Injection with the fourth generation of the common-rail principle

The new diesel unit from Mercedes-Benz ushers in the fourth generation of the tried-and-tested common-rail direct injection technology. The distinguishing characteristic of the latest generation is the increase of 400 bar in the maximum rail pressure, which now equals 2000 bar. This rise in pressure potential was of crucial importance for boosting the engine's output to 150 kW/204 hp and its torque to 500 Nm, whilst at the same time bringing about a marked improvement in the engine's untreated emissions.

Piezoelectric injectors which are a completely new development form one of the key components 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 the customary 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 in increase in the available injection volume as well as particularly fine and fast metering of the injection quantities. This enables the fuel injection process to be adapted to the momentary engine load and rev speed with yet greater exactness - 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.