Fuel System of Diesel Engine PDF

Chapter 7 Fuel system of diesel engine Overview of the fuel system of diesel engine 7.1 Overview of the fuel system of diesel engine Combustion process and chamber of the diesel engine 7.2 Combustion process and chamber of the...

Chapter 7 Fuel system of diesel engine Overview of the fuel system of diesel engine 7.1 Overview of the fuel system of diesel engine Combustion process and chamber of the diesel engine 7.2 Combustion process and chamber of the diesel engine Main components of the mechanical-type fuel system 7.3 Main components of the mechanical-type fuel system Click here to close the show Click here to close the show 7.1 Overview of the fuel system of diesel engine 7.1.3 Types of the fuel systems of diesel engines Many different types of fuel systems have been developed for modern vehicular diesel engines. In terms of control principle, these fuel systems may be classified into two types: mechanical and electronic. Click here to close the show Click here to close the show 1. Mechanical fuel system The mechanical fuel system is a traditional fuel system of diesel engines. According to the accelerator pedal controlled by drivers, this fuel system realizes pressure boost of diesel, adjustment to the fuel injection quantity, automatic control of injection timing, stability of the idle speed and limitations on over-speed. Click here to close the show Click here to close the show At present, most of the mechanical fuel systems applied to diesel engines for automobiles adopt the fuel injection pump – high-pressure fuel pipe – injection nozzle (PLN for short) system; in addition, there are also pump – nozzle system and PT type fuel injection system. Click here to close the show Click here to close the show (1) Fuel injection pump—high pressure fuel pipe—fuel nozzle system This fuel injection pump—high pressure fuel pipe— fuel nozzle system consists mainly of the injection pump, fuel injectors, fuel tank, fuel delivery pump, filter, timing advance unit, and speed governor (Figure 7-1). Fuel injection pumps can be divided into two types, i.e., the plunger pump type and the distribution pump type as per the forms. Click here to close the show Click here to close the show  High-pressure Injector fuel return Fuel Injector fuel Injection pump pipe component Diesel filter cleaner Filter cleaner fuel return pipe Jet spray component Fuel delivery pump Fuel tank Figure 7-1 Fuel system of diesel engine Click here to close the show Click here to close the show Figure 7-1 shows the plunger pump type fuel system. In the fuel injection pump there are plungers. The number of plungers is equal to the number of cylinders. The injection pump provides high- pressure fuel for the cylinders according to the specified firing order. The plungers pressurize the fuel then deliver it to the injectors. The fuel is injected into combustion chambers by the injectors. Click here to close the show Click here to close the show The arrangement of the distributor pump type fuel system is almost the same as that of the plunger pump type. However, the distributor pump has only one plunger generating high-pressure fuel. A rotating distribution rotor is utilized (or a pumping plunger with simultaneous reciprocating motions and rotational motions), to distribute the high-pressure diesel to the injection nozzles of various cylinders as per the inflammation sequences of engines. Click here to close the show Click here to close the show (2) Pump-injection nozzle system The pump-injection nozzle system combines the injection pump and the fuel atomizer into an integral whole. Each cylinder has a corresponding pump-nozzle, which is installed on the cylinder cover, driven by the camshaft of the engine through the rocker-arm push-rod mechanism. Its lower part is the fuel atomizer stretched into the combustion chamber. Click here to close the show Click here to close the show Considering that the high-pressure fuel pipe connected between the injection pump and the injection nozzle is cancelled, it avoids the adverse influences of the pressure fluctuation in pipes and the elastic compression of fuel on the injection process. Click here to close the show Click here to close the show (3) PT type injection system Figure 7-2 shows the composition of the PT type fuel injection system. The fuel is supplied to the fuel atomizer through the fuel pump from the fuel tank at a relatively low pressure. The fuel supply pressure is controlled with the speed controller and the throttle valve installed in the fuel pump. Click here to close the show Click here to close the show The start and stop of the fuel atomizer is manipulated with the camshaft of the engine and the rocker-arm push-rod mechanism. The so-called PT means that the fuel supply quantity is determined by the time for the opening of the metering orifice by the plunger of the fuel atomizer driven by the fuel supply pressure and the cam. Click here to close the show Click here to close the show  Fuel injection rocker-arm Fuel return pipe Push rod Fuel tank Fuel distribution pipeline Camshaft Injection pump Oil pump Filter cleaner Figure 7-2 PT type injection system Click here to close the show Click here to close the show 2. Electronically-controlled fuel system （1）First generation of electronically- controlled fuel systems The first generation of electronically-controlled fuel systems retain a great portion of mechanical construction of traditional “injection pump- high- pressure fuel pipe- nozzle” system, for example, the injection pump and nozzles. Difference is that, in the injection pump, the mode for controlling injection amount and injection timing is changed from mechanically to electronically, which makes control accuracy and speed of response improved. Click here to close the show Click here to close the show (2) Second generation of electronically- controlled fuel systems The second generation of fuel systems have a solenoid valve in the nozzle. Injection amount and injection timing of high- pressure fuel are controlled by ECU via the high-speed solenoid valve. Click here to close the show Click here to close the show This system can retain the original injection pump (plunger pump or distributor pump, pump nozzle, etc.), but the plunger is only responsible for pressurization and fuel supply, and the fuel supply quantity and time are completed by the high-speed solenoid valve solely. The fuel injection quantity is determined by the closed time of the solenoid valve. Therefore, it is also known as the time control type. Click here to close the show Click here to close the show (3) Third generation of electronically- controlled fuel systems All the third generation of fuel systems are common rail fuel systems. Main components of these