Common Rail Diesel

WHAT IS THE COMMON RAIL DIESEL SYSTEM?
Common Rail is a direct fuel injection system used in Diesel engines. Common Rail Diesel systems can now grant maximum performances and reliability to automotive engines, reducing noise and emissions.

The system is composed of an injection pump, the rail, injectors and sensors which detect the operating conditions of the engine for a centralized electronic unit (ECU) which manages all the components.

HOW DOES THE COMMON RAIL SYSTEM WORK?
The high pressure pump pressurizes the fuel and transfers it to the rail, a common conduit that serve as pressure accumulator and reservoir. The pressure is regulated by an electronically controlled valve, so that the rail maintains the correct pressure required by the ECU.

The fuel then reaches the injectors filling two spaces, one above and one below the needle of the nozzle. The two forces balance each other out and the needle is kept closed thanks to a spring. The upper space, called control chamber, can be vented when a solenoid or piezoelectric valve opens.

When the electronic control unit opens the valve, this upper space empties out, The pressure in the lower chamber lifts the needle up opening the nozzle, and the fuel is injected in the combustion chamber until the signal to the valve is cut and the valve closes again; at this point, the pressure building up in the control chamber causes the needle to close.