Description In general, fuel injection system of diesel engines is designed as above The rotation of the engine is delivered to camshaft through coupling or operating gear Feed pump is activated by the rotation of camshaft and it takes in fuel from the fuel tank to deliver it to the filter with pressure of 1.8~2.5kg/cm² Fuel filtrated by the filter is sent to the oil chamber then through injection pump via injection pipe finally it is injected from the nozzle of nozzle holder to the combustion chamber of engine The amount of fuel sent from feed pump is more than double the amount of maximum injection of injection pump and the residual fuel return to the fuel tank when it exceeds the pressure of valve set by the overflow valve Also, the fuel circulated through overflow nipple of nozzle holder via inside of nozzle holder returns to the fuel tank or filter Fuel pump Fuel pump consists of feed pump, timer, main body, governor It is a thermo-type(BOSCH PS3S) of fuel pump and is considered most important part over all the other part used in fuel system of diesel engine for it determines the performance of diesel engine This pump, unlike other conventional AD type pump, does not have cover plate in pump housing that it becomes an airtight type pump to make it durable against high pressure injection Plunger and delivery valve are installed independently in each cylinder and it makes easy to control the injecting quantity between each cylinder, especially for the combination with specified fuel system because of accurate injection period Description of Pump Operation There is fuel chamber in pump housing and it is filled with fuel of low pressure filtrated by fuel filter at all times that the exhaust and suction hole is connected to the fuel chamber Pump is operated by camshaft and when it is at its fall stroke, it starts sucking fuel into plunger barrel that when the plunger reaches its bottom dead center, the suction is completed When the camshaft is at its rise stroke, it compresses the spring of plunger and pushes it up then the front part of plunger blocks exhaust and suction hole That is when the fuel begins to flow and block and this moment is called still injection start When the plunger rises and the pressure of fuel raises the power of delivery valve spring and the residual pressure of fuel inside injection pipe, it pushes delivery valve to initiates fuel delivery to nozzle holder and injection continues by the rise of plunger Fuel increase and decrease harness Decrease and Increase of fuel delivered from plunger changes effective stroke of plunger Harness which changes effective stroke is as shown in the right Plunger barrel is fixed on flange sleeve by knock pin and it does not move Plunger is assembled in a way it could perform upward and downward motion and rotation Control sleeve is assembled on the "T" shaped part of wing of plunger, the ball in control sleeve is assembled in the groove of key of "L" shaped control rod Plunger in electric barrel is rotated by moving control rod and it causes changes in effective stroke to increase injection quantity An effective stroke defines as a period of delivering fuel from the moment still injection begins to inject to the moment it finishes and it is proportional to the injecting quantity 2.Function of Plunger Plunger makes fuel become of high pressure and it deceases and increases of injecting quantity and it is most important part out of all the other parts in injection pump Also, moving parts of plunger and its barrel are made and assembled with a high degree of precision Plunger barrel is fixed on pump housing that it is not supposed to move It has one exhaust and suction hole When the upper part of plunger blocks exhaust and suction hole, injection begins and it ends when incision groove (lead) meets exhaust and suction hole and this period is called effective stroke 3 Delivery valve(iso-pressure valve) When the pressure of fuel becomes higher than residual pressure and the pressure of delivery valve spring o fuel inside injection pipe, it compresses delivery valve spring that it opens delivery valve and fuel is delivered to nozzle from nozzle holder via injection pipe Then, when the lead of plunger meet exhaust and suction hole of plunger barrel, delivery of fuel stops by delivery valve spring shutting delivery valve in a moment and the injection is completed And to make it fa for next injection, the residual pressure inside injection pipe is accumulated Therefore, for the prevention of abnormal injection by changes of residual pressure, a valve which regulate residual pressure of injection nozzle(is- pressure valve) should be installed inside main body to regulate residual pressure of injection nozzle and set the level of residual pressure to be open valve pressure of isopressure valve Structure of RLD governor Operation Operation of governor Performance graph of RLD governor • Lever setting position at idling - Section C-D : A section where the setting force of start spring is bigger than centrifugal force of flyweight (quantity of flyweight lift:0) - Section D-E : A section where it operates control rack exceeding the setting force of start spring by centrifugal force of flyweight - Section E-E1 : Engine rotation speed control section by idling spring(idling section) - Section E-E3 : Engine rotation speed control section by idling spring and governor spring • Curve θ2, θ3 and θ4 may be obtained when the control levers are at all different position The more the control lever gets close to maximum speed, the lower the performance graph gets • Lever setting position at maximum speed - Section A1-A2-F : Engine rotation speed control section by torque cam - Section F-G-H : Engine rotation speed control section by governor spring Point G has no load and has maximum speed • Increase of start fuel injection quantity - Speed of engine increases after setting control lever at maximum speed while the engine is not running - Section T-U : It shows the range of start engine injection quantity This is when the sensor lever fits in cam notch of torque However, regular control rack is maintained at Rs by rack limiter engine start With the engine stationary, the flyweights are in closed position and the idling and governor springs remain in the free-length state free from set tension Placing the adjusting lever in the full position moves the adjusting lever shift, which causes the cancel spring B force to move the supporting lever This in turn causes the control rack to move in the direction of greater fuel delivery At the time, the sensor lever gets into the groove cut in the torque cam provided to increase the amount of fuel for startup, and the control rack, past the full load position, reaches the point to increase the amount of fuel for startup that is limited by the rack limiter By returning the adjusting lever to the idle position after the engine has started, the control rack is pulled to allow the sensor lever to leave off the groove in the