Fat Freddy wrote:Can this pressure drop shown here be attributed to the injector? It seems to occur over a large amount of crank degrees where most of the time the injector is closed.
Yes, the pressure drop is inevitable on each injection, as the injection itself will consist of a finite volume of fuel that has to be replenished with the HP pumping elements. As these elements are running at a fixed volume on this engine at idle, which is less than the injected quantity (for fuel economy reasons, the HP pump does not try to immediately compensate for the volume injected on the first one or two strokes of the pump after each injection) what you end up with is a sawtooth pressure. Or that is the theory, if you apply enough filtering to overcome the HP pump pressure fluctuations and other standing-waves in the main rail. The pressure drops suddenly as each delivery line to the injectors is purged of fuel, then there is a gradual rise as the HP pump catches-up.
The HP pump runs in open-loop control for the VCV (volume control valve) on this engine for most of the time - whatever the Marketing guys say!!, and the mapping for this is based on the injected quantity as well as engine speed.
aux_r wrote:The main wave we can see in this image is a combination of two harmonics: one with a frequency of one per engine's revolution (blue), and the other at the frequency of injection (green). About the main harmonic (blue) we must know the type of pump because if it is a pump with one or two elements as CP4 (Bosch) or DFP1, DFP3.3 or DFP3.4 (Delphi) for example the generation of pressure creates this kind of harmonic.
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