Presentation on theme: "Types of fuel feed system"— Presentation transcript:
1Types of fuel feed system Gravity systemPressure systemVaccum systemPump systemFuel injection system
2Types of fuel pumpsMechanical fuel pumpElectrical fuel pump
3Types of Carburettor According to the arrangement of float chamber: Eccentric andConcentricAccording to the number of unitsSingleDual andFour-barrelAccording to the type of metering systemAir-bleed jet andMetering rod typeAccording to the type of power systemManually operated andVacuum controlled
4Types of CarburettorAccording to the type of venturi - Plain venturi, - Double venturi, - Vane venturi, - Nozzle-bar venturi and - Triple venturi Depending upon the direction of air flow or forms of Carburettors: a) Up-drought b) Horizontal c) Down-drought Carburettors.
5Types of CarburettorDepending on the method of varying the mixture strength or choke area carburettors are classified as: 1.Open Choke or Constant Choke carburettor The mixture strength is determined by the varying depression of a fixed tube or venturi Eg: solex and zenith 2.Variable Choke or Constant Depression or Constant Vaccum carburettor Depression in the choke tube is reasonably constant and the size of the jet is varied to provide the correct mixture for all engine operating conditions. Eg: S.U. carburettor
6Simple CarburettorVenturiThrottle valveMetering system
7Various systems or circuits in the carburettor Float systemIdling and low speed systemHigh speed systemPower systemAnti-percolatorAccelerating pump systemChoke system
8Float system AIR CLEANER CHOKE VENTURI Float Valve Float Arm Float ChamberFloatTHROTTLE VALVE
9Idling and low speed system Rich mixture is needed- 10:1It consists of idle passages for fuel and airIdling system – starting, idling and low speedsCut off when speed increases to about 40kmph
10High speed system Throttle valve is sufficiently opened Faster air flow through the air horn and greater the vacuum created in the venturiAdditional fuel will be dischargedThis system comes in action as soon as the engine speed increases from 33 KMPH
11Power systemWhen the engine is under strain requiring more power, a richer, a more powerful mixturePower system is either manually operated or vacuum controlled
12Anti-percolatorThis device is to relieve the vapour pressure that develops in the carburettor due to the vaporization of fuel in hot weatherThis pressure causes flooding of fuelThis valve relieves the pressure by venting the passage in the discharge nozzle to the atmosphere
13Accelerating systemFor rapid acceleration, additional fuel must be delivered by carburettorQuick opening of throttle valveProduces leaner mixture instead of being richerAccelerating pump is used to provide correct A-F mixture, discharges directly into mixing chamber
14Choke For starting the cold engine, a rich mixture is needed Choke is operated to shut off the air supply to carburettorDuring the suction stroke less amount of air, and more amount of fuel is sucked thus a rich mixture is obtainedAfter starting the engine choke should be opened to atmosphere– else flooding
15Constant Choke or C.C. Carburettor Here the main orifice known as the choke tube or venturi is of fixed dimensions and metering is affected by varying the pressure drop across it.e.gSolex carburettorZenith carburettorCarter carburettorStromberg carburettor
18Working of Solex Carburettor StarterConsists of a starter valve in the form of flat disc having holes of different sizesThese holes connect the petrol jet and starter jet sides to the passage which opens to air hornStarter lever is operated by the driverAt starting bigger holes are connectedAfter starting smaller holesLater in off position
192. Idling and low speed operation From the lower part of the well of the emulsion system a hole leads off to pilot jet(13)At idling throttle partly closed and engine suction is applied at pilot jet. Fuel from the pilot jet mixes with small amount of air from the small pilot air bleed orifice(14)The rich mixture for idling is discharged into the throttle body past the idling control screw(15).By-pass orifice(17) provided on the venturi side of the throttle valve ensures smooth transfer of idle and low speed circuit to the main jet circuit .
203. Normal runningDuring normal running, the throttle valve is partly opened and the engine suction is applied at the main jet, which supplies the fuelAir enters directly through the venturi and mixes with the fuelThe air-fuel mixture is governed by the throttle valve
214.Acceleration:A diaphragm type acceleration pump supplies extra fuel needed for acceleration through pump injectorPump lever is connected to the accelerator so that pressing the pedal, the lever moves towards the left, pressing the membrane towards the left, thus forcing the petrol through pump jet and injector.On making the pedal free, the lever moves the diaphragm back towards right creating vacuum towards left which opens the pump inlet valve and thus admits the petrol from the chamber into pump.
