Ic engines
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    Ic engines Ic engines Presentation Transcript

    • INTERNAL COMBUSTION ENGINESINTERNAL COMBUSTION ENGINESMihir SenUniversity of Notre DameNovember 11, 20091/ 55
    • INTERNAL COMBUSTION ENGINESOutline1 Outline2 Basics3 Classification4 Terminology5 Components6 Operation7 Thermodynamics8 Parameters9 Output2/ 55
    • INTERNAL COMBUSTION ENGINESBasicsHistoricalLenoir, 1860: first autoOtto and Langen, 1867: efficiency about 11%Diesel, by 1892: compression ignition engine3/ 55
    • INTERNAL COMBUSTION ENGINESBasicsCombustion enginesChemical energy in fuel converted to thermal energy bycombustion or oxidationHeat engine converts chemical energy into mechanicalenergyThermal energy raises temperature and pressure of gaseswithin engine, and gas expands against mechanicalmechanisms of engineCombustionInternal: fuel is burned within the engine proper (includinge.g. rocket engines, jet Engines, firearms)External: combustion is external to the engine (e.g. steam,Stirling engine, gas turbine)4/ 55
    • INTERNAL COMBUSTION ENGINESClassificationClassification of IC enginesIgnitionNumber of strokesValve locationDesignPosition and number of cylindersAir intakeFuel input methodFuel usedCoolingApplication5/ 55
    • INTERNAL COMBUSTION ENGINESClassificationIgnitionSpark ignition (SI): high-voltage electrical dischargebetween two electrodes ignites air-fuel mixture incombustion chamber surrounding spark plugCompression ignition (CI): air-fuel mixture self-ignites dueto high temperature in combustion chamber caused by highcompression, Diesel engine6/ 55
    • INTERNAL COMBUSTION ENGINESClassificationNumber of strokesFour-stroke: four piston movements over two enginerevolutions for each engine cycleTwo-stroke: two piston movements over one revolution foreach engine cycle7/ 55
    • INTERNAL COMBUSTION ENGINESClassificationValve locationValves in headValves in blockOne valve in head and one in block (less common)8/ 55
    • INTERNAL COMBUSTION ENGINESClassificationDesignReciprocatingRotary9/ 55
    • INTERNAL COMBUSTION ENGINESClassificationReciprocating enginesEngine has one or more cylinders in whichpistons reciprocate back and forthCombustion chamber in closed end ofcylindersPower delivered to rotating outputcrankshaft by mechanical linkage withpistons10/ 55
    • INTERNAL COMBUSTION ENGINESClassificationRotary enginesEngine made of block (stator) built around largenon-concentric rotor and crankshaftCombustion chambers are built into the nonrotating blockhttp://www.youtube.com/watch?v=oGrD7FTFLJc11/ 55
    • INTERNAL COMBUSTION ENGINESClassificationPosition and number of cylindersSingle cylinder (e.g. lawnmowers)In-line or straight: cylinders in straight line, one behindthe other in length of crankshaftV: two banks of cylinders at an angle with each other alonga single crankshaft, angle typically 60-90◦Flat or opposed cylinder (V with 180◦): two banks ofcylinders opposite each other on a single crankshaft (smallaircrafts)W: three banks of cylinders on same crankshaft (notcommon)Opposed piston engine: two pistons in each cylinder,combustion chamber between pistonsRadial engine: cylinders positioned radially aroundcrankshaft12/ 55
    • INTERNAL COMBUSTION ENGINESClassificationIn-line V FlatRadialhttp://en.wikipedia.org/wiki/Radial_engine13/ 55
    • INTERNAL COMBUSTION ENGINESClassificationAir intakeNaturally aspirated: no air pressure boostSupercharged: air pressure increased with compressordriven by crankshaftTurbocharged: air pressure increased byturbine-compressor driven by exhaust gasesCrankcase compressed: two-stroke engine with crankcase asintake air compressor14/ 55
