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2. 2  Understand the different types of diesel fuel systems, how the components function to provide fuel to the engine, and how to service diesel fuel systems.  Understand the function and operation of governors and fuel system components.  Understand the principles and operation of the different diesel fuel systems.  Understand the basic maintenance required for a diesel fuel system  Understand general troubleshooting techniques used in the maintenance of a diesel fuel system.

3. 3  Compression ratios in the diesel engine range between 6:1 for a stationary engine and 24:1 for passenger vehicles.  Due to this high ratio causes increased compression pressures of 400 to 600 psi and cylinder temperatures reaching 800º F to 1200º F.  At the proper time, the diesel fuel is injected into the cylinder by a fuel-injection system, which usually consists of a fuel tank, fuel feed pump, fuel injection pump, injectors or nozzles and filters.  When the fuel oil enters the cylinder, it will ignite because of the high temperatures.  The diesel engine is known as a compression-ignition engine, while the gasoline engine is a spark-ignition engine.  The speed of a diesel engine is controlled by the amount of fuel injected into the cylinders.

4. 4  In a gasoline engine, the speed of the engine is controlled by the amount of air admitted into the carburetor or gasoline fuel injection systems.  Mechanically, the diesel engine is similar to the gasoline engine. The intake, compression, power and exhaust strokes occur in the same order.  The arrangement of the pistons, connecting rods, crankshaft and engine valves is about the same. The diesel engine is also classified as in-line or V-type.  In comparison to the gasoline engine, the diesel engine produces more power per pound of fuel, is more reliable, has lower fuel consumption per horsepower per hour, and presents less of a fire hazard.  These advantages are partially offset by higher initial cost, heavier construction needed for its high compression pressures, and the difficulty in starting which results from these pressures.

5. 5  The high injection pressures needed in the diesel fuel system result from close tolerances in the pumps and injectors. These tolerances make it necessary for the diesel fuel to have sufficient lubrication qualities to prevent rapid wear or damage.  It must also be clean, mix rapidly with the air, and burn smoothly to produce an even thrust on the piston during combustion.

6. The fuel injection system is the most vital component in the working of CI engines. The engine performance viz., power output, economy etc. is greatly dependent on the effectiveness of the fuel-injection system. The injection system has to perform the important duty of initiating and controlling the combustion process. In the preparation of the combustible charge, the purpose of carburetion and fuel-injection is the same. 6

7. In the fuel injection system, the fuel speed at the point of delivery is greater than the air speed to atomize the fuel. The amount of fuel delivered into the air stream going to the engine is controlled by a pump which forces the fuel under pressure. When the fuel is injected into the combustion chamber towards the end of compression stroke, it is atomized into very fine droplets. These droplets vaporize due to heat transfer from the compressed air and form a fuel-air mixture. Due to continued heat transfer from hot air to the fuel, the temperature reaches a value higher than its self-ignition temperature. This causes the fuel to ignite spontaneously initiating the combustion process. 7

8. The fuel is atomized by processes relying on the air speed greater than fuel speed at the fuel nozzle. In carburetors, air flowing through a venturi picks up fuel from a nozzle located there. The amount of fuel drawn into the engine depends upon the air velocity in the venturi. 8

9. 1)Accurate metering of the fuel injected per cycle. This is very critical due to the fact that very small quantities of fuel being handled. Metering errors may cause drastic variation from the desired output. The quantity of the fuel metered should vary to meet changing speed and load requirement of the engine. 2)Timing the injection of the fuel correctly in the cycle so that maximum power is obtained ensuring fuel economy and clean burning. 3)Proper control of rate of injection so that the desired heat-release pattern is achieved during combustion. 4)Proper atomization of fuel into very fine droplets. 9

10. 5) Proper spray pattern to ensure rapid mixing of fuel and air. 6) Uniform distribution of fuel droplets throughout the combustion chamber. 7)To supply equal quantities of metered fuel to all cylinders in case of multi cylinder engines. 8)No lag during beginning and end of injection i.e., to eliminate dribbling of fuel droplets into the cylinder. 10

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12.  In a constant pressure heat addition cycle or diesel cycle, only the pure air is compressed in the cylinder and then fuel is injected into the cylinder by means of a fuel-injection system. For producing the required pressure for atomizing the fuel either air or a mechanical means is used.  Accordingly the injection systems can be classified as: (i) Air injection system (ii) Solid injection system 12

