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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1. IC ENGINES: CYCLE OF OPERATION (Contd.)
Actual Indicator Diagrams of Two-Stroke and Four-Stroke SI Engines
1 IC ENGINES CYCLE OF OPERATION (C td )
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1. IC ENGINES: CYCLE OF OPERATION (Contd.)
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
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
COMPARISON OF SI AND CI ENGINES
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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
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