Common rail, as the name suggests, is a shared fuel line. The rail is an accumulator supplied by a pump, which maintains the fuel at a pressure of up to 2000 bar – which is equivalent to the weight of a luxury saloon on the space of one square centimetre.
Thanks to the high pressure and the very fine bore diameter of only one tenth of a millimetre in the nozzles, the injectors in the common rail system achieve very fine atomisation of the fuel. This provides an excellent, homogeneous mixture preparation and ensures extremely efficient combustion, which in turn results in enormous power, low emissions and low consumption.
The piezo injectors used by Audi open and close within fractions of a millisecond and can inject precise and minute quantities weighing less than a thousandth of a gram. The highly dynamic system allows the number of injection processes per power stroke to be widely varied – in the case of the 3.0 TDI for example, there are up to five partial injections. This strategy reduces emissions and, thanks to pre-injection, ensures a smoother combustion process, which in turn has an extremely positive effect on the engine acoustics.