generation of fuel systems are the fuel delivery pump, fuel filter, high-pressure fuel pump, high-pressure common rail, electronically-controlled fuel injectors, ECU, various sensors, and other actuators. See Figure 7- 3. Click here to close the show Click here to close the show  Common rail High pressure common rail pressure sensor Main fuel filter High- pressure fuel pump Primary Fuel Filter Sensor Actuator with oil-water separator Fuel Injector High pressure Low pressure Figure 7-3 Common rail fuel system Click here to close the show Click here to close the show Driven the diesel engine, the high-pressure fuel pump runs at a certain speed ratio, coantinuously delivering high-pressure fuel into the common rail(i.e. the common container). Fuel is then sent via the high-pressure fuel pipes to respective injectors. Click here to close the show Click here to close the show The system adopts the pressure-time type fuel metering principle to control the injection process with the high-speed solenoid valve. The injection pressure, the injection quantity and the injection timing are all controlled by the electronic control unit (ECU). These kind of fuel systems have the following merits: Click here to close the show Click here to close the show ① Being capable of realizing high-pressure injection. The injection pressure can double that of a common plunger pump system, and the maximum injection pressure has already exceeded 200Mpa. ② Being irrelevant to engine speed. This is good for improving the performances of engine operation at low speeds under low loads. ③ With the function of plot injection, it can realize ideal injection rules by adjusting the shape of the injection speed. Click here to close the show Click here to close the show ④ The injection timing and injection quantity can be selected as required. ⑤ Having excellent injection characteristics, and being capable of optimizing the combustion process, to substantially reduce fuel consumption, smoke intensity, noise level, and emission quantity of the engine, as well as the torque characteristics of the engine. ⑥ Having construction simplicity, high reliability, high adaptability, and broad application in all engines old and new. Click here to close the show Click here to close the show 7.2 Combustion process and chamber of the diesel engine 7.2.1 Combustion process of the gasoline engine The combustion of the diesel engine is finished within a narrow space in the combustion chamber. Under the environment of high temperature and high pressure, the combustible mixture formed by the mist-type fuel injected into the combustion chamber with high pressure and the air in the cylinder combusts within an extremely short period. Click here to close the show Click here to close the show The combustion period of the diesel engine can be divided into four stages, as shown in Figure 7-4. Click here to close the show Click here to close the show  Pressure Initial point of combustion Initial point of fuel injection Initial point of fuel supply Changes on pressure of the cylinder with no fuel supply TDC Crankshaft angle Fuel injection Fuel supply advance angle advance angle Figure 7-4 Combustion process of the diesel engine Click here to close the show Click here to close the show 1. Combustion delay period The combustion delay period (also known as the ignition delay period) refers to the time interval from injection of fuel to combustion (or the crank angle). The length of the combustion delay period is determined by the cetane number of diesel, which is also determined by the temperature and pressure of the combustion room at the end of the compression. Click here to close the show Click here to close the show 2. Rapid combustion period The rapid combustion period refers to the time interval from the deviation of the cylinder pressure from the compression line, i.e., the rapid rising point B, to the highest pressure point, i.e., point C (or the crank angle). Click here to close the show Click here to close the show The length of the combustion delay period leads to direct influences on the fuel combustion quantity during the rapid combustion period. The unnecessarily long combustion delay period will lead to very high pressure rise rate during the rapid combustion period, giving rise to rough running of the diesel engine, or even great increase in the displacement of NOx. Click here to close the show Click here to close the show 3. Slow combustion period The slow combustion period refers to the time interval from the highest pressure point, i.e., point C, to the highest temperature point in the cylinder, i.e., point D (or the crank angle). Some measures shall be adopted to provide the evaporated fuel with sufficient air during this combustion period, to ensure the rapid and complete combustion, so as to improve the thermal efficiency of the diesel engine as well as reduce the exhaust smoke. Click here to close the show Click here to close the show 4. Complementary combustion period The complementary combustion period (also known as the after combustion period) refers to the time interval from the highest temperature point, i.e., point D, to the point at the end of the fuel, i.e., point E (or the crank angle). Click here to close the show Click here to close the show 7.2.2 Combustion chamber of the gasoline engine The combustion chambers of diesel engines can be divided into the direct injection combustion chamber and the divided combustion chamber as per the forms. Click here to close the show Click here to close the show 1. Direct injection combustion chamber The direct injection combustion chamber is also known as the uniform combustion chamber, which is a single inner chamber encapsulated by the concave piston top and the cylinder cover bottom surface (please refer to Figure 7-5). It has tangible  and spherical forms as the common structures (please refer to Figure 7-6). Click here to close the show Click here to close the show (a) Shallow ῳ shape combustion (b) Deep ῳ shape combustion (c) Spherical combustion chamber chamber chamber Figure 7-6 Different direct injection combustion chambers Click here to close the show Click here to close the show  Fuel Injector Cylinder head Combustion chamber Piston Figure 7-5 Direct injection combustion chambers Click here to close the show Click here to close the show 2. Divided combustion chamber The divided combustion chamber is divided into two parts; one part is situated in the cylinder cover, and the other part is situated in the cylinder. The part in the cylinder is known as the main combustion chamber, and the part in the cylinder cover is known as the subsidiary combustion chamber. The main combustion chamber and subsidiary combustion chamber is connected with a channel. The divided combustion