    • INTERNAL COMBUSTION ENGINESClassificationSuperchargerSupercharger on AMC V8 engine for dragstrip racing15/ 55
    • INTERNAL COMBUSTION ENGINESClassificationTurbocharger16/ 55
    • INTERNAL COMBUSTION ENGINESClassificationFuel input methodCarbureted: air-fuel mixed atthroat17/ 55
    • INTERNAL COMBUSTION ENGINESClassificationFuel input methodFuel injectionMultipoint port fuel injection: one or moreinjectors at each cylinder intakeThrottle body fuel injection: injectorsupstream of intake manifold18/ 55
    • INTERNAL COMBUSTION ENGINESClassificationFuel usedGasolineDiesel or fuel oilGas (natural gas or methane)Liquefied petroleum gas (LPG): mainly propane,propylene, butane, and butyleneAlcohol (ethyl, methyl)Dual fuel (e.g. methane/diesel)Gasohol (e.g. 90% gasoline, 10% alcohol)Biodiesel: cleaner-burning diesel fuel made from natural,renewable sources such as vegetable oils19/ 55
    • INTERNAL COMBUSTION ENGINESClassificationCoolingAir cooledWater cooledhttp://www.innerauto.com/Automotive_Animations/Cooling_Syst20/ 55
    • INTERNAL COMBUSTION ENGINESTerminologyTerminology ITDC: top dead center, piston position farthest fromcrankshaftBDC: bottom dead center, piston position nearest tocrankshaftDirect fuel injection: into main combustion chamberIndirect fuel injection: into a secondary chamberBore: diameter of cylinder or piston faceStroke: distance that piston movesClearance volume: volume in combustion chamber at TDCDisplacement volume: volume displaced by pistonIgnition delay: Time between start of ignition and start ofcombustion21/ 55
    • INTERNAL COMBUSTION ENGINESTerminologyTerminology IIAir-fuel ratio: Ratio of mass flow rate of air to that of fuelSpecific fuel consumption: fuel used per unit powerEmissions: NOx, CO, HC, solids22/ 55
    • INTERNAL COMBUSTION ENGINESComponentsEngine components23/ 55
    • INTERNAL COMBUSTION ENGINESComponentsBlock: body of engine containing cylindersBearing: main bearing for crankshaftCamshaft: rotating shaft used to push open valves at theproper time in engine cycleCarburetor: Venturi flow device to draw fuel and mix withairCatalytic converter: reduces emissions by chemical reactionCombustion chamber: volume between cylinder head andpiston faceConnecting rod: connects piston with crankshaftCrankcase: part of engine block surrounding crankshaftCrankshaft: rotating shaft through which engine workoutput is supplied to external systems, rotated byreciprocating pistons through connecting rods24/ 55
    • INTERNAL COMBUSTION ENGINESComponentsExhaust manifold: piping which carries exhaust gases awayfrom engine cylindersFan: to increase air flow through radiatorFlywheel: to smoothen engine rotationFuel injector: pressurized nozzle to inject fuel into air orcylinderFuel pump: to move fuel from tank to engineGlow plug: electrical resistance inside combustion chamberto help cold startHead: piece which closes end of cylindersHead gasket: sealant between engine block and headIntake manifold: piping which delivers incoming air tocylindersOil pan: oil reservoir on bottom of engine block, part of thecrankcase25/ 55
    • INTERNAL COMBUSTION ENGINESComponentsOil pump: to distribute oil from sumpOil sump: reservoir for the oil system of the enginePiston rings: metal rings around piston to seal gap betweenpiston and cylinderPush rods: linkage between camshaft and valves on OHVenginesRadiator: liquid to air heat exchanger to cool engineRod bearing: rod connecting the piston with the rotatingcrankshaftSpark plug: creates high-voltage discharge across anelectrode gapSpeed control-cruise control: control systemStarter: hand starter, electric motor, or small IC enginesfor large IC engines26/ 55
