The diesel fuel system consists of the Common RAIL accumulator injection system, low-pressure and high-pressure fuel lines, intake and exhaust manifolds, turbocharger, fine and coarse fuel filters, air cleaner, fuel tank and charge air cooler.
The Common RAIL accumulator injection system consists of the fuel pump, injectors, high-pressure fuel accumulator, speed sensors (crankshaft and camshaft), working medium state sensors (fuel and air pressure and temperature), electromagnetic actuators (fuel pressure regulator, injector solenoid valves), electronic control unit, control, management and communication circuits, and the control and diagnostic panel.
The diagram of the control and management circuits of the Common RAIL fuel system is shown in Figure 2.
The high-pressure fuel pump (HPFP, mod. CP3.3, Fig. 4) is intended to create a fuel reserve, maintain and regulate the pressure in the fuel accumulator.
On the HPFP housing, the fuel priming pump 2, driven from shaft 9, and the electromagnetic pressure regulator 3 are secured.
In the HPFP housing, three plungers 5 (Fig. 5) are arranged radially at an angular interval of 120°, and on the drive shaft 3 a cam rotor 4 is mounted (the cams are arranged every 120° around the rotor circumference).
The HPFP drive shaft with the cam rotor has a gear drive from the reduction gear, the input shaft of which is in kinematic connection with the diesel crankshaft through the drive half-coupling and the timing gears.
The fuel that has passed through the coarse filter with water separator is delivered at a pressure of 0.8–0.9 MPa by the fuel priming pump through the fine fuel filter to the HPFP inlet union.
Lubrication and cooling of the HPFP parts is carried out by the diesel fuel entering the HPFP.
Under the effect of the created priming pressure, the protective valve 2 opens access for the fuel through the inlet channel 6 into the spaces above the plungers.
The incoming cam of the rotor moves the plunger upwards, the inlet orifice of the inlet channel is closed, and as the plunger continues to rise, the fuel is compressed in the space above the plunger.
When the increasing pressure reaches the level corresponding to that maintained in the high-pressure accumulator, the outlet valve 7 opens.
The compressed fuel enters the high-pressure circuit.
The plunger delivers fuel until it reaches TDC (delivery stroke). Then the pressure drops, the outlet valve closes.
The plunger begins to move downwards. In one revolution of the shaft, each of the three plungers performs one pumping stroke.
Since the HPFP is designed for a large delivery quantity, at idling and at partial loads an excess of compressed fuel arises, which through the pressure control valve 8 and the return line is returned to the fuel tank.
The pressure control valve sets the pressure value in the high-pressure accumulator depending on the engine load, speed and thermal state of the engine.
If the pressure in the accumulator is too high, the valve opens, and part of the fuel from the accumulator is diverted through the return line back to the fuel tank.
The pressure control valve is secured through a flange to the HPFP housing.
The armature 10 presses the valve ball 9 against the seat under the action of the valve spring, so as to separate the high-pressure and low-pressure circuits.
The energised electromagnet 11 moves the armature, applying additional force to press the ball against the seat.
The entire armature is washed by fuel, which lubricates the friction surfaces and removes excess heat.
The high-pressure fuel accumulator (Rail) is a volumetric store of fuel under high pressure (Fig. 6).
At the same time, the accumulator smooths out the pressure fluctuations that arise from the pulsating fuel delivery from the HPFP, as well as from the operation of the injectors during injection, due to the non-synchronism of the pressure pulses of the fuel doses coming from the HPFP and consumed through the injectors, as well as due to the excess of the fuel mass located in the accumulator and playing the role of a damper for the pulses of small fuel doses supplied and consumed.
The accumulator 1 generally has the form of a tube, at the ends of which the fuel pressure sensor 7 and the pressure limiting valve 5 are installed.
Along the generatrix of the tube perimeter, the unions for connecting the high-pressure fuel lines 2, 3 and the return union 4 are arranged.
The fuel from the HPFP is directed through the high-pressure line to the inlet union 3 of the rail.
The fuel accumulator communicates with the injectors by means of the high-pressure fuel lines connected to the outlet unions of the accumulator.
The volume of the accumulator is constantly filled with fuel under pressure.
The value of this pressure is maintained at a constant level and can be regulated by valve 8 (Fig. 5) depending on the diesel operating parameters.
The pressure limiting valve maintains a certain pressure value in the accumulator, performing the role of a reducing (safety) valve.
The valve housing, on the accumulator side, has a channel closed by the cone of the valve core 6.
The spring presses the cone firmly against the valve seat at normal operating pressure, so that the accumulator remains closed.
In the case when the pressure value in the accumulator exceeds the operating value, the cone, under the action of the pressure, moves away from the seat and the fuel under high pressure is diverted to the return line. As a result, the fuel pressure in the accumulator decreases.
The injector (Fig. 7) is intended for injecting fuel into the diesel cylinder and ensuring the required fuel atomisation.