chamber can be divided into the pre-combustion type combustion chamber and the eddy type combustion chamber. Click here to close the show Click here to close the show (1) Pre-combustion type combustion chamber The pre-combustion type combustion chamber is composed by two parts, i.e., the pre-combustion chamber and the main combustion chamber. The pre-combustion chamber is situated within the cylinder cover, occupying about 25%-40% of the compression volume, and one or several through-holes are connected with the main combustion chamber (please refer to Figure 7-7). Click here to close the show Click here to close the show Figure 7-7 Pre-combustion type combustion chamber Click here to close the show Click here to close the show The fuel is injected into the pre-combustion room, giving rise to rapid rise in pressure and temperature in the pre-combustion chamber after ignition. The huge pressure difference injects the mixed air into the main combustion chamber in a high speed, forming strong combustion turbulence in the main combustion chamber. It promotes the mixture of most fuels in the main combustion chamber with most air, leading to combustion. Click here to close the show Click here to close the show (2) Eddy type combustion chamber The eddy type combustion chamber is composed by the swirl chamber and the main combustion chamber. The swirl chamber is situated on the cylinder cover as a sphere or a revered bell shape, occupying about 50%-80% of the total compression volume, which is connected with the main combustion chamber with a tangential channel (please refer to Figure 7-8). Click here to close the show Click here to close the show  Preheating chamber Fuel Injector Eddy type combustion chamber Cylinder cover Main combustion chamber Piston Figure 7-8 Eddy type combustion chamber Click here to close the show Click here to close the show Most of the fuel injected into the eddy chamber is combusted in the eddy chamber. The part not combusted goes to into the main combustion chamber together with the high-pressure fuel gas at the beginning of the working stroke through the tangential channel, to further mix with air for combustion. Click here to close the show Click here to close the show 7.3 Main components of the mechanical-type fuel system 7.3.1 Fuel injector The fuel atomizer is adopted to atomize fuel into fine fuel drops, and inject them to specific parts in the combustion chamber. The mist shall have certain spray penetration distance and angle of cone as well as favorable atomization quality, leading to no leakage at the end of the injection. Click here to close the show Click here to close the show 1. Construction and working principle of fuel injector As shown in Figure 7-9. With the injector operating, high- pressure fuel coming from the injection pump passes through the pipe joint, and via the inlet passage in the injector body, enters the annular chamber in the center of the needle valve body, acting on the pressure-bearing cone of the needle valve. Hence, an upward axial thrust is applied to the needle valve. Once the thrust exceeds the pressure preliminarily exerted by the pressure regulating spring of the injector, the needle valve moves upward immediately to open the nozzle, squirting high- pressure fuel into the combustion chamber. Click here to close the show Click here to close the show  Oil return pipe joint Nut Adjustment screw Pressure Spring Fuel injectors body High-pressure fuel Push rod Steel ball Needle valve Fastening nut Needle valve body Figure 7-9 Construction of the orifice type injector Click here to close the show Click here to close the show When the injector pump stops running, the pressure in the high-pressure fuel passage drops rapidly. Due to the action of the pressure regulating spring, the needle valve returns in place timely to close the nozzle to stop fuel injection. Pressure setting for opening the needle valve (injection pressure) depends on the retightening force placed on the pressure regulating spring. Different engines set forth different requirements on injection pressure. Injection pressure is regulated with the pressure adjusting screw. Click here to close the show Click here to close the show 2. The type of fuel injector （1）Construction of the orifice type injector The injector with hole nozzles has the following characteristic: the needle valve in the matching parts of the fuel atomizer does not stretch from the nozzle, and the fuel atomizer has small and large numbers of nozzles at the head, with about 1-7 nozzles with diameter of 0.2-0.5mm. (see Figure 7- 10) Click here to close the show Click here to close the show  Needle valve lift Needle valve lift Figure 7-10 Types of the orifice type injector Click here to close the show Click here to close the show (2) Needle type atomizer The needle type atomizer has the following characteristic: the needle valve in the matching parts of the fuel atomizer stretches from the nozzle (please refer to Figure 7-11), and it has only one nozzle, with a larger diameter of 1-3mm. The needle is moving upward and downward in the nozzle during working, which eliminates the accumulated carbon in the nozzle automatically. Click here to close the show Click here to close the show  Figure 7-11 Needle type atomizer 1-Fuel return pipe screw 2-Pressure regulating screw helmet 3-Pressure regulating screw 4、9、13、15、16-Washer 5-Filter element 6-Fuel inlet pipe connector 7-Clamp nut 8-Needle valve 10-Needle valve body 11-Fuel injector body 12-Push-rod 14-Pressure regulating spring Click here to close the show Click here to close the show 7.3.2 Fuel Filter The fuel filter is adopted to filter the mechanical impurities and dusts in the diesel, so as to reduce the abrasion on the injection pump and the plunger and barrel assembly of the fuel atomizer, so as to ensure the reliable work of the diesel engine as well as extend the service life. The diesel filter is composed by the filter element and the shell (please refer to Figure 7-12). Click here to close the show Click here to close the show  Filter element Upper cover Manual fuel pump Filter element Housing Shell Fuel-water separator Inlet Kick-off plug Kick-off plug Outlet Figure 7-12 Diesel filter cleaner Click here to close the show Click here to close the show Many diesel engines have a fuel-water separator under the fuel filter, which eliminates the moisture in the diesel with fuel-water separation and sedimentation, so as to improve the quality of diesel and extend the service life of parts of the fuel system. Proportioning pump fuel systems often have a first-hand fuel pump above the fuel filter, which is utilized to discharge the air in the fuel pipe. Click here to close the show Click here to close the show 7.3.3 Fuel delivery pump Purpose