The piezo injectors appeared to displace the electromagnet ones, but now the latter seems to have a comeback. And there was talk of ever greater pressures. That's true, but not all manufacturers use these. Maybe a certain system would allow e.g. 2500 bar, but the best solution for the specific engine in option is 1800 bar.

Higher pressures cost performance and energy, and must be in proportion to the benefits. The third expectation was that the flow pump would be responsible for the fuel delivery instead of the positive displacement pump. But not so with the diesel when supply of the high-pressure pump without additional mechanical assistance needs 5 bar, not possible for flow pumps.

The diesel engine has also still several return flows, from the pressure regulator in the supply line and of the high pressure pump back into the tank, from the rail in the feed line just before the fuel filter and from the injectors to the high pressure pump. For diesel engines with not too high flow rates a single-piston high-pressure pump with double cam is sufficient. Pressure fluctuations due to injections are damped by a throttle on entry into the rail.

In injectors with electromagnetic valves, also not always all eight or nine injection-divisions are just used by the manufacturer. Example: 2 pre-, 1 main- and 3 post injections. The already explained principle of differential pressure above and below was maintained. New and useful for magnetic injectors is that in return a venturi, also known as suction jet pump in the saddle tank, produces a negative pressure in the return line from the injectors. 07/16

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