22Zenith carburettor 3 jets Main jet, compensating jet (around main jet) and idling jetChoke valve is used for startingIdling and slow speed running the air enters through the holesMixes with the fuel in idling passage and passes to the idling jet
23A separate knob is provided for idle adjustment i. e A separate knob is provided for idle adjustment i.e., supply of mixtureWhen the throttle valve is widely opened, the main jet comes into action along with idling jetOn further opening the throttle valve, the whole suction is applied on the main and compensating jet and idling jet is cut offThe compensating jet takes care of A-F correct ratios at different speeds
25Constant Depression or C.D. Carburettor or constant vacuum type SU CARBURETTORSU Carburetters (named for Skinners Union, company that produced them) were a brand of carburettor usually of the side draught type but down draught variants were also used.
27Working of SU carburettor It is a constant vacuum or depression type with automatically variable choke or venturiThe mixture compensation is achieved by maintaining constant vacuum over the jet and varying the effective size of the jetIt is a horizontal type of carburettorSpring loaded piston controls the air passage which is in the form of rectangular opening of constant width and adjustable heightThe position of piston at any instant depends upon the balance of it’s own weight against vacuum forceAs piston weight is constant, vacuum also remain constantConsists of single jet in which a tapered needle operatesA tapering needle is fixed to the piston
28Area of throat is varied by means of a piston which slides up and down When accelerator is operated the piston moves up and down to control the air supplyAnd there by needle moves up and down in the jet controlling the fuel supplyPiston moves up throat area increases and air flow increasesAlso needle moves up area of jet increases and fuel flow increasesSimilarly it reduces and maintain correct A-F mixture at different operating conditionsUsed in racing cars, scooters and motor cyclesNo separate idling or acceleration device is used
30Petrol InjectionPetrol is supplied into intake manifold through petrol Injectors . This process is called the petrol injection.The petrol is received by the injector from the pump and is sprayed into the air stream in atomized form.Adv:High powerQuick starting and warm upLow specific fuel consumptionNo necessity to maintain a stable ignition mixture in the manifoldNo necessity of induction heating
31Free from icing trouble Avoidance of acceleration disturbances during cornering and brakingQuick starting and warm-upGreater freedom in choice of fuelsDis adv:Higher initial costHigher maintenance costComplicated designDifficult in operationDifficult servicing
32Types According to location of injector Cylinder or direct injection systemPort injection system andManifold or throttle body injectionAccording to control methodMechanical injectionElectronic injectionAccording to number of injectorsMulti point injection systemSingle point injection system
33In port injection the Injector is placed on the side of the intake manifold and sprays petrol into the air inside the intake manifold. The petrol mixes with air completely. This mixture of petrol and air then passes through the intake valve and enters into the cylinder.
36Single point fuel injection Single Injector is placed slightly above throat of the throttle body. The Injector sprays petrol into the air in the intake manifold where petrol mixes with air.This mixture then passes through the throttle valve and enters the intake manifold.
37Octane numberThe anti-knock value of fuel is measured in octane number rating (ONR).The fuel iso-octane is highly knock resistant and it is rated 100Normal heptane (n-heptane) knocks easily and it is rated zeroThe percentage of iso-octane by volume in a mixture if iso-octane and n-heptane, which exactly matches the knocking intensity of a given fuel in a standard engine under prescribed operating conditions is termed as “Octane Number” of the fuel
38Cetane numberThe cetane number of diesel fuel refers to the ease with which the fuel ignitesThe best diesel fuel is that which ignites readily and burns steadily and rapidlyIt is rated by means of a scale called cetane ratingThe cetane number assigned to a diesel fuel is a mesure of its ignition qualities compared to those of a standard fuel, normal cetane (C16H34)Lower the cetane number there is more possibility of fuel to knock
39Fuel Injection System in Diesel Engines Functions of a Fuel injection system:Filter the fuelMeasure the correct quantity of fuel to be injectedTime the fuel injectionControl the rate of fuel injectionAtomize the fuelDistribute the fuel in the combustion chamber
40Methods of fuel injection Individual pump injection Air blast injectionAirless injectionCommon rail injectionIndividual pump injectionDistributor system
41Air blast injectionIn this method the, air is compressed in a compressor to high pressure and injected air blast along with fuel into the cylinder.The rate of fuel admission can be controlled by varying the pressure of injection air.Used in large stationary and marine enginesAdv:It provides better atomization and distribution of the fuelAs the combustion is more complete the BMEP is higherInferior fuels can be used
42Dis Adv:It requires high pressure multi stage compressionA separate mechanical linkage is required to time the operation of fuel valveDue to compression and linkage the size of the engine increasesSince the fuel burns very near to the nozzle it is overheated
43Airless or Solid Injection In this method the fuel under high pressure is directly injected into the combustion chamberIt burns due to the heat of compression of the airThis method requires a fuel pump to deliver the fuel at high pressure- 300kg/cm2This method is used for all types of small and big diesel engines
44Comparison between Air blast and Air less injection DescriptionAir blast injectionAir less injectionConstructionComplicatedSimpleWeightHeavyLightCostCostlyCheapFuel atomizedNot properProperlySuitable for enginesLower outputHigher outputAccuracy in manufacturingLessMore is required for pump barrel and fuel injection plungerCompressorMulti stage compressor is requiredNot required
45Types of modern airless or solid fuel injection system: Common Rail Injection SystemIndividual Pump Injection SystemDistributor System
46COMMON RAIL INJECTION SYSTEM A single pump supplies high pressure fuel to header, a relief valve holds the pressure constant.The control wedge adjusts the lift of mechanically operated valve to set amount and time of injection.