of the fuel delivery pump is to draw fuel from the fuel tank and send it to the injection pump. Fuel delivery pump types include plunger, diaphragm, gear, and blade types. Click here to close the show Click here to close the show The piston-type fuel delivery pump is installed on the housing of the plunger-type injection pump. It consists mainly of the pump body, mechanical pump, hand pump, fuel inlet valve, fuel outlet valve, and fuel gallery (Figure 7-13). Click here to close the show Click here to close the show  Manual Manual fuel fuel pump pump Spring Fuel outlet Inlet valve valve Suction Outl Inlet strainer et Connect to oil outlet pipe Piston Roller rod Push rod Eccentric wheel of Connect to the fuel injection oil inlet pipe pump Figure 7-13 Piston-type fuel delivery pump Click here to close the show Click here to close the show The eccentric when on the camshaft of injection pump drives via the roller body the piston of mechanical fuel pump to reciprocate realizing pumping fuel. As shown in Figure 7-14. Click here to close the show Click here to close the show  Figure 7-14 Working principle of fuel delivery pump 1-Eccentric wheel of the fuel injection pump 2-Idler wheel 3-Push rod 4- Pressure oil chamber 5-Piston 6-Storage cavity 7-Fuel outlet valve 8-Spring 9-Fuel inlet valve Click here to close the show Click here to close the show The hand pump is used when the injection pump lacks fuel. Fuel in drawn manually from the fuel tank so that the injection pump is full of fuel expelling air from the fuel pipes and injection pump. Then the engine can start smoothly. (see Figure 7-13(b)). Click here to close the show Click here to close the show 7.3.4 Plunger-type injection pump The purpose of the injection pump is to deliver high-pressure fuel to the injectors at the specified amount and time and according to the operating conditions of the engine as well as the firing order of the cylinders. The following requirements shall be satisfied on the injection pump of the multi-cylinder diesel engine for automobiles. Click here to close the show Click here to close the show ① Various cylinders have equivalent fuel supply quantity. The fuel supply quantity shall change with the working conditions of the diesel engine; therefore, a fuel supply quantity adjusting mechanism is required for the injection pump. Click here to close the show Click here to close the show ② Fuel supply advance angle The fuel supply advance angle shall change with the working conditions of the diesel engine; therefore, a time advance unit is required. Click here to close the show Click here to close the show ③ Various cylinders shall have consistent fuel supply duration angle. ④ They shall stop fuel supply rapidly, to avoid leakage of the fuel atomizer. Click here to close the show Click here to close the show 1. General construction of the plunger-type injection pump Generally a plunger-type injection pump consists of the pump body, pumping mechanism, fuel amount regulating mechanism, drive mechanism, and timing advance unit (Figure 7-15). Clean fuel coming from the fuel filter enters the injection pump via the fuel inlet bolt. With high- pressure created, the fuel flows off the fuel outlet valve holder. Click here to close the show Click here to close the show  Governor Pump Timing advance Fuel delivery pump unit Figure 7-15 Plunger-type injection pump Click here to close the show Click here to close the show 2． Pump The pump body is the skeleton of the injection pump, which is generally casted by aluminum alloy. 3． Pumping mechanism At the core of the injection pumps are the pumping mechanism (Figure 7-16). Each injection pump has several pumping mechanisms, with each corresponding to a cylinder. Click here to close the show Click here to close the show  Figure 7-16 Pumping mechanism of the injection pump 1-Fuel outlet valve holder 2-Fuel outlet valve spring 3-Fuel outlet valve 4-Fuel outlet valve seat 5-Plunger sleeve 6-Low pressure fuel chamber 7-Plunger 8-Injection pump body 9-Fuel delivery amount adjusting screw 10-Fuel delivery amount adjusting sleeve 11-Plunger spring 12-Fuel delivery timing adjusting screw 13-Locating slide 14- Camshaft 15-Cam 16-Tappet body 17-Lower seat of plunger spring 18-Upper seat of plunger spring 19-Gear ring 20-Inlet and return fuel hole 21-Sealing gasket Click here to close the show Click here to close the show The pumping mechanism consists mainly of the plunger set (plunger (7) and plunger sleeve (5)), fuel outlet valve set (fuel outlet valve (3) and fuel outlet valve seat (4)), fuel outlet valve spring (2), and plunger spring (11). Click here to close the show Click here to close the show (1) Plunger set The plunger and barrel assembly are composed by the plunger and the plunger bushing (please refer to Figure 7-17), with extremely small tolerance clearance, 0.001?8-0.003mm, which shall be grinded after precise abrasive machining, known as couples. The plunger bushing is compressed on the pump body, with a fuel return hole on it. Click here to close the show Click here to close the show Oil inlet hole Plunger sleeve Plunger set Chute Plunger Joint tongue Figure 7-17 Plunger set Click here to close the show Click here to close the show The plunger finishes reciprocating motions in the plunger bushing. There is a beveling grooving on the upper cylindrical surface, which is connected to the plunger top through the central fuel channel or the straight channel in the plunger (please refer to Figure 7-17). The plunger has a false tongue or a pressure regulating arm on the bottom part for fuel supply adjustment. Click here to close the show Click here to close the show (a) Right-handed (b) Upper-left (c) Upper-right (d) Double-placed (e) Second level rotation straight- rotary notch rotary notch spiral notch straight-through notch through notch Figure 7-18 Plunger notch Click here to close the show Click here to close the show (2) Delivery valve matching parts The delivery valve matching parts include the delivery valve 2 and the delivery valve seat 1 (please refer to Figure 7-19), which is a one-way valve. The delivery valve matching parts include a pair of precise matching parts, with the radial-direction gap between the orienting surface of the delivery valve and the decompression band and the internal surface of the delivery valve seat of 0.006-0.016mm, and no exchange is allowed during the usage. Click here to close the show Click here to close the show  Figure 7-19 Delivery valve matching parts 1-Fuel outlet valve seat 2-Outlet valve 3-Conical tube surface 4- Decompression belt 5-Cross cutting groove Click here to close the show Click here to close the show The delivery valve matching parts are placed on the upper end of the plunger bushing, which are compressed on