Common rail direct fuel injection is a modern variant of direct injection system for diesel engines. It features a high-pressure (1000+ bar) 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. Third generation common rail diesels now feature piezoelectric injectors for even greater accuracy, with fuel pressures up to 180 MPascal / 1800 bar.

Contents
1 History
2 Common rail today
3 Principles
4 See also
5 External links


History 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 and finally turned into its first practical use on their ECD-U2 Common Rail system, which was mounted on the Hino Raising Ranger truck and sold for general use in 1995.

Both Detroit Diesel & Cummins Engine Co (America) incorporated the common-rail diesel design into their heavy duty engines during the 1970's, one of which was the Cummins L10 series, which was a standard straight-6 diesel two-valve per-cylinder engine. Obviously in normal circumstances with 12 valves this engine would normally require a single camshaft with 12 lobes operating 12 pushrods which in turn operated the valves, one inlet, one exhaust per cylinder. However these new engine has 3 pushrodsper cylinder, 1 inlet, 1 exhaust, 1 injector. Total of 18 pushrods.

The Cummins L10 and Detroit Diesel engines in the 70's and 80's had injectors like any other diesel engine, but instead of each injector opening under pressure with delivery from a timed fuel pump which was mounted remotely and controlled everything, with the injector being an ancillary component atomising the delivered diesel, the L10 had a central pump delivering fuel to a "common-pipe" shared by all injectors at relatively low pressure, and then each injector when opened by the pushrod acted as its own "pressuriser" with the injector opening by force, giving the fuel the extra pressurisation, or "kick" that is required for higher combustion, this proved to be highly more effecient than relying on pressure delivered to the injectors by the pump located some distance away.

The elimination of the pressure-loss in pipes which was brought on by remotely situated delivery pumps was eliminated as the injector was as close as possible to the piston crown as could be done. The L10 was an engine featuring a common-rail diesel fuel system combined with turbocharger. The L10 engine was centred a 10.5 litre block, but was available in several different power levels, 185 -310 bhp, depending on specification and demand.

The modern ECU controlled common rail system whilst working on the same principle, is controlled by an electronic control unit which opens each injector electronically, rather than mechanically. This was extensively prototyped in the 1990's, 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 making suitable for mass-production. 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 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 know 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. Delphi Automotive Systems make common rail systems. Different car makers refer to their common rail engines by different names:

BMW D-engines
DaimlerChrysler's CDI (and on Jeep vehicles simply as CRD) Fiat Group's (Fiat, Alfa Romeo and Lancia) JTD (also branded as MultiJet and Ecotec CDTi) Honda's i-CTDi
Hyundai-Kia's CRDi
Ford Motor Company's TDCi Duratorq and PowerStroke
Renault's dCi
General Motors'/Opel's Vauxhall's CDTi (manufactured by Fiat and GM Daewoo) and DTi (Isuzu)
GM Daewoo's/Chevrolet's VCDi (licensed from VM Motori; also branded as Ecotec CDTi)
Mitsubishi's DI-D
PSA Peugeot Citroën's HDI or HDi
SsangYong's XDi (most of these engines are manufactured by DaimlerChrysler)
Volkswagen Group's TDi
Toyota's D-4D
Nissan's NEO-Di
Mazda's CiTD
Tata's DICOR
Mahindra's CRDe
Maruti Udyog's DDiS (Manufactured under license from Fiat)


Solenoid or piezoelectric valves make possible fine electronic control over the injection time and amount, 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.

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—up to 1,800 bar (180 MPa)—in a "common rail", basically a tube which in turn branches off to computer-controlled injector valves, each of which contains a precision-machined nozzle and a plunger driven by a solenoid. Driven by a computer (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 easily and burns cleanly, reducing exhaust emissions and increasing efficiency.

Most European automakers have common rail diesels in their model lineups, even for commercial vehicles. Some Japanese manufacturers, such as Isuzu, Toyota, Nissan and recently Honda, have also developed common rail diesel engines. Some Indian companies have also successfully implemented this technology, notably Mahindra & Mahindra for their 'Scorpio-CRDe' and Tata Motors for their 'Safari-DICOR'.