03. Fuel and Air Feed System

Transcription

1 Page 11 of 03. Fuel and Air Feed System Content (16 Marks) 3.1 Petrol fuel supply system. 8 Marks Conventional Petrol Engine: Gravity feed, Pump feed (Layout,Function of Components and location). Construction and working of components: Fuel Tank, Fuel Filter, S. U. Electrical Fuel Pump, Air cleaners dry type and Oil wetted types. Working Principle of Simple Carburettor, Air Fuel ratio requirements, Circuits in Two-wheeler carburettor and Solex carburettor. 3.2 Diesel fuel supply system 8 Marks Diesel Engine: Need and requirements of Fuel Injection Systems. Layout of Fuel Injection systems Individual pump, Unit injector system, Distributor system and Common rail system. Fuel Injector and types of nozzles. Fuel metering in Fuel Injection Pump ( Inline pump and Distributor pump ) Working principle of Mechanical Governor in Fuel Injection Pump. 3.1 Petrol fuel supply system. In petrol engine fuel from the fuel tank can be supplied to the engine cylinder by following systems Gravity System Pressure System Vacuum System Pump System Fuel injection System Gravity System: The gravity system of fuel feed, the fuel tank is mounted at a place higher than that of the carburetor. The fuel flows from the tank to the carburetor due to the gravitational force. Pressure System: In pressure system, a pressure sealed tank is used. The pressure is created in the tank by means of a separate air pump. For starting, the pump is primed by cam which produces pressure in the tank and the fuel flows to the carburetor. In this system tank can be placed above or below the carburetor. Vacuum System: In vacuum system, the engine suction is used for sucking the fuel from main tank to the auxiliary fuel tank from where it flows by gravity to the carburetor.

2 Page 22 of Fuel injection System: In fuel injection system, a fuel injection pump is used in place of carburetor. The fuel is atomized by means of a nozzle and then delivered in to an air stream. Separate fuel injection system is used for each cylinder which controls the mixture under different load and speed conditions. Pump System: Fuel pump is used in fuel system to deliver fuel from fuel tank to the carburettor. Generally there are 2 types of fuel pumps; A) Mechanical fuel pumps. B) Electrical fuel pump. Construction and working of components: Fuel Tank: The fuel tank is made of sheet metal. It is usually attached to the frame at the rear of vehicle. Its capacity ranges from 70 to 120 lit. The filler neck of the tank is closed by a cap. A drain plug is provided at the bottom for emptying the tank. Vapor recovery system prevents escape of vaporized gasoline in to the air. Fuel Filter: The fuel filter screens and filter dirt in the fuel pump and carburetor. Dirt causes poor performance of engine and improper functioning of pump and carburetor. A) MECHANICAL FUEL PUMP: (W12 / S12/ W11) This pump is also called as A.C. mechanical pump. The construction features of this type of pump are as follows; 1) It is bolted to the engine block or the crankcase. 2) Drive is taken from the camshaft by means of an eccentric. The eccentric operates the rocker arm. Rocker arm operates the Diaphragm. 3) Diaphragm consists of high grade cotton; impregnated with the synthetic rubber. 4) The movement of the diaphragm sucks the fuel from fuel tank and pushes it to the carburettor. 5) Pressure in the petrol pipeline is between 20 to 35 kpa.

3 Page 33 of Working: The mechanical fuel pump works in following manner; 1) As the cam shaft rotates, the eccentric on the camshaft operates the rocker arm; which in turn pushes the diaphragm upward. 2) The downward movement of the diaphragm sucks the fuel through strainer from the fuel tank. 3) The upward movement of the diaphragm pushes the fuel up, which causes Suction valve to close and Pressure valve to open. 4) The fuel passing through outlet valve is supplied to the carburettor. 5) If the float chamber of the carburettor is completely filled up, then there is no need of pumping more fuel. 6) Diaphragm return spring restricts the supply of petrol. It remains compressed if the float chamber is full of fuel and due to the line pressure. Thus movement of the diaphragm is restricted. Reliability is main advantage of the mechanical pump. However these pumps have some disadvantages; 1) They have to be situated close to the engine due to which they are exposed to engine heat, which may result in vapour lock in the fuel supply system. 2) They operate only after the engine has started.

