VCR ENGINE PROJECT PART 2
- 1. 1 INTRODUCTION A heat engine is a machine, which converts heat energy into mechanical energy. The combustion of fuel such as coal, petrol, diesel generates heat. This heat is supplied to a working substance at high temperature. By the expansion of this substance in suitable machines, heat energy is converted into useful work. Heat engines can be further divided into two types: (i) External combustion Engine (ii) Internal combustion Engine. In a steam engine the combustion of fuel takes place outside the engine and the steam thus formed is used to run the engine. Thus, it is known as external combustion engine. In the case of internal combustion engine, the combustion of fuel takes place inside the engine cylinder itself. APPLICATIONS OF IC ENGINE: I.C. engines have many applications, including: Road vehicles(e.g. scooter , motorcycle , buses etc.) Aircraft Motorboats Small machines, such as lawn mowers, chainsaws and portable engine-generators
- 2. 2 FUNDAMENTALS OF IC ENGINE ENGINE CLASSIFICATIONS: 1. Types of Ignition Spark Ignition (SI). Compression Ignition (CI). 2. Engine Cycle Four-Stroke Cycle Two-Stroke Cycle 3.Types of fuel used Petrol engine Diesel engine Gas engine 4.Number of strokes per cycle Otto cycle Diesel cycle Dual cycle 5. Speed of the engine Slow speed Medium speed High speed 6.Cooling system Air- cooled Water cooled 7. Method of fuel injection Carburetors engine Air injection engines 8. Number of cylinders Single cylinder Multi cylinder 9. Arrangement of cylinders Horizontal Vertical Radial In-line multi- cylinder V-type multi- cylinder Opposite cylinder Opoosite piston 10. Method of governing Hit and Miss governed Quality governed Quantity governed 11.Valve arrangement Over Head Valve L-head type T-head type F-head type
- 3. 3 CONSTRUCTIONAL FEATURES & FUNCTIONS OF IC ENGINE : 1. Cylinder :- It is a container fitted with piston, where the fuel is burnt and power is produced. 2.Cylinder Head/Cylinder Cover:-One end of the cylinder is closed by means of cylinder head. This consists of inlet valve for admitting air fuel mixture and exhaust valve for removing the products of combustion. 3. Piston:- Piston is used to reciprocate inside the cylinder. It transmits the energy to crankshaft through connecting rod. 4. Piston Rings:- These are used to maintain a pressure tight seal between the piston and cylinder walls and also it transfer the heat from the piston head to cylinder walls. It is of two types- Compression rings & Oil control/scrapper rings. 5. Piston /Wrist/Gudgeon pins: It connects the piston to the end of connecting rod.The pin is retained in the piston with chips or plugs to prevent cylinder wall storing & constructed of hardened steel Fig. Cylinder Block 6.Connecting Rod:- One end of the connecting rod is connected to piston through piston pin while the other is connected to crank through crank pin. It transmits the reciprocatory motion of piston to rotary crank. Fig. Piston & pins Fig. Connecting rod
- 4. 4 6. Crank:- It is a lever between connecting rod and crank shaft. 7. Crank Shaft:- The function of crank shaft is to transform reciprocating motion in to a rotary motion. 8. Crank Case:- It supports and covers the cylinder and the crank shaft. It is used to store the lubricating oil. Fig. Crankshaft 9. Fly wheel:- Fly wheel is a rotating mass used as an energy storing device It stores energy during power stroke and returns back the energy during the idle strokes, providing a uniform rotary motion of flywheel. The rear surface of the flywheel serves as one of the pressure surfaces for the clutch plate. 10. Cam Shaft: The shaft that has intake and exhaust cams for operating the valves. Fig. Camshaft 11.Valves: Minimum two valves per Cylinder Exhaust Valve: lets the exhaust gases escape the combustion Chamber. (Diameter is smaller then Intake valve) Intake Valve: lets the air or air fuel mixture to enter the combustion chamber. (Diameter is larger than the exhaust valve) Fig. Valves 12. Spark Plug: It provides the means of ignition when the gasoline engine’s piston is at the end of compression stroke, close to Top Dead Center(TDC) Fig. Spark plug
- 5. 5 Materials used for engine parts: Sl. No. Name of the Parts Materials of Construction 1. Cylinder head Cast iron, Cast Aluminium 2. Cylinder liner Cast steel, Cast iron 3. Engine block Cast iron, Cast aluminum, Welded steel 4. Piston Cast iron, Aluminium alloy 5. Piston pin Forged steel, Casehardened steel. 6. Connecting rod Forged steel. Aluminium alloy. 7. Piston rings Cast iron, Pressed steel alloy. 8. Connecting rod bearings Bronze, White metal. 9. Main bearings White metal, Steel backed Babbitt base. 10. Crankshaft Forged steel, Cast steel 11. Camshaft Forged steel, Cast iron, cast steel, 12. Timing gears Cast iron, Fiber, Steel forging. 13. Push rods Forged steel. 14. Engine valves Forged steel, Steel, alloy. 15. Valve springs Carbon spring steel. 16. Manifolds Cast iron, Cast aluminium. 17. Crankcase Cast iron, Welded steel 18. Flywheel Cast iron. 19. Studs and bolts Carbon steel. 20. Gaskets Cork, Copper, Asbestos.