On the diesel engines, injectors of the CRIN2 type manufactured by «BOSCH» (Germany) are used.
The required injection start moment and fuel delivery quantity are ensured by the action of the injector solenoid valve.
The injection start moment, in the "angle-time" coordinates, is set by the electronic control system of the diesel operation.
The formation by the electronic unit of the injector control signals occurs on the basis of "reading" the signals generated by the crankshaft speed sensors and the primary shaft of the HPFP drive reduction gear (sensors 1 and 2 in Fig. 2), installed in a coordinated interrelation according to a certain scheme.
The principle of operation of the injector is presented in Figure 8.
The fuel is supplied along the high-pressure line through the supply channel 4 to the injector nozzle 11, as well as through the fuel inlet throttle orifice 7 into the control valve chamber 8. Through the fuel outlet throttle orifice, which can be opened by the solenoid valve, the chamber communicates with the return line 1.
With the throttle orifice 6 closed, the hydraulic force acting from above on the control valve piston exceeds the force of the fuel pressure from below on the cone of the nozzle needle.
As a result, the needle is pressed against the nozzle seat and tightly closes the nozzle orifices. Consequently, the fuel does not enter the combustion chamber.
When the solenoid valve 3 is actuated, the electromagnet armature moves upwards, opening the throttle orifice 6.
Correspondingly, both the pressure in the control valve chamber and the hydraulic force acting on the control valve piston decrease.
Under the action of the fuel pressure on the cone, the nozzle needle moves away from the seat, so that the fuel through the nozzle orifices enters the combustion chamber of the cylinder.
The control delivery is an additional quantity of fuel intended for lifting the needle, which after use is diverted to the fuel return line.
In addition to the control delivery, there are fuel leaks through the nozzle needle and the control valve piston guide.
All this fuel is diverted to the return line, to which all the other units of the injection system are connected, and is returned to the fuel tank.
The quantity of fuel injected is proportional to the solenoid valve energisation time and the pressure value in the rail, and does not depend either on the engine crankshaft speed or on the HPFP operating mode (time-controlled injection).
When the solenoid valve is de-energised, the armature is pressed downwards by the force of the valve locking spring and the valve ball 5 closes the throttle orifice.
After the fuel outlet throttle orifice is closed, the pressure in the control valve chamber again reaches the same value as in the accumulator.
This increased pressure moves the control valve piston together with the nozzle needle downwards.
When the needle fits tightly against the nozzle seat and closes its orifices, the injection stops.
The coarse fuel filter serves for the preliminary purification of the fuel from mechanical impurities and water.
Since the engine HPFP is not equipped with a manual fuel priming pump, necessary for filling the fuel system with fuel without air, the filter design must contain a manual fuel priming pump.
Fig. 9 shows the coarse fuel filter with manual fuel priming pump "PreLine 270".
The drainage of sediment from the filter is carried out through cock 5, located in the lower part of the water separator 4.
When operating the diesel engine at ambient temperatures below –25 °C, the filter housing must be equipped with a heater 3 for the incoming fuel.
Heater supply voltage — 24 V, power — 350 W. Connection: positive and earth.
The heater operates autonomously, switching on and off automatically at temperatures below +5 °C.
The fine fuel filter serves for the final purification of the fuel. The fine fuel filter is non-detachable.
The fuel, passing through the curtains of the paper filter element, is purified from mechanical impurities.
The diesel air supply system (Fig. 10) consists of the air filter, turbocharger, charge air cooler, unions, pipelines and fastening clamps.
The dry-type air filter with replaceable paper filter elements serves to purify the air entering the cylinders.
The air filter (Fig. 11) consists of housing 5, two filter elements 6 and 7, cover 4. Rubber gaskets are provided to ensure tightness.
The small (inner) filter element ensures air purification in the event of mechanical destruction of the outer filter element.
Attention! The suction of unpurified air into the engine cylinders, arising from depressurisation of the intake tract, leads to a sharp reduction in the engine service life.
To facilitate monitoring of the air filter clogging, a sensor is installed between the filter and the turbocharger, and a warning device on the instrument panel.
As the filter becomes clogged, the vacuum in the inlet pipeline increases and, upon reaching a value of 6.5 kPa, the warning device is actuated and the "Air filter clogging" warning lamp illuminates on the instrument panel.
When the lamp illuminates, the filter element should be cleaned or replaced.
The turbocharger (Fig. 12) consists of a single-stage centrifugal compressor and a radial centripetal turbine.
The boost is regulated by bypassing part of the exhaust gases past the turbine wheel when the boost pressure exceeds a certain value.
A bypass valve is built into the turbine housing of the controlled turbocharger.
The bypass valve lever is connected by an adjustable rod to the actuator, which is connected by the air duct to the outlet union of the compressor housing.
Changing the length of the actuator rod of the turbocharger during operation is not permitted.
Disassembly and repair of the turbocharger during operation are not permitted and must be carried out in a specialised repair workshop.
