BME Lecture Notes PDF

BME Lecture Notes by Sathishkumar B NIT Trichy T Basics of Mechanical engineering IT...

BME Lecture Notes by Sathishkumar B NIT Trichy T Basics of Mechanical engineering IT Mf.BTSathishkumar N Research Scholar Department of Mechanical Engineering Office -No.1, first floor, Mechanical dept. Email - [email protected] BME Syllabus Introduction to Mechanical Engineering, Thermal Engineering, Design, manufacturing Engineering. T IC Engines-2 Stroke and 4 stroke systems in IC Engines. Automobiles -Transmission systems, Suspension system, E-Vehicles. IT Energy Systems - Power plants, Types, Gas Turbines, Steam Turbines, Utility boilers, R & A/C system-Green Energy production and Devices. Engineering materials, Machine elements, Transmission, Fasteners, Support systems. N Manufacturing, Classification, Metal forming, Casting, Lathe, Drilling machines, Milling machines, Metal joining. Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy Mechanical Engineering What is mechanical engineering? Mechanical engineering is the branch of engineering focused on the design, analysis, manufacture T and improvement of the mechanical systems (machines, devices, etc) with the aid of physics and mathematics to attain the specific functional requirement. Mechanical engineers design, manufacture, and evaluate the mechanical devices. Mechanical engineers are developing... New materials. New forms of transport. New way to generate energy. IT Advanced devices in medicine field. N Q Mechanical engineering improving the quality of life. Manufacture X Improvement Mr B Sathishkumar - MEIR11 Basics of Mechanical Engineering Mechanical Engineering T Thermal Manufacturing * Thermodynamics Mechanical Engineering Metallurgy Fluid Mechanics Manufacturing * Heat Transfer Production Control IT * IC Engines Design Automobile Engineering * Energy Conversion Industrial Automation Refrigeration & Air CAD Robotics Conditioning * Engineering Economics Structural mechanics Power plants Statics Theory of Turbo machinery N Machines Jet Propulsion Dynamics Kinematics Materials Science Machine Design Vibrations Mr.B.Sathishkumar - MEIR 11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy T IT N Mr B Sathishkumar MEIR11 - Basics of Mechanical Engineering T IT N Mr.B.Sathishkumar BME Lecture Notes by Sathishkumar B NIT Trichy T IT N T IT N BME Lecture Notes by Sathishkumar B NIT Trichy Thermodynamics The study of the relations between temperature, heat, work and energy. It gives the foundation for heat engines, power plants, chemical reactions, refrigerators, etc. T Laws Zeroth law (Temperature) - Two systems equilibrium with third system, they are in thermal equilibrium with each other. IT First law (Energy conservation) - Energy can neither be created nor be destroyed. One form to another form. For a system under a cyclic process, heat input to the system is equal to the work output of the system when the system is closed one. Second law (Energy degradation) - Clausius Statement and kelvin-planck statement N Third law (Entropy) - The entropy of a perfect crystal at absolute zero temperature is zero. The laws of thermodynamics describe how the energy in a system changes and whether the system can perform useful work on its surroundings. Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering Thermodynamics Carnot Theorem T It states that of all heat engines operating between a given constant temperature source and sink, none has a higher efficiency than a reversible engine. Carnot Cycle IT Assumptions: Working fluid is air. No friction in cycle. No pressure drops in the working fluid. All expansions and compressions are N reversible. X Kinetic and potential energy changes are negligible. Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy T IT N Fluid Mechanics V = ui vj wk Buoyancy It is the study of fluid behavior at rest and motion as well. Weight of the obiect /u(x. y. z. t) T z(t) Basic principles involves in fluid mechanics. x(t) > Conservation of mass > Conservation of momentum Buoyant tores > Conservation of energy IT The major topics in the fluid mechanics a) Fluid properties - density, viscosity, specific volume and specific gravity. X’X"*"*'* b) Fluid pressure measurements - Manometer (pressure measurement device) c) Hydrostatic pressure measurement - for submerged surfaces N d) Buoyancy (B) and Floatation - (B - upward force exerted on an object which immersed in a fluid) e) Kinematics of fluid flow - velocity and acceleration (conservation of mass and momentum) O f) Dynamics of fluid flow - forces (conservation of energy - Bernoulli's principle) Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering 12 BME Lecture Notes by Sathishkumar B NIT Trichy Fluid Mechanics Viscous flow and turbulent flow in pipe and over a plate. > Flow through pipes - (considering friction losses). T Hydraulic machines (turbines) - converts potential to mechanical energy (later electrical). Pumps (centrifugal and reciprocating) - converts electrical to potential energy. Dimensionless numbers - Reynolds, Froude, Weber, Mach, Euler's Number. J IT N Heat Transfer Transmission of energy from one region to another region due to the temperature difference. T Conduction Transfer of heat from one medium to another medium (solid, liquid and gas) which has a physical IT contact with each other, (free electron, collision and diffusion of molecules). It is governed by Fourier law. qx = -k A dT LI Convection dx Transfer of heat within the fluid by mixing one with another and it is possible only in fluid medium. It is governed by Newton's law of cooling, q = h A (Tw - T®) N Radiation Transfer of heat through the space (no medium). It is governed by stefan boltzman’s law. E = o T4 Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy Heat Transfer Heat transfer through the plane wall, cylinder and sphere - Conduction. Insulation for heat carrying pipes and current carrying wires. T Heat transfer through the fins. J Unsteady state heat transfer. J Heat transfer from plate and pipe with fluid flow - Convection Heat exchangers IT Radiation on black and grey surface. N Mr B Sathishkumar - MEIR11 Basics of Mechanical Engmeenng Power Plant Engineering Power plant is an industrial facility that generates electricity from primary energy sources. T Most of the power plant like Thermal and nuclear power plants works on the Rankine cycle. IT N Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy Power Plant Engineering T IT N Mr B Sathishkumar - MEIR 11 Basics of Mechanical Engineering Power Plant Engineering Nuclear power plant containment structure T steam transmission lines turbine electric generator & control rods pressure vessel IT steam nonradioactive generator warm water vapour condenser water warm moist air water pump core water N condenser spray water pump water cool condenser water cool water basin cooling tower nuclear reactor © 2013 Encyclopaedia Britannica, Inc. intake from lake or river Mr.B.Sathishkumar MEIR 11 - Basics of Mechanical Engineering 18 BME Lecture Notes by Sathishkumar B NIT Trichy T IT N Power Plant Engineering T Cooling tower concrete. Turbine stainless stool, carbon steel reinforcement nickel molybdenum. Power tones Pipework 304. 316 aluminum. stainless stool copper carbon steel \ iron Transformer copper. IT silicon iron Housing structure concrete N Mr.B.Sathishkumar MEIR11 - Basics of Mechanical Engineering 20 BME Lecture Notes by Sathishkumar B NIT Trichy Power Plant Engineering T IT N Mr B Sathishkumar MEIR11 - Basics of Mechanical Engineering T IT N BME Lecture Notes by Sathishkumar B NIT Trichy T IT N Structural Mechanics It deals with the computation of deformations, strains, deflections, and internal forces or stresses T within structures under loading and non loading conditions. 