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Unit IBasics of IC EnginesandFuel-Air & Actual CyclesSyllabus Unit-I : BASICS OF IC ENGINES (5)Heat Engines, IC and EC engines, IC engines construction- components and materials, engine nomenclature, valve diagrams,intake and exhaust systems, engine classification, applications Standard Cycles & Fuel-Air Cycles (5)Fuel-air cycle, assumptions, comparison with air standard cycle, effect of variables on performance, actual engine cycle and various lossesLecture No 1Learning Objectives: To learn basics of heat engines, IC and EC engines, IC engines construction- components and materials, engine nomenclature, applications

I. C. EnginesEngine of a car

7Basics of IC Engines Heat Engines Internal Combustion (IC) Engines External Combustion (EC) Engines Engine Construction components and material Engine Nomenclature Applications*External combustion engine. *Internal combustion engine. -Ex: steam engine -Ex: car engineWhat is an engine?Types of engines:- a machine which converts chemical energy of fuel into mechanical energy

Type of Heat Enginestypes of heat enginesexternal combustioninternal combustionsteam enginesGas turbinesStirling engineOtto engineDiesel engineVankel engine10

Internal Combustion Engine11Gas turbine engines are, theoretically, extremely simple. They have three parts:

Compressor - Compresses the incoming air to high pressureCombustion area - Burns the fuel and produces high-pressure, high-velocity gasTurbine - Extracts the energy from the high-pressure, high-velocity gas flowing from the combustion chamber

INTERNAL COMBUSTION ENGINE (JA304)

CompressorCombustion area TurbineInternal Combustion Engines-ApplicationsThe internal combustion engine is an engine in which the combustion of fuel-oxidizer mixture occurs in a confined space

applied in: automotiverail transportationpower generationshipsaviationgarden appliances

How engine works?AirFuelMixingCombustionExhaustPowerUseful WorkCarburetorIgnition (Spark plug / Compressed ignition)ValvesPiston/connecting rodCrankshaftFlywheelClutchGear boxWheels15History of Internal Combustion Engine

History of IC engines:1700s -Steam engines (external combustion engines)

1860 -Lenoir engine (h = 5%)

1867 -Otto-Langen engine (h = 11%, 90 RPM max.)

1876 -Otto four stroke spark ignition engine (h = 14%, 160 RPM max.)

1880s - Two stroke engine

1892 -Diesel four stroke compression ignition engine

1957 -Wenkel rotary engine16Historical IC Engines

FLYWHEELClassification of IC EnginesBased on No of stroke per cycle: Four stroke Two strokeBased on thermodynamic cycle: Otto/Constant volume heat addition cycle Diesel/Constant pressure heat addition cycle Dual Cycle (Heat addition-At const Pressure and vol)Based on No of cylinders: Single cylinder Multi-cylindersClassification of IC EnginesBased on arrangement of cylinders: Inline engines V engines Radial engines Opposed cylinders engines Opposed pistons enginesBased on ignition systems: SI engines CI enginesBased on cooling system: Air cooled Liquid cooledClassification of IC EnginesBased on fuel used: Petrol engines Diesel engines Gas engines Bi-fuel enginesBased on fuel supply systems: Carburetor engines Solid injection enginesBased on lubrication system: Wet sump lubrication Dry sump lubrication Mist lubrication Engine ComponentsParts of an Engine

