.Cap

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Crankshaft

Made of drop-forged steelThe main turning part of the engine having the eccentric armThe connecting rod is attachedTakes or receive the downward thrust of the piston and connecting rod when air-fuel is burned

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In-line engine type

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Flywheel – absorb the violent thrust of power stroke and then release the energy back to the crankshaft

- provide additional power to the engine to run smoothly and helps overcome increased load

- Contributes uniform rotation of crankshaftLubrication system – provides a constant supply

of oil to the engine- to lubricate and cool the moving parts

Engine Accessory System

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Fuel system – supplies the engine with the properly proportioned fuel and air mixture-regulates the amount of the mixture supplied to the engine to control engine speed and power output

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Ignition system – ignites the fuel and air mixture in the combustion chamber at the precise moment needed

Cooling system – removes the excess heat from the engine, generated by combustion


Lecture 2 fp lecture notes engine1

Engineering