13.  Fuel is forced into the cylinder by means of compressed air. This system is little used nowadays, because it requires a bulky multistage air compressor.  This causes an increases in engine weight and reduces the brake power output.  One advantage of air injection system is good mixing of fuel with the air that will result in higher mean effective pressure.  Another advantage is that high viscosity fuels can use with this system and high viscosity fuel is less expensive than those used by the engines with solid injection systems.  These two advantages are offset by the requirement of a multistage compressor. 13

14.  The liquid fuel is injected directly into the combustion chamber without the aid of compressed air. It is also called airless mechanical injection or solid injection system.  Solid injection systems can be classified into four types: 1. Common rail system 2. Individual pump system 3. Distributor system 4. Unit injector system 14

15.  All injection systems comprise mainly of the following components: 1.Fuel tank 2.Fuel feed pump to supply fuel from the main fuel tank to the injection system. 3.Injection pump to meter and pressurize the fuel for injection. 4.Governor to ensure that the amount of fuel injected is in accordance with variation in load. 5.Injector to take the fuel from the pump and distribute it in the combustion chamber by atomizing it into fine droplets. 6.Fuel filters to prevent dust and abrasive particles from entering the pump and injectors thereby minimizing the wear and tear of the components. 15

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17. The pressure required to inject the fuel is developed in the pump. The timing and metering of the fuel is accomplished in the injector. The high pressure fuel is supplied to a common rail by the high-pressure fuel pump. The spring loaded bypass valve maintains constant pressure on the common rail and returns the excess fuel. The pressure of the common rail can be adjusted by adjustment of the spring tension on the bypass valve. From common rail, the fuel is distributed to the individual injectors by different fuel lines. Each injector contains a needle valve seated against the valve seat by a spring. 17

18. The valve is operated by a cam-follower-pushrod-rocker mechanism. The pushrod is in two portions and control wedge is between the two portions of the pushrod. The control wedge is controlled by the governor or hand control. When the thicker portion of the control wedge, the effective length of the pushrod increase causing increase in the valve lift and in the quantity of the fuel injected. With the thicker portion of the wedge in action resulting in increase in the total opening time of the valve. The common-rail system is not suitable for small-diameter, high-speed engines because of the difficulty of controlling the very small quantity of fuel injected in a cycle. 18

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20. The development of high pressure, metering and timing the fuel supply are accomplished in the fuel injection pump. The injector performs the functions of atomizing and distributing of the fuel. This type of injection pump has as many individual pump elements (plunger- barrel assemblies) as the number of cylinder of the engine. In large engines, there is one pump for each cylinder. Each pump element delivers the fuel to a spring loaded injector mounted on an engine cylinder. The fuel to an individual injector is supplied at the desired time by the pump. The majority of diesel engines utilize the system which is also known as the Jerk pump system. 20

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22. The functions of developments of pressure, metering and timing of fuel supply are accomplished in the pump. A distributor type pump has only one pump element ( plunger-barrel assembly ) common to all fuel outlets servicing the different injectors. The plunger has two motions, reciprocating and rotary. By rotation of the plunger, the pressurized fuel is distributed to the individual pressure outlets. 22

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25. The high pressure required for fuel spray is developed in the injector itself, thus eliminating the high pressure fuel piping. The timing is also done at the injector. A fuel pump of the gear type supplies fuel at a moderate pressure to the injector. The metering of the fuel is done by varying the pump-delivery pressure. This variation at the pump can be done by a governor or by throttle control. The higher the pressure, the more the fuel pushed through the hole in the time available. This system is knows as the Pressure-Time system. 25

26. Fuel feed pump is a spring loaded plunger type. The plunger is actuated through a push rod from the cam shaft. 26

27.  At the minimum lift position of the cam the spring force on the plunger creates a suction which causes fuel flow from the main tank into the pump. When the cam is turned to its maximum lift position, the plunger is lifted upwards. At the same time the inlet valve is closed and the fuel is forced through the outlet valve.  When the operating pressure gets released, the plunger return spring ceases to function resulting in varying of the pumping stroke under varying engine loads according to the quantity of fuel required by the injection pump. 27

28.  The main objectives of fuel injection pump is to deliver accurately metered quantity of fuel under high pressure ( in the range from 120 to 200 bar) at the correct instant to the injector fitted on each cylinder.  Injection pumps are generally of two types: (i) Jerk type pumps (ii) Distributor type pumps 28

