 Common Rail 1
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It is the 'common rail' through which the fuel enters the combustion chamber. This means a supply line with a larger cross-section, which is already under the pressure at which is injected too. The high pressure is
therefore generated for all cylinders together. This line should be dimensioned so that the injection process in one cylinder does not result in too great a reduction in pressure in the entire system. This is a significant
contrast to earlier systems and also pump nozzles, where the high pressure is generated for each cylinder individually.
The pressures have not increased that much, because in earlier systems the injector opening pressure was specified, but not the injection pressure, which could be double or four times higher. That is why the pumps at
that time were able to cope with an increase in the injector opening pressure, e.g. when using fuels with a different viscosity. It is difficult to say where the limit is at the moment. The vast majority of systems can cope with
pressures of up to 2300 bar. The absolute minimum pressure in certain operating conditions is probably 200 bar, but usually a little higher.
Since we're already talking about pressures, we should mention the 3 to 6 bar delivery pressure, which is generated either electrically by an in-tank pump or mechanically by a gear, rotor or vane pump. The complete
system is shown in the picture above. It starts at the tank at the bottom right to the mechanical delivery pump at the top, here driven directly by the crankshaft.
With its consistent delivery rate, the gear pump is ideally suited to ensuring the supply of fuel to the high-pressure pump, in contrast to the piston pump. You can clearly see that the right, lighter wheel drives with
counterclockwise rotation so that both wheels can transport the fuel upwards in the gaps between the teeth and close off any possible return flow by meshing with each other. So the bottom right is the inlet and the top right
is the outlet, both marked by arrows on the connections on the right.
This is a vane cell pump. Its inner part is correctly arranged somewhat eccentrically, but the four vane cells are unfortunately not. You should now imagine how these are pushed outwards by centrifugal force and thus seal
four compartments against each other. Where it slowly gets quite tight when turning clockwise is the outlet, and a quarter turn further is the inlet.
Inlet and outlet cannot only be created by drilling holes. Basically, there would be two pockets on the left and right, each separated by 90° of the circumference (picture above). It must be the case that one is always opened
when the other is closing, otherwise fluid pressure will build up that could destroy the mechanism.
This is a suction jet pump. It only works if there is another pump already in place. In this sketch, this pumps the fuel from above to the right. The decisive factor is the constriction, which creates a vacuum in the line coming
from below through its jet effect (Bernoulli effect). This could take fuel from another low point in a comparatively large and flat tank or from the second tank, which is separated from the first by a cardan shaft.
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