- 6. 6 IC ENGINE – TERMINOLOGY Cylinder Bore (d) : inner diameter of the working cylinder (mm) Piston Area (A) : cross section area of bore (cm2) Stroke(L): The linear distance along the cylinder axis between the two limiting positions of the piston is called stroke(mm) Stroke to Bore Ratio (L/d) d<L - under-square Engine d = L - Square Engine d>L - Over Square Engine. Dead center :Position of working piston at the moment when the direction of the piston is reversed at the ether end of the stroke Top Dead Centre (T.D.C) : The top most position of the piston towards cover end side of the cylinder” is called top dead centre. In case of horizontal engine, it is called as inner dead centre Bottom Dead Centre (B.D.C):The lowest position of the piston towards the crank end side of the cylinder is called bottom dead centre. In case of horizontal engine, it is called outer dead centre (O.D.C). Displacement or Swept Volume (VS): Volume swept by the piston when travelling from one dead center to the other (cc) Cubic Capacity or Engine Capacity :Displacement volume ×No. of cylinders Clearance Volume (VC): The volume contained in the cylinder above the top of the piston, when the piston is at the top dead centre is called clearance volume. Compression ratio : It is the ratio of total cylinder volume to clearance volume. Compression ratio (r) = 𝑉 𝑇/ 𝑉c =(𝑉 𝐶+𝑉 𝑆 )/𝑉 𝐶
- 7. 7 SEQUENCE OF OPERATION: A. Four Stroke Engine: A four-stroke engine is an internal combustion engine in which the piston completes four separate strokes which comprise a single thermodynamic cycle. A stroke refers to the full travel of the piston along the cylinder, in either direction. 1 piston stroke = ½ crankshaft revolution. 4 piston strokes = 2 crankshaft revolutions. The four separate strokes are termed: 1. SUCCTION: this stroke of the piston begins at top dead center. The piston descends from the top of the cylinder to the bottom of the cylinder, increasing the volume of the cylinder. A mixture of fuel and air is forced by atmospheric (or greater) pressure into the cylinder through the intake port. 2. COMPRESSION: with both intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the air or fuel-air mixture into the cylinder head. 3. POWER: this is the start of the second revolution of the cycle. While the piston is close to Top Dead Centre (TDC), the compressed air–fuel mixture in a gasoline engine is ignited, by a spark plug in gasoline engines, or which ignites due to the heat generated by compression in a diesel engine. The resulting pressure from the combustion of the compressed fuel-air mixture forces the piston back down toward Bottom Dead Center (BDC). 4. EXHAUST: during the exhaust stroke, the piston once again returns to top dead center while the exhaust valve is open. This action expels the spent fuel-air mixture through the exhaust valve(s).