Engines Components & Materials1. Cylinder block & Crank case: To hold engine components, water jackets Cooling jackets, oil passages, passages for push rods, fitment for crank shaft, lubrication pump etc Grey CI, Al alloy2. Cylinder head: SP, injectors, valve openings, comb chamber, mounting for valve operating mechanism CI , Al alloy3. Oil pan: Oil sump Pressed steel sheet, Al alloyEngines Components & Materials1. Cylinder block/ Crank case: For holding major components like crankshaft, cylinder head, liners, gears, pumps etc. Cooling jackets, oil passages, passages for push rods etc Grey CI, Al alloy2.Cylinder head: For fitment of SP/ injectors, valve openings, comb chamber, valves & valve operating mechanism CI , Al alloy3. Oil pan: Oil sump Pressed steel sheet, Al alloyEngines Components & Materials4. Manifolds: Inlet & exhaust tubing for AF intake & exhaust CI5. Gaskets: For leak proof sealing between two components Embossed steel, cork, special rubber6. Cylinder liners (Replaceable): Pistons reciprocket in cylinders for comb space Steel alloyed with Si, Mn, Nickel, Chromium Centrifugally cast, hardened by nitriding, chromium plating Dry & Wet linersEngines Components & Materials7. Piston: For transmission of force, light weight, high thermal k, low thermal coeff of expansion Al alloy8. Piston rings: For high pr leak proof sealing between piston & cylinder, 2 to 4 + 1 to 2 oil scrapper rings Alloy CI with Si, Mn with chromium plating9. Connecting rod: For transmitting force on piston to crankshaft I-section, drop forged from steel Axial and bending stressesEngines Components & Materials10. Piston/Gudgeon Pin: For connecting piston with connecting rod Case hardened steel11. Crankshaft: For converting reciprocketing motion of piston to rotary motion of crankshaft by connecting rod, vibration damper and fly wheel fitted Main journal, crank pins, crank webs, counterweights Forged from spheroidal graphite iron12. Main & Big end bearings: For facilitating holding & friction free rotation of crankshaft Babbitt material- alloy steelEngines Components & Materials13. Engine Valves: Inlet for air/AF intake; Silicon-chrome steel (C+Ni +Mn+Si) Exhaust- for exiting burnt gases (C+Ni+Mn+Si+Mb)14. Camshaft: For operating valves (rotates at half speed of C/S) Forged alloy steel 15. Silencer/Mufler: For reducing exhaust/comb sound Metal sheet

Parts of an IC EngineCROSS SECTION OF OVERHEAD VALVE FOUR STROKE SI ENGINEName as manyparts as you can28

Parts of an IC EngineAir cleanerChokeThrottle Intake manifoldExhaust manifoldPiston ringsPistonWrist pinCylinder blockConnecting rodOil gallery to pistonOil gallery to headCrankcaseCrankpinCrankshaftCylinder headBreather capRocker armValve springValve guidePushrodSparkplugCombustion chamberTappetDipstickCamCamshaftWater jacketWet linerConnecting rod bearingMain bearingOil pan or sumpIf you scored:25 32- Excellent15 24- Good10 14- OK 1, hence for diesel cycle will always be lower than Otto for same CR With increase in CR, initially increases at faster rate Diesel engs operate at much higher CR as compared to petrol engs, hence for diesel eng is actually higher decreases as Cut off increasesDual Combustion or Limited Pressure CyclepV0123451-2 : Adiabatic Compression2-3 : Heat Addition at Const Volume3-4 : Heat Addition at Const Pressure4-5 : Adiabatic Expansion5-1 : Heat Rejection at Const Volume

Theoretical/ Air Std EfficienciesOtto Cycle:

Diesel Cycle:

Dual Cycle:

Lecture No 5Learning Objectives: Learning Air Standard Engine Cycles through Numerical ProblemsQ1: In an ideal Otto Cycle, the compression ratio is 8.Initial pressure and temp of air are 1 bar and 100C.Max pr in the cycle is 50 bar. For 1 kg of air flow, calculate the values of pr, vol and temp at four salient points of the cycle. What is the ratio of heat supplied to heat rejected? Take R=0.287 kJ/kg; =1.4 for air.Solution:Point 1: p1=1bar; T1=373K; V1=?

We know that p1V1=mRT1

Solution (contd):Point 2: (1-2 adiabatic compn)

Solution (contd):Point 3:(2-3 const vol process)

Solution (contd):Point 4:(3-4 Adiabatic process)

Solution (contd):

Q2. An engine working on Otto Cycle has a clearancevolume of 17% of the total volume. Initial conditions are 93 kPa & 30C. At the end of constant volume heating, pressure is 2747 kPa. Find(i) Air std efficiency(ii) Max temp (iii) Mean pressure (iv) Relative efficiencyif actual efficiency is 26.85%.Take Cv=0.716 kJ/kgK

Solution:

Now Vc=0.17V1=0.17(Vs+Vc)

Solution (Contd):

Max Temp T3=?