29. It consists of a reciprocating plunger inside a barrel. The plunger is driven by camshaft. 29

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34. Near the port A, fuel always available under relatively low pressure. The axial movement of the plunger is by means of cam shaft, its rotational movement about its axis is by means of control rack D. Port B is the orifice through which fuel is delivered to the injector. The delivery is closed by means of a spring loaded check valve. When the plunger is below port A, the fuel gets filled in the barrel above it. As the plunger rises and closes the port A the fuel will flow out through port C. This is because of the fuel pressure cannot overcome the spring force of the check valve. When the rack rotates the plunger, port C is closed. The only escape route for the fuel is past the check valve through orifice B to the injector. This is the beginning of injection and also the effective stroke of the plunger. 34

35. The injection continues till the helical indentation on the plunger uncovers port C and the fuel will take the easy way out through C and the check valve will close the orifice B. The fuel injection stops and the effective stroke ends. Hence the effective stroke of the plunger is the axial distance traversed between the time port A is closed off and the time port A is uncovered. It is important to remember that the axial distance traversed by the plunger is same for every stroke, the rotation of the plunger by the rack determining the length of the effective stroke and thus the quantity of fuel injected. 35

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38. 38 Rotor and Plunger

39. 39 Plunger ChargingPlunger Discharging

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42. This pump has only a single pumping element and the fuel is distributed to each cylinder by means of a rotor. There is a central longitudinal passage in the rotor and also two sets of radial holes (each equal to the number of engine cylinders) located at different pressure. One set is connected to pump inlet via central passage whereas the second set is connected to delivery lines leading to injectors of the various cylinders. The fuel is drawn into the central rotor passage from the inlet port when the pump plunger move away from each other. Whereas, the radial delivery passage in the rotor coincide with the delivery port for any cylinder the fuel is delivered to each cylinder in turn. The advantage of distributor pump is that lies in its small size and its light weight. 42

43.  In a CI engine the fuel delivered is independent of the injection pump characteristic and the air intake. Fuel delivered by a pump increases with speed whereas the opposite is true about the air intake. This results in over fueling at higher speeds. And at idling speeds (low speeds) the engine tends to stall due to insufficiency of fuel.  Quantity of fuel delivered increases with load causing excessive carbon deposits and high exhaust temperature. Drastic reduction in load will cause over speeding to dangerous values.  It is duty of an injection pump governor to take care of the above limitations. Governors are generally of two types (i) Mechanical governor and (ii) Pneumatic governor 43

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45.  When the engine speed tends to exceed the limit the weights fly apart. This causes the bell crank levers to raise the sleeve and operate the control lever in downward direction.  This actuates the control rack on the fuel-injection pump in a direction which reduces the amount of fuel delivered.  Lesser fuel causes the engine speed to decrease. The reverse happens when engine speed tends to decrease. 45

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48.  The amount of vacuum applied to the diaphragm is controlled by the accelerator pedal through the position of the butterfly valve in the venturi unit.  A diaphragm is connected to the fuel pump control rack.  Therefore, position of the accelerator pedal also determines the position of the pump control rack and hence the amount of fuel injected. 48

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50. Quick and complete combustion is ensured by a well designed fuel injector. By atomizing the fuel into vary fine droplets, it increases the surface area of the fuel droplets resulting in better mixing and subsequent combustion. Atomization is done by forcing the fuel through a small orifice under high pressure. 50

51.  The injector assembly consists of the following (i)a needle valve (ii)a compression spring (iii)a nozzle (iv)an injector body  When the fuel is supplied by the injection pump it exerts sufficient force against the spring to lift the nozzle valve, fuel is sprayed into the combustion chamber in a finely atomized particles.  After delivering of fuel from pump gets exhausted, the spring pressure pushes the nozzle valve back on its seat. 51

52.  For proper lubrication the clearance between them and its guide a small quantity of fuel is allowed to leak through the clearance between them and then drained back to fuel tank through leak off connection.  The spring tension and hence the valve opening pressure is controlled by adjusting the screw provided at the top. 52

53.  Nozzle is the part of an injector through which the liquid fuel is sprayed into the combustion chamber. The nozzle is should fulfill the following functions: (i)Atomization: This is a very important function since it is the first phase in obtaining proper mixing of the fuel and air in the combustion chamber. (ii)Distribution of fuel : Distribution of fuel to the required areas within the combustion chamber. Factors affecting this are: (a)Injection Pressure : Higher the injection pressure better the dispersion and penetration of the fuel into all the desired locations in combustion chamber. (b)Density of air in the cylinder : If the density of compressed air in the combustion chamber is high then the resistance to the movement of the droplets is higher and dispersion of the fuel is better. 53

