advanced ic engines unit 1

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ME2041 Advanced Internal Combustion EnginesDepartment of Mechanical Engineering, St. Josephs College of Engineering Unit ISyllabus:Air-fuel ratio requirements ,Design of carburettor fuel jet size and venture size, Stages of combustion-normal and abnormal combustion, Factors affecting knock, Combustion chambers, Introduction to thermodynamic analysis of SI Engine combustion process.Unit I SPARK IGNITION ENGINESME2041 Advanced Internal Combustion EnginesUnit IISyllabus:Stages of combustion-normal and abnormal combustionFactors affecting knock,Direct and Indirect injection systems, Combustion chambers, Turbo charging ,Introduction to Thermodynamic Analysis of CI Engine Combustion process.Unit II COMPRESSION IGNITION ENGINESDepartment of Mechanical Engineering, St. Josephs College of Engineering ME2041 Advanced Internal Combustion EnginesUnit IIISyllabus:Formation of NOX , HC/CO mechanism , Smoke and Particulate emissions, Green House Effect , Methods of controlling emissions , Three way catalytic converter and Particulate Trap, Emission (HC,CO, NO and NOX , ) measuring equipments, Smoke and Particulate measurement, Indian Driving Cycles and emission normsUnit III ENGINE EXHAUST EMISSION CONTROLDepartment of Mechanical Engineering, St. Josephs 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 CI Engines using these alternate fuels.Unit IV ALTERNATE FUELSDepartment of Mechanical Engineering, St. Josephs College of Engineering ME2041 Advanced Internal Combustion EnginesUnit VSyllabus:Homogeneous Charge Compression Ignition Engine, Lean Burn Engine, Stratified Charge Engine, Surface Ignition Engine , Four Valve and Overhead cam Engines,Electronic Engine Management, Common Rail Direct Injection Diesel Engine, Gasoline Direct Injection Engine , Data Acquisition System pressure pick up, charge amplifier PC for Combustion and Heat release analysis in Engines.Unit V RECENT TRENDSDepartment of Mechanical Engineering, St. Josephs College of Engineering ME2041 Advanced Internal Combustion EnginesUnit ICarburetionThe process of formation of combustible air-fuel mixture, by mixing correct amount of fuel and air in a device called carburetor, before it enters the engine cylinder.Factors Affecting CarburetionCarburetor Designhas influence on distribution of air-fuel mixture to cylinders.Ambient Air conditionAmbient pressure and temperature influence the efficiency of carburetion. Higher ambient temperature increases the vaporization rate of fuel forming a homogeneous mixture.Fuel CharacteristicsEvaporation characteristics (indicated by distillation curve) is critical for carburetion; presence of volatile HC also is important for quick evaporationDepartment of Mechanical Engineering, St. Josephs College of Engineering ME2041 Advanced Internal Combustion EnginesUnit IEngine Speed and LoadAt higher engine speed, the carburetion time is less causing strain on carburetor to deliver uniform mixture in a short time; thus provision of venturi has to be such that the carburetion is done efficiently at higher pressure dropsHigher loads will demand richer mixture and lower load leaner mixtures.