47Adv:System is simple and less maintenance costOnly one pump is sufficient for multi cylinder engineIt fulfills requirements of either constant load with variable speeds or variable loads with constant speedVariation in pump supply pressure effects all the cylinders equallyDis adv:Leaks in the injection valveAccurate design and workmanship is required
48Individual pump injection system In this system an individual pump or pump cylinder connects directly to each fuel nozzle.Pump meters charge and control injection timing.
49Each cylinder has its own individual high pressure pump and metering unit It is quite compact method and involve higher costDis adv:This system has to be designed accurately to pump small quantity of fuel
50Distributor SystemIn this system the fuel metered at a central point, a pump pressurizes, meters the fuel and times the injection.From here fuel is distributed to cylinders in correct firing order by cam operated poppet valves which open to admit fuel to the nozzles.
51Fuel injection pumpGenerally the fuel injection pumps are classified asJerk pump typeDistributor type
52FUEL PUMPL is the plunger driven by a cam and tappet mechanism at the bottom . B is the barrel in which plunger reciprocates.There is a rectangular vertical groove in the plunger which extends from top to another helical groove.V is the delivery valve which lifts off its seat under the liquid fuel pressure and spring force.The fuel pump is connected to the fuel atomizer through passage P. SP and Y are the spill and the supply port respectively.When the plunger is at the bottom both ports SP and Y are uncovered by the plunger and fuel enters from the port SP into the barrel.On further upward movement of the plunger both the ports are closed and fuel is compressed and delivered through passage P to the atomizer as delivery valve lifts off from its seat.
53With further rise of the Plunger at certain moment, the port SP is connected to the fuel in the upper part of the plunger through rectangular vertical groove through helical groove , as a result of which sudden fall in pressure occurs and delivery valve occupies seat against the spring force.The plunger is rotated by the Rack R which is moved in or out by the governor. By changing the Angular position of the helical groove according to the load and speed of the vehicle amount of fuel delivered can be varied.
55FUEL INJECTOR OR ATOMISER It consist of a nozzle valve(NV) fitted in the nozzle body (NB).The nozzle valve is held on its seat by a spring ‘S’ which exerts pressure through spindle E. ‘AS’ is the adjusting screw by which nozzle valve lift can be adjusted.The fuel under pressure from the fuel pump enters the injector through the passages B and C and lifts the nozzle valve.The fuel travels down nozzle N and injected into the engine cylinder in the form of fine spray.Then the pressure of the oil falls, the nozzle valve occupies its seat under the spring force and fuel supply is cut off.
56Any leakage of fuel accumulated above the valve is led to the fuel tank through passage-A. The leakage occurs when the nozzle valve is worn outFP is the feeling pin which indicates whether valve is working properly or notUsually the nozzle valve is set to lift at 135 to 175 bars pressure.
57Fuel Filter Types of filters: Cloth Felt Combination of cloth and felt- heavy vehiclesPaper – better since even smallest dust and dirt particles are removedFelt with paper element- commonly used in heavy vehicles
59Fuel governor Different methods to control the flow of fuel: Hit and miss method- fuel supply is cut off during few cycles, Used in gas enginesQuality governing- A:F ratio varied based on engine load, used in diesel enginesQuantity governing- quantity of A:F ratio according to engine load, used in petrol enginesTypes of governors:Mechanical or centrifugal governorPneumatic governorHydraulic governor