Lecture2+Basic+Components+and+Working+Principles

8/7/2019 Lecture2+Basic+Components+and+Working+Principles

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IC Engines

Units- 1 and 2

Lecture-2

Basic Components andWorking Principles

of IC Engines



Basic Components of Internal Combustion Engine



� 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 acting

engine, 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.



� Basic Engine Components : Nomenclature (contd.)

� Dead Centre:

The position of the working piston top surface at the

moment 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 the

piston 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 the

piston is at the farthest point from the crank shaft (Vertical engine)



� Basic Engine Components : Nomenclature (contd.)

BDC (referred to as ODC or Outer Dead Centre) for

Horizontal 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)



� Basic Engine Components: Nomenclature (contd.)

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

plus 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



2. WORKING PRINCIPLES OF IC ENGINES

A. FOUR STROKE ENGINES

FOUR 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



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



B. CONSTANT PRESSURE HEAT ADDITION CYCLE

ENGINE:DIESEL CYCLE ENGINE ± DIESEL ENGINE

ALSO KNOWN AS

COMPRESSION IGNITION ENGINE / CI ENGINE

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



a. Intake Stroke b. Compression Stroke

c. Expansion Stroke d. Exhaust Stroke

Working Principle of a Four-stroke S I Engine



Four Stroke SI Engine

The four strokes of the cycle are

Intake,

Compression,

Power and

Exhaust.

Each corresponds to one full stroke of the piston,

therefore the complete cycle requires two revolutions of the crankshaft to complete the process.

Intake. During the intake stroke, the pistonmoves downward, drawing a fresh charge of vaporized fuel/air mixture. The illustrated

engine features a 'poppet' intake valve whichis drawn open by the vacuum produced bythe intake stroke. Some early engines workedthis way, however most modern enginesincorporate an extra cam/lifter arrangement as seen on the exhaust valve. The exhaust valve is held shut by a spring (not illustratedhere).



Compression. A s the pistonrises the poppet valve is forced

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

mixture.Power. A t the top of thecompression stroke thespark plug fires, igniting

the compressed fuel. A sthe fuel burns it expands, driving thepiston downward.



Exhaust. A t thebottom of the powerstroke, the exhaust valve is opened by

the cam/liftermechanism. Theupward stroke of thepiston drives theexhausted fuel out of the cylinder.



Working of a Four StrokeSI Engine

This animation also

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



� Suction Or Intake Stroke (0 1)

� Compression Stroke ( 1 2)

+ Burning (2 3)

� Expansion Or Power Stroke (3 4)

� Exhaust Stroke (4 5) + (5 0)

Ideal p-V Diagram of a Four-Stroke S I Engine



FOUR STROKE COMPRESSION IGNITION ENGINE

(CI ENGINE)

a. Intake Stroke b. Compression Stroke

c. Expansion Stroke d. Exhaust Stroke

Cycle of Operation of a C I Engine



W ORKING PRINCIPLE OF FOUR STROKE CI ENGINE:

Suction Stroke Air Alone Inducted (0 1)

Compression Stroke Air Compressed IntoClearance Volume (1 2)

Iii. Expansion Stroke Fuel Injection Maintaining ConstantPressure During Combustion

+ Expansion(2 3) + (3 4)

Iv. Exhaust Stroke Exhaust Gases Pushed Out(4 5) + (5 0)




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




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

CYCLECYCLE TWO STROKE ENGINETWO STROKE ENGINE FOUR STROKE ENGINEFOUR STROKE ENGINE

00--11 Suction AndSuction And ScavengingScavenging SuctionSuction

11--22 CompressionCompression CompressionCompression

22--33 Heat AdditionHeat Addition Heat AdditionHeat Addition

33--44 ExpansionExpansion ExpansionExpansion

44--00 ExhaustExhaust ExhaustExhaust



COMPARISON OF SI AND CI ENGINES



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

11 Basic cycleBasic cycle Otto cycle (const. VolOtto cycle (const. Volheat addition)heat addition) Diesel cycle (const.Diesel cycle (const.Press. Heat addition)Press. Heat addition)

22 FuelFuel Gasolene (petrol)Gasolene (petrol)

Highly volatileHighly volatile

Self ignition temp. HighSelf ignition temp. High

Diesel oilDiesel oil

NonNon--volatilevolatile

Self ignition temp.Self ignition temp.Comparatively lowComparatively low

33 Introduction of Introduction of fuelfuel

Gaseous mixture of fuelGaseous mixture of fuel+air introduced during+air introduced duringsuction strokesuction stroke

Fuel directly injected asFuel directly injected asdroplets intodroplets intoComb.Chamber at highComb.Chamber at high

pressure at the end of pressure at the end of comp. Strokecomp. Stroke

COMPARISON OF SI AND CI ENGINES



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

44 Introduction of Introduction of fuel (contd.)fuel (contd.)

Carburetor andCarburetor andIgnition system areIgnition system arerequired.required.