1111m: Important topics: fb) Suuply tuppcMled > Stress and strain ? (C) Overhanging Elastic constants IT —- Strain > Shear force and bending moment diagrams in beams (»1 Fixed ruled (DCautilccrt muplv tuppocled > Bending stress in beams > Deflections of beams > Thin cylinders and spheres N > Columns and struts > Theories of failure Mr.B.Sathishkumar MEIR 11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy Theory of machines Study of relative motion between the machine components and the forces act on them. Important topics: T > Structure, degree of freedom, linkage and mechanism. > Velocity and acceleration analysis > Cams and followers > Belt, Rope and Chains Gears and gear trains > Brakes and clutches > Balancing, governors IT > Static and dynamic. analysis. of mechanisms ,. SLIDER CONNECTING ROD CRANK Larger sprocket N Chain link Ml MM DTOI M > Vibrations Mr.B.Sathishkumar MEIR11 - Basics of Mechanical Engmeenng Theory of machines T IT N Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy Machine Design The process of selection of the materials, shapes, sizes and arrangements of mechanical elements so that the resultant machine will perform the specified task. T Important topics: Engineering materials (study of materials and its properties) Simple, torsional and bending stresses > Variable stresses in machine part IT Rivet, Weld, Screw, cotter and knuckle joints Shafts, bearings and flywheels Belt and chain drives N Brakes and clutches Gears (Spur, Helical, Bevel and Worm) Mr B Sathishkumar - MEIR11 Basics of Mechanical Engineering T IT N BME Lecture Notes by Sathishkumar B NIT Trichy Production Engineering Casting > pouring The process of producing metal parts by T molten metal into the mould cavity of the required shape and allowing the metal to solidify. Sand, die, shell and mould casting, & > two investment casting. Welding or more metal parts IT Welding is a fabrication process whereby are fused together by means of heat, pressure or both forming Slag covering Wire electrode Weld metJ.Coaong Direction of ”* welding Parent metal N a join. > Gas, Arc, welding. Resistance and solid state Molten crater Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering Production Engineering Metal forming T > Itsubjected is a process in which the materials are to plastic deformation by the application of heat or pressure to obtain the required size, shape, and change the IT Extruded Container physical and chemical properties. IwMerCoobng Product > Forging, Rolling, Extrusion, and drawing. Machining process > The process of obtaining the desired shape and size of material part by N removing the excess material using a machine tool. > Turning, Facing, Drilling, Milling, and Shaping. Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy T IT N Combustion Engines - History 1858: Jean J. Lenoir (Belgium engineer) T 1895: Rudolf Diesel developed commercially successful internal (German Engineer) combustion engine - Lenoir's engine. invented four stroke IT diesel engine 1876: Nicklaus A. Otto (German Engineer) invented compressed charge four stroke engine (in-cylinder compression engines) N 1878: Dugald Clerk designed the with in-cylinder compression Mr.B.Sathishkumar - MEIR11 Basics of M 32 BME Lecture Notes by Sathishkumar B NIT Trichy T IT N Classification of Engine Heat Engines T IC Engines EC Engines IT Rotary Reciprocating Reciprocating Rotary N Open Cycle Wankel Gasoline Diesel Steam Stirling Steam Closed Cycle Gas Turbine Engine Engine Engine Engine Engine Turbine Gas Turbine Mr.B.Sathishkumar - MEIR 11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy IC Engine Terminologies Top Dead Centre (TDC) - Position when the piston is farthest from crank shaft T Bottom Dead Centre (BDC) - Position when the piston is nearest to crank shaft Bore - Inner diameter of cylinder IT Stroke - Distance travelled by the piston Swept or displacement volume - Volume swept by piston Clearance volume - Volume above the TDC N Compression ratio - Total volume / Clearance volume Cubic Capacity (CC) - Swept volume x No of cylinder Mr B Sathishkumar MEIR11 - Basics of Mechanical Engineering IC Engine Components camshaft 5C Components valve spring T > Cam Shaft exhaust > Connecting Rod mixture in valve > Cylinder head intake cylinder head IT valve > Crank shaft combustion cooling > Cylinder block chamber water Spark Plug / Fuel injectors cylinder piston block Valves (Inlet & Exhaust) connecting crankcase N Gudgeon pin rod Piston and piston rings crankshaft Crank case Mr.B.Sathishkumar MEIR11 - Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy IC Engine Components Piston - transmits the force developed by the combustion gases to the crank shaft through the connecting rod. T It reciprocates