    • INTERNAL COMBUSTION ENGINESComponentsSupercharger: compressor powered from crankshaft tocompress incoming airThrottle: butterfly valve at upstream end of intakemaniford to control air flow rate into SI engineTurbocharger: turbine-compressor powered by exhaust flowto compress incoming airvalves; controls flow of air in and out of the cylindersWater jacket: liquid flow passages around cylinder forcoolingWater pump: to circulate coolant27/ 55
    • INTERNAL COMBUSTION ENGINESOperation4-stroke SI engine operationhttp://en.wikipedia.org/wiki/Four-stroke_enginehttp://www.youtube.com/watch?v=L-kYu0k5lF428/ 55
    • INTERNAL COMBUSTION ENGINESOperation4-stroke SI engine operationFirst stroke: intake or inductionPiston travels from TDC (top dead center) to BDC(bottom dead center) with intake valve open and exhaustvalve closedVolume increases in combustion chamber and createsvacuumAir pushed through cylinderAs air passes through intake system, fuel is added29/ 55
    • INTERNAL COMBUSTION ENGINESOperationSecond stroke: compressionPiston reaches BDC, intake valve closes and piston travelsback to TDC with all valves closedAir-fuel mixture compresses and temperature and pressureincreaseNear end of compression stroke, spark plug fired andcombustion initiated30/ 55
    • INTERNAL COMBUSTION ENGINESOperationCombustionPiston near TDC: nearly constant-volume combustionChanges composition of gas mixture to exhaust productsand temperature and pressure increases31/ 55
    • INTERNAL COMBUSTION ENGINESOperationThird stroke: expansionAll valves closedHigh pressure pushes piston away from TDC: produceswork output of engine cyclePiston moves from TDC to BDC: volume increases andpressure and temperature drop32/ 55
    • INTERNAL COMBUSTION ENGINESOperationExhaust blowdownLate in power cycle exhaust valve is openedpressure differential pushes hot exhaust gas out of cylinderand through exhaust system when piston is at BDCExhaust gas carries away high amount of enthalpy, whichlowers cycle thermal efficiency33/ 55
    • INTERNAL COMBUSTION ENGINESOperationFourth stroke: exhaustWhen piston is at BDC cylinder is still full of exhaustgases at atmospheric pressureExhaust valve stays open and piston moves from BDCto TDC pushing out most of the remaining exhaustgases into the exhaust systemNear end of exhaust stroke before TDC, intake valvestarts to open and is fully open by TDC when intakestroke starts next cycleNear TDC the exhaust valve starts to close and isfully closed sometime after TDCPeriod where both intake valve and exhaust valve areopen is called valve overlap34/ 55
    • INTERNAL COMBUSTION ENGINESOperationFour-stroke SI operating cycle35/ 55
    • INTERNAL COMBUSTION ENGINESOperation4-stroke CI engine operationFirst stroke: intakeSecond stroke: compressionCombustionThird stroke: powerExhaust blowdownFourth stroke: exhaust36/ 55
    • INTERNAL COMBUSTION ENGINESOperation2-stroke SI engine operationCombustion: occurs quickly with piston at TDCFirst stroke: expansion powerExhaust blowdownIntake and scavenging: simultaneous intake and exhausthttp://www.youtube.com/watch?v=LuCUmQ9FxMUhttp://en.wikipedia.org/wiki/Two-stroke_engine37/ 55
    • INTERNAL COMBUSTION ENGINESOperation2-stroke CI engine operationDifferences with respect to 2-stroke SINo fuel added to incoming air; only air is compressedFuel injector located in cylinder38/ 55
