le2 basic components and working principles

8/2/2019 Le2 Basic Components and Working Principles

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IC Engines

Units- 1 and 2

Lecture-2

Basic Components and

Working Principles

of IC Engines


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Basic Components of Internal Combustion Engine


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Basic Engine Components: Nomenclature

Cylinder Bore: The nominal diameter of cylinder

(mm)Piston Area (A): The area of a cylinder of

diameter equal to the cylinder bore (cm2)

Note: Where cylinder rod passes through the

combustion space as in a double actingengine, this area must be reduced by the area

of cross-section of the piston rod.

Stroke L: The nominal distance through which a

working piston moves through two

successive reversal of its direction of motion

It is expressed in mm.


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Basic Engine Components : Nomenclature (contd.)

Dead Centre:

The position of the working piston top surface at themoment when the direction of the piston movement is

reversed, at either end of the stroke, is called the dead

centre.

Top Dead centre T.D.C.: It is the dead center when thepiston is at the farthest point from the crank shaft

(Vertical engine)

(Inner Dead Centre/ I.D.C.) for a horizontal engine

Bottom Dead Centre B.D.C.): It is the dead center when thepiston is at the farthest point from the crank shaft (Verticalengine)


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Basic Engine Components : Nomenclature (contd.)

BDC (referred to as ODC or Outer Dead Centre) forHorizontal engine

Displacement or Swept Volume (Vs):

The nominal volume swept by the working pistonwhen traveling from one dead centre to the other

(cm3 or cc)

Vs = pi/4* d2 * L

Clearance Volume (Vc):

The nominal volume of the combustion chamber

above the piston when it is at the top dead centre.

(cm3 or cc)


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Basic Engine Components: Nomenclature (contd.)

Cylinder volume (V): It is the sum of the swept volumeplus the clearance volume

V = Vs + Vc

Compression ratio (r ):

It is the ratio of cylinder volume (V) to the clearance

volume

r = V/ Vc = (Vc + Vs)/ Vc = 1 + Vs/ Vc


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2. WORKING PRINCIPLES OF IC ENGINES

A. FOUR STROKE ENGINESFOUR STROKE SPARK IGNITION ENGINE

(SI ENGINE)

FOUR STROKE COMPRESSION IGNITION ENGINE

(CI ENGINE)COMPARISON OF SI ENGINE AND CI ENGINE

B.TWO STROKE ENGINES

TWO STROKE SI ENGINES

TWO STROKE CI ENGINES

C.COMPARISON OF FOUR STROKE AND

TWO STROKE ENGINES


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A. CONSTANT VOLUME HEAT ADDITION CYCLE ENGINE:

OTTO CYCLE ENGINE- ALSO KNOWN AS

SPARK IGNITION ENGINE/ SI ENGINE/ GASOLENE ENGINE

1. IC ENGINES: CYCLE OF OPERATION


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B. CONSTANT PRESSURE HEAT ADDITION CYCLE

ENGINE:

DIESEL CYCLE ENGINEDIESEL ENGINEALSO KNOWN AS

COMPRESSION IGNITION ENGINE / CI ENGINE

1. IC ENGINES: CYCLE OF OPERATION (Contd.)


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a. Intake Stroke b. Compression Stroke

c. Expansion Stroke d. Exhaust Stroke

Working Principle of a Four-stroke S I Engine


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Four Stroke SI EngineThe four strokes of the cycle are

Intake,

Compression, Power and

Exhaust.

Each corresponds to one full stroke of the piston, thereforethe complete cycle requires two revolutions of thecrankshaft to complete the process.

Intake.During the intake stroke, the pistonmoves downward, drawing a fresh charge ofvaporized fuel/air mixture. The illustratedengine features a 'poppet' intake valve which isdrawn open by the vacuum produced by theintake stroke. Some early engines worked thisway, however most modern enginesincorporate an extra cam/lifter arrangement asseen on the exhaust valve. The exhaust valve

is held shut by a spring (not illustrated here).


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Compression. As the piston risesthe poppet valve is forced shut

by the increased cylinderpressure. Flywheel momentumdrives the piston upward,compressing the fuel/airmixture.

Power.At the top of thecompression stroke thespark plug fires, igniting

the compressed fuel. Asthe fuel burns it expands,driving the pistondownward.


