Advanced Ic engines unit 1
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Framed as per the anna university syllabus

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Advanced Ic engines unit 1 Advanced Ic engines unit 1 Presentation Transcript

  • ME2041 Advanced Internal Combustion EnginesDepartment of Mechanical Engineering, St. Joseph’s College of EngineeringUnit ISyllabus:• Air-fuel ratio requirements ,• Design of carburettor –fuel jet size and venture size,• Stages of combustion-normal and abnormalcombustion,• Factors affecting knock,• Combustion chambers,• Introduction to thermodynamic analysis of SI Enginecombustion process.Unit I SPARK IGNITION ENGINES
  • ME2041 Advanced Internal Combustion EnginesUnit IISyllabus:• Stages of combustion-normal and abnormalcombustion• Factors affecting knock,• Direct and Indirect injection systems,• Combustion chambers,• Turbo charging ,• Introduction to Thermodynamic Analysis of CI EngineCombustion process.Unit II COMPRESSION IGNITION ENGINESDepartment of Mechanical Engineering, St. Joseph’s College of Engineering
  • ME2041 Advanced Internal Combustion EnginesUnit IIISyllabus:• Formation of NOX , HC/CO mechanism , Smoke andParticulate emissions,• Green House Effect ,• Methods of controlling emissions ,• Three way catalytic converter and Particulate Trap,• Emission (HC,CO, NO and NOX , ) measuringequipments, Smoke and Particulate measurement,• Indian Driving Cycles and emission normsUnit III ENGINE EXHAUST EMISSION CONTROLDepartment of Mechanical Engineering, St. Joseph’s College of Engineering
  • ME2041 Advanced Internal Combustion EnginesUnit IVSyllabus:• Alcohols , Vegetable oils and bio-diesel, Bio-gas,Natural Gas , Liquefied Petroleum Gas ,Hydrogen ,• Properties , Suitability, Engine Modifications,Performance ,• Combustion and Emission Characteristics of SI and CIEngines using these alternate fuels.Unit IV ALTERNATE FUELSDepartment of Mechanical Engineering, St. Joseph’s College of Engineering
  • ME2041 Advanced Internal Combustion EnginesUnit VSyllabus:• Homogeneous Charge Compression Ignition Engine,Lean Burn Engine, Stratified Charge Engine, SurfaceIgnition Engine , Four Valve and Overhead camEngines,• Electronic Engine Management, Common Rail DirectInjection Diesel Engine, Gasoline Direct InjectionEngine ,• Data Acquisition System –pressure pick up, chargeamplifier PC for Combustion and Heat releaseUnit V RECENT TRENDSDepartment of Mechanical Engineering, St. Joseph’s College of Engineering
  • ME2041 Advanced Internal Combustion EnginesUnit I• CarburetionThe process of formation of combustible air-fuel mixture,by mixing correct amount of fuel and air in a device calledcarburetor, before it enters the engine cylinder.• Factors Affecting Carburetion1. Carburetor Designhas influence on distribution of air-fuel mixture to cylinders.2. Ambient Air conditionAmbient pressure and temperature influence the efficiency ofcarburetion. Higher ambient temperature increases thevaporization rate of fuel forming a homogeneous mixture.3. Fuel CharacteristicsEvaporation characteristics (indicated by distillation curve) is criticalfor carburetion; presence of volatile HC also is important for quickevaporationDepartment of Mechanical Engineering, St. Joseph’s College of Engineering
  • ME2041 Advanced Internal Combustion EnginesUnit I4. Engine Speed and Load• At higher engine speed, the carburetion time is less causing strain oncarburetor to deliver uniform mixture in a short time; thus provision ofventuri has to be such that the carburetion is done efficiently at higherpressure drops• Higher loads will demand richer mixture and lower load leaner mixtures.• Types of Air-Fuel Mixtures1. Chemically Correct MixtureStoichiometric or balanced chemical mixture in which air isprovided to completely burn the fuel; the excess air factor is unity2. Rich MixtureFuel is in excess of what is required to burn the fuel completely.The excess air factor is less than unity.3. Lean MixtureAir is in excess of what is required to burn the fuel completely. Theexcess air factor is greater than unity.Department of Mechanical Engineering, St. Joseph’s College of Engineering
  • ME2041 Advanced Internal Combustion EnginesUnit I• Range of Air-Fuel Ratio in SI Engines9:1 (rich) to 19:1(lean) ; The stoichiometric value forgasoline is 14:1, The SI engine will not run for too rich ortoo lean mixtures.• Mixture Requirements at Different EngineConditionsDepartment of Mechanical Engineering, St. Joseph’s College of EngineeringThe air fuel ratio affects the power output and brakespecific fuel consumption of the engine as shown in theFigure1.PowerOutput(kW)BSFC(kg/kWh)PowerBSFCA/F ratio
  • ME2041 Advanced Internal Combustion EnginesUnit I• Mixture Requirements at Different Engine Conditions(Contd.)Department of Mechanical Engineering, St. Joseph’s College of Engineering• The mixture corresponding to maximum output on thecurve is called best power A/F mixture, which is richerthan the stoichiometric mixture.• The mixture corresponding to maximum BSFC on thecurve is called best economy mixture, which is leanerthan the stoichiometric mixture.• The actual A/F ratio requirement for an automativecarburetor falls in 3 ranges: Idling (rich) Cruising (lean) High Power (rich)
  • ME2041 Advanced Internal Combustion EnginesUnit I• Mixture Requirements at Different Engine Conditions(Contd.)Department of Mechanical Engineering, St. Joseph’s College of EngineeringIdlingA/FRatioThrottleOpening12340 50%100%CruisingPowerFigure 2. A/F Ratio Vs Throttle opening
