The main concern of the automobile industries is to reduce the fuel consumption by making vehicles more efficient, and to reduce harmful emissions. Efforts are on to improve the injection system, since it is high impact on combustion process. Research is also on to develop new technologies. One of the new technologies developed is common rail technology.
The common rail system is one of the simplest system available to adopt in any engine. High pressure pumps are used in common rail fuel supply system. The pressure produced in the common rail engine offers advantage of flexible control of the injection process. It has a high injection pressure that is not influenced by engine speed. Due to constant pressure, it has a good fuel atomization.
Common rail system has a high pressure pump with low torque to reduce material stress produced during ignition process. One of the inherent problems with the injection system is lack of control of injection pressure.
Components of common rail fuel supply system
High pressure fuel pump
The high pressure fuel pump is used to supply the fuel from the fuel tank to the high pressure reservoir called rail. The fuel pump maintains a high pressure in the system. The pressure required for the ignition system is available anytime even when the engine speed is low. In a common rail system, the pressure generated is not linked with the engine speed. Therefore, a high pressure is maintained at all times in the supply system. Most pressure pumps used in the common rail ignition system use radial piston pumps. The fuel pressure is maintained at a range of 1200-1500 bar in a high pressure fuel pump.
Control pressure valve
It consist of a solenoid valve for the opening the inlet valve of the piston. The opening of the valve is controlled by the coil mounted on the solenoid valve. When the valve is activated, the coil mounted on the solenoid valve reduces the opening of the valve and increases the fuel pressure. When it is not activated, the internal pressure of the coil maintains a pressure of 100 bar.
The common rail is arranged between the pressure pump and the injection cylinder. The injector is fed with fuel constantly maintained at high pressure through common rail. The common rail distribution system is arranged with sensors to maintain the fuel pressure before feeding the injector.
The injectors contain nozzles for injecting atomizes fuel into the combustion chamber.
The common rail injection system mainly uses two types of injectors – the Pezo injectors and the solenoid injectors.
The actuators are mounted for the Pezo injectors and solenoid valve is for solenoid injectors. Hydraulic and electrical connections are used for the actuation of nozzle.
The injectors are connected to each cylinder and to the common rail via high a pressure pump.
The injectors are controlled by electronic connection called electric diesel control system.
Working of common rail fuel injectors
The high pressure common rail system uses a high pressure computer controlled injectors. The fuel present in the fuel tank is supplied to the high pressure pumps through fuel liners. Before supplying it to the pressure pumps the dirt and debris in the fuel are removed through the filters. The high pressure pumps pressurizes the fuel and it continuously supply it to the common rail where the sensors are arranged to maintain the pressure of the fuel. The common rail supplies the pressurized fuel to the injector through rigid steel lines and the opening and the closing of the valves are monitored through electrical connections. In the ignition chamber combustion is produced with less noise and smoke emission.