Siemens-Common Rail System – Fuel rail (common rail) and high pressure fuel lines
The illustration shows the system in the 2.0L Duratorq-TDCi (DW) diesel engine
1 High pressure fuel lines (to the fuel injectors)
2 High pressure pump line (to high pressure pump)
3 Fuel rail
4 Fuel pressure sensor
The fuel rail is made of forged steel.
The fuel rail performs the following functions:
• stores fuel under high pressure and
• minimizes pressure fluctuations.
Pressure fluctuations are induced in the high pressure fuel system due to the operating movements of the high pressure chambers in the high pressure pump and the opening and closing of the fuel injectors.
The fuel rail is therefore designed in such a way that its volume is sufficient, on the one hand, to minimize pressure fluctuations. On the other hand, the volume in the fuel rail is small enough to build up the required fuel pressure for a quick start in the shortest possible time.
The fuel supplied by the high pressure pump flows via a high pressure line to the fuel rail (high pressure accumulator). The fuel is then delivered to the individual fuel injectors via the four injector tubes which are all the same length.
When fuel is taken from the fuel rail for an injection process, the pressure in the fuel rail is kept almost constant.
Fuel pressure sensor
NOTE: The fuel pressure sensor must not be removed from the fuel rail during servicing. If the fuel pressure sensor is faulty the fuel rail must be replaced along with the fuel pressure sensor.
In order that the engine management system can determine the injected fuel quantity precisely, as a function of current fuel pressure in the fuel rail, a fuel pressure sensor is located on the fuel rail.
High pressure fuel lines
NOTE: The bending radii are exactly matched to the system and must not be changed.
NOTE: After disconnecting one or more high pressure fuel lines, these must always be replaced. Reason: The reason for this is that leaks can occur when re-tightening, due to distortion of the connections of the old lines. The high-pressure fuel lines connect the high-pressure pump to the fuel rail and the fuel rail to the individual fuel injectors.