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 Engine Oil-Finder

Common Rail

Decoupled, quieter and better exhaust gas properties

Common Rail is characterized by the ability to hold a relatively constant pressure in all parts of the high pressure equipment. The substantially steadier pressure build-up is also easier on the timing belts, in contrast e.g., to the unit-injector (pump-jet) system. In the past there were pipes with pressure pulsations, which in this case, one would prefer to avoid if possible. This determines the size of the common rail (see picture 3), from where the system also gets it's name.

The rail-volume is sufficient to hold the pressure when injecting

In the past, the disadvantage of pressure pulsation was, that the full pressure was not available from the word go, because it had to be provided from a central injection pump, through the conduction system. The storage size must be calculated in such a way that, on the one hand, the pressure when injecting from one injector does not drop too low, and on the other hand, does not last too long when starting the engine.

Independent parameters, multiple injection is possible

Injection pressure- and timing can be selected freely by the control device and independent of each other. Through multiple, short pre-injecting of approx 0,4 milliseconds in the partial-load range, the temperature increase (nitrogen oxide emission) and peak pressure can be kept lower and a certain air movement in the cylinder can be supported. The more the injection is divided, the more the hardness of the combustion is increased thus, also a reduction of combustion noise.

Up to seven partial injections are possible

Nowadays in theory, up to seven partial amounts are quite possible. Post-injections raise the temperature in the exhaust system and create regeneration possibilities for NOX storage catalytic converters and particle filters. At the same time the injection pressures rise to up to almost 2000 bar.

Electrically driven low- and mechanically driven high-pressure pump

The Diesel fuel for the rail comes from the high-pressure pump (see picture 4), which is mechanically driven from the engine. Nowadays, for the fuel supply, the electric tank-internal pump, with it's 3 - 6 bar supply pressure, is almost always used, in the past there were also mechanical gearwheel pumps. Depending on the outside temperature a pre-heating element is also active.

First high- and later only low-pressure regulation

The high pressure costs engine performance and lowers the efficiency. For certain araes of operation it's not absolutely necessary. Even from the first generation, it could be reduced by the control device. Under driving conditions, e.g., during fuel cut-off, it can be completely switched off. From the second generation onwards the regulation is done on the low pressure side.

Long- and ball rail

The high pressure rail, which should have the same transport distance to all the cylinders is connected with all the injectors (see picture 5). The pressure valve (on the right of the rail in picture 1) allows excess fuel to flow, through the cooler (only first generation) back to the tank. The control device gets it's pressure control signals from a sensor on the left of the rail. The rail can also be sperical in shape. 10/11

Pressure sensor on the Rail
Hot membrane - air-mass gauge
Inductive transducer
on the crank- and/or camshaft
Temperature transducer
for coolant and intake air
Accelerator transducer
Glowing equipment

Pressure valve on the rail
Magnetic valves in the injectors
Substituted by: Piezo valves
which have faster switching (< 1 ms)
exhaust gas recirculation

Application in:
All Diesel-motor cars/transporters
Occasionlly in heavy utility vehicles

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