    • INTERNAL COMBUSTION ENGINESThermodynamicsOtto cycle39/ 55
    • INTERNAL COMBUSTION ENGINESThermodynamicsPiston is essentially stationary during combustion: constantvolume40/ 55
    • INTERNAL COMBUSTION ENGINESThermodynamicsDiesel engineUses heat of compression to initiate ignition and burn fuelFuel injected into the combustion chamber during finalstage of compression41/ 55
    • INTERNAL COMBUSTION ENGINESThermodynamicsCombustion occurs at a constant pressure, as the piston moves42/ 55
    • INTERNAL COMBUSTION ENGINESThermodynamicsVariationsDual cycle: cross between SI and CIAtkinson cycleMiller cycleHomogeneous charge compression ignition: well-mixed fueland air are compressed to auto-ignition. Ignition occurs atseveral places simultaneously.Homogeneous charge spark ignition gasoline enginesStratified charge compression ignition diesel engine43/ 55
    • INTERNAL COMBUSTION ENGINESParametersEngine parametersTDCBDCVcVdBSs raθStrokeS = 2aAverage piston speedUp = 2SNN = engine speedDisplacement for one cylinderVd =π4B2S44/ 55
    • INTERNAL COMBUSTION ENGINESParametersDistance between crank axis and wrist pin axiss = a cos θ + r2 − a2 sin2θDifferentiating and dividing by UpUpUp=π2sin θ 1 +a cos θr2 − a2 sin2θ45/ 55
    • INTERNAL COMBUSTION ENGINESParametersClearance volume, VcVc = VTDCVBDC = Vc + VdCompression ratiorc =VBDCVTDC=Vc + VdVcHigh compression ratio allows engine to extract moremechanical energy from a given mass of air-fuel mixture due toits higher thermal efficiency46/ 55
    • INTERNAL COMBUSTION ENGINESParametersCylinder volumeV = Vc +πB24(r − a − s)Cross-sectional area of cylinder and the surface area of aflat-topped piston are given byAp =π4B2Combustion chamber surface areaA = Ach + Ap + πB r + a − sAch is the cylinder head surface area47/ 55
    • INTERNAL COMBUSTION ENGINESOutputWorkWork is the output of any heat engineIt is generated by the gases in the combustion chamber ofthe cylinderForce due to gas pressure on the moving piston generatesworkW = F dx = pAp dxAp dx = dVW = p dVP = pressure in combustion chamberAp = area against which the pressure acts (piston face)x = distance the piston moves48/ 55
    • INTERNAL COMBUSTION ENGINESOutputIndicator diagrampVABIETDC BDC4-stroke SII = ignition, E = exhaust opens49/ 55
    • INTERNAL COMBUSTION ENGINESOutputSpecific work w: per unit mass of air within cylinderBrake work: actual work available in the crankshaftwb = wi − wfwi = indicated specific work generated inside combustionchamberwf = specific work lost due to friction and parasitic loadsMechanical efficiencyηm =wbwiModern automobile engines at high speeds ηm = 75% to 95%50/ 55
    • INTERNAL COMBUSTION ENGINESOutputEngine parametersMean effective pressure (MEP)MEP =wvdSpecific displacementvd = vBDC − vTDCUsing brake workBMEP =wbvdUsing indicated workIMEP =wbvd51/ 55
    • INTERNAL COMBUSTION ENGINESOutputTorqueFor one revolution2πT = Wb=BMEP Vdnso thatT =BMEP Vd2π2-strokeBMEP Vd4π4-stroke52/ 55
    • INTERNAL COMBUSTION ENGINESOutputPowerPower is the rate of work of the engineP = 2πNT=12nMEPApUp=MEPApUp/2 2-strokeMEPApUp/4 4-stroken = number of revolutions per cycle, and N = engine speed53/ 55
    • INTERNAL COMBUSTION ENGINESOutputEffect of engine speedPTn4-stroke SI54/ 55
    • INTERNAL COMBUSTION ENGINESOutputTypical valuesModel Automobile Largeairplane stationary2-stroke 4-stroke 2-strokeBore (cm) 2.00 9.42 50.0Stroke (cm) 2.04 9.89 161Displacement/cyl (L) 0.0066 0.69 316Speed (rpm) 13,000 5,200 125Power (kW) 0.72 35 311Average piston speed (m/s) 8.84 17.1 6.71Power/displacement (kW/L) 109 50.7 0.98BMEP (kPa) 503 1170 47255/ 55