  • ME2041 Advanced Internal Combustion EnginesUnit I• Mixture Requirements at Different Engine Conditions(Contd.)Department of Mechanical Engineering, St. Joseph’s College of EngineeringIdling Range (1-2)• During idling, engine operates at no load and closed throttle.• The engine requires rich mixture for starting at idling.• Rich mixture is required to compensate for the charge dilution due toexhaust gases from the combustion chamber.• Also, the amount of fresh charge admitted is less due to smaller throttleopening.• Exhaust gas dilution prevents efficient combustion by reducing the contactbetween the fuel and air particles.• Rich mixture improves the contact of fuel and air by providing efficientcombustion at idling conditions.• As the throttle is opened further, the exhaust gas dilution reduces and themixture requirement shifts to the leaner side.
  • ME2041 Advanced Internal Combustion EnginesUnit I• Mixture Requirements at Different Engine Conditions(Contd.)Department of Mechanical Engineering, St. Joseph’s College of EngineeringCruising Range (2-3)• Focus is on fuel economy.• No exhaust gas dilution.• Carburetor has to give best economy mixture i.e.. Lean mixture.High Power Range (3-4)• As high power is required, additional fuel has to be supplied to achieverich mixture in this range.• Rich mixture also prevents overheating by reducing the flame temperatureand cylinder temperature.
  • ME2041 Advanced Internal Combustion EnginesUnit I• Principle of Operation of Simple CarburettorDepartment of Mechanical Engineering, St. Joseph’s College of Engineering
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Principle of Operation of Simple Carburettor• The carburettor works on Bernoullis principle: the faster air moves, thelower its static pressure, and the higher its dynamic pressure.• The throttle (accelerator) linkage does not directly control the flow of liquidfuel. Instead, it actuates carburettor mechanisms which meter the flow ofair being pulled into the engine. The speed of this flow, and therefore itspressure, determines the amount of fuel drawn into the airstream.• A simple carburetor consists of a float chamber, fuel discharge nozzle, ametering orifice, a venturi a throttle valve and choke.• The float and needle valve maintain the fuel level• Fuel strainer is used to trap debris from the fuel and prevent choking ofthe fuel nozzle. It is removed periodically for cleaning.• During suction stroke air is drawn through the venturi.• Venturi accelerates the air causing a pressure drop.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Principle of Operation of Simple Carburettor• This pressure drop provides vacuum necessary to meter the air-fuelmixture to the engine manifold.• Fuel is fed to the fuel discharge jet, the tip of which is located at the throatof the venturi• Pressure drop is proportional to the throttle opening or load on the engine.• Throttle valve achieves governing of SI engine by varying the A/F ratio. Itis a butterfly valve located after the venturi tube. When the load is less, thethrottle is in near closed position and if the load is high throttle is fullyopened.• The choke valve is located between the entrance and venturi throat. It isalso of butterfly type. When choke is partly closed, a large pressure dropoccurs at the venturi throat, which provides a rich mixture by induction oflarge amount of fuel as required during idling or high load conditions.Choke valves are spring loaded to prevent excessive choking and aresometimes automatically controlled by thermostat.• For providing rich mixture during idling, an idling adjustment is provided. Ithas an idling passage and idling port.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Principle of Operation of Simple Carburettor• The system operates at starting and shuts off when 20% throttle openingis reached.• Normal venturi depression is not sufficient to provide rich mixture due tolower throttle opening. But this low pressure causes fuel rice in idlingpassage and it is discharged through idling port downstream of the throttlevalve.• The idling air bleed sucks some air for mixing with the idling fuel andvaporizes the mixture. The additional fuel-air supply makes the mixturerich for idling.• Simple carburettor has the drawback of providing rich mixture withincreasing throttle opening.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Compensating systems in Carburettors• For part load conditions, the carburettor must supply economic air-fuelratio mixture. The main metering system will not satisfy this requirement.The following compensating systems are used to achieve this:• Air Bleed Jet• Compensating Jet• Emulsion Tube• Back Suction Control Mechanism• Auxiliary Air Valve• Auxiliary Air Port• Altitude Compensating Device
