Common rail

Common rail direct fuel injection is a modern variant of direct fuel injection system for diesel engines. It features a high-pressure (over 1,000 bar/15,000 psi) fuel rail feeding individual solenoid valves, as opposed to low-pressure fuel pump feeding unit injectors (Pumpe Düse or pump nozzles), or high-pressure fuel line to mechanical valves controlled by cams on the camshaft. Third-generation common rail diesels now feature piezoelectric injectors for increased precision, with fuel pressures up to 1,800 bars (26,000 psi), although a new version of Delphi’s proven diesel common rail system will allow compliance with Euro 6 and US Tier 2 Bin 5 without costly next-generation injection technologies

History
The common rail system prototype was developed in the late 1960s by Robert Huber of Switzerland. After that, the technology was further developed by Dr. Marco Ganser at the Swiss Federal Institute of Technology in Zurich, later of Ganser-Hydromag AG (est.1995) in Oberägeri. In the mid-1990s, 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 and turned it into practical use on their ECD-U2 common-rail system, which was mounted on the Hino Rising Ranger truck and sold for general use in 1995.

Modern common rail systems, whilst working on the same principle, are governed by an engine control unit (ECU) which opens each injector electronically rather than mechanically. This was extensively prototyped in the 1990s, with collaboration between Magneti Marelli, Centro Ricerche Fiat and Elasis. After research and development by the Fiat Group, the design was acquired by the German company Robert Bosch GmbH for completion of development and refinement for mass-production. In hindsight, the sale appeared to be a tactical error for Fiat as the new technology proved to be highly profitable. However, the company had little choice but to sell, as it was in a poor financial state at the time, and lacked the resources to complete development on its own.[1] In 1997 they extended its use for passenger cars. The first passenger car that used the common rail system was the 1997 model Alfa Romeo 156 1.9 JTD,[2] and later on that same year Mercedes-Benz E 320 CDI.

Common rail engines have been used in marine and locomotive applications for some time. The Cooper-Bessemer GN-8 (circa 1942) is an example of a hydraulically operated common rail diesel engine, also known as a modified common rail.

The engines are suitable for all types of road cars with diesel engines, ranging from city cars such as the Fiat Nuova Panda to large family cars like the Alfa Romeo 159.

Common rail today
Today the common rail system has brought about a revolution in diesel engine technology. Robert Bosch GmbH, Delphi Automotive Systems, Denso Corporation and Siemens VDO are the main suppliers of modern common rail systems. Different car makers refer to their common rail engines by different names:

BMW's D-engines (also used in the Land Rover Freelander TD4
Daimler's CDI (and on Chrysler's Jeep vehicles simply as CRD)
Fiat Group's (Fiat, Alfa Romeo and Lancia) JTD (also branded as MultiJet, JTDm, Ecotec CDTi, TiD, TTiD , DDiS, Quadra-Jet)
Ford Motor Company's TDCi Duratorq and Powerstroke
General Motors Opel/Vauxhall CDTi (manufactured by Fiat and GM Daewoo) and DTi (Isuzu)
General Motors Daewoo/Chevrolet VCDi (licensed from VM Motori; also branded as Ecotec CDTi)
Honda's i-CTDi
Hyundai-Kia's CRDi
Mahindra's CRDe
Maruti Suzuki's DDiS (manufactured under license from Fiat)
Mazda's CiTD
Mitsubishi's DI-D
Nissan's dCi
PSA Peugeot Citroën's HDI or HDi (Volvo S40/V50 uses engines from PSA 1,6D & 2,0D, also branded as JTD)
Renault's dCi
SsangYong's XDi (most of these engines are manufactured by DaimlerChrysler)
Subaru's Legacy TD (as of Jan 2008)
Tata's DICOR
Toyota's D-4D
Volkswagen Group: The 4.2 V8 TDI, and the latest 2.7 and 3.0 TDI (V6) engines featured on current Audi models use common rail, as opposed to the earlier unit injector engines. The 2.0 TDI in the Volkswagen Tiguan SUV uses common rail, as does the 2008 model Audi A4. Volkswagen Group has announced that the 2.0 TDI (common rail) engine will be available for Volkswagen Passat as well as the 2009 Volkswagen Jetta.[3]
Volvo D5-engines are called common rail

Principles
Solenoid or piezoelectric valves make possible fine electronic control over the injection time and quantity, and the higher pressure that the common rail technology makes available provides better fuel atomisation. In order to lower engine noise, the engine's electronic control unit can inject a small amount of diesel just before the main injection event ("pilot" injection), thus reducing its explosiveness and vibration, as well as optimising injection timing and quantity for variations in fuel quality, cold starting, and so on. Some advanced common rail fuel systems perform as many as five injections per stroke.[citation needed]

Common rail engines require no heating up time,[citation needed] 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 — up to 2,000 bars (29,000 psi) — in a "common rail", basically a tube that branches to supply ECU-controlled injector valves, each of which contains a precision-machined nozzle and a plunger driven by a solenoid. Driven by an ECU (which also controls the amount of fuel to the pump), the valves, rather than pump timing, control the precise moment when the fuel injection into the cylinder occurs, and also allow the pressure at which the fuel is injected into the cylinders to be increased. As a result, the fuel that is injected atomises[citation needed] easily and burns cleanly, reducing exhaust emissions and increasing efficienc.