- 8. 8 B. Two Stroke Engine: In two stroke cycle engines, the suction and exhaust strokes are eliminated. There are only two remaining strokes i.e., the compression stroke and power stroke and these are usually called upward stroke and downward stroke respectively. Also, instead of valves, there are inlet and exhaust ports in two stroke cycle engines. The burnt exhaust gases are forced out through the exhaust port by a fresh charge which enters the cylinder nearly at the end of the working stroke through the inlet port. The process of removing burnt exhaust gases from the engine cylinder is known as scavenging. COMPARISON BETWEEN TWO STROKE AND FOUR STROKE ENGINES Four stroke engine Two stroke engine 1. One power stroke for every two revolutions of the crankshaft. One power stroke for each revolution of the crankshaft. 2. There are inlet and exhaust valves in the engine. There are inlet and exhaust ports instead of valves. 3. Crankcase is not fully closed and air tight. Crankcase is fully closed and air tight. 4. Top of the piston compresses the charge. Both sides of the piston compress the charge. 5. Size of the flywheel is comparatively larger. Size of the flywheel is comparatively smaller. 6. Fuel is fully consumed. Fuel is not fully consumed. 7. Weight of engine per hp is high. Weight of engine per hp is comparatively low. 8. Thermal efficiency is high. Thermal efficiency is comparatively low. 9. Removal or exhaust gases easy. Removal of exhaust gases comparatively difficult. 10. Torque produced is even. Torque produced is less even. 11. For a given weight, engine would give only half the power of two stroke For same weight, two stroke engine gives twice the power that of four stroke engine.
- 9. 9 Otto Cycle: An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile engines. The processes are described by: Process 0–1 a mass of air is drawn into piston/cylinder arrangement at constant pressure. Process 1–2 is an adiabatic (isentropic) compression of the air as the piston moves from bottom dead centre (BDC) to top dead centre (TDC). Process 2–3 is a constant-volume heat transfer to the working gas from an external source while the piston is at top dead centre. This process is intended to represent the ignition of the fuel-air mixture and the subsequent rapid burning. Process 3–4 is an adiabatic (isentropic) expansion (power stroke). Process 4–1 completes the cycle by a constant-volume process in which heat is rejected from the air while the piston is at bottom dead centre. Process 1–0 the mass of air is released to the atmosphere in a constant pressure process. The Otto cycle consists of isentropic compression, heat addition at constant volume, isentropic expansion, and rejection of heat at constant volume. In the case of a four-stroke Otto cycle, technically there are two additional processes: one for the exhaust of waste heat and combustion products at constant pressure (isobaric), and one for the intake of cool oxygen-rich air also at constant pressure; Efficiency of Otto Cycle
- 10. 10 Diesel Cycle: The Diesel cycle is a combustion process of a reciprocating internal combustion engine. In it, fuel is ignited by heat generated during the compression of air in the combustion chamber, into which fuel is then injected. This is in contrast to igniting the fuel-air mixture with a spark plug as in the Otto cycle (four-stroke/petrol) engine. Diesel engines are used in aircraft, automobiles, power generation, diesel-electric locomotives, and both surface ships and submarines. The image on the left shows a p-V diagram for the ideal Diesel cycle; where is pressure and V the volume or the specific volume if the process is placed on a unit mass basis. The ideal Diesel cycle follows the following four distinct processes: Process 1 to 2 is isentropic compression of the fluid Process 2 to 3 is reversible constant pressure heating Process 3 to 4 is isentropic expansion Process 4 to 1 is reversible constant volume cooling Work in ( ) is done by the piston compressing the air (system) Heat in ( ) is done by the combustion of the fuel Work out ( ) is done by the working fluid expanding and pushing a piston (this produces usable work) Heat out ( ) is done by venting the air Net work produced = - Thermal efficiency of a Diesel cycle is dependent on the compression ratio and the cut-off ratio. Where, is the cut-off ratio (ratio between the end and start volume for the combustion phase) r is the compression ratio
