Common Rail - 4th generation
Mercedes of course, highlighted several advantages of this engine, among other things, the two-stage turbo-charging. We however, only wish to deal with the fourth generation common rail equipment installed in this
The original 1800 bar pressure has now become 2000, at least in the case of the Delphi. Already well known from the previous generation, are the Piezo-layers and their in-line construction method in the shaft of the
injectors. What's now new is that they no longer work through any auxiliary facilities or hydraulic conversion ratios, but directly on the nozzle needles. The fuel-cooler had already been discarded since the second
generation. A small sensation is the now the lack of the flow-back, which should also be responsible for a (very) slight increase in the efficiency.
A Piezo layer reacts extremely quickly to a certain voltage and developes a huge force. Unfortunately it can only manage 1/1000 of the distance of ist own thickness, i.e. a multi-layer actuator with a thickness of 1
millimeter only opens the nozzle needle about 1 micrometer. The advantage is, that it lasts the entire life of the engine without wear and tear and thus needs, no re-adjustment.
Unfortunately,the direct control of the jet-needles, at least at the moment, is only possible for the pre-injection. To achieve larger injection their path has to be enlarged, via a hydraulic system with staging pistons. What
remains, is the normal tension drop to open the needles.
Due to the smaller moving mass, as many as seven injections per power stroke are now possible. The faster opening and closing, now in less than 0,05 milliseconds, improves the spray pattern and the mixture
formation. According to the Delphi company, this should have a positve influence on the NOX-emmision. One disadvantage is still the higher cost of the system. 09/09