Function

There are several manufacturers of Common-Rail-systems featuring different designs. Besides the Bosch system, described earlier, and here once again displayed as an overall view, there is the Delphi system, making use of high-pressure pumps, operating with the established technological basis of the radial piston pump. Presumably also the 'sphere-rail' in the figure on top is an economic and space-saving alternative. The company Denso and Siemens are also important, particularly in respect of the newest exhaust gas regulations.

How it works

In the light of the exhaust gas regulation Euro 5, the cheapest solutions (e.g., distributor type injection pumps) will not do. The development concentrates upon the injectors. Originally they were controlled by magnetic valves. The piezo technique is new. Switch times of approx. 0.1 ms are possible and thereby very low injection amounts and their subdivision. A crystal reacts by volume change to the polarity of the charge. To generate effective valve lift, a lot of (more than 200!) thin layers above one another are necessary and a mechanical enlargement of the stroke. Because of the extremely low switch times and particularly break times, almost arbitrarily many injections are possible. This does not only improve the so- called raw emissions (e.g., nitrogen oxide), but also noticeably the operational behaviour (e.g., noise decrease). All-important for a post combustion of filtered particles is also the possibility of an after-injection. One wants to avoid costly additional tanks for the passenger car (e.g., with urea). The only disadvantage is perhaps that the oil becomes thinner.

Important

Plug in injectors featuring piezo technique may not be drawn off while the engine is operative. Though they are opened by putting on a tension, however, make use of the wire connection to be able to discharge when switching off the tension. If one separates the connection in the open state, they stay open. Too much liquid fuel in the cylinder has, in principle, the same destructive effect as a solid. 09/08