the injection pump with the delivery valve compression seat. Some delivery valve seats are equipped with a volume reduction body, so as to reduce the high- pressure volume and restrain the fuel fluctuation, to improve the diesel injection. Click here to close the show Click here to close the show (3) Fuel pumping process The plunger finishes upward and downward reciprocating motions with the function of the cam and the plunger spring on the camshaft of the injection pump, so as to finish the fuel pumping tasks. The fuel pumping process can be divided into the following three stages. Click here to close the show Click here to close the show ① Fuel taking process After the turning around of the bulge of the cam, the plunger moves downward with the effect of the spring force, generating the vacuum in the upper space of the plunger (known as the fuel pumping chamber). When the fuel supply hold on the plunger cashing on the upper end of the plunger is opened, the diesel filled in the upper fuel channel of the fuel pump flows into the fuel pumping chamber through the fuel hole. The fuel supply process finishes when the plunger moves to the bottom dead center (please refer to Figure 7-20 (a)). Click here to close the show Click here to close the show  Figure 7-20 Schematic diagram of plunger-type injection pump 1-Plunger 2-Plunger gasket 3-Chute 4-Plunger hole 5-Fuel outlet valve seat 6-Fuel outlet valve 7-Fuel outlet valve spring Click here to close the show Click here to close the show ② Fuel supply process When the bulge of the cam jacks up the idler wheel body, the plunger moves upward, and the plunger spring is compressed. In this condition, the fuel is compressed, and some of the fuel flows back to the upper fuel chamber of the injection pump through the fuel hole. Click here to close the show Click here to close the show When the top surface of the plunger covers the upper border of the fuel supply hole of the sleeve, a seal fuel chamber is formed in the fuel pumping chamber on top of the plunger due to very small matching space between the plunger and the bushing. Click here to close the show Click here to close the show The plunger continues to move upward, leading to a sharp rise on the fuel pressure in the fuel pumping chamber. When the fuel pumping pressure is larger than the sum of the delivery valve spring force and the residual pressure in the high-pressure fuel pipe, the delivery valve is pushed away, and the high- pressure diesel enters into the high-pressure fuel pipe through the delivery valve, to inject into the combustion chamber through the atomizer (please refer to Figure 7-20 (b) and (c)). Click here to close the show Click here to close the show ③ Fuel return process When the chute of the plunger is connected with the fuel return hole of the sleeve during the upward motion of the plunger, the low-pressure fuel circuit in the fuel pumping chamber is connected with the middle hole, the radial direction hole and the chute on plunger head, leading to sudden fuel pressure drop. The delivery valve is closed rapidly under the effect of the spring force, to stop fuel supply (please refer to Figure 7-20 (d)). Click here to close the show Click here to close the show The plunger continues moving upward hereafter; after the turning of the bulge of the cam, the plunger moves downward with the effect of the spring. Next circulation starts. Click here to close the show Click here to close the show 4. Fuel delivery amount adjusting mechanism The fuel delivery amount adjusting mechanism is used for adjusting fuel delivery amount per working cycle by turning the plunger according to engine load. See Figure 7-21. Click here to close the show Click here to close the show (a) No oil supply (b) Oil supply(partial) (c) Oil supply(max) Figure 7-21 Fuel delivery amount adjusting of the injection pump 1-Plunger gasket 2-Inlet and return fuel hole 3-Adjusting toothed bar 4- Plunger of injection pump 5-Adjusting ring gear 6-Controlling sleeve 7-Plunger tenon Click here to close the show Click here to close the show Some diesel engines have shifting-fork pull- rod type (please refer to Figure 7-22) or pull-rod bushing type fuel control mechanism of fuel injection pump. Click here to close the show Click here to close the show  Figure 7-22 Shifting-fork pull-rod type fuel control mechanism 1-Plunger gasket 2-Plunger 3-Plunger adjustment arm 4-Fork fastening screws 5-Shift fork 6-Fuel rod Click here to close the show Click here to close the show 5. Drive mechanism The fuel injection pump is often driven by the timing gear 1 of the crankshaft on front end of the diesel engine with a group of wheel gear (please refer to Figure 7-23). The driving gear and the intermediate gear (not indicated in the figure) of the injection pump are marked with the timing signs, and it is required to install with the aligned signed to ensure the timing of the fuel supply of the injection pump. Click here to close the show Click here to close the show  Figure 7-23 Driving and fuel supply timing of the injection pump 1-Crankshaft timing gear 2-Driving gear 3-Air compressor 4-Coupler 5- Fuel supply advance angle regulator 6-Injection pump 7-Supporting board 8-Speed governor 9-Valve drive gear 10-Injection timing mark on the flywheel A-All timing marks Click here to close the show Click here to close the show It is necessary to ensure the fuel injection timing when installing the injection pump on the diesel engine, and corresponding timing signs are required to be aligned correspondingly, to ensure the correct fuel injection time of the injection system. Click here to close the show Click here to close the show 6. Fuel injection advance unit The injection advance unit is utilized to change with the rotation speed of the diesel engine, so as to adjust the fuel supply starting angle of the injection pump automatically. The fuel supply starting angle of the injection pump refers to the camshaft angle of the injection pump corresponding at the moment the injection pump starts to provide fuel to the high-pressure fuel pipe, which leads to a direct influence on the fuel injection advance angle of the diesel engine. Click here to close the show Click here to close the show The fuel injection advance angle of the diesel refers to the turning angle of the fuel atomizer from start of fuel injection to the travelling of the piston to the top dead center. It is a critical and sensitive factor giving rise to influences on working performance of the diesel engine. Click here to close the show Click here to close the show The premature injection may lead to premature ignition and combustion and the premature rise on cylinder pressure, which result in increased compressed negative work, decline in power and rise on fuel