Solution (Contd):

WD= x QsWD=647.9x0.5076=328.88kJ/kgTo find out Stroke Vol (V1-V2) ; we have V1/V2=5.88V1 can be found out from p1V1=mRT1 taking m=1kg Hence V1=(1x0.287x303)/93=0.935m3/kgTherefore, V2=V1/5.88=0.935/5.88=0.159m3/kgSolution (Contd):

Lecture No 6Learning Objectives: Learning Air Standard Engine Cycles through Numerical ProblemsQ3. An air standard diesel cycle has a compression ratio of 14. Pressure at the beginning of compn strokeis 1 bar and temp 27C. Max temp in the cycle is 2500C. Determine the thermal efficiency and meanEffective pressure.Solution:

Qs=mCp(T3-T2)& QR=mCv(T4-T1)

Since T1 & T3 are given, T2 & T4are required to be found out ?Solution (Contd):

Solution (Contd):

Solution (Contd):

Q4. An oil engine works on the ideal diesel cycle. CR is 18 and constant pr energy addition ceases at 10% of stroke. Intake conditions are 1 bar and 20C.Determine (a) Max temp and pressure in the cycle(b) Thermal efficiency of the engineSolution:

Max pressure p3=p2 = ?Max Temp T3=?

r=V1/V2=18 (given)=V3/V2=?Let Clearance Volume V2=1Then, V1 will be 18Hence stroke vol=V1-V2=17Now, 10% of stroke vol=17x0.1=1.7Solution (Contd):

Therefore, =V3/V2=2.7/1=2.7Hence, V3=1+1.7=2.7

Solution (Contd):

Importance ofBeing PunctualLecture No 7Learning Objectives: Theoretical Fuel-Air CyclesTheoretical Fuel-Air Cycles Cycles, which take in to account the variations of specific heats, effects of molecular structure, effects of composition of mixture of fuel, air & residual gases approximating to working substance, are called Fuel-Air CyclesFuel-air cycles largely take the following in to consideration:Actual composition of cylinder gases i,e. fuel, air, water vapor and residual gases Variation (increase) of specific heats with temp Specific heats vary (increase) with increase in temp (hence = Cp/Cv with T) Cp = a + bT + cT2 + dT3 Cv = a1 + bT + cT2 + dT3; a1 > a Theoretical Fuel-Air Cycle After combustion process, mixture is in chemical equilibrium (No dissociation ) Intake and exhaust processes take place at atmospheric pressure Compression & expansion processes are adiabatic without friction In case of Otto Cycle, mixture of air & fuel is homogenous and it burns at constant volume Change in KE is negligible No heat exchange between gases and cylinder walls Mixture of fuel & air (A/F ratio)Theoretical Fuel-Air Cycle1. Effect of Composition of Fuel and Air (A/F Ratio):

Leaner mixture has higher thermal efficiency Richer mixture will have lower efficiency as unburnt fuel will go to exhaust Efficiency increases with CR

Vp12342344Actual Cycle 1-2-3-42. Effect of Variation Specific Heats :Ideal Otto Cycle 1-2-3-4Theoretical Fuel-Air Cycle2. Effect of Variation Specific Heats : Cp=a+bT+cT2 & Cv=a1+bT+cT2 During adiabatic compn process 1-2, as the temp increases, Cp & Cv increase and decreases

During process 2-3, for a given heat supplied Qs, temp T3 will lower down to T3 as per the expression Qs=mCv(T3-T2)QsTheoretical Fuel-Air Cycle2. Effect of Variation Specific Heats (Contd) : And, therefore, process 3-4 will now become 3-4 But process 3-4 represents process with const . Since eng is in expansion stroke, the temp of gases decreases, Cp & Cv decrease and hence increases