torque cam Thereafter, no fuel delivery increase can be obtained for start up even by moving the adjusting lever to the full position Idling Speed control Placing the adjusting lever in the idle position with the engine started makes Q the fulcrum of the floating lever As engine speed decreases, the centrifugal force of flyweights yields to the tension of idling spring, closing the flyweights This causes the floating lever to pivot about Q, moving the control in the direction of greater fuel delivery, thus preventing the engine from stalling As engine speed increases, on the other hand, the idling spring tension yields to the flyweight cetrifugal force, casing the control rack to move the direction of smaller fuel delivery, thereby decreasing the speed (Condition indicated by dotted line) An idle speed is thus maintained at a point where the flyweight cantrifugal force balance with the set tension of the start and idling springs The torque cam and sensor lever are not in contact with each other while the engine runs at idle Control of fuel injection rate at full load by torque cam When the adjusting lever is placed in the full position under load, the floating lever pivots about P to move the control rack in the direction of greater fuel delivery The sensor lever, at the same time, comes in contact with the torque cam As speed varies, the shifter moves in the axial direction, which causes the tension lever to be pushed forward and backward around the tension lever shaft, making the torque cam to rotate around its shaft The sensor lever movement tracing along the cam surface displaces the control rack, thereby increasing or decreasing the fuel injection rate The tension lever movement from varying speeds does not, however, move the point R; it moves only P of guide lever Q of supporting lever The control rack is therefore moved through the sensor lever by the movement of torque cam Full Speed Control When the adjusting lever at full position, the engine speed increase while the fuel injection rates under full load are controlled by the torque cam and sensor lever As speed further builds up and as the supporting lever contacts the L lever on the adjusting lever shaft by the cancel spring B, the floating lever pivots about Q to move the control rack in the direction of smaller fuel delivery, thus controlling the full speed The sensor lever, on the other hand, leaves the torque cam surface as this control advances Boost Compensator When the boost pressure in the engine intake manifold rises by turbo charger operation, it acts on the compression chamber of the boost compensator As the boots pressure overcomes the boots compensator spring tension, the diaphragm and push rod A move to the night The motion of push rod A causes the lever to turns clockwise with the push rod B following the lever by the return spring At the time, the U-lever in governor housing turns clockwise by the cancel spring force in accordance with the push rod B motions, which moves the center fulcrum of sensor lever to right Since the sensor lever is in contact with the torque cam at its bottom, the control rack moves in the direction of greater fuel delivery as the fulcrum moves of the sensor lever at the center Engine is stopped Generally, lever in shaft part does not stay contacted with rack connecting link when stop lever is not being manipulated(normal position) Lever of shaft part shifts rack connection link by manipulating stop lever so that injection quantity of fuel decreases and it becomes possible to stop engine SPG True angle of fuel injection timing is needed to maintain effectiveness of fuel as the RPM of engine increases It is injection timing regulator that changes such things as above according to RPM of engine Timer rub is placed in camshaft and operated between centrifugal pendulum by operating flange Timer spring is installed in between bearing pin fixed in centrifugal pendulum holder and journal of operating flange and the journal of flange is in contact with special curved surface of centrifugal pendulum Also, centrifugal pendulum is to vibrate with respect to the center of bearing pin At a low speed rotation of engine, centrifugal pendulum can not be vibrated by force of timer spring set Centrifugal pendulum vibrates as a result of overcoming the force of timer spring set as the centrifugal force increases by increased engine rotation Therefore, large cam and small cam begins to move Large cam is attached to a hole in flange that the shift of big cam is delivered to timing flange to form true angle Especially for the timer that is in use currently is SPG timer and it is intended to improve starting ability and decrease white smoke in starting engine besides the foregoing Fuel For diesel engines, fuel of good quality should be used Use of fuel of poor quality deteriorates engine performance and shorten the life of injection pump and nozzle inside injection system as well as engine Fuel serves as lubricant for nozzle, plunger and delivery valve 2.Poor quality of fuel accelerates wear and tear of each part Fuel with poor viscosity causes unstable operation of nozzle, plunger, delivery valve 4.Reversely for the fuel with high viscosity, good combustion can not be achieved because small amount of fuel which is injected from nozzle gets bigger than its size that it mixes with air unstably 5.Combustion of great amount of fuel containing sulfur produces great amount of sulfur carbon dioxide containing water inside combustion chamber where sulfur acid is generated that it causes corrosion of nozzle or the other parts Fuel containing water causes unstable operation and rusty of nozzle, plunger, delivery valve 7.Fuel containing great amount of carbon cinders erodes carbon at the end of nozzle and it deteriorate injection Fuel filter Generally, fuel filter contains many kinds of impurities which is invisible with the eyes and if it is used as fuel, it may cause difficulties in starting vehicles That is why filtration of fuel is important Cleaning of fuel tank If fuel tank gets rusty, it contaminates fuel So, fuel tank should be cleaned with gasoline regulary 2.Filter of each part of engine should be cleaned and replaced according to its specified running mileage or time A/S Fuel injector is considered of great importance that one might compare this to the heart of a man High quality of fuel must be injected with highly proper amount and at most appropriate time and should be controlled according to the capability of engine Those primal parts must be assembled and finished with high degree of quality and precision [...]... does not stay contacted with rack connecting link when stop lever is not being manipulated(normal position) Lever of shaft part shifts rack connection link by manipulating stop lever so that injection quantity of fuel decreases and it becomes possible to stop engine SPG True angle of fuel injection timing is needed to maintain effectiveness of fuel as the RPM of engine increases It is injection timing