consumption, giving rise to difficulty in start and generation of cylinder knocking noises. The late injection may lead to late ignition and combustion. In this condition, the piston is moving downward, leading to increased space volume and deterioration of combustion condition. It may lead to black smoke during exhaust, increased fuel consumption, declined power, rise on exhaust temperature and overheated engine. Click here to close the show Click here to close the show Under a fixed working condition of the engine, the fuel injection advance angle achieving the largest power and the lowest fuel consumption for the engine is known as the optimal fuel injection advance angle. Engines have different optimal fuel injection advance angles under different rotation speeds and loads. Click here to close the show Click here to close the show The mechanical centrifugal timing advance unit is adopted for most injection pumps (please refer to Figure 7-24), which makes the camshaft of the injection pump turn around certain angle automatically at the rise of the rotation speed of the engine by utilizing the centrifugal force of the fly ball, to achieve advance fuel supply. Click here to close the show Click here to close the show  (a) Structure of the fuel injection advance device (b) Initial position (c) Ultimate position Figure 7-24 Fuel injection advance unit 1-Protective cover 2-Advance device spring 3-Driving pin 4-Driving disc 5-Power paw 6-Driving disc flange 7-Driving pin 8-Flying hammer arc surface 9-Flying hammer 10-Fuel injection pump camshaft 11-Flying hammer pin 12-Driven disc L1-Spring start position L2-End of the spring location θ-Advance Angle adjusting range Click here to close the show Click here to close the show 7.3.5 Governor 1． Function of governor The speed controller adjusts the fuel supply quantity of the injection pump automatically according to the changes on rotation speed of the diesel engine at the premise of keeping the accelerator pedal of automobiles unchanged, so as to restrain or stabilize the rotation speed. Click here to close the show Click here to close the show Different from gasoline engines, diesel engines have relatively smooth torque characteristic curve (please refer to Figure 7-25), leading to unfavorable working stability. Any small change on external load M (increased to M2from M1) will lead to large fluctuation n on rotation speed of the diesel engine. Click here to close the show Click here to close the show Especially, sudden discharge of load during high- speed working of the diesel engine may lead to “galloping” (it is difficult to control the diesel engine due to sharp rise on the rotation speed), giving rise to serious accidents such as damage on crankshaft, connecting rod, air cylinder and piston. Click here to close the show Click here to close the show Figure 7-25 Torque characteristic of diesel engine Click here to close the show Click here to close the show 2． Types of governor At present, the variable speed governor and the two-plate mechanical speed governor are frequently adopted on diesel engines. 3． RAD-type two-plate speed governor The structure of the RAD-type two-plate speed governor is as shown in Figure 7-26. Click here to close the show Click here to close the show  Figure 7-26 RAD-type two-plate speed governor 1-Flyweight 2-Support lever 3-Control lever 4-Idler wheel 5-Crankshaft 6-Floating lever rod 7-Speed governing spring 9-Oil supplied regulating gear lever 10-Pulling level 11-Speed adjusting screw 12-Staring spring 14-Guiding lever 15-Idle spring 16-Gear lever stroke adjustment bolt Click here to close the show Click here to close the show When the diesel engine is operating within the idling scope, the centrifugal force of the flyweight is balanced to the resultant force of the idling spring and the stating spring, to keep the fixed position of the fuel supply control rack. Click here to close the show Click here to close the show The centrifugal force of the flyweight changes with the changes on rotation speed of the diesel engine, leading to changes on the opening position. Such changes on position will be delivered to the fuel control rack with the slide bushing through the guiding lever and the floating level, to control the fuel supply quantity. (Please refer to Figure 7-27), to achieve stable operation of the diesel engine at idle. Click here to close the show Click here to close the show Figure 7-27 Schematic diagram for the rotational speed control of the two-plate speed governor 1-Floating lever rod 2-Speed governing spring 3-Oil supplied regulating gear lever 4-Pulling level 5-Control lever 6-Support lever 7-Idle spring 8-Sliding sleeve I-The original position of control lever II-Control levers starting position III- Location of the control lever operation Click here to close the show Click here to close the show When the rotation speed of the diesel engine exceeds the control scope, the idling spring 7 is totally compressed, and the bushing 8 contacts with the pulling level 4 directly. Within the normal speed scope, the flyweight has relatively centrifugal force, which is not sufficient to drive the pulling level. The pivot B cannot move in this condition, and the speed governor does not work. Click here to close the show Click here to close the show In this way, the direct control on level 5 will be delivered to the control rack 3 through the level 6, to conduct direct control to the rotational speed of the diesel engine. Click here to close the show Click here to close the show When the diesel engine rotates to the stipulated highest rotational speed, the centrifugal force of the flyweight overcomes the tension of the governing spring, leading to rightward moving of the bushing and the pulling level. In this condition, the pivot B (please refer to Figure 7-27) moves to B′; the point D of the pulling level moves to D′; the lower pivot point C of the floating level moves to C′; the fuel supply control rack reduces the moving to the fuel supply quantity direction, to make the rotational speed of the diesel engine not exceed the stipulated highest rotational speed. Click here to close the show Click here to close the show Figure 7-28 Schematic diagram for overspeed restriction of the two-plate speed governor 1-Floating lever rod 2-Speed governing spring 3-Pulling level 4-Sliding sleeve Click here to close the show Click here to close the show 7.3.6 Distributor fuel injection pump The distributor fuel injection pump is equipped with a distributor rotor (or a distributor plunger) and multiple fuel outlets (please refer to Figure 7- 29). Distributor fuel injection pumps can be divided into the rotator type (radial direction compression type) and the single plunger type (axial direction compression type). Click here