4 Page 44 of B) ELECTRICAL FUEL PUMP: (W 12) It is also known as S.U. electric fuel pump. The construction & working features of this fuel pump are as follows; 1) It consists of a diaphragm, but it is operated electrically. 2) An ignition switch is turned on, thus the solenoid winding generates magnetic flux, which pulls the armature upward and the diaphragm moves up. 3) The upward movement of the diaphragm creates suction & thus the fuel is drawn into chamber through the inlet valve. 4) But as soon as armature moves up, the electric supply is disconnected at contact breaker point. The magnetic flux dies and the armature falls down, causing the diaphragm to move downward & creating pressure in the pump chamber. 5) This causes the outlet valve to open and inlet valve to close & the fuel goes to the carburettor via outlet valve. 6) The downward movement of the armature again sets electric supply to the solenoid. The process keeps on repeating, the pump continues to operate until the ignition switch is turned off. The advantage of Electrical pump are that; (W 12) 1) They need not need to be situated near the engine; mostly they area located near the fuel tank. So they are not subjected to the engine heat. 2) It starts operating as soon as the ignition is switched on, it does not waits for engine to start.

5 Page 55 of Fuel Filter: Air cleaner are classified on the basis of principle of filtration. The air cleaners generally used are of the following types. 1. Dry type air cleaner 2. Oil wetted type air cleaner Dry type air cleaner It is light duty air cleaner. It does not contain oil path. It consists of cleaning element only. Cleaning element is made up of paper which is enclosed in silencing chamber. Oil wetted type air cleaner It is heavy duty air cleaner. It consists of cleaning element made up of wire mesh coated with an oil film. When air passes through this element, the dust particles collects on oil film.

6 Page 66 of 5.2 PRINCIPLES OF CARBURETTOR: FUNCTION OF CARBURETTOR: (W 11) The main functions of the carburettor are: 1) To keep a small reserve of fuel at a constant head. 2) To vaporize the fuel to prepare a homogeneous air fuel mixture. 3) To supply correct amount of the air fuel mixture at the correct strength under all conditions of load and speed. SIMPLE CARBURETTOR: (S 12 / W 11) To understand working of the carburettor, consider a simple carburattor. The main parts of carburettor are float chamber, fuel jet, venturi, nozzle and throttle valve. This figure is schematic presentation of carburettor; The round cylinder is called as air horn & the constricted section is called venture. The venturi & the float chamber are connected by the fuel nozzle. The throttle valve tilts to open or close the air horn. The construction & function of these parts are as follows;

7 Page 77 of A. FLOAT CHAMBER: The construction features of float system are as follows; 1) The float system consists of a float chamber or bowl, a float and a needle valve arrangement. 2) The float is a closed air tight vessel, pivoted to the float chamber by a lever. The lever is attached with the needle valve. The needle valve consist of cylinder stem with conical tip, which sits on the valve seat through which the fuel comes into float chamber. 3) The float and the needle valve maintain a constant level of the fuel in the float chamber If the level of fuel in the float chamber is too high, then too much fuel will be feed from the nozzle, making mixture rich. If the level is too low, then too little fuel will be feed from nozzle, making mixture lean. Both the cases are not desired & will affect the engine performance. 4) Float in the float chamber is made of brass sheet, nylon plastic or expandable synthetic rubber. 5) The needle valve attached to float; it serves closing & opening of the fuel inlet to the float chamber. B. VENTURI: The fuel supply from the float chamber at any time is metered by means of fuel jet from where the fuel flows to the venturi through discharge nozzle. 1) The venturi is simple restriction in the air passage. 2) The passage area is minimized. Thus due to less area, the velocity of air increases & because of this increase in velocity the pressure in venturi decreases. 3) Nozzle is located in the venturi. Due to decreased pressure, fuel comes out from nozzle & vaporizes by coming air stream. 4) The mixture then goes to inlet manifold & then to engine cylinder. C. THROTTLE VALVE: (S 12) The function & construction features of throttle valve are as follows; 1) The purpose of the throttle valve is to control the quantity of air fuel mixture.