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Compensating systems in CarburettorsAir Bleed Jet• It contains an air bleed to the mainnozzle.• Air flow through the bleed passage isrestricted by orifice.• When engine is not operating the bleedpassage is filled with fuel.• When the engine starts the fuel from thebleed passage is displaced by air flowfrom the orifice.• The air and fuel form an emulsion at thetip of the bleed passage.• This causes faster delivery of fuel due tolow viscosity and fuel discharged rises.• Thus uniform mixture ratio is supplied.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Compensating systems in CarburettorsCompensating Jet• The purpose of this is to make themixture leaner as the throttle opensprogressively.• An additional jet called compensating jetis provided with the main jet.• This jet is also connected to the fuel welland the fuel is metered throughcompensating orifice.• As the throttle opening increases themain jet makes the mixture richer byadding more fuel.• The compensating jet makes themixture leaner proportionately. The totalmixture will make A/F ratio constant.• When the main jet is lean,compensating jet is rich.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Compensating systems in CarburettorsEmulsion Tube• It is also known as submerged jetdevice.• Here, the main metering jet is kept at alevel 25 mm below the fuel level in floatchamber.• The jet is called submerged jet. The jetis placed in a well that has holesexposed to atmosphere.• When the throttle opening increases, theholes in the well are uncovered causingadditional fuel and air to enter the air-fuel stream, causing the faster A/Fmixture delivery during part loadoperation.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Compensating systems in CarburettorsBack Suction Control Mechanism• In this device, the top of the fuelchamber is connected to air entry bymeans of a large vent line fitted with acontrol valve.• The second line connects the fuel floatchamber to venturi throat via a meteringorifice.• When the control valve is opened, thepressure in float chamber is p1 and thethroat pressure is p2 which is lower thanp1. This causes the fuel to flow. Whenthe valve is closed, there is nodifference in pressure and hence no fuelflow.• Thus the control valve achieves thedesired air fuel ratio during part loadoperation.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Compensating systems in CarburettorsAuxiliary Air Valve• When the engine is not in operation, thepressure p1 acting on the valve isambient. The pressure p2 acting at theventuri is negative (vacuum). Thispressure differential lifts the auxiliaryvalve against the spring tensile force.• Additional air is thus infused in the air-fuel mixture preventing rich mixtureduring part load operation.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Compensating systems in CarburettorsAuxiliary Air Port• If the butterfly valve is opened,additional air passes through this port,reducing air flow through venturi. Thuspressure differential is comparativelysmaller. Thus fuel drawn is reduced tocompensate for loss in density of air athigh altitudes.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Compensating systems in CarburettorsAltitude Compensation Device• This was used in high altitude car driving and for aircrafts.• At high altitudes, air density decreases and hence engine poweroutput is affected.• A/F ratio is affected at high altitudes as carburettors are designed tooperate on sea level.• To compensate for the change in air density, fuel flow has to bereduced from the calibrated value at sea level.• A mixture control system comprising a needle valve, which restrictsfuel flow in proportion to altitude change acts as an altitudecompensating device.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Calculation of A/F ratio for a Simple Carburettor• Let be the difference in height between the tip of the nozzle and fuellevel in the float chamber• 21,CC21, pp- Pressures at inlet and exit- Air density- Air velocities at inlet and exitZApplying Bernoulli‟s Equation across the venturi,22212122pCpCAs ,21 CC 22212pCp
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Calculation of A/F ratio for a Simple CarburettorpC22Mass flow rate of air through the venturi,;ACCm da  ;2pACm da pACm da  2Similarly Mass flow rate of fuel,;fffdf CACm f )(2 ZgpACm fffdf f Due to thedifference in levelbetween tip of jetand fuel level inchamberA/F ratio is,)()(22ZgppAACCZgppAACCmmfffddfffddfaffWhere , A- area of venturi, Af – Area of fuel jet, f – density of fuel
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Combustion in SI Engines• Combustion is the process of oxidation of fuel resulting into therelease of energy equivalent to calorific value of fuel. Energy releasedin combustion is in the form of heat.• Combustion process in spark ignition engine has requirement of the• mixture of fuel and air in right proportion• mechanism for initiation of combustion process and• stabilization and propagation of flame for complete burning• For complete combustion of every fuel there is chemically correct fuel-air ratio also called stoichiometric fuel-air ratio.• This fuel air ratio may be rich or lean depending upon the proportion offuel and air present in mixture. In SI engine this fuel air ratio generallyvaries between 1 : 7 to 1 : 30 with lean mixture at 1 : 30 and rich mixtureat 1 : 7.• Stoichiometric fuel-air ratio is around 1 : 14 to 1 : 15 for hydrocarbonfuel. The extreme values of fuel-air ratio permissible in SI engine onboth rich and lean ends put limits as „lower ignition limit’ and ‘upperignition limit’.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Combustion in SI Engines• Varying fuel-air ratio is required in SI engine due to varying loads onengine between no load to full load on engine. The ratio of actual fuel-air ratio to stoichiometic fuel-air ratio is given by „equivalence ratio‟ or„relative fuel-air ratio‟.• Appropriate fuel-air ratio is maintained in SI engines through„carburettor‟ (the fuel metering system).