Hence, actual process becomes 3-4 from 3-4 Therefore, actual cycle becomes 1-2-3-4 although ideal Otto Cycle was 1-2-3-4Theoretical Fuel-Air Cycle3. Effect of Molecular Structure : Pressure of gases in comb chamber is proportional to number of moles for given temp and volume by the relation pV=nRT; where n is the no of moles If the no of moles before and after combustion are different, pressure will change accordingly Take example of combustion : C + O2 = CO2 1 mole 1 mole 1 mole2H2 + O2 = 2H2O2 moles 1 mole 2 moles MolecularContractionC8H18 + 12.5O2 = 8CO2 + 9H2O1 mole 12.5 moles 8 moles 9 molesMolecularExpansionTheoretical Fuel-Air Cycle From the foregoing, it is clear that no of moles may be more or less after the combustion This phenomenon is called molecular contraction or molecular expansion Therefore, actual pressure in combustion chamber will be different compared to theoretical cycle Actual pressure in combustion chamber shall be more in case of molecular expansion and lesser in case of molecular contraction compared to theoretical cycle Theoretical Fuel-Air Cycle4. Dissociation Losses: Products of combustion dissociate in to its constituents at higher temp beyond 1000C Rate of dissociation increases with increase in temp Dissociation process absorbs heat energy from comb gases being chemically endothermic reaction and association releases energy being exothermic reaction 2CO2=2CO+O2 : (Dissociation) Endothermic Reaction2CO+O2=2CO2 : (Association) Exothermic Reaction118Theoretical Fuel-Air Cycle This results in lowering of temp and hence pressure which in turn reduces power output and thermal efficiency However, at the end of expansion stroke, temperatures become low and dissociated gases start combining releasing heat energy. But, it is too late as most of this heat energy is carried away by exhaust gases. This loss of power is called dissociation loss Dissociation losses have been shown in Fig

Comparison of Fuel-Air Cycles with Air Standard Cycle Air std cycle has highly simplified approximations Therefore, estimate of engine performance is much higher than the actual performance For example, actual indicated thermal efficiency of a petrol engine for CR 7, is around 30% whereas air std efficiency is around 55%. This large difference is due to non-instantaneous burning of charge, incomplete combustion and largely over simplifications in using values of properties of working fluid for analysis In air std cycle, it was assumed that working fluid was air, which behaves like perfect gas and had constant specific heats In actual engine , working fluid is not air but a mixture of air, fuel and residual gases Also, specific heats of working fluid are not constant but increase as the temp rises And, products of combustion are subjected to dissociation at high temperatures Engine operation is not frictionlessComparison of Fuel-Air Cycles with Air Standard CycleLecture No 8Learning Objectives: To learn fuel-air cycle through numerical problemsNumerical ProblemsOnFuel-Air CyclesQ1. A petrol engine having CR of 6 uses a fuel with CV=42000kJ/kg. A/F ratio is 15:1. Pressure and temp at the end of suction stroke are 1 bar and 57C respectively. Determine max pressure in the cylinder if n=1.3 and Cv=0.678 + 0.00013 T, where T is in K. Compare this value with that obtained when Cv=0.71 kJ/kgK. (Ans: T2=564.8K; T3=3380K; p3=61.45bar/77.5bar)

SolutionLine of approach:Max pr p3=?For process 2-3 (2-3)