8 Page 88 of 2) It is attached to the accelerator pedal by means of suitable linkage so that when the pedal is depressed, the valve opens out. 3) The throttle valves are of 2 types; a. Butterfly valve b. Cylinder valve. a. The butterfly valve, is more commonly used because of its simplicity; it is merely a disc hinged at the center. b. The cylindrical valve has an advantage; that it does not obstruct the passage when fully open. Working Principle of the Throttle valve: 1) When throttle valve is completely closed, no air will pass the venturi. 2) When throttle valve is partially open, less air passes through venturi & less air fuel mixture goes to engine cylinder. Thus lesser power is developed & engine runs slowly. 3) When throttle valve is completely open, more air passes through venturi & more air fuel mixture goes to the engine cylinder. Thus engine develops more power & tends to run faster.

9 Page 99 of AIR FUEL RATIO: (W 12) The carburettor must supply the air-fuel mixture of varying proportions to suit the different operating requirements. The mixture must be rich for starting, idling & must be relatively lean for general speed. The figure shows air fuel ratio at different speeds of vehicle; 1) For starting, Air-Fuel ratio is 9 : 1. It is rich mixture. 2) For idling the ratio is 12 : 1, it is comparatively leaner w. r. t. starting mixture. 3) For intermediate speed (35 to 105 km/h), the mixture is further leaner 15 : 1. 4) But at higher speed (120 to 150 km/h), the throttle valve is completely open, the mixture is enriched to about 13 : 1. 5) Stoichiometric mixture: At normal operation, 14.6 : 1 i.e.: 14.6 parts of air & 1 part of gasoline (by mass) is the ratio, which would give chemically complete combustion of petrol under ideal condition. At starting and at idle, the mixture must be rich for initial start, because the engine and the carburettor are cold, the fuel vaporizes very poorly. Thus extra amount of fuel is needed so that enough fuel will be available for vaporization. At acceleration, sudden opening of the throttle valve occurs, air rushes suddenly. Hence extra fuel must come at the same time. Thus carburettor must be designed to supply correct air fuel mixture for all the above operating conditions.

10 VARIOUS CIRCUITS OF THE CARBURATOR: Page 1010 of A carburettor has following circuits, through which air fuel mixture is feed through according to engine operating conditions. Following are the types of circuits; 1) Starting circuit 2) Idling & slow speed circuit 3) Main metering system 4) Acceleration Circuit 5) Choke system 1) STARTING CIRCUIT: The features of the starting circuit are as follows; The choke is used for starting the engine (choke will be closed during starting). Choke is mounted eccentrically, to facilitate automatic opening after engine starts. As the choke valve is closed, the whole engine suction is applied at the main nozzle, which delivers fuel. As the air supplied is quite small in quantity, the air fuel mixture supplied is rich.

11 2) IDLING & SLOW SPEED CIRCUIT: Page 1111 of An idling passage is provided with separate slow speed port & idling port. The features of idling & slow speed circuit are as below; a) IDLING CIRCUIT: For idling, rich mixture is required in small quantity. The throttle valve is almost closed as shown in the figure. The whole engine suction is now applied at the idle port. A rich mixture is supplied to the engine cylinder. b) SLOW SPEED CIRCUIT: Throttle valve is slightly open as shown in the figure. The main nozzle also starts supplying the fuel. At this stage, fuel is supplied both by the main venturi & low speed port through idle passage.