- 11. 11 Dual Cycle: The dual combustion cycle (also known as the limited pressure or mixed cycle, Trinkler cycle, Seiliger cycle or Sabathe cycle) is a thermal cycle that is a combination of the Otto cycle and the Diesel cycle, first introduced by Russian-German engineer Gustav Trinkler. Heat is added partly at constant volume and partly at constant pressure. The dual cycle consists of following operations: 1-2Adiabatic compression 2-3 Addition of heat at constant volume. 3-4 Addition of heat at constant pressure. 4-5Adiabatic expansion. 5-1 Rejection of heat at constant volume. 1)1( 11 1 1 c k c k cconst Dual rk r rv 2 3 5.2 3 andwhere P P v v rc COMPARISON OF DIESEL ENGINE WITH PETROL ENGINE : Diesel engine Petrol engine i) It has got no carburetor, ignition coil and spark plug. It has got carburetor, ignition coil & spark plug. ii) Its compression ratio varies from 14:1 to 22:1 Its compression ratio varies from 5:1 to 8:1. iii) It uses diesel oil as fuel. It uses petrol (gasoline) or power kerosine as fuel. iv) Only air is sucked in cylinder in suction stroke. Mixture of fuel and air is sucked in the cylinder in suction stroke. v) It has got ‘fuel injection pump’ and injector It has got no fuel injection pump and injector, instead it has got carburetor and ignition coil. vi) Fuel is injected in combustion chamber where burning of fuel takes places due to heat of compression. Air fuel mixture is compressed in the combustion chamber when it is ignited by an electric spark. vii) Thermal efficiency varies from 32 to 38% Thermal efficiency varies from 25 to 32% viii)Engine weight per horse-power is high. Engine weight per horsepower is comparatively low. ix) Operating cost is low. Operating cost is high. x) Compression pressure inside the cylinder varies from 35 to 45 kg/cm2 and temperature is about 500°C. Compression pressure varies from 6 to 10 kg/cm2 and temperature is above 260°C.
- 12. 12 VALVE TIMING DIAGRAM : The valve timing of an engine is set to give the best possible performance. This means that the valves must be opened and closed at very precise times. The traditional way of showing exactly when the valve opens and closes is by the use of a valve-timing diagram. As can be seen the valves are opened and closed in relation to the number of degrees of movement of the crankshaft. Valve timing diagram of 4- stroke single cylinder diesel engine. IVO - 25 before TDC IVC - 30 after BDC EVO - 45 before BDC EVC - 15 after TDC FVO - 15 before TDC FVC - 25 after TDC Valve timing diagram of 4- stroke single cylinder petrol engine.(low speed) IVO - 10 before TDC IVC - 20after BDC EVO - 25 before BDC EVC - 5 after TDC
- 13. 13 Valve timing diagram of 4- stroke single cylinder petrol engine.(high speed) IVO - 10 before TDC IVC - 50 after BDC EVO - 45before BDC EVC - 20 after TDC
- 14. 14 ENGINE PERFORMANCE PARAMETERS RELATED TO IC ENGINE: 1.Indicated Power- It is defined as the power developed by combustion of fuel in the cylinder of engine is called (ip). It is always more than brake power. It is given by, where: is the mean pressure, is the area of the piston is the number of cylinders 2.Brake Power- The power developed by an engine and measured at the output shaft is called the brake power (bp) and is given by, where: is the torque, in Newton meter (N.m), is the rotational speed, in minutes, is the brake power, in watt. 3.Friction Power- Friction power is the difference between indicated power and brake power. FP = BP-IP 4.Volumetric Efficiency-It is the ratio of actual volume sucked to the displacement volume. ȵvol = Va/ Vs 5.Mechanical Efficiency- It is defined as ratio of brake power to the indicated power. ȵmech= BP/IP= BP/(BP+FP) 6.Fuel-Air Ratio-It is the ratio of mass of fuel to mass or volume of air in mixture. It effects the phenomenon of combustion and used for determining flame propagation velocity, the heat released in combustion chamber. For practise always relative air fuel ratio is defined. It is the ratio of actual air -fuel ratio to that of the stoichiometric air fuel ratio required for burning of fuel which is supplied. 7.Brake specific fuel consumption(bsfc)-It is defined as the amount of fuel consumed for each unit of brake power per hour . It indicates the efficiency with which the engine develops the power from fuel. it is used to compare performance of different engines. Bsfc = mf/ BP 8. Indicated Thermal Efficiency(ȵith)- It is the ratio of Indicated Power to energy supplied to the cylinder. ȵith = IP/ (mf * CV) where, mf= mass flow rate CV= Calorific Value of fuel
