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Mercedes "fourth generation" fuel injection

The new diesel unit from Mercedes-Benz – click here for the news story – uses the fourth generation of the tried-and-tested common-rail direct injection technology, says Mercedes.

The distinguishing characteristic of the latest generation is the increase of 400 bar in maximum rail pressure, which now equals 2000 bar. This rise in pressure potential was crucial for boosting the engine's output to 150 kW/204 hp and its torque to 500 Nm, while bringing about a marked improvement in the engine's untreated emissions.

Piezoelectric injectors which Mercedes says are a completely new development form a key component in the fourth-generation CDI technology. They harness the ability of piezoelectric ceramic to alter its crystalline structure with microsecond speed when an electrical voltage is applied.

The actual spatial movements produced are tiny however, For this reason, the new injectors are fitted with a piezo stack, which is basically made up of piezoelectric elements connected in series.

In contrast to systems used to date, the movement of these elements controls the injector needle directly and enables even greater alterations in volume that are accurate to within a few thousandths of a millimetre.

The benefits of this are an increase in the available injection volume as well as particularly fine and fast metering of injection quantities. This enables the fuel injection process to be adapted to the momentary engine load and rev speed with greater accuracy – by means of high-precision multiple injections of fuel for example – which has a positive impact on emissions, consumption and combustion noise. Plus, the engine runs even more quietly when idling than its predecessor.

As a result of the innovative actuation concept, injector operation is leak free. This dispenses with the need for a leak oil line to return the negligible quantities of fuel that used to accumulate in the system on account of the operating principle.

This improves the injection system’s thermal circuit to such an extent that, even at a rail pressure of 2000 bar, fuel cooling is superfluous to requirements. Not only does this save energy, it reduces the high pressure pump’s operating energy input by around one kilowatt at high engine loads.

In order to continue to deliver optimum injection quantities over the engine’s entire service life, an adaptive learning function compensates for any tolerance deviations that may occur as a result of minimal component wear.

For the full news story on the new diesels click here

For the detail about the twin turbocharge system click here