12 Page 1212 of 3) MAIN METERING SYSTEM: (W 12) When the throttle vale is partially open, the fuel is delivered by the main nozzle only. The fuel is supplied to the main nozzle by means by metering circuit. Metering rod controls the fuel supply through metering circuit. Metering rod consists of number of steps of different diameters. Metering rod is connected to the accelerator pedal through linkages. As the accelerator pedal is pressed, the throttle valve is held wide open & at the same time metering rod is lifted up. Now the smaller diameter of the rod is inside the fuel - hole, providing larger flow area, thus delivering more fuel. 4) ACCELERATION CIRCUIT: The construction of the pump is clear from above given figure. When accelerator pedal is pressed, the pump is actuated. This provides extra spray of fuel for acceleration. Leaving accelerator pedal causes pump piston to move up, there by sucking more fuel from float chamber. Thus the pump is now ready for next operation. (* Note: Purpose of the accelerating pump is not to provide a continuous fuel supply for acceleration, but only to provide extra spray of fuel to avoid flat spot.)

13 Page 1313 of 5) CHOKE SYSTEM: It is simply butterfly valve fitted at the top of the air horn. It may be operated by hand or it may be operated automatically. While starting the engine, the choke is closed so that very small amount of air gets past it & the throttle valve is open due to which whole of the suction is applied at the nozzle, which delivers sufficient fuel to provide rich mixture, though smaller in quantity. The choke valve must be opened as soon as the engine starts; otherwise the engine cylinder will be flooded with fuel, which is not desired. The choke system consists of choke shaft, choke lever assembly, choke valve, spring etc The choke shaft is generally off centre, so that one side of the valve has larger area than the other. The unbalanced condition helps in opening the valve during the engine operation due to the greater force of the incoming air on the larger surface.

14 Page 1414 of S.U. CARBURETOR: (W12 / S12) The figure shows simplified figure of a S.U. carburettor. The construction & working features of S.U. carburettor are as follows; 1) This carburettor is example of constant vacuum or variable venturi type of carburettor 2) The Throttle valve (14) is ordinary butterfly type valve. 3) This carburettor consists of a single main jet, in which tapered needle (8) operates. 4) The area of throat is varied by means of a spring loaded piston (6) which slides up & down. Piston controls the air passage. 5) The tapered needle is connected to the accelerator. When accelerator is operated; the piston moves up & down in the throat controlling the supply of air. The needle also moves up & down in the jet, controlling the supply of fuel. 6) When piston moves up, throat area increases, more air passes through it & when piston moves down, lesser air passes through it.

15 Page 1515 of 7) When the needle moves up, the annular area in the jet increases which causes more fuel supply & when needle moves down the annular area decreases & less fuel passes through the jet. 8) A damper plunger (17) is installed in the hollow piston rod (16), in which oil of suitable viscosity is also filled. It regulates the rate of lift of the piston. 9) Jet adjustment nut (12) is meant to adjust mixture strength. Tightening the nut will raise the jet, thereby reducing annular area for fuel flow. Similarly lessening nut will increase the fuel supply. SOLEX CARBURETTOR: (W 11) Below given figure shows a solex carburettor. It supplies richer mixture for starting & then gradually weakens the mixture, till engine reaches normal operating speed. Various circuits of carburettor are explained below; 1) Starting circuit 2) Idling or low speed circuit 3) Normal running circuit 4) Acceleration circuit

16 Page 1616 of 1) STARTING CIRCUIT: carburettor; Below shown is a simplified figure of progressive starting circuit of solex The starter valve is in the form of a flat disc with holes of different sizes. The holes connect Petrol jet & Starter jet sides to the passage; this passage opens into the air horn just below the throttle valve. The starter lever is operated by the driver from the dashboard, which adjust the position of the starter valve so that either bigger or smaller holes come opposite to the passage. At the time of starting; I. The bigger holes are the connecting holes, so that more fuel may go to the engine. II. The throttle valve being closed, whole of the engine suction is applied to the starting passage 1, at the same time petrol from float chamber passes through Petrol jet & rises into passage 2. III. Some of it comes out & mixes with the air entering through the air jet. This air fuel mixture is rich enough to start the engine.