Q2. Combustion in a diesel engine is assumed to beginat inner dead centre and to be at constant pressure. A/F ratio is 287:1, CV of fuel is 42000kJ/kg and sp. heatof products of combustion is given as Cv=0.71+20x10-5 T; R for combustion products =0.287kJ/kgK. If the CR is14:1 and the temp at the end of compression is 800 K, find at what percentage of stroke, the combustion is completed? (Ans: T3=1940K; 10.96%)Lecture No 9Learning Objectives: To learn fuel-air cycle through numerical problemsQ3. A diesel engine uses a compression ratio of 16 and at the end of compression stroke, the temp of air is 1100K. Now the air is supplied heat at const pr by burning fuel of CV of 44200kJ/kg and the fuel air ratiois 0.04:1. Specific heat at constant volume is given as Cv=0.762+2x10-4 T; where T is in K. Find out cut off percentage/ratio of the engine. R for combustion products =0.287kJ/kgK. (Ans 2.11/7.4%)Q4. The following data relate to a petrol engine:CR=7; CV of fuel used=44MJ/kg; A/F ratio=15:1 Temperature and pressure of charge at the end ofstroke = 65C, 1 bar, Index of compression = 1.33Sp. heat at const volume Cv = 0.71+ 20x10-5 T kJ/kg K, where T is in Kelvin. Determine maximum pressure in the cylinder. Compare this value with that of constant specific heat Cv = 0.71 kJ/kg K [Ans. p3=65.5 bar; p3 (with const Cv )=93.5 bar] Lecture No 10Learning Objectives: To learn actual fuel-air cycleActual/Real Fuel-Air CyclesActual cycle efficiency is much lower than the air std efficiency due to various losses occurring in actualengine operation. These are:1. Losses due to variation of specific heats with temp2. Dissociation or chemical in-equilibrium losses3. Time losses4. Incomplete combustion losses5. Direct heat losses from comb gases to surroundings6. Exhaust blow-down losses7. Pumping losses8. Friction lossesActual/Real Fuel-Air Cycle Working substance is mixture of fuel, air & residual gases (not air or perfect gases) Specific heats vary (increase) with temp (hence = Cp/Cv with T) Cp = a + bT + cT2 + dT3 Cv = a1 + bT + cT2 + dT3; a1 > a Effect of molecular structure due to comb of fuel. (Beyond 1000C, products of comb dissociate & absorb heat energy, thus lowering comb temp and hence the power) Comb is not instantaneous (at const volume) as piston continuously keeps moving resulting in time losses Heat addition is not from reservoir but due to comb of fuel, which alters composition of working fluidActual/Real Fuel-Air Cycle Compression & Expansion processes are polytropic due to direct heat transfer to surroundings Opening and closing of valves are not instantaneous. All 4 strokes do not take place in 180 crank rotation. Early opening of exhaust valve causes blow down losses Suction stroke takes place below atmospheric pressure and exhaust stroke above atm pressure (Pumping losses) Thus, work developed in actual cycle is much less than the theoretical cycle Friction losses also take placeLosses In Actual Cycle Other Than Fuel-Air Cycle1. Time Losses: Work developed in actual cycle is much less than theoretical cycle as shown in Fig (Area enclosed by Blue Curve) Due to this time lag, actual max pr in comb chamber lowers down to point x. In ideal cycles, heat addition is assumed at constant volume but actually, combustion takes some finite time while piston continues to move (30-40rotation of crank shaft) Loss of work represents time losses

Losses In Actual Cycle Other Than Fuel-Air Cycle2. Heat Losses: Due to this, lot of work is lost There is considerable quantity of heat loss during combustion and expansion processes Ideal Compression and Expansion processes are assumed to be adiabatic but in actual processes, heat transfer does take place from working fluid to cylinder walls These work losses are called Heat LossesLosses In Actual Cycle Other Than Fuel-Air Cycle3. Exhaust Blow-down Losses: But due to this, lot of heat energy is carried away by exhaust gases resulting in to loss of work In ideal cycle, exhaust valve is assumed to open at BDC, when exhaust stroke starts but in actual cycle, it opens 30 to 40 before BDC in power stroke itself This helps in reducing pressure in the cylinder during exhaust stroke, so that work required to push out exhaust gases, reduces This work losses are called Exhaust Blow-down LossesLosses In Actual Cycle Other Than Fuel-Air Cycle4. Pumping Losses: In ideal cycle, suction and exhaust processes are assumed to be taking place at atmospheric pressure But in actual cycle, suction is carried out below and exhaust above atm pressures and for these operations, work is required to be done on gases which comes from actual work developed, thus reducing over all power output These work losses are called Pumping losses (shown in pink in Fig)

Losses In Actual Cycle Other Than Fuel-Air Cycle5. Friction Losses: All this comes from power developed by the engine, thus reducing actual power out put In ideal cycle, engine operation is considered frictionless but in actual it is not so. Friction losses do occur between sliding or rotating components like piston rings and cylinder walls, bearings etc and it increases rapidly with speed of the engine. Also, power is required to run various auxiliary equipment like fans, pumps etc These power losses are called Friction LossesReal/Actual Otto Cycle

Latest DevelopmentsRecent Trends in Engine Development Compact Size Fuel Economy (VCR, VVT, MPFI, Stratified Charge, HCCI) More Power Reduced Emissions/ Hybrid/ Electric vehicles Cheaper Fuel Low Cetane / Octane No Lighter engines/ better materials for eng components DI combustion chambers; IDI being phased out Two stage boosting Increase in specific power output-90kW/LitreEnd of Unit I