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Exhaust. At the bottom of the powerstroke, the exhaust valve is opened by

the cam/lifter mechanism. The upwardstroke of the piston drives theexhausted fuel out of the cylinder.


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Working of a Four Stroke SIEngine

This animation also

illustrates a simple ignitionsystem using breakerpoints, coil, condenser, andbattery.


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Suction Or Intake Stroke (0 1) Compression Stroke ( 1 2)

+ Burning (2 3) Expansion Or Power Stroke (3 4) Exhaust Stroke (45) + (5 0)Ideal p-V Diagram of a Four-Stroke S I Engine


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FOUR STROKE COMPRESSION IGNITION ENGINE

(CI ENGINE)

a. Intake Stroke b. Compression Strokec. Expansion Stroke d.Exhaust Stroke

Cycle of Operation of a C I


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WORKING PRINCIPLE OF FOUR STROKE CI ENGINE:

i Suction Stroke Air Alone Inducted (0 1)ii. Compression Stroke Air Compressed Into

Clearance Volume (1 2)ii i. Expansion Stroke Fuel Injection Maintaining ConstantPressure During Combustion+ Expansion (2 3) + (3 4)iv. Exhaust Stroke Exhaust Gases Pushed Out

1 IC ENGINES CYCLE OF OPERATION (C td )


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Actual Indicator Diagrams of Two-Stroke and Four-Stroke SI Engines

1 IC ENGINES CYCLE OF OPERATION (C td )


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Actual Indicator Diagrams of Two-Stroke and Four-Stroke SI Engines

CYCLEYCLE TWO STROKE ENGINEWO STROKE ENGINE FOUR STROKE ENGINEOUR STROKE ENGINE0-10-1 Suction Anduction And Scaveng i ngc aveng i ng Suctionuction1-21-2 Compressionompression Compressionompression2-32-3 Heat Additioneat Addition Heat Additioneat Addition3-43-4 Expansionxpansion Expansionxpansion4-04-0 Exhaustxhaust Exhaustxhaust


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COMPARISON OF SI AND CI ENGINES



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Sl.NoSl.No DESCRIPTIONDESCRIPTION SI ENGINESI ENGINE CI ENGINECI ENGINE

11 Basic cycleBasic cycle Otto cycle (const.Vol heatOtto cycle (const.Vol heat

addition)addition)

Diesel cycle (const.Diesel cycle (const.

Press. Heat addition)Press. Heat addition)

22 FuelFuel Gasoline (petrol)Gasoline (petrol)

Highly volatile Highly volatile

Self ignition temp. HighSelf ignition temp. High

Diesel oilDiesel oil

Non-volatileNon-volatile

Self ignition temp.Self ignition temp.

Comparatively lowComparatively low

33 Introduction ofIntroduction of

fuelfuelGaseous mixture of fuelGaseous mixture of fuel

+air introduced during+air introduced during

suction strokesuction stroke

Fuel directly injected asFuel directly injected as

droplets into Comb.droplets into Comb.

Chamber at highChamber at high

pressure at the end ofpressure at the end of

comp. Strokecomp. Stroke



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Sl.NoSl.No DESCRIPTIONDESCRIPTION SI ENGINESI ENGINE CI ENGINECI ENGINE

44 Introduction ofIntroduction offuel (contd.)fuel (contd.)

Carburetor and IgnitionCarburetor and Ignitionsystem are required.system are required.

Modern engines haveModern engines have

gasoline injectiongasoline injection

Fuel pump and InjectorFuel pump and Injectorare necessaryare necessary

55 Load ControlLoad Control Throttle controls theThrottle controls theair-fuel mixtureair-fuel mixture

introduced.introduced.

Quantity of fuel isQuantity of fuel isregulated. Air quantityregulated. Air quantity

is not regulated.is not regulated.

66 IgnitionIgnition Requires an ignitionRequires an ignition

system with spark plugsystem with spark plug

in the combustionin the combustionchamber. Primarychamber. Primary

voltage provided byvoltage provided by

battery or a magnetobattery or a magneto

Self ignition occurs dueSelf ignition occurs due

to high temperature ofto high temperature of

air because ofair because ofcompression. Ignitioncompression. Ignition

system and spark plugsystem and spark plug

are not required.are not required.


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Sl.Sl.

no.no.DESCRIPTIONDESCRIPTION SI ENGINESI ENGINE CI ENGINECI ENGINE

77 Compression ratioCompression ratio6 to 10. Upper limit is6 to 10. Upper limit is

fixed by anti-knockfixed by anti-knock

quality of the fuel.quality of the fuel.