17 Page 1717 of After the engine has started; I. The starter lever is brought to the second position, so that smaller hole connects the passage & reducing the amount of petrol supplied. II. In this position the throttle valve is also partly open, so that the petrol is also coming from the main jet. III. The reduced mixture supply from the starter system in this situation is sufficient to keep engine running. IV. When engine reaches to normal working speed and temperature, the starter is brought to off position. 2) IDLING OR LOW SPEED CIRCUIT: The idle port is controlled by idle screw. It is provided near the throttle valve. As the throttle is almost closed the engine suction is applied at the pilot petrol jet, which supplies the petrol. The jet itself draws the petrol from the main jet circuit. The air is drawn in form the pilot air jet. The petrol & the air mix in the idle passage & the mixture comes out of the idle port. Slow speed opening are provided on the venturi side of the throttle valve, to ensure smooth transfer from idling circuit to main jet circuit, without occurrence of flat spot. When the throttle valve is opened, the suction decreases at the idle port & is applied at slow speed opening. 3) Normal running circuit: During normal running, the throttle valve is opened & engine suction is applied at the main jet, which supplies the fuel. The air enters directly through venturi & mixes with the fuel. The air fuel mixture is governed by the throttle valve. 4) Acceleration circuit: For acceleration, extra fuel is required by the engine, which is supplied by the membrane pump. The pump lever is connected to the accelerator. When the accelerator pedal is depressed, the pump lever presses the membrane forcing the fuel into main jet.

18 Page 1818 of When the pedal is returned, the membrane moves back, sucking the fuel from the float chamber through the ball valve.

19 3.2 Diesel fuel supply system Page 1919 of Need and requirements of Fuel Injection Systems: (W 12) If the engine is to develop full power and operate efficiently, its fuel system must do the following; 1) METERING: The fuel system must measure the fuel supplied to the engine very accurately since fuel required vary greatly from low to high engine speed. Fuel is measured as it leaves the pumping element. 2) TIME: The timing of fuel injected into cylinder is very important during engine starting, full load & high speed operation. 3) PRESSURE: The fuel system must pressurize the fuel to open the injection nozzle i.e.: it must develop sufficient pressure to open the nozzle. The pressure setting of injection nozzle or injector tip is directly related to the degree of atomization required. 4) ATOMIZE (The Breaking- up of fuel into Small particles): The fuel must be atomized when it is injected into the combustion chamber since atomized fuel will burn easily. 5) DISTRIBUTE: It is closely related to the timing, the distribution of fuel must be accurate & according to the engine firing order. Distributor pump, delivers fuel to each pump outlet in succession & the lines are hooked to the cylinder in correct firing order. In-line pump, the camshaft operates the pump outlet to fire in required engine cylinder firing order. 6) CONTROL, START & STOP INJECTION: Injection of fuel must start quickly & end quickly. The delay in beginning will alter the pump to engine timing, causing hard starting & poor running engines. Any delay in injection ending can cause to smoky exhaust and irregular exhaust sound. At end of injection, secondary injection should not occur.

20 Page 2020 of DIESEL FUEL INJECTION SYSTEM (Layout of Fuel Injection systems ) : The function of the fuel injection system is to inject proper quantity of fuel into engine cylinder at the correct time & at predetermined rate. There are 2 types of injection systems: A) Individual Pump system. A) INDIVIDUAL PUMP SYSTEM: B) Common rail system. In this system each cylinder has its own individual high pressure pump & a metering unit. It is compact method and involves higher cost. B) COMMON RAIL SYSTEM: In this system, the fuel is pumped by multi cylinder pump into common rail; the pressure in this rail is controlled by relief valve. The metered quantity of fuel is supplied to each cylinder from the common rail.