Types of Air-Fuel MixturesChemically Correct MixtureStoichiometric or balanced chemical mixture in which air is provided to completely burn the fuel; the excess air factor is unityRich MixtureFuel is in excess of what is required to burn the fuel completely. The excess air factor is less than unity.Lean MixtureAir is in excess of what is required to burn the fuel completely. The excess air factor is greater than unity.Department of Mechanical Engineering, St. Josephs College of Engineering ME2041 Advanced Internal Combustion EnginesUnit IRange of Air-Fuel Ratio in SI Engines9:1 (rich) to 19:1(lean) ; The stoichiometric value for gasoline is 14:1, The SI engine will not run for too rich or too lean mixtures. Mixture Requirements at Different Engine ConditionsDepartment of Mechanical Engineering, St. Josephs College of Engineering The air fuel ratio affects the power output and brake specific fuel consumption of the engine as shown in the Figure1. Power Output (kW)BSFC (kg/kWh)PowerBSFCA/F ratioME2041 Advanced Internal Combustion EnginesUnit IMixture Requirements at Different Engine Conditions (Contd.)Department of Mechanical Engineering, St. Josephs College of Engineering The mixture corresponding to maximum output on the curve is called best power A/F mixture, which is richer than the stoichiometric mixture. The mixture corresponding to maximum BSFC on the curve is called best economy mixture, which is leaner than the stoichiometric mixture. The actual A/F ratio requirement for an automative carburetor falls in 3 ranges:Idling (rich)Cruising (lean)High Power (rich) ME2041 Advanced Internal Combustion EnginesUnit IMixture Requirements at Different Engine Conditions (Contd.)Department of Mechanical Engineering, St. Josephs College of Engineering Idling A/F RatioThrottle Opening1234050%100%Cruising PowerFigure 2. A/F Ratio Vs Throttle openingME2041 Advanced Internal Combustion EnginesUnit IMixture Requirements at Different Engine Conditions (Contd.)Department of Mechanical Engineering, St. Josephs College of Engineering Idling 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 to exhaust gases from the combustion chamber.Also, the amount of fresh charge admitted is less due to smaller throttle opening. Exhaust gas dilution prevents efficient combustion by reducing the contact between the fuel and air particles.Rich mixture improves the contact of fuel and air by providing efficient combustion at idling conditions.As the throttle is opened further, the exhaust gas dilution reduces and the mixture requirement shifts to the leaner side.ME2041 Advanced Internal Combustion EnginesUnit IMixture Requirements at Different Engine Conditions (Contd.)Department of Mechanical Engineering, St. Josephs College of Engineering Cruising 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 achieve rich mixture in this range. Rich mixture also prevents overheating by reducing the flame temperature and cylinder temperature.

ME2041 Advanced Internal Combustion EnginesUnit IPrinciple of Operation of Simple CarburettorDepartment of Mechanical Engineering, St. Josephs College of Engineering

ME2041 Advanced Internal Combustion EnginesUnit IDepartment of Mechanical Engineering, St. Josephs College of Engineering Principle of Operation of Simple CarburettorThe carburettor works onBernoulli's principle: the faster air moves, the lower itsstatic pressure, and the higher itsdynamic pressure. Thethrottle(accelerator) linkage does not directly control the flow of liquid fuel. Instead, it actuates carburettor mechanisms which meter the flow of air being pulled into the engine. The speed of this flow, and therefore its pressure, determines the amount of fuel drawn into the airstream.A simple carburetor consists of a float chamber, fuel discharge nozzle, a metering orifice, a venturi a throttle valve and choke.The float and needle valve maintain the fuel levelFuel strainer is used to trap debris from the fuel and prevent choking of the 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 IDepartment of Mechanical Engineering, St. Josephs College of Engineering Principle of Operation of Simple CarburettorThis pressure drop provides vacuum necessary to meter the air-fuel mixture to the engine manifold.Fuel is fed to the fuel discharge jet, the tip of which is located at the throat of 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. It is a butterfly valve located after the venturi tube. When the load is less, the throttle is in near closed position and if the load is high throttle is fully opened.The choke valve is located between the entrance and venturi throat. It is also of butterfly type. When choke is partly closed, a large pressure drop occurs at the venturi throat, which provides a rich mixture by induction of large amount of fuel as required during idling or high load conditions. Choke valves are spring loaded to prevent excessive choking and are sometimes automatically controlled by thermostat.For providing rich mixture during idling, an idling adjustment is provided. It has an idling passage and idling port. ME2041 Advanced Internal Combustion EnginesUnit IDepartment of Mechanical Engineering, St. Josephs College of Engineering Principle of Operation of Simple CarburettorThe system operates at starting and shuts off when 20% throttle opening is reached. Normal venturi depression is not sufficient to provide rich mixture due to lower throttle opening. But this low pressure causes fuel rice in idling passage and it is discharged through idling port downstream of the throttle valve.The idling air bleed sucks some air for mixing with the idling fuel and vaporizes the mixture. The additional fuel-air supply makes the mixture rich for idling.Simple carburettor has the drawback of providing rich mixture with increasing throttle opening.ME2041 Advanced Internal Combustion EnginesUnit IDepartment of Mechanical Engineering, St. Josephs College of Engineering Compensating systems in CarburettorsFor part load conditions, the carburettor must s