- 15. 15 9.Brake Thermal Efficiency(ȵbth)- It is the ratio of Indicated Power to energy supplied to the cylinder. ȵbth = BP/ (mf * CV) where, mf= mass flow rate CV= Calorific Value of fuel 10.Relative Efficiency(ȵrel)- It is the ratio of Actual thermal efficiency to Air- standard efficiency. ȵrel = ȵact / ȵair- std CHARACTERISTICS CURVES OF VARIOUS PERFORMANCE PARAMETERS: 1.Brake Specific Fuel Consumption vs Size • BSFC decreases with engine size due to reduced heat losses from gas to cylinder wall. • Note: cylinder surface to volume ratio increases with bore diameter. • rLr rL volumecylinder areasurfacecylinder 12 2 2. Brake Specific Fuel Consumption vs Speed There is a minimum in the bsfc versus engine speed curve At high speeds the bsfc increases due to increased friction At lower speeds the bsfc increases due to increased time for heat losses from the gas to the cylinder and piston wall Bsfc increases with compression ratio due to higher thermal efficiency
- 16. 16 3. Performance Maps Performance map is used to display the bsfc over the engines full load and speed range. Using a dynamometer to measure the torque and fuel mass flow rate you can calculate: bmep = 2 T nR / Vd Pb = 2 N T FUEL-AIR CYCLE & THEIR ANALYSIS By air-standard cycle analysis, it is understood how the efficiency is improved by increasing the compression ratio. However, analysis cannot bring out the effect of air-fuel ratio on the thermal efficiency because the working medium was assumed to be air. The fuel-air cycle analysis takes into account the following: (i) The actual composition of the cylinder gases: The cylinder gases contains fuel, air, water vapour and residual gas. The fuel-air ratio changes during the operation of the engine which changes the relative amounts of CO2 , water vapour, etc. (ii) The variation in the specific heat with temperature: Specific heats increase with temperature except for mono-atomic gases. Therefore, the value of also changes with temperature. (iii) The effect of dissociation: The fuel and air do not completely combine chemically at high temperatures (above 1600 K) and this leads to the presence of CO, H2 , H and O2 at equilibrium conditions. (iv)The variation in the number of molecules: The number of molecules present after combustion depend upon fuel-air ratio and upon the pressure and temperature after the combustion. Fig. Effect of Variation of Specific Heats Fig. Effect of Dissociation on Power
- 17. 17 Fig. Effect of Dissociation on Power ACTUAL INDICATOR DIAGRAM
- 18. 18 V.C.R ENGINE SPECIFICATIONS Product Research Engine test setup 1 cylinder, 4 stroke, Multifuel VCR with open ECU for petrol mode (Computerized) Product code 240PE Engine Type 1 cylinder, 4 stroke, water cooled, stroke 110 mm, bore 87.5 mm. Capacity 661 cc. Diesel mode: Power 3.5 KW, Speed 1500 rpm, CR range 12:1-18:1. Injection variation:0- 25 Deg BTDC ECU Petrol mode: Power 4.5 KW @ 1800 rpm, Speed range 1200-1800 rpm, CR range 6:1-10:1 Dynamometer Type eddy current, water cooled, with loading unit Propeller shaft With universal joints Air box M S fabricated with orifice meter and manometer Fuel tank Capacity 15 lit, Type: Duel compartment, with fuel metering pipe of glass Calorimeter Type Pipe in pipe Piezo sensor Combustion: Range 5000 PSI, with low noise cable Diesel line: Range 5000 PSI, with low noise cable Crank angle sensor Resolution 1 Deg, Speed 5500 RPM with TDC pulse. Data acquisition device NI USB-6210, 16-bit, 250kS/s Piezo powering unit. Make-Apex, Model AX-409 Engine control unit. PE3 series ECU, full build potted enclosure Sensors for ECU Air temp, coolant temp, Throttle position and trigger. Engine Controlhardware Fuel injector, Fuel pump, ignition coil, idle air Digital voltmeter Range 0-20V, panel mounted Temperature sensor Type RTD, PT100 and