21 Fuel Injector and types of nozzles.: Page 2121 of Function: Its function is to inject fuel in the cylinder, in properly atomized form & in proper quantity. (S 12) Construction & Working: (S12 / W11) The construction & working features of fuel injector are as follows; 1) A spring loaded spindle in the nozzle holder keeps the nozzle valve pressed against its seat in the nozzle body, till the fuel supplied by FIP through inlet passage exerts sufficient pressure, so as to lift the nozzle valve against the spring force. Thus a spray of atomized fuel is fed into the combustion chamber. 2) The fuel spray continuous till the delivery from injection pump is exhausted. Later the spring pressure again suddenly closes the nozzle back on its seat. 3) The opening of the fuel line pressure can be varied by adjusting the initial degree of spring compression. 4) A small quantity of fuel is purposely allowed to leak between nozzle valve & its guide for lubrication purpose. 5) The fuel accumulated around spindle is drained back to the fuel tank through the leak off connection. 6) An adjusting screw provided at the top serves to adjust the tension in the spring. With the help of this adjusting screw we can set the pressure at which the nozzle valve opens.

22 Page 2222 of TYPES OF NOZZLE: (S 12) The nozzle are broadly classified according to number of hole, the pintle & the pintaux type nozzles; 1) Single hole nozzle: This nozzle has one hole drilled centrally through its body which is closed by the nozzle valve. The hole can be of any diameter from 0.2mm upwards. In this nozzle a single hole is bored at an angle to the vertical centre line of the valve. 2) Multi hole nozzle: This nozzle has number of holes drilled in the bulging end under the valve seat. The number & size of the holes depends on requirement of the engine. 3) Long stem nozzle: These nozzles find application in direct fuel injection engines. Due to limited space between the valves in the cylinder head, it is not possible to provide adequate cooling for standard small stem nozzle. Thus this nozzle is an alternative for short stem nozzles with a small diameter extension.

23 4) Pintle nozzle: The pintle is much longer & has a reduced cone shape at the lower end. Page 2323 of The valve stem is extended to form a pin or pintle, which protrudes through the mouth of nozzle body. Because of this shape, only small amount of the fuel is injected at the start of injection & the rate of injection increasing gradually. 5) Pintaux nozzle: It has an auxiliary spray hole to assist starting under cold conditions. As the engines staring speed being low, the nozzle valve is not lifted sufficiently to clear the pinhole & the fuel is discharged through auxiliary hole. This auxiliary hole helps while starting the engine. At normal running condition, the pressure in fuel system is high; thus the nozzle valve lifts easily & allows the bulk of the fuel to be discharged through it. TYPES OF FUEL INJECTION PUMPS: (W 11) Function of the fuel injection pump is to deliver accurately, metered quantity of fuel under high pressure, at the correct instant and in the correct sequence, to the injector fitted on the engine cylinder. The injection pump is driven from the engine s timing gear & outlet is controlled by the driver through accelerator pedal. There are 2 types of Fuel Injection pumps; A) Inline Fuel Injection Pump. B) Rotary or Distributor type FIP.

24 Page 2424 of A) INLINE FUEL INJECTION PUMP: Construction: The construction features of a single cylinder jerk pump are discussed below. Below given is a single element of an inline pump. 1) The main parts of the pump are the delivery valve, the plunger, the control sleeve & the control rack. 2) The delivery valve is of special construction & is spring loaded. 3) The delivery valve has an annular groove & 4 longitudinal grooves. 4) The plunger contains a helix at its upper end, which serves to control the quantity of fuel to be injected. 5) The plunger is operated by means of cam & tappet.

25 Page 2525 of Working: The working of Inline injection pump is discussed below; 1) Fig A shows, the position of the plunger at the bottom of the stroke. Both the intake & spill ports are uncovered. 2) As plunger moves up, it covers the two ports as shown in FIG B. 3) The upward plunger movement exerts pressure on the fuel at the top & hence the delivery valve opens against the spring force, thereby delivering the fuel under pressure. 4) The extreme upward position of plunger is shown in FIG C. 5) As soon as the helix uncovers the spill port, the fuel escapes from vertical slot in the plunger & passes through the spill port. The pressure now is released. 6) When pressure is released; delivery valve moves downward on its seat. 7) Lowering of delivery valve at end of delivery; increases space on the delivery side, due to which a sudden decrease of pressure occurs in the delivery line causing the injector to close immediately. 8) Fig D shows; the position of plunger is such a that, the lowermost point on the helix is opposite to the spill port. 9) FIG E & F shows; the plunger starts rotating in anti - clockwise direction & finally the vertical slot comes opposite to the spill port. Thus when vertical slot is opposite to spill port it is called no delivery position.

