The common rail system supplies pressurised fuel from a common rail to the fuel injectors.
The advantages of the common rail system are as follows:
- Reduces operating noise.
- Reduces the volume of pollutant gases and particles.
- Produces high engine torque at low engine speeds.
The common rail system comprises four basic components:
- A high pressure pump with an integral pressure regulator.
- The common rail, which is an accumulator containing fuel.
- The fuel injectors.
- The engine control unit.
The fuel injectors for each cylinder are fed with high pressure fuel from the common rail.
Injection pressures in the common rail system can reach 1600 bar, resulting in the formation of finer particles of injected fuel, ensuring an improved mixing with combustion air when compared with a conventional fuel injection system. Therefore, combustion is more complete and emissions of smoke and particulates, including carbon dioxide, are reduced.
The engine control unit functions as follows:
- Continuously monitors the operating conditions of the engine.
- Determines the injection pressure necessary for the engine to operate correctly, then adjusts the pressure regulator accordingly. The engine control unit ensures that the injection pressure is correct by analysing a signal from a pressure sensor, located on the common rail.
- Determines the injection timing at which to inject the correct quantity of fuel.
- Controls each fuel injector individually after determining injection pressure and injection timing.
In conclusion, the flow of injected fuel is determined by the following:
- The duration of injection.
- The injector opening and closing speed.
- The needle travel (determined by the type of injector).
- The nominal injector hydraulic flow (determined by the type of injector).
- The common rail pressure.