up (TDC) and down (BDC) inside the engine cylinder (combustion chamber) using the pressure developed by the combustion. Piston rings - rings are used to provides the gas-tight IT sealing for combustion gases and scraps the lubricating oil. Rings housed in the grooves provided on the outer surface of the piston. Compression rings - maintains the compression N pressure inside the cylinder and prevents the leakage of combustion gases into the crank case by forming gas-tight seal. Oil ring - scraps the lubricating oil in the cylinder wall. Mr B Sathishkumar MEIR11 - Basics of Mechanical Engineering IC Engine Components j Connecting rod - connects the piston and crank shaft am T transmits the force from piston to the crank shaft. > It receives the force from the piston and transmits to the cran shaft. > Small and big end of the rod is connected with the piston am IT crank shaft respectively. Gudgeon pin - connects piston with small end of Conn, rod j Crank shaft - Shaft which receives power from connecting rod in a designated sequence for transmission to the wheels. N > It converts the reciprocating motion of the piston to the rotary motion with aid of connecting rod. > It made of alloy steel to withstand the high stress produced by the combustion event. Mr.B.Sathishkumar - MEIR 11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy IC Engine Components Cylinder block - main supporting structure. A cylinder allows the piston to move up and down. T It made of steel, aluminium alloy and cast iron The cylinder liner is a thin cylindrical component installed in the cylinder block. It protects wear and tear. bolts and nuts. Crank case - IT Cylinder head - mounted on the cylinder block and it houses the spark plug/injector, inlet and exhaust values. Cylinder head is connected with cylinder block using many lower part of the engine block and it N accommodates the connecting rod, crank, crank shaft. It houses the oil pan as well and sometimes acts as an oil sump. Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering IC Engine Components Cam shaft - shaft consist of different type of cams and it T converts the rotary motion of shaft into reciprocating motion of value stem. It controls the opening and closing of the values (inlet and exhaust) using the accessories like rocker arms, valve IT springs, push rod and tappets. Valves - Inlet valve - placed in the inlet manifold and allows the air or air-fuel mixture inside the chamber. Exhaust valve - placed in the exhaust manifold and allows the burnt gases out. N Flywheel - flywheel stores the excess energy during the power stroke of the engine and helps the movement of the piston during the remaining idle strokes. It is mounted on crank shaft. MrB.Sathishkumar - MEIR11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy IC Engine Components Spark plug - used to initiate the combustion process in the Spark ignition (SI) engines. T It is connected to the ignition coil system to provide a spark energy (12-25 kV). Spray timing are controlled by the crank angle. chamber and atomize the fuel. IT Copper, Platinum and Iridium spark plugs. Injector - used to inject the fuel inside the combustion The quantity of fuel injection in the mechanical injector is controlled by the pump with cam shaft arrangements. N Modern injectors with control circuits are used to deliver the accurate the fuel quantity based on the sensor data. Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering Simple carburetor Carburetor is a device used to provide the correct quantity of homogeneous air-fuel mixture. T The nozzle attached to the fuel metering orifice is placed in the throat section of venturi where the carburetor depression is maximum. The carburetor depression is a pressure difference between the float chamber and the venturi throat. IT The nozzle tip of the fuel metering orifice is placed above the fuel level in the float chamber to avoid overflow. This distance is called tip of nozzle. Because of the pressure depression in the throat zone, the fuel is discharged in the nozzle and the fuel get mixed with the airflow due to the suction stroke. Then the air-fuel mixture is passes through the throttle valve which controls the quantity of the air¬ N fuel mixture into the cylinder. The choke is used to provide the rich mixture by closing the butterfly valve. Once the choke closed, the air quantity become less and rich mixture formed. Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy Simple carburetor T IT N Air Fuel Mixture Outlet Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering 43 SI Engine vs Cl engine |S||||||^ Description SI Engine Cl Engine |] o T Basic cycle Otto cycle Diesel cycle Fuel Gasoline, a highly volatile fuel Diesel oil, a non-volatile fuel Introduction of fuel in carburetor Fuel injector cylinder IT Air-fuel Mixture Homogeneous Heterogeneous Ignition Spark plug Self ignition Compression ratio 6-10 16-22 Controlling of air-fuel mixture Controlling the injection Load control by throttle in carburetor quantity N Speed High speed engine Low speed engine Thermal efficiency Low High Weight Low High Mr.B.Sathishkumar MEIR 11 Basics of Mechanical Engineering 44 BME Lecture Notes by Sathishkumar B NIT Trichy Four Stroke - SI Engine Ideal Cycle Processes Actual Cycle 0-1 Intake T 1-2 Isentropic Compression 2-3 Heat addition at Constant IT Volume 3-4 Isentropic Expansion 4-1 Heat rejection at Constant N Volume 1-0 Exhaust Mr.B Sathishkumar - MEIR11 Basics of Mechanical Engineering Four Stroke - SI Engine Theoretical Valve timing Diagram Actual Valve timing Diagram T TDC - Top Dead Center TDC BDC- Bottom Dead Center IVO Inlet Valve Opens EVC IVC - Inlet Valve Closes IS (Fl) EVO - Exhaust Valve Opens EVC - Exhaust Valve Closes Suction IT IS - Ignition Starts IVO Fl -Fuel Injection Expansion < (power) Compression N IVC I EVO Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy 4 Stroke SI engine Working (Ideal) LI Suction stroke - starts when the piston is about to move downward from TDC. At this instant, the inlet valve opens and the exhaust valve is closed. T The air and fuel mixture is drawn into the cylinder due to the suction created by the downward piston motion. When the piston reaches the BDC the suction stroke ends and inlet valve closes instantaneously. LI IT Compression stroke - The piston moves from BDC to TDC and compresses the air-fuel mixture (15-20 bar). Both valves kept closed. The air-fuel mixture is ignited by the spark produced at the end of the compression stroke. Intake Stroke N The combustion process is assumed to be a heat addition which takes place at constant volume when piston is at TDC. LI The pressure (50-60 bar) and temperature are increased to high range due to the combustion process at this stage. Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering Compression Stroke 4 Stroke SI engine Working (Ideal) LI Power stroke - The piston moves forcefully from TDC to BDC due T to the high pressure of the burnt gases. Both the valves are in closed position during power stroke. The pressure and temperature are decreasing during the expansion of the burn gases. IT Exhaust stroke - The piston moves from BDC to TDC. At the BDC the exhaust valve opens instantaneously and the inlet valve remains closed. The pressure falls to atmospheric level as a part of the burnt gases pushes out through exhaust valve by upward movement of the N piston. The exhaust valve closes when the piston reaches TDC. The cycle repeats... Mr.B.Sathishkumar MEIR11 - Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy 4 Stroke SI engine Working (Ideal) T IT N Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering 49 4 Stroke SI engine Working (Actual) T IT N Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering 50 BME Lecture Notes by Sathishkumar B NIT Trichy Four Stroke - Cl Engine Ideal Cycle Processes Actual Cycle fuel injection and 0-1 Intake Q#dd T combustion Qadd ER =— 1-2 Isentropic Compression 2-3 Heat addition at Constant o intake stroke ^04^ exhaust stroke x IT Qou. Pressure 3-4 Isentropic Expansion 4-1 Heat rejection at N Constant Volume V2 V3 Volume V* 1-0 Exhaust Mr B Sathishkumar - MEIR11 Basics of Mechanical Engineering 51 Four Stroke - Cl Engine Theoretical Valve timing Diagram Actual Valve timing Diagram T TDC - Top Dead Center TDC TDC Top Dead Center BDC - Bottom