Modern engines haveModern engines havegasoline injectiongasoline injection

Fuel pump andFuel pump andInjector are necessaryInjector are necessary

55 Load ControlLoad Control Throttle controls theThrottle controls theairair--fuel mixturefuel mixtureintroduced.introduced.

Quantity of fuel isQuantity of fuel isregulated. A ir quantityregulated. A ir quantityis not regulated.is not regulated.

66 IgnitionIgnition Requires an ignitionRequires an ignitionsystem with sparksystem with sparkplug in theplug in thecombustion chamber.combustion chamber.Primary voltagePrimary voltageprovided by batteryprovided by batteryor a magnetoor a magneto

Self ignition occursSelf ignition occursdue to highdue to hightemperature of airtemperature of airbecause of because of compression. Ignitioncompression. Ignitionsystem and spark plugsystem and spark plugare not required.are not required.



Sl.Sl.no.no.

DESCRIPTIONDESCRIPTION SI ENGINESI ENGINE CI ENGINECI ENGINE

77 CompressionCompression

ratioratio

6 to 10. Upper limit is6 to 10. Upper limit is

fixed by antifixed by anti--knockknockquality of the fuel.quality of the fuel.

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

set by the weight set by the weight increase of the engine.increase of the engine.

88 SpeedSpeed Due to light weight Due to light weight and homogeneousand homogeneouscombustion, they arecombustion, they are

high speed engineshigh speed engines

Due to heavy weight Due to heavy weight and due toand due toheterogeneousheterogeneous

combustion, they arecombustion, they arelow speed engines.low speed engines.

99 ThermalThermalefficiencyefficiency

Because of the lowerBecause of the lowercompression ratio, thecompression ratio, themax. value of thermalmax. value of thermal

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

Because of higherBecause of highercompr. ratio, the maxcompr. ratio, the maxvalue of thermalvalue of thermal

efficiency that can beefficiency that can beobtained is higherobtained is higher

1010 Weight Weight Lighter constructionLighter constructiondue to lower peakdue to lower peakpressures.pressures.

Heavier due to higherHeavier due to higherpeak pressurespeak pressures



TWO STROKE ENGINE

� Douglas Clarke Invented The Two StrokeEngine In 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



METHOD OF FILLING FRESH CHARGE AND

REMOVING BURNT GASES FROM THE ENGINE

� The piston acts in a four stroke engine during suction and

exhaust 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 out

through 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.



CRANK CASE SCAVENGED TWO STROKE ENGINE.



a. Compression/ Ignition b. Expansion and c. Exhaust and(and Induction of fresh charge) (Compression) (Transference)

Working of a Two-stroke Gasoline Engine





Four Events of 2Four Events of 2--S EngineS Engine



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



Transfer/Exhaust. Toward 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 theopposite side of thecylinder. Unfortunately, some of the fresh fuel mixture is usuallyexpelled as well.

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

happening beneath the piston).



Power. A t the top of thestroke the spark plug

ignites the fuel mixture.The burning fuel expands,driving the pistondownward, to complete the

cycle.

Two Stroke Engine (contd.)



Two Stroke Engine(contd.)

The two strokeengine employsthe crankcase aswell as thecylinder toachieve all theelements of theOtto cycle in only two strokes of

the piston.Intake. Thefuel/air mixture



IDEAL INDICATOR DIAGRAM OF A TWO STROKE SI ENGINE



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 expansion

follows 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.



� Further movement of the piston uncovers the transfer

ports, thus permitting the slightly compressed charge in thecrank case to enter the engine cylinder .

� The top of the piston has usually a projection to deflect the

fresh charge towards the top of the cylinder before flowing

through the exhaust ports.

� This has the dual purpose of

A.Scavenging the upper part of the cylinder of thecombustion products and

B. Preventing the fresh charge from flowing directly

towards the exhaust ports.

TWO STROKE ENGINE - CYCLE OF OPERATIONS (contd.)



� Same objective can be achieved without piston

deflector 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.)



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 ±



� 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.)



Features of Two Stroke Engine (contd.)

� INCOMING CHARGE CONSISTS OF FUEL AND AIR

� DURING SCAVENGING, BOTH INLET AND EXHAUST PORTS AREOPEN 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



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.



Sl.No.Sl.No. FourFour--stroke Enginestroke Engine Two Stroke EngineTwo Stroke Engine

11 Thermodynamic Cycle IsThermodynamic Cycle IsCompleted In Four StrokesCompleted In Four StrokesOne Power Stroke In 2One Power Stroke In 2Crank Shaft RevolutionsCrank Shaft Revolutions

Thermodynamic Cycle IsThermodynamic Cycle IsCompleted In Two Strokes OneCompleted In Two Strokes OnePower Stroke In Each Crank Shaft Power Stroke In Each Crank Shaft RevolutionRevolution

22 Hence Turning Moment IsHence Turning Moment IsNot So UniformNot So Uniform-- Needs A Needs A Larger Fly WheelLarger Fly Wheel

Hence Turning Moment Is MoreHence Turning Moment Is MoreUniformUniform-- Needs A Lighter FlyNeeds A Lighter FlyWheelWheel

33 Power Produced For ThePower Produced For The

Same Size Engine Is Less,Same Size Engine Is Less,Or For Same Power, EngineOr For Same Power, EngineIs Heavier A nd Bulkier.Is Heavier A nd Bulkier.

