How does a common rail-injector work?

truck image by Greg Pickens from

Fuel injection refers to a system used to mix air with fuel in an internal combustion engine in order to generate power. A common rail-injector is a fuel-injector system used in diesel and gasoline engines.

Common Rail

The fuel injectors in a common rail-injector system are all supplied by a common rail, or pressure accumulator, that stores fuel at high pressure. The accumulator directly supplies the injectors with fuel. A high pressure pump contained in the common rail-system holds a reservoir of fuel at a maintained pressure of up to 29,000 psi.

Fuel Injector

The common rail-fuel-injectors are controlled by the vehicle's Engine Control Unit. When the injectors are activated by the ECU via a signal, a hydraulic valve made up of a plunger or nozzle, either hydraulically or mechanically, opens and sends fuel into the engine cylinders.

Square Injection Rate

The accumulator enables fuel pressure energy to be remotely stored at a constant maintained pressure. The ECU reads this pressure and determines when to electrically activate the injectors. This enables injection pressure at the start of the injection process to be approximately equal to the pressure in the accumulator, thus creating a square injection rate.