Common rail injection is a fuel injection system used on some diesel engines.
With common rail injection, a fuel supply gallery (the 'rail') supplies all the fuel injectors. The rail is maintained at a high pressure by a pump and pressure regulator.
In older diesel injection systems, an injection pump controls both the pressure and timing of the injection and as a result the two are related. In a common rail system the injection pressure is maintained separately from the injection timing, resulting in greater accuracy and flexibility of the injection timing. As a result, diesel engines with common rail injection often produce more power and lower emissions than older diesel engines.