Common Rail Diesel Injection (CRDi)

Common rail direct fuel injection is a modern variant of direct injection system for diesel engines. It features a high-pressure fuel rail feeding individual solenoid valves, as opposed to low-pressure fuel pump feeding pump nozzles or high-pressure fuel line to mechanical valves controlled by cams on the camshaft.

The common rail system prototype was developed in the late 1960s by Robert Huber of Switzerland. After that, Ganser of the Swiss Federal Institute of Technology developed the common rail technology further. In the mid-nineties, Dr. Shohei Itoh and Masahiko Miyaki, of the Denso Corporation, a Japanese automotive parts manufacturer, developed the Common Rail Fuel System for Heavy Duty Vehicles.

Common rail engines require no heating up time, and produce lower engine noise and lower emissions than older systems. In older diesel engines, a distributor-type injection pump, regulated by the engine, supplies bursts of fuel to injectors which are simply nozzles through which the diesel is sprayed into the engine's combustion chamber. 

As the fuel is at low pressure and there cannot be precise control of fuel delivery, the spray is relatively coarse and the combustion process is relatively crude and inefficient. In common rail systems, the distributor injection pump is eliminated. Instead an extremely high pressure pump stores a reservoir of fuel at high pressure. Most European automakers have common rail diesels in their model lineups, even for commercial vehicles.