Some Thing to know about Diesel Engine Common Rail Fuel System

Recent advances in injection technology have transformed diesel engines into quiet, clean-burning and efficient power plants. The common rail diesel injection system currently used in the vast majority of modern diesel engines is the single most important factor in increasing efficiency and performance of the diesel combustion cycle. 

Historically, diesel engines have used the unit injection system and the distributor type/pump in line PLN fuel system. These older systems had main disadvantages: Firstly, they were cam-driven and as a result the maximum pressure for fuel injection was only achieved at high engine speeds. Secondly, they were limited in the number of injections that they could deliver per combustion cycle.

The common-rail injection diesel systems build upon direct-injection technology which allows fuel to be injected directly into the combustion chamber. Common-rail injection systems use a rail to store the fuel at pressures in excess of 2,000 bar. This rail is shared between all cylinders, hence the name common-rail. The common rail allows a steady high-pressure supply of fuel independent of engine speed. The transfer pump is electronically activated to maintain the optimal pressure in the rail.

Early generations of common-rail injectors used magnetic solenoids to control the injection of fuel into the cylinders.

The latest generation of common-rail injectors use piezoelectric inline actuators to control fuel injection. These new actuators use hundreds of piezo-crystal wafers which expand very rapidly when a current is applied. Piezoelectric inline actuators can be integrated very close to the injector jet needle, providing friction-free movement. These injectors allow for much more precise fuel-injection times with shorter response times, as well as improved atomization of the fuel.

Common Rail diesel injection systems have several main advantages over older fuel injection systems. The high pressure fuel supply from the rail allows for the fuel to be injected quickly and at high pressure into the cylinders. This allows the electronic diesel control unit (EDU) to very accurately control the fuel injection. Such accurate control allows for up to 5 fuel injections per combustion stroke ("pilot", "pre", "main", "after", and "post" injections). The "pilot" injection, which occurs before ignition allows for good fuel-air mixture. The subsequent "pre" injection shortens the delay in the main injection, drastically reducing NOx gases, vibrations and other noise. The "after" injection occurring immediately after the "main" injection ensures that all particle matter is burned. Finally, the "post" injection allows for control of exhaust gas temperature, increasing after-treatment efficiency.

The overall result of using advanced common rail diesel injection systems is an engine that operates more efficiently, and is capable of outperforming it's gasoline-powered counterpart. Virtually all previous downsides of operating a diesel engine, such as noise, weak performance, vibrations and particle emissions have been eliminated with common rail direct injection diesel engine technology.

Electronic Control Unit (ECU)

The ECU for the EDC (Electronic Diesel Control) uses a microcontroller and a program and a data storage utilizing Flash technology. Its major assignments are control of the high-pressure generation, and of start-of-injection and duration of injection. In addition, the ECU is responsible for a range of other functions such as glow control (GZS) and system monitoring.

By means of CAN (Controller Area Network), it is a simple matter to network the ECU with other systems in the vehicle. For instance with the electronic transmission-shift control, the Antilock braking system (ABS) or the air-conditioning system

Sensors:

Speed Sensor - In combination with the cam sensor signal the speed sensor delivers the absolute crankshaft position to the combustion TDC of the first cylinder. The speed sensor works on the principle of variable reluctance.

Phase Sensor -The Hall Effect camshaft sensor identifies the position of the cam shaft in combustion engines.Together with the speed sensor signal the camshaft sensor signal supplies the absolute angular position of the crankshaft referred to top dead center (TDC) of the first fired engine cylinder.

Accelerator pedal module - is used to measure Accelerator pedal angle. It features a sensor integrated into the accelerator pedal which recognizes the driver's command and forwards a corresponding signal to the control unit.

Water temperature sensor: The temperature sensor measures the temperature of the engine, e.g. in the coolant water circuit.

Fuel temperature sensor - The temperature sensor measures the temperature of the fuel e.g. in the fuel filter

Boost Pressure sensor - The Boost- pressure sensor is used to measures the pressure of the aspirated or charged air in the intake-manifold with pressure controlled injection system.

Hot-film air mass meter - The hot-film air mass meter serves for the measurement of the air mass sucked by the engine of diesel injection systems independently of the atmospheric pressure and temperature

Rail pressure sensor - The high pressure sensor serves for the measurement of the fuel pressure in the fuel pressure accumulator (High pressure Rail) by diesel engines with common rail injection Systems.

History

1997 First Common Rail system in Passanger vehicle - 1350 Bar (Mercedes)

1999 First Common Rail System in Trucks – 1400 Bar

2001 second generation Common Rail - 1600 Bar (Volvo, BMW)

2003 Third Generation Common Rail with Piezo Injector – 1600 Bar (Audi)

2006 Third Generation Improvements – 1800 Bar Higher Efficiency

Common Rail Engine Names by Manufacturer:

   Audi: TDI

   BMW: D-engines

   Daimler: CDI

   Fiat Group: JTD

   Ford: TDCi Duratorq and Powerstroke

   GM Opel/Vauxhall: CDTi and DTi

   GM Daewoo/Chevrolet: VCDi 

   Honda: i-CDTi 

   Hyundai/Kia: CRDi 

   Land Rover: TD5 

   Mazda: CiTD 

   Mitsubishi: DI-D 

   Nissan: dCi 

   Peugeot: HDI or HDi 

   Renault: dCi 

   Subaru: TD 

   Toyota: D-4D 

   Volkswagen: TDI 

   Volvo: D and D5 

Common Rail Pumps, Rail Injector Manufacturers are Bosch, Continental, Delphi, Denso

For any training requirement please contact

Vijay Tharad, Mobile 8801282689,Email vijay_tharad@yahoo.com