Common Rail fuel injection

A Common Rail fuel injection system is a tubular high-pressure accumulator which stores the fuel constantly under high pressure. It is replenished by a pump driven by the engine. The injectors are connected to the rail by short steel pipes, and opened and closed by electrical impulses. Common Rail technology separates the pressure generation from the fuel injection, so the developers can define all injections in the map at will.

Audi’s Common Rail fuel injection system runs in most engines up to peak pressures of 2,000 bar; the next target is 2,500 bar. The nozzle holes in the piezo injectors Audi uses in its V-engines are only about 0.1 millimeters in diameter, enabling the fuel to be finely atomized even under low load. The higher the pressure, the more precise the mixture formation – and that boosts power output and torque, as well as making the engine run more smoothly and helping to cut emissions.

The Common Rail system of the new 3.0 TDI is able to deliver nine single injections per stroke. The pre-injections help the engine run smoothly at low speeds especially, while the post-injections regenerate the exhaust gas cleaning components. Audi fuel injection systems must assure milligram precision for tens of thousands of miles.