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Stages of Combustion in SI Engines
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Stages of Combustion in SI EnginesCombustion in SI engine may be described to be occurring in followingsignificant phase:(i) preparation phase• After compression of fuel-air mixture in cylinder the high temperaturespark is delivered by spark plug in the compressed fuel-air mixture.Temperature at the tip of spark plug electrode may go even more than10,000ºC at the time of release of spark.• Sparkles released have sufficiently high temperature to initiate thecombustion of fuel. For complete combustion of fuel mere initiation ofcombustion does not serve the purpose instead a sustainable combustionprocess is required.• After setting up of combustion, a sustainable flame front or flame nuclei isneeded so that it proceeds across the combustion space to ensurecomplete combustion. Thus, this phase in which spark is first releasedfollowed by setting up of sustainable flame front is called “preparationphase” and may consume around 10º of crank angle rotation.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Stages of Combustion in SI Engines• Crank angle rotation consumed in “preparation phase” depends upon thespeed of engine, constructional feature of cylinder, piston, location of sparkplug, strength of spark, characteristics of fuel, fuel-air ratio etc.• Preparation phase is shown to occur from „a’ to ‘b’ with small or negligiblepressure rise as initially rate of burning is very small.(ii) Flame Propagation Phase• After sustainable combustion flame is set up, then the flame nuclei getscattered due to excessive turbulence in combustion space causingpressure to rise from „b’ to ‘c’.• This phase of combustion depends upon the turbulence inside cylinder,strength of combustion nuclei, fuel-air ratio, strength of spark, cylindergeometry, fuel properties etc.• This phase of combustion is called as “flame propagation phase” and isaccompanied by the excessive pressure rise. Flame propagation phaseshould also be as small as possible.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Stages of Combustion in SI Engines(iii) After Burning Phase• After the maximum amount of fuel-air mixture is burnt, the residual getsburnt after the piston has moved across the TDC.• This last phase is termed as “after burning phase” and occurs during theexpansion stroke.• Hence, it can be summarised that the complete combustion in SI engineoccurs in three distinct zones i.e. preparation phase, flame propagationphase and after burning phase.• In order to have complete combustion in smallest possible time the flamepropagation phase and preparation phase should be shortened.• Out of total distance travelled in combustion space in first phase i.e.Preparation phase about 10% of combustion space length is covered inabout 20–30% of total time for combustion.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Stages of Combustion in SI Engines• Flame propagation phase is spread in about 80% of combustion spacelength and is covered in 60–70% of total time of combustion.• „After burning‟ occurs in less than 10% of combustion space in less than10% of total combustion time.• Abnormal Combustion• Combustion may also sometimes occur abnormally. “Abnormal combustion”is said to occur when combustion begins inside the cylinder on its‟ ownbefore the stipulated time for it.• This abnormal combustion may be due to pre-ignition (i.e. ignition of fueleven before spark plug ignites it) or auto-ignition (i.e. Ignition of fuel due tohot spots in the combustion space like valve seats, spark plug) and resultsin uncontrolled pressure rise.• Abnormal combustion is also termed as detonation or knocking and can befelt by jerky operation of engine, excessive noise, reduced power output etc
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Factors affecting knock• FuelA „low self ignition temperature‟ fuel promotes knock.• Induction pressureIncrease of pressure decreases SIT and increases induction time; tendency of knockincreases. Eg. At full throttle knock tends to occur more.• Engine SpeedLow engine speed will give low turbulence and low flame velocity and hence knocktendency is more.• Ignition TimingAdvancing ignition timing increases peak pressure and promotes knock.• Compression RatioHigh compression ratio increases cylinder pressures and increases the tendency forknock.• Combustion Chamber DesignPoor design results in long flame path, low turbulence and insufficient cooling all ofwhich increase knock tendency.• Cylinder CoolingPoor cylinder cooling increases the temperature and hence the chances of knocktemperature‟ fuel promotes knock.