Dead Center BDC - Bottom Dead Center FIS TDC EVC EVC IVO Inlet Valve Opens FIS- Fuel Injection Starts IVC - Inlet Valve Closes IS (Fl) FIC- Fuel Injection Closes EVO - Exhaust Valve Opens IVO - Inlet Valve Opens Suction Suction EVC Exhaust Valve Closes IVC - Inlet Valve Ooses IT IS - Ignition Starts EVO - Exhaust Valve Opens Fl - Fuel Injection EVC - Exhaust Valve Closes Expansion Expansion 4 (power) (power) Exhaust Compression Compression EVO N | EVO BDC BDC Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering 52 BME Lecture Notes by Sathishkumar B NIT Trichy 4 Stroke Cl engine Working (Ideal) LI Suction stroke - starts when the piston is about to move downward from TDC. At this instant, the inlet valve opens and the exhaust valve is closed. T The air alone is drawn into the cylinder due to the suction created by the downward piston motion. When the piston reaches the BDC the suction stroke ends and inlet valve closes instantaneously. LI Compression LI Fuel IT stroke - The piston moves from BDC to TDC and compresses the air (30-45 bar). Both valves kept closed. injection starts from the injector nearly at the end of the compression stroke (at TDC). The combustion process is assumed to be heat a addition which N takes place at constant pressure when piston is starts moving down. The pressure (80-100 bar) and temperature are increased to high range due to the combustion process at this stage. Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering 4 Stroke Cl engine Working (Ideal) LI Power stroke - The piston moves forcefully from TDC to BDC due T to the high pressure of the burnt gases. Both the valves are in closed position during power stroke. The pressure and temperature are decreasing during the expansion of the burn gases. IT Exhaust stroke - The piston moves from BDC to TDC. At the BDC the exhaust valve opens instantaneously and the inlet valve remains closed. The pressure falls to atmospheric level as a part of the burnt gases pushes out through exhaust valve by upward movement of the N piston. The exhaust valve closes when the piston reaches TDC. The cycle repeats... Mr.B.Sathishkumar MEIR11 - Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy 4 Stroke Cl engine Working (Actual) TDC - Top Dead Center BDC- Bottom Dead Center FIS TDC EVC FIS- Fuel Injection Starts FIC- Fuel Injection Closes T IVO - I nlet Valve Opens Suction IVC - Inlet Valve Closes EVO - Exhaust Valve Opens IVO EVC - Exhaust Valve Closes Expansion (power) Exhaust Compression IT EVO N BDC Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering 2 Stroke SI engine Working (Ideal) Suction and Compression stroke - The air-fuel mixture is drawn T into the crankcase through inlet port due to the upward motion of the piston from BDC to TDC. The mixture (admitted through transfer port from crank case) above the piston is compressed during the upward motion of the piston. IT When the piston at TDC, only the inlet port is kept open and other two ports (transfer and exhaust port) are closed. When the spark ignites the compressed air-fuel mixture, combustion starts and the piston is pushed down due to the pressure developed by combustion gases. N Power and exhaust stroke - When a piston moves from TDC to BDC, power obtained and the burnt gases are pushed out through exhaust port by compressed mixture from transfer port. During the power stroke, both the transfer and exhaust ports remain closed, and open during the exhaust stroke to expel the burnt gases. Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy 2 Stroke Cl engine Working (Ideal) Suction and Compression stroke - The air is drawn into the crankcase through inlet port due to the upward motion of the piston T from BDC to TDC. The air (admitted through transfer port from crank case) above the piston is compressed during the upward motion of the piston. When the piston at TDC, only the inlet port is kept open and other IT two ports (transfer and exhaust port) are closed. When the injected fuel contacts with hot compressed air, combustion starts and the piston is pushed down due to the pressure developed by combustion gases. Power and exhaust stroke - When a piston moves from TDC