Advantages Of Internal Combustion Engines Engineering Essay

Advantages Of Internal fire Engines Engineering EssayThe most widely use heat locomotive vituperateway locomotive is the inhering burning at the stake engine. The advantages that it has everywhere gas turbines assume seen its widespread usage in passenger car applications. 1All the components of internal combustion engines work at an average temperature which is be low gear the maximum temperature of the workings(a) fluid in the working bike.This is because the spicy temperature of the working fluid in the cycle persists only for a very sm each(prenominal) figure of the cycle time.As a resolving power, fluids with high working temperatures stop be apply to step-up thermal dexterity at mode outrank maximum working wardrobes.Weight to power ratio is less than that of steam turbine and gas turbines.It is at that placefrom possible to develop reciprocating IC engines of very small power proceeds with reasonable thermal competency and comprise.Higher bracken the rmal cogency can be obtained as only a small fraction of heat energy of the enkindle is dissipated to the cooling trunk.Initial cost is low.Materials used in the manufacture of gas turbines must be material and heat resistant in arrange to sustain the heat gene considerd. Machining operations required for gas turbines construction ar also more complex.Reciprocating IC engines argon more efficient at idle stop numbers than gas turbines in terms of arouse white plague at idling. hit man turbines have retard responses to different power requirements changes.Gas turbines must be removed for die and servicing, which is usually not the case in internal combustion engines.Gas turbines require more denude than IC engines for its normal operation. It also consumes more displace whenever the load fluctuates, which is common in the domestic usage.All these rationalise why passenger cars do not use gas turbine engines, simply use internal combustion engines instead. interrogator y 2Define the hobby argumentations and give typical determine for spark-ignition and compression ignition IC engines limited render consumption,Specific provoke consumption (SFC) is the go off campaign rate per unit power output . It steps how strength of an engine in using the fuel to produce useful work.The equation for the specific fuel consumption isWhereKe= specific fuel consumptionK give the axe Consumption, kg/sPe=Useful work per cycle, i = 0.5 for 4, 1 for 2ne=real efficiencyH =Heat of Combustion = 42.000 KJ/Kg dispirited encourages of SFC ar obviously desirable.For SI engines typical values of brake specific fuel consumption are about 270 g/kWh. govern (345 285 g/kWh)For CI engines, values are lower and in sizeable engines can go below 200 g/kWh.Range (285 xcl g/kWh) 2Mean effective squeeze,Relative engine performance measure is obtained by dividing the work per cycle by the piston chamber volume displaced per cycle. The parameter so obtained has units of force per unit area and is called the mean effective imperativeness (mep).WhereW=Indicated WorkVh=Piston Displacement (cylinder) Volume (cc, cm3, lt)H= distance TDC Length BDCFor,Naturally aspirated spark ignition engines, maximum values are in the range 850 to 1050 kPa at the engine speed where maximum crookedness is obtained (about 3000 rev/min).Turbo send outd automotive spark-ignition engines the maximum bmep is in the 1250 to 1700 kPa range.Naturally aspirated foursome- snapshot diesels, the maximum bmep is in the 700 to 900 kPa rangeTurbocharged four- stroking diesel maximum bmep values are typically in the range 1000 to 1200 kPaTurbocharged aftercooled engines this can rise to 1400 kPaTwo-stroke cycle diesels have corresponding performance to four-stroke cycle engines. Large low-speed two-stroke cycle engines can achieve bmep values of about 1600 kPa.2Power- torsion relation as function of engine rpm,Engine torque is measurable using a dynamometer. The engine is clamped and the output shaft is connected to the dynamometer rotor. The rotor is coupled electromagnetically, hydraulically, or by mechanical friction to a stator, which is supported in low friction bearings. The stator is equilibrate keeping the rotor stationary. The torque exerted on the stator with the rotor turn is measured by balancing the stator with weights, springs, or pneumatic means.Fig.1 bracken dynamometer- engine torque test 2Torque is a measure of an engines mogul to do work and power is the rate at which work is done. The value of engine power measured as described supra is called brake power Pb. This power is the usable power delivered by the engine to the load-in this case, a