to close the show Click here to close the show Figure 7-29 Distributor fuel injection pump Click here to close the show Click here to close the show 1. Structure of the distributor fuel injection pump The VE type fuel injection pump is an axial compression distributor pump, which is mainly composed by the pump body, the pump cover, the vane fuel supply pump, the fuel pumping mechanism, the fuel cut-off electromagnetic valve and the fuel injection advance device (please refer to Figure 7-30). Click here to close the show Click here to close the show  Speed governi Tension ng Fuel-water separator ofManu lever of Secondary handle Flywe Gove Overflow Fuel return pipe the preliminary fuel al fuel control the speed diesel filter ight rning filter pump valve governor sprin g Fuel cut-off valve Housing Distribution plunger Fuel Injector 90° rotation expanded view) Fluid pressure type fuel Fuel outlet valve Drive Shaft Second-level injection advance deviceHigh- vane fuel (90° rotation expandedpressure supply pump view) pump head Fuel tank Figure 7-30 Schematic diagram for the structure of the VE type distributor fuel injection pump Click here to close the show Click here to close the show The VE type distributor fuel injection pump has the key component of the fuel pumping mechanism, which is composed by the plunger, the plunger bushing, the fuel control sleeve, the plunger spring and the deliver valve matching parts (please refer to Figure 7-31), so as to generate high-pressure fuel with fixed time and quantity. Click here to close the show Click here to close the show  (a) Pumping mechanism (b) Plane cam (c) Plunger Figure 7-31 Fuel pumping mechanism of the VE type distributor pump 1-Idler wheel 2-Plane cam 3-Oil quantity adjusting sleeve 4-Oil drain hole 5-Fuel cut-off electromagnetic valve 6-Oil inlet hole 7-Plunger 8-Plunger gasket 9-Pressure oil chamber 10-Fuel delivery groove 11-Delivery valve matching parts 12-Oil outlet hole 13-Plunger spring 14-Pressure equalizing groove 15-Fuel supply groove 16-Central fuel channel Click here to close the show Click here to close the show 2. Working process of the distributor type fuel injection pump The fuel supply process of the VE type distributor injection pump can be divided into fuel taking, fuel pumping, fuel returning and pressure equalizing Click here to close the show Click here to close the show (1) Fuel taking process When the concave part of the plane cam plate contacts with the idler wheel, under the effect of the plunger spring, the rotating plunger moves leftward to the end point, and the drainage hole 4 is enclosed totally by the fuel control sleeve. Click here to close the show Click here to close the show When a fuel supply groove of the plunger is corresponding to the fuel supply hole, the fuel in the pump chamber enters into the central fuel channel of the plunger. The fuel supply process is not finished until the staggering between the fuel supply groove of the plunger and the fuel supply hole of the plunger bushing (please refer to Figure 7-32 (a)). Click here to close the show Click here to close the show (2) Fuel pumping process When the plane cam plate rotates from the concave part to the bulge, and contacts with the idler wheel, the plunger moves leftward to rightward. At this time, there is a sharp rise on the fuel pressure in the central fuel channel of the plunger. When the fuel delivery groove of the plunger is facing to a fuel delivery hole of the plunger bushing, the high-pressure fuel is delivered to the fuel atomizer of corresponding cylinder through the fuel outlet, the delivery valve and the high-pressure fuel pipe (please refer to Figure 7-32 (b)). Click here to close the show Click here to close the show The plunger finishes 4 fuel supply and 4 fuel delivery and it injects to each air cylinder during each rotation circle. Click here to close the show Click here to close the show (3) Fuel return process The plunger keeps moving rightward under the effect of the plane cam. When the drainage hole of the plunger is exposed, and the fuel control sleeve is connected to the pump chamber, the high- pressure fuel in the central fuel channel of the plunger flows back to the pump chamber, leading to sharp decline on the fuel pressure and the end of the fuel supply (please refer to Figure 7-32 (c)). Click here to close the show Click here to close the show (4) Pressure equalizing process There is a pressure equalizing groove on the plunger, which is situated between the fuel delivery groove and the drainage hole, forming a 180° included angle with the fuel delivery groove. After the stop of the fuel supply of a certain air cylinder when the plunger continues to rotate to the point that the pressure equalizing groove is facing to the distributor fuel channel of the corresponding air cylinder, the distributor fuel channel is connected to the internal chamber of the fuel injection pump, leading to balance on the fuel pressure between the two positions (please refer to Figure 7-32 (d)). Click here to close the show Click here to close the show The stroke between the connection of the fuel delivery groove and the fuel delivery hole of the plunger bushing and the closing is known as the effective stroke of the plunger. Larger effective stroke indicates more fuel supply quantity. Move the position of the fuel control sleeve, to change the effective stroke of the plunger, so as to change the fuel supply quantity of the distributor pump. Click here to close the show Click here to close the show During the rotational process of the plunger, the pressure equalizing groove is connected o the distributor fuel channel of each cylinder, leading to uniform and balanced pressure in various distributor fuel channels, so as to ensure the uniformity of fuel supply of various cylinders. Click here to close the show Click here to close the show  Fuel cut-off electromagnetic valve Fuel delivery Inlet Oil inlet hole groove Fuel supply groove Plunger Fuel supply Plunger Plunger sleeve groove Plunger Fuel chamber outlet Pump head Distributor fuel Fuel outlet valve channel Equali Fuel delivery zing amount adjusting groove sleeve Plunger sleeve Fuel Plunger Plunger supply groove Fuel outlet Relief port Fuel outlet valve Distributor fuel Fuel outlet valve channel Figure 7-32 Working process of the VE type distributor injection pump Click here to close the show Click here to close the show 3. Fuel cut-off electromagnetic valve VE type distributor injection pump is equipped with a fuel cut-off electromagnetic valve. During the start and operation of the engine, the power supply of the accumulator applies to the solenoid coil of the solenoid valve, and the valve opens to open the fuel supply hole, and the fuel enters into the fuel pumping mechanism (Figure 7- 33 (a)). Click here to close the show Click here to close the show When the engine stops operation, rotate the starting witch to the OFF position, to disconnect the circuit and close the valve, so as to cut off the fuel circuit and stop fuel supply (please refer to Figure 7-33 (b)). Click here to close the show Click here to close the show  Fuel Fuel cut-off electromagnetic valve Pump head Plunger Oil inlet hole Figure 7-33 Fuel cut-off electromagnetic valve Click here to close the show Click here to close the show 4. Fuel injection advance unit The fuel injection advance device of the VE type distributor injection pump belongs to a hydraulic type, with the structure as shown in Figure 7-34. Click here to close the show Click here to close the show  Idler wheel seat Idler wheel Drive Shaft High-pressure side Advance piston Low pressure side Driving pin Spring Figure 7-34 Fuel injection advance unit Click here to close the show Click here to close the show The idler wheel is connected to the advance piston through the driving pin and the connecting pin. There is a small hole on the right end of the piston, connected to the fuel in internal chamber of the pump body. There is a spring installed on the left end of the piston, connected to the fuel supply chamber of the vane fuel supply pump. When the engine is operating in a stable way, the pressure on the left end and the right end of the piston achieves balance, with fixed piston and idler wheel seat. Click here to close the show Click here to close the show When the engine speed is increased, the vane fuel supply pump accelerates operating, leading to rise on fuel pressure in the pump chamber, which makes the right end pressure of the piston of the advance device larger than the left end, and it compresses the spring. In this condition, the piston moves leftward, and it drives the idler seat to rotate clockwise through the driving pin (rotating reverse to the direction of the driving shaft). It leads to early jacking up of the plane cam by the idler wheel, to supply fuel and inject in advance. Click here to close the show Click here to close the show Higher engine speed indicators larger fuel pressure in the pump chamber. Larger leftward moving distance of the piston indicates earlier fuel injection. Click here to close the show Click here to close the show 5. Governor The speed governor of the VE type distributor injection pump is a centrifugal variable speed governor, with the basic structure as shown in Figure 7-35. Click here to close the show Click here to close the show  Governing spring Speed governing handle Support of the flyweight Idling spring Maximum fuel supply Governor shaft adjusting screw Governor gear Tension lever Flyw Guide rod eight Driving pin Speed governing sleeve Fuel delivery amount Plunger adjusting sleeve Figure 7-35 VE type distributor pump governor Click here to close the show Click here to close the show Under the idling condition, the adjusting handle is situated at the idling position, and the tension of the governing spring is almost zero. The flyweight will stretch outward even in a very low rotation speed of the transmission shaft of the governor, to drive the speed governing sleeve, so as to make the tension lever swing rightward and the idling spring compressed. Click here to close the show Click here to close the show If the rotation speed of the diesel engine increases due to certain reasons, the centrifugal force of the flyweight is increased, and breaks the above balance. The flyweight drives the speed governing sleeve, to make the tension lever further compress the idling spring to swing rightward. The fuel supply regulating sleeve moves leftward, to reduce the fuel supply, and the rotation speed drops and recover. Click here to close the show Click here to close the show If the speed of the diesel engine reduces, the centrifugal force of the flyweight is reduced, and the idling spring drives the tension lever and the guide rod to swing leftward. The fuel supply regulating sleeve moves rightward, to increase the fuel supply and increase the rotation speed. Click here to close the show Click here to close the show When the speed governing handle is positioned at a position between the idling and the maximum opening limitation screw, the governing spring is stretched, and it pulls the tension lever and the guide rod to swing leftward. The ball pin on the bottom stirs the fuel supply regulating sleeve rightward, to increase the fuel supply. Click here to close the show Click here to close the show The centrifugal force of the flyweight is increased due to increased rotation speed. In condition that the rightward thrust force applied to the speed regulating sleeve is balanced to the leftward tension applied to the tension lever of the regulating spring, the fuel supply regulating sleeve is stable at a moderate fuel supply position, and the diesel engine operates at the moderate speed in a stable way. Click here to close the show Click here to close the show If any change on rotation speed is caused due to changes on loads, the balance between the centrifugal force of the flyweight and the regulating spring force is destroyed. In this condition, the speed governor acts immediately, to recover the rotation speed by increasing or reducing the fuel supply quantity. Click here to close the show Click here to close the show Questions 1. What is the characteristic for the forming of the combustible mixture of the diesel engine? 2. What are the two main types for the combustion chambers of diesel engines? What are the characteristics of each? Analyze the process for the forming of the combustible mixture according to the knocked-down diesel engine. Click here to close the show Click here to close the show 3. What are the main components of mechanical- type fuel supply system of diesel engine? What are the main roles played by various components? 4. What is the purpose of fuel injectors? What are the types? Click here to close the show Click here to close the show 5. What are the determinative factors for the fuel injection pressure of the fuel atomizer? How to adjust? 6. What is the purpose of the fuel injection pump? What are the types? 7. How does the plunger type injection pump to control the fuel injection quantity? Click here to close the show Click here to close the show 8. What is a fuel supply advance angle? What are the consequences for excessively large or small injection quantity? 9. What id the function of governor? What are the standards for classification? Please illustrate the reason for the speed governor for diesel engines, which is not necessary for gasoline engines? 10. How does the distributor pump operate? Click here to close the show Click here to close the show