Power Produced For The SamePower Produced For The Same

Size Engine Is Twice, Or For TheSize Engine Is Twice, Or For TheSame Power, The Engine IsSame Power, The Engine IsLighter A nd More Compact.Lighter A nd More Compact.

Comparison Of Four And Two Stroke Cycle Engines




44 Lesser Cooling A ndLesser Cooling A ndLubrication Requirements.Lubrication Requirements.Lower Rate Of Wear A ndLower Rate Of Wear A ndTear Because Of One PowerTear Because Of One PowerStroke/ Two C.SStroke/ Two C.S

RevolutionsRevolutions

Greater Cooling A nd LubricationGreater Cooling A nd LubricationRequirements. Higher Rate Of Requirements. Higher Rate Of Wear A nd Tear Because Of OneWear A nd Tear Because Of OnePower Stroke/ C.S RevolutionPower Stroke/ C.S Revolution

55 Require Valves A nd ValveRequire Valves A nd ValveA ctuating Mechanisms ForA ctuating Mechanisms ForOpening A nd Closing Of Opening A nd Closing Of The Intake A nd Exhaust The Intake A nd Exhaust

ValvesValves

Two Stroke Engines Have NoTwo Stroke Engines Have NoValves But Only Ports (SomeValves But Only Ports (SomeEngines Have Exhaust Valve OrEngines Have Exhaust Valve OrReed Valve).Reed Valve).

66 Initial Cost Of The EngineInitial Cost Of The EngineIs HigherIs Higher

Initial Cost Of The Engine IsInitial Cost Of The Engine IsHigherHigher

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




77 VolumetricVolumetric EfficiencyEfficiency IsIsMoreMore DueDue ToTo MoreMore TimeTime ForForInductionInduction Of Of ChargeCharge

VolumetricVolumetric EfficiencyEfficiency IsIs LessLess DueDueToTo LessLess TimeTime ForFor InductionInduction Of Of ChargeCharge

88 ThermalThermal EfficiencyEfficiency IsIsHigherHigher.. Part Part--loadload EfficiencyEfficiency

IsIs BetterBetter..

ThermalThermal EfficiencyEfficiency IsIs LowerLower..

Part Part--loadload EfficiencyEfficiency IsIs PoorPoor..

99 Used Where Efficiency IsUsed Where Efficiency IsImportant,viz., In Cars,Important,viz., In Cars,Buses, Trucks, Tractors,Buses, Trucks, Tractors,Industrial Engines,Industrial Engines,

A eroplanes, PowerA eroplanes, PowerGeneration Etc.Generation Etc.

UsedUsed WhereWhere LowLow Cost,Cost,CompactnessCompactness A ndA nd Light Light Weight Weight A reA re Important,Important, VizViz..,, InIn Mopeds,Mopeds,Scooters,Scooters, MotorMotor Cycles,Cycles, HandHand

SprayersSprayers EtcEtc..

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



ENGINE PERFORMANCE PARAMETERS

Sl. No.Sl. No. ParameterParameter NotationNotation

i.i. Indicated Thermal EfficiencyIndicated Thermal Efficiency ithith

iiii Brake Thermal EfficiencyBrake Thermal Efficiency bthbth

iiiiii Mechanical EfficiencyMechanical Efficiency mm

iviv Volumetric EfficiencyVolumetric Efficiency vv

vv Relative Efficiency/ Efficiency RatioRelative Efficiency/ Efficiency Ratio relrel

vivi Mean Effective PressureMean Effective Pressure ppmm

viivii Mean Piston SpeedMean Piston Speed sspp

viiiviii Specific Power Output Specific Power Output PPss

ixix Specific Fuel ConsumptionSpecific Fuel Consumption sfcsfc

xx Inlet Valve Mach IndexInlet Valve Mach Index ZZ

xixi FuelFuel--A ir or A irA ir or A ir--Fuel RatioFuel Ratio F/A or A/FF/A or A/F

xiixii Calorific value of the FuelCalorific value of the Fuel CV (HCV/CV (HCV/



Valve TimingValve Timing Low SpeedLow Speed High SpeedHigh Speed

I.V.OI.V.O 101000 Before. TDCBefore. TDC 101000 Before. TDCBefore. TDC

I.V.CI.V.C 101000 A fter. TDCA fter. TDC 606000 A fter. BDCA fter. BDC

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

E.V.CE.V.C 5500 A fter. TDCA fter. TDC 202000 A fter TDCA fter TDC



Port Timing Diagram of a Two Stroke Engine

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Lecture2+Basic+Components+and+Working+Principles