54. (c) Physical properties of fuel : The properties like self-ignition temperature, vapour pressure, viscosity, etc. play an important role in the distribution of fuel. (iii) Prevention of impingement on walls : Prevention of the fuel from impinging directly on the walls on combustion chamber or piston. This is necessary because fuel striking the walls decomposes and produces carbon deposits. This causes smoky exhaust as well as increase in fuel consumption. (iv) Mixing : Mixing the fuel and air in case of non-turbulent type of combustion chamber should be taken care of by the nozzle. 54

55.  The most common types of nozzle are: (i)The pintle nozzle (ii)The single hole nozzle (iii)The multi-hole nozzle (iv)Pintaux nozzle 55

56. The stem of the nozzle valve is extended to form a pin or pintle which protrudes through the mouth of the nozzle. The size and shape of the pintle can be varied according to the requirement. It provides a spray operating at low injection pressures of 8-10 Mpa. The spray cone angle is generally 60º. Advantage of this nozzle is that it avoids weak injection and dribbling. It prevents the carbon deposition on the nozzle hole. 56

57. At the centre of the nozzle body there is a single hole which is closed by the nozzle valve. The size of the hole is usually of the order of 0.2 mm. Injection pressure is of order of 8-10 Mpa and spray cone angle is about 15º. Major disadvantage with such nozzle is that they tend to dribble. Besides, their spray angle is too narrow to facilitate good mixing unless higher velocities are used. 57

58. It consists of a number of holes bored in the tip of the nozzle. The number of holes varies from 4 to 18 and the size from 35 to 200 μm. The hole angle may be from 20º upwards. These nozzles operate at high injection pressures of the order of 18 Mpa. Their advantage lies in the ability to distribute the fuel properly even with lower air motion available in open combustion chambers. 58

59. It is a type of pintle nozzle which has an auxiliary hole drilled in the nozzle body. It injects a small amount of fuel through this additional hole (pilot injection) in the upstream direction slightly before the main injection. The needle valve does not lift fully at low speeds and most of the fuel is injected through the auxiliary hole. Main advantage of this nozzle is better cold smarting performance. A major drawback of this nozzle is that its injection characteristics are poorer than the multihole nozzle. 59

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61.  At the start of the fuel injection, the pressure difference across the orifice is low. Therefore single droplets are formed initially.  Then the pressure difference increases and the other processes are happening.  A stream of fuel emerges from the nozzle.  The stream encounters aerodynamic resistance from the dense air present in the combustion chamber (12 to 14 times the ambient pressure) and breaks into a spray, l 3. The distance of this point where this event occurs from the orifice is called the break-up distance.  With further and further increase in the pressure difference, the break-up distance decreases and the cone angle increases until the apex of the cone practically coincides with the orifice. 61

62.  At the exit of the orifice the fuel jet velocity V f is of the order of 400 m/sec. It is given by the following equation V f = C d √2(P inj - P cyl )/ρ f Cd = coefficient of discharge for the orifice P inj = fuel pressure at the inlet to injector, N/m² P cyl = pressure of charge inside the cylinder,N/m² ρ f = fuel density, kg/m³ 62

63.  The spray, from a circular orifice of injector, has a denser and compact core that is surrounded by a cone of fuel droplets of various sizes and vaporized liquid. Larger droplets provide a higher penetration into the chamber but smaller droplets are required for quick mixing and evaporation of the fuel.  The diameter of most of the droplets in a fuel spray is less than 5 microns.  The droplet sizes depends on various factors which are listed below; - Mean droplet size decreases with increase in injection pressure. - Mean droplet size decreases with increase in air density. - Mean droplet size increases with increase in fuel viscosity. -Size of droplets increases with increase in the size of the orifice. 63

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65.  For good atomization of the injector, the velocity of fuel through the nozzle into the combustion chamber is 400 m/sec. The velocity of fuel in terms of h is V f = C d √2gh h = the pressure difference between injection and cylinder pressure, m of fuel column. 65

66.  The volume of the fuel injected per second Q is Q = Area of all orifices x fuel jet velocity x time of one injection x number of injections per second for one orifice 66 Ni = rpm/2 for four-stroke engine and rpm for two-stroke cycle engine d = diameter of one orifice in m n = the number of orifices θ = the duration of injection in crank angle degrees N i = the number of injections per second

67.  Gasoline injection system is coming into vogue in SI engines because of the following drawbacks of the carburetion. 1.Non uniform distribution of mixture in multi-cylinder engines. 2.Loss of volumetric efficiency due to the restrictions imposed by the presence of carburetor and other components. 3.Possibility of back firing. 67

