09-11-2016, 10:14 AM
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Common Rail Diesel Fuel Systems
The aim of this presentation is to give a generic technical overview of the main features and operating principles of the common rail diesel fuel injection system..
All facts and figures quoted are intended to show typical examples only for explanation purposes.
Common Rail Diesel Fuel Systems
Advantages of common rail:
Fuel pressure available on demand...
Higher injection pressures and finer atomization of fuel...
Injection pressure created independent of engine speed...
Multiple injections per cylinder combustion are possible.
Benefits of common rail:
Reduction of overall exhaust emissions...
Reduction of particulate emissions...
Reduction of noise emissions...
Improved fuel efficiency...
Higher performance.
Common Rail Diesel Fuel Systems
Examples of typical common rail system maximum fuel pressures:
Bosch:Generation 1: up to 1350 Bar (19845 psi). Unijet
Generation 2: up to 1600 Bar (23520 psi) EDC 16
Generation 3: up to 2000 Bar + (29400 psi)
Denso: 1st generation: up to 1450 Bar (21315 psi) ECD-U2P 2nd generation: 1800 Bar + (26460 psi) HP3/HP4
Delphi : Multec: up to 2000 Bar
Direct acting diesel common rail system: up to 2000 Bar
Various systems differ in design, components layout and specific functions. However, all operate in a similar way.
Bosch EDC16
Common Rail Diesel Fuel Systems
High pressure fuel pump
The High pressure pump is the interface between the low pressure and the high pressure side of the fuel system.
Basic function:
To ensure that enough fuel is delivered at sufficient pressure across the engine’s entire operating range. This includes delivery of sufficient fuel for a rapid engine start and pressure increase in the rail.
Common Rail Diesel Fuel Systems
High pressure fuel pump
Transfer pump supplies fuel from the fuel tank to the pumping chambers of the high pressure pump.
Fuel metering valve regulates the fuel intake volume to the pumping chambers of the high pressure pump
Common Rail Diesel Fuel Systems
Fuel volume intake control
Pump piston
Pressure valve
to common rail
Suction valve
Return
Safety valve
Feed (from the tank)
Gear pump
Fuel metering control valve
Throttle bore
Control piston
Lubricating-oil bore
High-pressure pump
Common Rail Diesel Fuel Systems
Advantages of fuel intake volume regulation:
Only the required volume of fuel is supplied to the common rail from the high pressure pump...
Reduced fuel flow around system results in lower fuel return flow temperature...
Reduced parasitic load on engine from high pressure pump contributes towards further reductions in exhaust emissions.
Common Rail Diesel Fuel Systems
High pressure accumulator (common rail)
Fuel is supplied to the common rail at high pressure from the high pressure pump.
The rail stores the fuel and distributes it to the individual injectors.
It also damps pressure vibrations caused by the high pressure pump and injection processes.
Typical volume of fuel held in common rail: 16 – 20cm³.
Common Rail Diesel Fuel Systems
Fuel system diagnosis
Injector leak back test
There should not normally be any fuel collected in receptacles during engine cranking.
Example of acceptable leak back value with engine idling: approximately 20ml per injector over a 2 minute period.
(Always refer to manufacturer data for exact specifications
Common Rail Diesel Fuel Systems
The fuel system can be divided into three basic circuits
Low pressure supply circuit
High pressure delivery circuit
Fuel leak back and return