The term common rail is used to refer to a certain type of direct fuel injection. With common rail, pressure generation and fuel injection are separate processes. A separate pump, installable anywhere in the engine, continuously generates pressure which is stored in a distributor pipe. The injectors of all the cylinders are connected in parallel with the pipe, called a common rail. A constant pressure is continuously available at the injectors of all cylinders. The amounts and timings of the injected fuel are controlled by solenoid valves on the individual injectors.
The common rail system is used, for example, in diesel engines or our modern, fuel-efficient FSI® engines with direct petrol injection.