26 Page 2626 of B) ROTARY OR DISTRIBUTOR TYPE FIP: (W 11) The construction & working feature of Rotary type pump is discussed below; Construction:

27 The construction features of rotary pump are discussed below; Page 2727 of 1) It consists of a single pumping element. In this pump fuel is distributed to each cylinder by means of a rotor. 2) The rotor has a central longitudinal passage & a set of radial holes, called ports. 3) Suction ports are equal to the number of engine cylinders; they are at the level AA inside the rotor. 4) Similarly outer sleeve has equal number of holes (Delivery ports), at a different level BB. 5) Delivery port is connected to the high pressure delivery lines leading to injectors. 6) There is a Metering port in the sleeve for fuel intake at level AA. 7) A Distributor port is in the rotor at level BB, it is connected to central passage Working: in the rotor. The working of Rotary type FIP is discussed below; 1) As the rotor rotates, the Suction ports align with the intake Metering port & the Fuel is sucked in the rotor. 2) Later the Distribution port aligns with the delivery ports, to deliver the fuel. 3) At the lower end of the rotor, there are 2 opposed plungers. 4) As the rotor rotates inside a stationary ring with internal cams. These cams operate the plunger & the plungers push the fuel to Delivery port. 5) As the plungers move away from each other, the fuel is drawn into central rotor passage through Suction ports. This process keeps on repeating itself. The fuel is delivered to each cylinder at high pressure.

28 Page 2828 of VARIOUS COMPONENTS & DIESEL FUEL INJECTION SYSTEM: Fuel system in diesel engine has to perform certain functions. These functions along with the names of the components which perform the same are given below; 1) STORING OF FUEL: Fuel tank is usually positioned along the side of the vehicle chassis. 2) FILTERING: Water and dirt must be removed from the diesel for which 2 filters are employed. Primary filter: It is usually in the form of a coarse wire gauge and is often optional. It prevents large solid particles & water from going to the feed pump. Secondary filter: It is used after the fuel feed pump & is meant to remove fine particles of dust. 3) DELIVERY OF FUEL TO INJECTION PUMP: Fuel from fuel tank is delivered to fuel injection pump by means of Fuel Feed Pump. The rate of fuel delivery depends upon the engine requirements. 4) INJECTING THE FUEL INTO ENGINE CYLINDER: Exact amount of fuel is metered, atomized & injected under high pressure to each cylinder in correct sequence & at the correct moment according to engine requirements. This is done by the means of Fuel Injection Pump & Injector for each cylinder. 5) CONTROLLING THE ENGINE SPEED: Diesel engine speed tends to overshoot to dangerous value on reduction of load. This is controlled by means of a Governor, which limits the maximum speed of engine & regulates the fuel supply under all conditions.

29 Air fuel mixture ratio in a petrol and diesel engine and Comparison: Page of Sr. no. PETROL ENGINE 1. A/F ratio DIESEL ENGINE 2. Combustion Spark Ignition Compression Ignition 3. Compression Ratio 4. Weight per unit power 5. Power per Unit displacement 6. Thermodynamic cycle 7. Fuel Supply Method 8. Initial cost 6 11 (average 7 9) ( average 15 18) Low weight (0.5 to 4.5 kg / High weight (3.3 to 13.5 kg/ kw) kw) High (30 kw / L) Low (15 kw / L) Otto Cycle Diesel Cycle Carburettor & MPFI. Fuel Pump & CRDI. High, due to heavy weight & sturdy Low construction. 9. Application 2 wheelers & cars etc Bus, Trucks & heavy duty vehicle s etc.