to N BDC, power obtained and the burnt gases are pushed out through exhaust port by compressed mixture from transfer port. During the power stroke, both the transfer and exhaust ports remain closed, and open during the exhaust stroke toof expel the burnt gases. Mr.B Sathishkumar MEIR11 - Basics Mechanical Engineering 2 Stroke engine Working (Ideal) Actual 2 stroke SI engine Actual 2 stroke Cl engine T IT N Mr.B.Sathishkumar - MEIR 11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy Engine Performance Parameters Indicated power > The heat energy from combustion is used to drive the piston and converted to power. T Brake power > The useful mechanical energy available at the crank shaft. > Indicated power = brake power + frictional power LI Specific power output > > IT The power output per unit piston area. Indicated Thermal Efficiency The ratio of indicated power to the input fuel energy (product of mass and calorific value of fuel). Brake Thermal Efficiency N > The ratio of brake power to the input fuel energy. Mechanical Efficiency > The ratio of brake power to indicated power. Mr B Sathishkumar MEIR11 - Basics of Mechanical Engineering Engine Performance Parameter Volumetric efficiency T > The ratio of actual volume flow rate of air into the intake system to the rate at which the volume is displaced by the system. Mean effective pressure > The average pressure on the piston in an engine. IT Mean piston speed > Average speed of the piston in a reciprocating engine. For 2 stroke sp = 2LN LI Specific fuel consumption > The ratio of fuel consumption per unit time to the power developed. N LI Equivalence ratio Actual fuel-air ratio Stoichiometric fuel-air ratio Mr.B.Sathishkumar - MEIR 11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy T IT N 4 Stroke Engine vs 2 Stroke Engine k 4©oi*° s. 4 Stroke Engine 2 Stroke Engine T No 1 One power stroke in two crank revolutions One power stroke in one crank revolutions 2 Power generation is lower Power generation is higher IT 3 Uses inlet and exhaust valve Uses inlet and exhaust ports 4 Higher Thermal efficiency Lower Thermal efficiency 5 Higher Volumetric efficiency Lower Volumetric efficiency 6 Lower Mechanical efficiency Higher Mechanical efficiency 7 Lubrication requirement is low Lubrication requirement is high N 8. Weight is more Weight is less 9. Noise is less Noise is more 10. Design and manufacturing cost is more Design and manufacturing cost is less Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering 62 BME Lecture Notes by Sathishkumar B NIT Trichy T IT N Automobiles An automobile is a self-propelled vehicle driven by IC engine and used for transportation of T passengers and goods on road ways. Classifications: > Purpose Passenger vehicle - Car, Jeep, Bus IT Goods vehicle - Truck, Pick-up > Load Capacity Light duty vehicle - Motor cycle, Scooter, Car Heavy duty vehicle - Bus, Truck, Tractor Number of wheels N Two wheeler, Three wheeler, Four wheeler, Six wheeler > Drive of vehicle Real wheel drive, front wheel drive, left hand drive, right hand drive. Mr.B.Sathishkumar - MEIR11 Basics of Mechanical Engineering BME Lecture Notes by Sathishkumar B NIT Trichy Automobiles Major components of automobile: Prime mover - produce the power to run the vehicle. T Chassis - supports the engine, wheels, car body and other components. Power train (transmission system) - transmits the power from prime mover to wheels. - Suspension system absorbs the vibrations due to the vertical motion of wheels. Fuel supply system - supplies the required quantity of the fuel. IT Ignition system - provides the ignition source (spark) for SI engine at right time. Electrical system - starts the starter motor and provides energy to other parts. Steering system - changes the automobile direction. x Braking system - reduces the speed of the automobile and used to stop as well. Cooling system - prevents the overheating and overcooling. N Lubrication system - minimize the friction due to the moving parts. x Exhaust treatment system - reduces the exhaust Body and accessories - provided the accommodation with protection. Mr B Sathishkumar MEIR11 - Basics of Mechanical Engineering 65 T IT N