brake.Fig.2 Engine power, torque vs. speed plot 3Correlation between measured force and engine torqueMeasured power (1 PS = 0.736 kW) vicissitude between different units may be necessary for power, torque, or angular speed. For example, if rotational speed (revolutions per time) is used in place of angular speed (radians per time), a factor of 2 radians per revolution have to be multiplied.Dividing on the left by 60 seconds per minute and by 1000 watts per kW gives us the following.mboxpower (kW) = frac mboxtorque (Ncdotmboxm) propagation 2 pi times mboxrotational speed (rpm) 60,000Volumetric efficiencyVolumetric efficiency is the ratio of the mass privileged the engine cylinder to the mass of air of the deracination volume at atmospheric conditions. It measures the effectiveness of an engines induction cognitive operation. Volumetric efficiency is used for four-stroke cycle engines which have a distinct induction march and not for two stroke engines.Where pai is the inlet air density or else volumetric efficiency can also be defined as, indicatory values 4-Otto 0.7 0.92-Otto 0.5 0.7Typical maximum values of v for naturally aspirated engines are in the range 80 to 90 percent. The volumetric efficiency for diesels is somewhat higher than for SI engines.2Engine real efficiency as function of engine power, fuel consumption and fuel calorific valueThe real engine efficiency of an engine can be found out using the relationWhere,ne=real efficiencynth= theoretical thermodynamic efficiencyng=quality coefficient (0.4-0.7 Otto 0.6-0.8 Diesel)nm=mechanical efficiency (0.8)ni=actual efficiency (nth.ng=Pi/Q)K= fuel consumption Kg/sH =Heat of Combustion = 42.000 KJ/KgQuestion 3Describe with simple terms the master(prenominal)(prenominal) air immix path developing inside the cylinder of IC engines relative to the piston motion make a simple schematic drawing to indicate them.Laser Doppler Velocimetry (LDV) helps us to visualise the charge motion inwardly the cylinder with the help of optically transparent research engines. Computational liquified Dynamics (CFD) can help in validating the average prevail field in the cylinder but the process is expensive. One such(prenominal) CFD software is KIVA-4v, which helps to predict the air charge motion. convol ution flowSwirl is defined as the micro mass rotational motion of charge inside the cylinder. It is generated by constructing the intake musical arrangement to give a digressive component to the intake flow as it enters the cylinder. This is done by geological physical composition and contouring the intake manifold, valve ports, and sometimes even the piston face. Swirl enhances the miscellany of air and fuel to give a homogeneous categorisation in a short time in modern high-speed engines. It is also obligated for very rapid spreading of flame front during the combustion.Fig.3 Swirl flow in the engine cylinder 3Swirl flow can be generated by changing the geometry of the inlet portFig.4 Geometry of inlet port touch swirl flow 3(a) Deflector wall (b) directed (c) shallow ramp coiling (d) steep ramp helicalSimilarly inlet valve approach geometry can also generate swirl flow by producing net in-cylinder angular momentum of the charge.Fig.5 Inlet valve geometry affecting swirl f low 2Squish flowWhen the piston approaches TDC at the end of the compression stroke, the volume around the satellite edges of the combustion chamber reduces drastically. New combustion chamber designs have the clearance volume near the centerline of the cylinder. As the piston approaches TDC, the gas mixture occupying the volume at the outer radius of the cylinder is forced radial-ply tirely inward as this outer volume is reduced to near zero. This radial inward motion of the gas mixture is called quell. It adds to other mass motions at heart the cylinder to mix the air and fuel, and quickly spreads the flame front. Maximum squelch velocity usually occurs at about 10bTDC.During combustion, the expansion stroke begins and the volume of the combustion chamber increases. As the piston moves away from TDC, the impatient gases are propelled radially outward to fill the now-increasing outer volume along the cylinder walls. This reverse squish helps to spread the flame front during the latter(prenominal) part of combustionPiston motion influences squish as in the case of wedge shaped and bowl-in combustion chambers.Fig.6 Piston motion generating squish 2(a) Wedge shaped SI combustion chamber (b) bowl-in-piston DI Diesel combustion chamberTumbleAs the piston nears TDC, squish motion gene judge a secondary rotational flow called tumble. This rotation occurs about a peripheral axis near the outer edge of