  • ME2041 Advanced Internal Combustion EnginesUnit I Department of Mechanical Engineering, St. Joseph’s College of Engineering• Combustion Chambers
  • ME2041 Advanced Internal Combustion EnginesUnit ITHERMODYNAMIC ANALYSIS OF SI ENGINE COMBUSTIONBecause combustion occurs through a flame propagation process, thechanges instate and the motion of the unburned and burned gas are much morecomplexthan the ideal cycle analysis.The gas pressure, temperature and density changes as a result ofchanges in volume due to piston motion.During combustion, the cylinder pressure increases due to the release ofthe fuelschemical energy.As each element of fuel-air mixture burns, its density decreases by abouta factor of four.This combustion-produced gas expansion compresses the unburnedmixture ahead of the flame and displaces it toward the combustionchamber walls.The combustion-produced gas expansion also compresses those parts ofthe charge which have already burned, and displaces them back towardDepartment of Mechanical Engineering, St. Joseph’s College of Engineering• Burned and Unburned Mixture States
  • ME2041 Advanced Internal Combustion EnginesUnit ITHERMODYNAMIC ANALYSIS OF SI ENGINE COMBUSTIONDuring the combustion process, the unburned gas elements move awayfrom the spark plug; following combustion, individual gas elements moveback toward the spark plug.Further, elements of the unburned mixture which burn at different timeshave different pressures and temperatures just prior to combustion, andtherefore end up at different states after combustion.The thermodynamic state and composition of the burned gas is,therefore, non-uniform.A first law analysis of the spark-ignition engine combustion processenables us toquantify these gas states.Work transfer occurs between the cylinder gases and the piston (to thegas before TC; to the piston after TC).Department of Mechanical Engineering, St. Joseph’s College of Engineering• Burned and Unburned Mixture States
  • ME2041 Advanced Internal Combustion EnginesUnit ITHERMODYNAMIC ANALYSIS OF SI ENGINE COMBUSTIONHeat transfer occurs to the chamber walls, primarily from the burnedgases.At the temperatures and pressures typical of spark-ignition engines it is areasonable approximation to assume that the volume of the reaction zonewhere combustion is actually occurring is a negligible fraction of thechamber volume even though the thickness of-the turbulent flame maynot be negligible compared with the chamber dimensions.With normal engine operation, at any point in time or crank angle, thepressure throughout the cylinder is close to uniform.The conditions in the burned and unburned gas are then determined byconservation of mass :Department of Mechanical Engineering, St. Joseph’s College of Engineering• Burned and Unburned Mixture States
  • ME2041 Advanced Internal Combustion EnginesUnit ITHERMODYNAMIC ANALYSIS OF SI ENGINE COMBUSTIONThe conservation of energy:where V is the cylinder volume, m is the mass of the cylinder contents, vis the specific volume, xb is the mass fraction burned, Uo is theinternal energy of the cylinder contents at some reference point 0, u isthe specific internal energy, W is the work done on the piston, and Q isthe heat transfer to the walls. The subscripts u and b denote unburnedand burned gas properties, respectively.The work and heat transfers are:Where is the instantaneous heat-transfer rate to the chamber walls.Department of Mechanical Engineering, St. Joseph’s College of Engineering• Burned and Unburned Mixture States
  • ME2041 Advanced Internal Combustion EnginesUnit ITHERMODYNAMIC ANALYSIS OF SI ENGINE COMBUSTIONUseful results can be obtained by assuming that the burned andunburned gases are different ideal gases, each with constant specificheats. i.e.Combining these eqns.Department of Mechanical Engineering, St. Joseph’s College of Engineering• Burned and Unburned Mixture States
  • ME2041 Advanced Internal Combustion EnginesUnit ITHERMODYNAMIC ANALYSIS OF SI ENGINE COMBUSTIONThe above equations may be solved to obtainIf we now assume the unburned gas is initially uniform and undergoesisentropic compression, thenDepartment of Mechanical Engineering, St. Joseph’s College of Engineering• Burned and Unburned Mixture States