68.  The injection of fuel into an SI engine can be done by employing any of the following methods. 1.Direct injection of fuel into the cylinder 2.Injection of fuel close to the inlet valve 3.Injection of fuel into the inlet manifold  There are two types of gasoline injection systems 1.Continuous Injection : Fuel is continuously injected and it is adopted when manifold injection is contemplated. 2.Timed Injection : Fuel is injected only during induction stroke over a limited period. Injection timing is not a critical factor in SI engines. 68

69.  Major advantage of fuel-injection in an SI engine are 1.Increased volumetric efficiency 2.Better thermal efficiency 3.Lower exhaust emissions 4.High quality fuel distribution  The use of petrol injection is limited by its high initial cost, complex design and increased maintenance requirements.  The petrol injection has a promising future compared to carburetion and may replace carburettor in the near future. 69

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71. Example(1)A six cylinder, four-stroke diesel engine develops 125kW at 3000rpm. Its brake specific fuel consumption is 200 gm/kW-hr. Calculate the quantity of fuel to be injected per cycle per cylinder. Specific gravity of the fuel may be taken as 0.85. 71

72. Example (2) Calculate the diameter of the fuel orifice of a four-stroke engine which develops 25 kW per cylinder at 2500rpm. The specific fuel consumption using 0.3 kg/kW-hr fuel of 30º API. The fuel is injected at a pressure of 150 bar over a crank travel of 25º. The pressure in the combustion chamber is 40 bar. Coefficient of velocity is 0.875 and specific gravity is given by S.G = 141.5/ (131.5 + º API) 72

73. Example (3) A four-cylinder, four-stroke diesel engine develops a power of 180 kW at 1500 rpm. The bsfc is 0.2 kg/kW hr. At the beginning of injection pressure is 30 bar and the maximum cylinder pressure is 50 bar. The injection is expected to be 200 bar and maximum pressure at the injection is set to be about 500 bar. Assuming the following: Cd for injector= 0.7 S.G of fuel= 0.875 Atmospheric pressure= 1 bar Effective pressure difference = Average pressure difference over the injection period Determine the total orifice area required per injector if the injection takes place over 15º crank angles. 73

74. Example (4) A closed type injector has a nozzle orifice diameter of 0.9 mm and the maximum cross sectional area of the passage between the needle cone and the seat is 1.75 mm2. The discharge coefficient for the orifice is 0.85 and for the passage is 0.80. The injection pressure is 175 bar and the average pressure of charge during injection is 25 bar, when the needle cone is fully lifted up. Calculate the volume rate of flow per second of fuel through the injector and the velocity of jet at that instant. Density of fuel is 850 kg/m3. 74

75. Example (5) At injection pressure of 150 bar a spray penetration of 25 cm in 20 milliseconds is obtained. If an injection pressure of 250 bar had been used, what would have been the time taken to penetrate the same distance. Assume the same orifice and combustion chamber density. The combustion chamber pressure is 25 bar. Use the relation S α t √ΔP where S is penetration in cm t is time in millisecond ΔP is the pressure difference between injection pressure and combustion chamber pressure. 75

76. Example (6) A six cylinder diesel engine produces 100 kW at 1500 rpm. The specific fuel consumption of the engine is 0.3 kg/kWhr. Each cylinder has a separate fuel pump, injector and pipe line. At the beginning of effective plunger stroke of one fuel pump, the fuel in the pump barrel is 4 cc, fuel inside the injector is 2 cc and fuel in the pipe line is 3 cc. If the average injector pressure is 300 bar and average pressure of charge during injection is 40 bar. Calculate the displacement volume of one plunger per cycle and power lost in pumping fuel to the engine (for all cylinders). Specific gravity of fuel is 0.9 and the fuel enter the pump barrel at 1 bar. Coefficient of compressibility of fuel may be taken as 80x10-6 per bar. 76

77. Example (7) Before commencement of the effective stroke the fuel in the pump barrel of a diesel fuel injection pump is 6 cc. The diameter of the fuel line from pump to injector is 2.5 mm and is 600 mm long. The fuel in the injection valve is 2 cc. (i)To deliver 0.10 cc of fuel at a pressure of 150 bar, how much displacement the plunger undergoes. Assume a pump inlet pressure of 1 bar. (ii)What is the effective stroke of the plunger if its diameter is 7 mm. Assume coefficient of compressibility of oil as 75x10-6 per bar at atmospheric pressure. 77

78. THANK YOU VERY MUCH 78