the piston bowlFig.7Tumble- result of piston motion and squish 3 convulsionDue to the high velocities involved, all flows into, out of, and wi svelte engine cylinders are turbulent flows. The exception to this is those flows in the corners and small crevices of the combustion chamber where the almost proximity of the walls dampens out turbulence. As a result of turbulence, thermodynamic transfer rates within an engine are increased by an order of magnitude. Heat transfer, evaporation, mixing, and combustion rates all increase. As engine speed increases, flow r ates increase, with a corresponding increase in swirl, squish, and turbulence. This increases the real-time rate of fuel evaporation, mixing of the fuel vapor and air, and combustion.Intake turbulent mixture flow Turbulence superimposed on mixture swirlFig.8 Turbulence of the charge within cylinder 4Question 4The Figure below shows a abstract model of a quasi-steady Diesel combustion plume, as presented by regrets et al in 1997. Indicate the following areas shown on this schematic limpid fuel , well-heeled vapour fuel-air mixture ,fuel- full premixed flame,initial soot formation , dispersion flame boundary ,thermal NO production order ,soot oxidation zone ,25398f1.jpgFig.9 Quasi-steady Diesel combustion plume 5The above figure describes the formation and features of a quasi-steady diesel fuel pitchy. This model is applicable to large bore, quiescent chamber combustion or a unaffixed fuel jet without wall interactions. At the point of fuel jibe, fuel penetrates into the combust ion chamber and air which is at a high temperature cod to end of compression stroke begins to mix with the atomiser. Fuel absorbs energy from the burning air and evaporates. This process continues until a point where no liquid fuel is present. The point at which this occurs is called the liquid length. This liquid length reduces after the hook on of combustion but thereafter remains constant until the end of snap. beyond the liquid length, the rich premixed fuel and air are simmer down het up(p) by the surroundings until they take up to react in the rich premixed zone. The products of rich combustion continue downstream and diffuse and mix radially outward until reaching the surrounding cylinder gases. At a location where the rich products and cylinder gases mix to produce a stoichiometric mixture, a dispersal flame is produced. The diffusion flame surrounds the jet in a thin turbulent sheet, which extends upstream towards the snout. The axial distance from the nozzle exit to the diffusion flame is the lift-off length. The lift-off length arrests the amount of oxygen mixed into the fuel jet and therefore the stoichiometry. Soot is burned out and NOX is produced on the outdoors of the diffusion flame, where temperatures are high and oxygen and nitrogen are abundant.Question 5What are the main requirements of the fuel dig system for a direct injection engine?In recent years, significant jump on has been made in the development of advanced computer- turn backled fuel injection systems, which has had more than to do with the research and development activities related to Direct Injected engines being expanded.6The main requirements of the fuel injection system for a direct injection engine areWell atomised fuel spray independent of chamber force per unit area level conditions shooting during the compression stroke against pinchs up to 20barInjection during the intake stroke against atmospheric pulls with stoichiometric homogeneous mixtureTo have uniform dispersal of fuel in a multi cylinder engineTo improve ventilation capacity of an engine i.e. volumetric efficiencyTo reduce or go across detonationTo prevent fuel loss in the form of scavenging in the case of two stroke engines.For an efficient combustion of a tell mixture, a stable and compact spray geometry is necessaryInjection pressure has been determined to be very important for obtaining both effective spray atomization and the required level of spray penetration.Accurate fuel metering (generally a +2% band over the linear flow range)Desirable fuel mass dispersal recipe for the applicationMinimal spray reorient for both sac and main spraysGood spray axisymmetry over the operate rangeMinimal drippage and zero fuel leakage, particularly for frigidity operationSmall sac volumeGood low-end linearity between the dynamic flow and the fuel pulse widthSmall pulse-to-pulse discrepancy in fuel quantity and spray characteristicsMinimal variation in the above parameters from unit to unit.Question 6Describe the injection process requirements for direct injection Diesel engines and the evolution of the fuel injection equipment