16 to 20. Upper limit is16 to 20. Upper limit is

set by the weightset by the weight

increase of the engine.increase of the engine.

88 SpeedSpeed Due to light weight andDue to light weight and

homogeneoushomogeneous

combustion, they arecombustion, they are

high speed engineshigh speed engines

Due to heavy weight andDue to heavy weight and

due to heterogeneousdue to heterogeneous

combustion, they are lowcombustion, they are low

speed engines.speed engines.

99 ThermalThermal

efficiencyefficiencyBecause of the lowerBecause of the lower

compression ratio, thecompression ratio, the

max. value of thermalmax. value of thermal

efficiency that can beefficiency that can beobtained is lower.obtained is lower.

Because of higher compr.Because of higher compr.

ratio, the max value ofratio, the max value of

thermal efficiency thatthermal efficiency that

can be obtained is highercan be obtained is higher

1010 WeightWeight Lighter constructionLighter construction

due to lower peakdue to lower peak

pressures.pressures.

Heavier due to higherHeavier due to higher

peak pressurespeak pressures


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TWO STROKE ENGINE

Douglas Clarke Invented The Two Stroke EngineIn 1878

Power Stroke In Each Revolution Of The Crank

Shaft

The Suction And Exhaust Stroke Achieved By

Alternate Arrangement

Theoretically, Power Output Of The Engine Can

Be Doubled For The Same Speed As Compared

To A Four Stroke Engine

Cycle Is Completed In One Revolution Of The

Crank Shaft


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METHOD OF FILLING FRESH CHARGE AND

REMOVING BURNT GASES FROM THE ENGINE

The piston acts in a four stroke engine during suction andexhaust strokes respectively.

In a two stroke engine, the filling is accomplished by the

charge compressed in the crank case or by a blower.

Simultaneously, the products of combustion are moved outthrough the exhaust ports.

No separate piston strokes are required.

Two strokes are sufficient for the cycle.

One for compressing the fresh charge

Two for expansion or power stroke.


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CRANK CASE SCAVENGED TWO STROKE ENGINE.


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a. Compression/ Ignition b. Expansion and c. Exhaust

Working of a Two-stroke Gasoline Engine


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Four Events of 2-S EngineFour Events of 2-S Engine


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Intake. The fuel/air mixture isfirst drawn into the crankcase by

the vacuum created during theupward stroke of the piston. Theillustrated engine features apoppet intake valve, however

many engines use a rotary valueincorporated into the crankshaft.

During the downward stroke

the poppet valve is forcedclosed by the increasedcrankcase pressure. The fuelmixture is then compressed inthe crankcase during the

remainder of the stroke.


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Transfer/Exhaust. Towards theend of the stroke, the pistonexposes the intake port, allowing

the compressed fuel/air mixture inthe crankcase to escape around thepiston into the main cylinder. Thisexpels the exhaust gasses out theexhaust port, usually located on the

opposite side of the cylinder.Unfortunately, some of the freshfuel mixture is usually expelled aswell.

Compression.The piston then rises,driven by flywheel momentum, andcompresses the fuel mixture. (At thesame time, another intake stroke is

happening beneath the piston).


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Power.At the top of thestroke the spark plug ignites

the fuel mixture. Theburning fuel expands,driving the pistondownward, to complete the

cycle.

Two Stroke Engine (contd.)


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Two Stroke Engine(contd.)The two strokeengine employsthe crankcase aswell as thecylinder toachieve all theelements of theOtto cycle inonlytwo strokes ofthe piston.Intake. Thefuel/air mixture


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IDEAL INDICATOR DIAGRAM OF A TWO STROKE SI ENGINE

O S O G C C O O O S


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TWO STROKE ENGINE - CYCLE OF OPERATIONS

Air charge simultaneously inducted into the crank case

through spring loaded inlet valve, as the pressure in the

crank case drops due to the upward motion of the piston

during the compression stroke.

After the compression and ignition, the expansionfollows in the usual way. During the expansion stroke,

the charge in the crank case is compressed.

Near the end of the expansion stroke, the pistonuncovers the exhaust ports and the cylinder pressure

drops to atmospheric pressure, as the combustion

products leave the cylinder.


