Location of injection system elements «Common Rail» on diesel 4-cylinder engine
1 - air flow meter; 2 - ECU; 3 - high pressure fuel pump; 4 – high pressure accumulator; 5 - fuel injectors; 6 - crankshaft speed sensor; 7 - coolant temperature sensor; 8 - fuel filter; 9 – the gauge of provision of a pedal of management of giving of fuel
The main element of the fuel injection system is the fuel pump, which is installed on all diesel engines. An injection pressure of up to 1350 bar is needed to increase the power to 160 kW per cylinder.
In recent years, many diesel fuel injection systems have been developed, in particular, direct injection (Dl). At the same time, the task was not only to increase engine power, but also to reduce fuel consumption and noise and reduce exhaust gas toxicity. Compared to previous systems, the Bosch fuel injection system «Common Rail» (common rail system) for direct fuel injection (Dl) provides more flexibility in adapting to the diesel engine power supply system, for example:
- wide range of applications (for passenger cars and commercial vehicles with power outputs of 30 kW per cylinder, as well as for heavy trucks, locomotives and ships with power outputs of 200 kW per cylinder;
- high fuel injection pressures up to 1400 bar;
- injection changes when starting the engine;
- the possibility of control, main and late injection;
- ensures that the injection pressure matches the operating mode of the engine.
Function of the injection system
Distinctive characteristic of the common piping system «Common Rail» (common rail system) consists in separating the pressure generating unit and the fuel injection unit.
The basis of the system is the reservoir (battery). The injection pressure is independent of the amount of fuel injected and the engine speed. The pressurized fuel supply is in the high pressure accumulator «Common Rail» and ready to spray. The amount of fuel injected is determined by the driver's request, and the injection pressure is calculated by the control unit (ECU) based on information from various sensors. The ECU sends an excitation signal to the injector solenoid at exactly the right time, indicating the start of fuel delivery. The amount of injected fuel is determined by the opening period of the nozzle and the pressure in the system. ECU and fuel injection sensors include:
- ECU;
- crankshaft speed sensor;
- camshaft position sensor;
- accelerator pedal position sensor;
- pressure sensor in a system with a common pipeline;
- coolant temperature sensor;
- air flow meter.
Based on the information from the above sensors and the requirement of the driver (accelerator pedal position) The ECU determines the instantaneous operating characteristics of the engine and the vehicle as a whole. The unit processes the signals generated by the sensors and transmitted over the communication lines, and based on this information controls the injection system in open or closed loop mode. The engine speed is measured by the crankshaft speed sensor, and the camshaft position sensor determines the fuel injection sequence (phase length). The electrical signal from the accelerator pedal position potentiometer sends a signal to the ECU about how much the driver presses on the accelerator pedal.
The air mass meter transmits a signal to the ECU with data on the instantaneous air flow, which allows you to calculate the process of complete combustion of the fuel with a minimum content of harmful substances in the exhaust gases. Since the engine is equipped with a turbocharger and boost control, an additional sensor also measures this pressure. When the outside temperature is low and the engine is cold, the ECU determines the injection timing and other parameters appropriate for the specific operating mode. Depending on the vehicle and increasing safety and comfort requirements, additional sensors may be used to provide information to the ECU. The figure shows an example of a diesel 4-cylinder engine with a fuel injection system «Common Rail».
Attention! The shown arrangement of elements does not correspond to their actual arrangement.
Main functions
The main functions of the system are to ensure the injection of the required amount of fuel at a strictly defined moment and under the required pressure. This ensures not only smooth operation of the diesel engine, but also economical fuel consumption.
Additional functions
Additional functions in closed loop operation and open loop control functions serve to reduce exhaust emissions and fuel consumption and are used to improve safety, comfort and convenience.
For example: exhaust gas recirculation (EGR), boost pressure adjustment, gear shifting, electronic immobilizer, etc. The CAN system communicates with other vehicle systems. The diagnostic check of the vehicle can retrieve the data that is in the system data reserve.