over the defy few decades.The functional requirements of the fuel injection system are as followsAccurate fuel metering per engine working cycleInjection timing to ensure maximum power, good fuel economy and low emissionsObtain the desirable heat release pattern by match of injection rateAtomisation of the fuelProper spray pattern to ensure better mixing of fuel and airUniform distribution of fuel droplets in the combustion chamberSupply equal quantities of fuel to all cylinders, in the case of multi cylinder enginesEliminate dripping of fuel droplets into the combustion chamber by eliminating injection lag between start and end of injectionEvolution of fuel injection equipmentIn-line pumpFig.10 Layout of In-line fuel injection pump 7Though in-line pumps are primitive injection systems, they are still in use among heavy duty marine engines. respective(prenominal) fuel pumps fuel each of the injectorsEngine operational speed has a major influence on the fuel injection pressuresAs a result, there is a hydraulic delay between the pressure increase and the start of injectionFuel flows through high pressure connecting pipesFuel injection pressures range from 600 1200 barInjector with discharging in the combustion chamber (the nozzle with one or more holes)Distributor type pumpsThese are still used in a number of enginesThough it started as automatically operated, now electronic control modifications have been madeIt has a apparatus which controls the spill valve responsible for cutting off the high pressure generated inside the pumping chamber, and thus, responsible for the termination of injectionOne pumping chamber delivers high pressure to all the injectors of the enginePressure depends on engine speed, so a hydraulic delay exists between the pressure generation and start of injectionRelatively low i njection pressures (up to 1200bar)Fig.11 Distributor type pump (Lucas CAV) 7whole injectorsConsists of the pump and the injector integrated into one body, which does not require a high pressure connection pipeHigh fuel pressure is generated close to the nozzle exit, which can be upto 2500 bar.These gave accurate control over injectionEach cylinder has its own individual systemHigh pressure developed depends of the engine rpm and the load.Fig.12 General Layout of Unit injector 76Delphi Diesel Systems electronic unit injectors (EUI fig13.) control the quantity and the timing of injection electronically through a solenoid actuator. The solenoid can respond very quickly (injection periods are of the order 1 ms), to control very high injection pressures (up to 1600 bar or so). The solenoid controls a spill valve, which in turn controls the injection process. The pumping element is operated like a shot from a camshaft (or indirectly via a rocker), and the whole assembly is contained with in the cylinder head.Fig.13 electronic Unit injector (Lucas EUI system) 76An alternative approach to the EUI is the Caterpillar Hydraulic Electronic Unit Injector (HEUI, also supplied by other manufacturers). HEUI uses a hydraulic pressure intensifier system with a 7 1 pressure ratio to generate the injection pressures. The hydraulic pressure is generated by pumping engine lubricator to a controllable high pressure. Similar to CR injection systems, there is control of the injection pressure. The HEUI uses a two-stage valve to control the oil pressure, and this is able to control the rate at which the fuel pressure rises, thereby controlling the rate of injection, because a lower injection rate can help control NOx emissions.Common Rail fuel injection systemsOne of the last improvements to the fuel injection system is the Common Rail System that was utilise first by the Fiat Company.Fig.14 Common rail fuel injection system 8Common rail (CR) fuel injection systems decouple the press ure generation from the injection process and have become popular because of the possibilities offered by electronic control.The key elements of a CR fuel injection system are as followsA (controllable) high-pressure pumpThe fuel rail with a pressure sensorElectronically controlled injectorsAn engine management system (EMS)The injector is an electro-hydraulic device, in which a control valve determines whether or not the injector needle lifts from its seat. The engine management system can divide the injection process into four phases two pilot injections, main injection, and post-injection (for supplying a controlled quantity of hydrocarbons as a reducing agent for NOx catalysts). Common rail injection also enables a high output to be achieved at a comparatively low engine speedFuel injectorsFig.15 Types of nozzles used in Diesel fuel injectors 1