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Same objective can be achieved without pistondeflector through proper shaping of the transfer

port.

During the upward motion of the piston fromBDC, the transfer ports close first and then the

exhaust ports close when the compression of the

charge begins and the cycle is repeated.

TWO STROKE ENGINE - CYCLE OF OPERATIONS (contd.)


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COMPARISON OF 2 AND 4 STROKE ENGINES

Features Of Two Stroke Engine

. Developed to get a greater power output for a

given engine size

Eliminates valves (only ports; some have an exhaust

valve) hence mechanically simpler construction

Cheaper to produce

Easier maintenance

Theoretically should develop twice the power


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Actual power output is higher by only about 30% than a

comparable to four stroke engine - due to

Reduced effective expansion stroke

Increased heating because of increased number of

power strokes

This limits the maximum operating speed

It gives more uniform torque on crank shaft and smaller

fly wheel is sufficient.

Less exhaust gas dilution

With these inherent disadvantages, Two stroke SI engines

are presently suitable for only smaller engines.

Features Of Two Stroke Engine (contd.)


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Features of Two Stroke Engine (contd.)

INCOMING CHARGE CONSISTS OF FUEL AND AIR

DURING SCAVENGING, BOTH INLET AND EXHAUST PORTS ARE

OPEN SIMULTANEOUSLY FOR SOME TIME.

THERE IS A POSSIBILITY FOR SOME FRESH CHARGE

CONTAINING FUEL MAY ESCAPE WITH THE EXHAUST.

THIS RESULTS IN

A HIGHER FUEL CONSUMPTION AND

A LOWER THERMAL EFFICIENCY

AT PART THROTTLE OPERATION, THE AMOUNT OF FRESH

MIXTURE ENTERING IS NOT ENOUGH TO CLEAR ALL THE

EXHAUST GASES. A PART OF IT REMAINS IN THE CYLINDER TO CONTAMINATE

THE FRESH CHARGE RESULTS IN IRREGULAR OPERATION


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Two Stroke Diesel Engine

More Advantageous Than Two Stroke SI Engine!No Loss Of Fuel With Exhaust Gases As The Intake Charge

Is Only Air.

Hence Many Of The High Output Diesel Engines Work On

This Cycle.

A General Disadvantage Common To Both Two Stroke

Gasoline And Diesel Engines Is

Greater Cooling And Lubricating Oil Requirements Due To

One Power Stroke Per Crank Shaft Rotation And Higher

Temperatures.

Results In Higher Consumption Of Lubricating Oil.


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Sl.No.Sl.No. Four-stroke EngineFour-stroke Engine Two Stroke EngineTwo Stroke Engine

11 Thermodynamic Cycle IsThermodynamic Cycle IsCompleted In Four StrokesCompleted In Four Strokes

One Power Stroke In 2 CrankOne Power Stroke In 2 Crank

Shaft RevolutionsShaft Revolutions

Thermodynamic Cycle Is CompletedThermodynamic Cycle Is CompletedIn Two Strokes One Power StrokeIn Two Strokes One Power Stroke

In Each Crank Shaft RevolutionIn Each Crank Shaft Revolution

22 Hence Turning Moment Is NotHence Turning Moment Is Not

So Uniform- Needs A LargerSo Uniform- Needs A LargerFly WheelFly Wheel

Hence Turning Moment Is MoreHence Turning Moment Is More

Uniform- Needs A Lighter Fly WheelUniform- Needs A Lighter Fly Wheel

33 Power Produced For ThePower Produced For The

Same Size Engine Is Less, OrSame Size Engine Is Less, Or

For Same Power, Engine IsFor Same Power, Engine IsHeavier And Bulkier.Heavier And Bulkier.

Power Produced For The Same SizePower Produced For The Same Size

Engine Is Twice, Or For The SameEngine Is Twice, Or For The Same

Power, The Engine Is Lighter AndPower, The Engine Is Lighter AndMore Compact.More Compact.

