Solenoid valves and common rail units

Common rail technology: the silent revolution of diesel engines

The innovation introduced by common rail injection technology has paved the way for a new generation of diesel engines designed to deliver higher power and smoother performance.

The common rail—literally a “shared pipe” or “common manifold”—is a fuel supply system composed of multiple components working in synergy to optimise fuel consumption.

A high-pressure injection pump (up to 3,000 bar) regulates fuel distribution through the rail to the injectors, active sensors that deliver fuel into the cylinders. Piezoelectric injectors are controlled by a solenoid valve, which in turn is managed by the ECU control unit. Thanks to the solenoid (or piezoelectric) valve system, fuel is maintained at constant pressure. A pressure sensor connected to the ECU monitors the value and, when necessary, a pressure limiter compensates fluctuations and restores optimal conditions.

The advantages of common rail technology are clear:

The ability to modulate fuel quantity and split injection into multiple close phases (pre-injection, main injection, post-injection) allows engine performance to be optimised while reducing fuel consumption.
Thanks to improved fuel management, the engine runs more efficiently, smoothly, and quietly. Precise diesel dosing also contributes to lower emissions.

Historical notes

Common rail technology was conceived by Italian physicist Mario Ricco and first developed at the FIAT Research Centre in Orbassano (Turin). In the 1990s, the rights to the technology were sold to the German company Robert Bosch, which completed its industrial development and large-scale implementation. The first common rail diesel engine entered production in 1997, installed on the Alfa Romeo 156 1.9 JTD.

Common rail engines are identified as JTD in FIAT, TDCi in Ford, dCi in Renault, CDTi in Opel, and CDI in Mercedes-Benz.