Thermocouple, Type K Temperature transmitter Type two wire, Input RTD PT100, Range 0–100 Deg C, Output 4– 20 mA and Type two wire, Input Thermocouple, Range 0–1200 Deg C, Output 4–20 mA Load indicator Digital, Range 0-50 Kg, Supply 230VAC Load sensor Load cell, type strain gauge, range 0-50 Kg Fuel flow transmitter DP transmitter, Range 0-500 mm WC Air flow transmitter Pressure transmitter, Range (-) 250 mm WC Software “Enginesoft” Engine performance analysis software ECU software peMonitor & peViewer software. Rotameter Engine cooling 40-400 LPH; Calorimeter 25-250 LPH Pump Type Monoblock Overall dimensions W 2000 x D 2500 x H 1500 mm Shipping details: Gross volume 1.33m3, Gross weight 796kg, Net weight 639kg
- 19. 19 DESCRIPTION The setup consists of single cylinder, four stroke, Multi-fuel, research engine connected to eddy current type dynamometer for loading. The operation mode of the engine can be changed from diesel to ECU Petrol or from ECU Petrol to Diesel mode by following some procedural steps. In both modes the compression ratio can be varied without stopping the engine and without altering the combustion chamber geometry by specially designed tilting cylinder block arrangement. In Diesel mode fuel injection point and pressure can be manipulated for research tests. In Petrol mode fuel injection time, fuel injection angle, ignition angle can be programmed with open ECU at each operating point based on RPM and throttle position. It helps in optimizing engine performance throughout its operating range. Air temp, coolant temp, Throttle position and trigger sensor are connected to Open ECU which control ignition coil, fuel injector, fuel pump and idle air. Set up is provided with necessary instruments for combustion pressure, Diesel line pressure and crank-angle measurements. These signals are interfaced with computer for pressure crank-angle diagrams. Instruments are provided to interface airflow, fuel flow, temperatures and load measurements. The set up has stand-alone panel box consisting of air box, two fuel tanks for duel fuel test, manometer, fuel measuring unit, transmitters for air and fuel flow measurements, process indicator and hardware interface. Rotameters are provided for cooling water and calorimeter water flow measurement. A battery, starter and battery charger is provided for engine electric start arrangement. The setup enables study of VCR engine performance for brake power, indicated power, frictional power, BMEP, IMEP, brake thermal efficiency, indicated thermal efficiency, Mechanical efficiency, volumetric efficiency, specific fuel consumption, A/F ratio, heat balance and combustion analysis. Labview based Engine Performance Analysis software package “Enginesoft” is provided for on line engine performance evaluation.
- 20. 20 FUTURE WORKS & DISCUSSION The compression ratio strongly affects the working process and provides an exceptional degree of control over engine performance. By the VCR Engine we can easily get Engine performance parameters. And also we can compare the theoretical & experimental characteristics of PV plot, IP, Heat release ,Max power test ,BSFC and brake thermal efficiency, brake mean effective pressure at different compression ratio(CR) at certain engine speed. We also studyValve timing diagram ,Open ECU Experimentation which includes 1) Fuel Quantity, 2) Fuel angle 3) Ignition angle 4) Coolant temp . VCR Engine measure Emission Parameter i.e. Carbon Monoxide (CO) Emission, Hydrocarbon (HC) Emission, NOX Emission at different Compression ratio.
- 21. 21 CONCLUSION A VCR engine offers the potential to increase combustion efficiency and decrease emissions under varying load and speed conditions. High CR increases theoretical thermal efficiency, but decreases mechanical efficiency. The maximal pressure within a cylinder, and mechanical loses, increases with an increase of both engine load and CR. After performing this project work under supervision and guidance of Dr. Dipak Kumar Mondal(HOD, Mechanical Engg. Dept.) , we have gained the ideas about the various features of this research engine setup & what are the things that can be done by this engine. So, We think that this research engine project is immensely beneficial to our educational as well as industrial career in future.