Comparison Of Four And Two Stroke Cycle Engines


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Sl.No.Sl.No. Four-stroke EngineFour-stroke Engine Two Stroke EngineTwo Stroke Engine

44 Lesser Cooling AndLesser Cooling AndLubrication Requirements.Lubrication Requirements.

Lower Rate Of Wear AndLower Rate Of Wear And

Tear Because Of One PowerTear Because Of One Power

Stroke/ Two C.S RevolutionsStroke/ Two C.S Revolutions

Greater Cooling And LubricationGreater Cooling And LubricationRequirements. Higher Rate Of WearRequirements. Higher Rate Of Wear

And Tear Because Of One PowerAnd Tear Because Of One Power

Stroke/ C.S RevolutionStroke/ C.S Revolution

55 Require Valves And ValveRequire Valves And Valve

Actuating Mechanisms ForActuating Mechanisms For

Opening And Closing Of TheOpening And Closing Of The

Intake And Exhaust ValvesIntake And Exhaust Valves

Two Stroke Engines Have NoTwo Stroke Engines Have No

Valves But Only Ports (SomeValves But Only Ports (Some

Engines Have Exhaust Valve OrEngines Have Exhaust Valve Or

Reed Valve).Reed Valve).

66 Initial Cost Of The Engine IsInitial Cost Of The Engine Is

HigherHigherInitial Cost Of The Engine IsInitial Cost Of The Engine Is LessLess

COMPARISON OF FOUR AND TWO STROKE CYCLE ENGINES (CONTD.)

C i Of F A d T S k C l E i (C d )


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Sl. No.Sl. No. Four-stroke EngineFour-stroke Engine Two Stroke EngineTwo Stroke Engine

77 Volumetric Efficiency Is More Volumetric Efficiency Is More

Due To More Time ForDue To More Time ForInduction Of ChargeInduction Of Charge

Volumetric Efficiency Is Less Due Volumetric Efficiency Is Less Due

To Less Time For Induction OfTo Less Time For Induction OfChargeCharge

88 Thermal Efficiency Is Higher.Thermal Efficiency Is Higher.

Part-load Efficiency Is Better.Part-load Efficiency Is Better.Thermal Efficiency Is Lower.Thermal Efficiency Is Lower.

Part-load Efficiency Is Poor.Part-load Efficiency Is Poor.

99 Used Where Efficiency IsUsed Where Efficiency Is

Important, viz., In Cars,Important, viz., In Cars,

Buses, Trucks, Tractors,Buses, Trucks, Tractors,

Industrial Engines,Industrial Engines,

Aeroplanes, Power GenerationAeroplanes, Power GenerationEtc.Etc.

Used Where Low Cost,Used Where Low Cost,

Compactness And Light Weight AreCompactness And Light Weight Are

Important, Viz., In Mopeds,Important, Viz., In Mopeds,

Scooters, Motor Cycles, HandScooters, Motor Cycles, Hand

Sprayers Etc.Sprayers Etc.

Comparison Of Four And Two Stroke Cycle Engines (Contd.)

ENGINE PERFORMANCE PARAMETERS


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ENGINE PERFORMANCE PARAMETERS

Sl. No.Sl. No. ParameterParameter NotationNotation

i.i. Indicated Thermal EfficiencyIndicated Thermal Efficiency iththiiii Brake Thermal EfficiencyBrake Thermal Efficiency bththiiiiii Mechanical EfficiencyMechanical Efficiency miviv Volumetric EfficiencyVolumetric Efficiency vvv Relative Efficiency/ Efficiency RatioRelative Efficiency/ Efficiency Ratio relelvivi Mean Effective PressureMean Effective Pressure pmviivii Mean Piston SpeedMean Piston Speed spviiiviii Specific Power OutputSpecific Power Output Psixix Specific Fuel ConsumptionSpecific Fuel Consumption s f cf cxx Inlet Valve Mach IndexInlet Valve Mach Index Zxixi Fuel-Air or Air-Fuel RatioFuel-Air or Air-Fuel Ratio F/A or A/F/A or A/Fxiixii Calorific value of the FuelCalorific value of the Fuel CV (HCV/ LCV)V (HCV/ LCV)


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Valve TimingValve Timing Low SpeedLow Speed High SpeedHigh SpeedI.V.OI.V.O 101000 Before. TDCBefore. TDC 101000 Before. TDCBefore. TDC

I.V.CI.V.C 101000 After. BDCAfter. BDC 606000 After. BDCAfter. BDC

E.V.OE.V.O 252500 Before. BDCBefore. BDC 555500 Before. BDCBefore. BDC

E.V.CE.V.C 5500 After. TDCAfter. TDC 202000 After TDCAfter TDC


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Port Timing Diagram of a Two StrokeEngine

le2 basic components and working principles

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