When diesel is burned in an engine, soot particles are formed in some areas of the combustion chambers. To eliminate these particles, Audi installs what is known as a wall flow filter, a closed-circuit system with an efficiency of more than 95 percent. As the particles flow into the filter, they adhere to its porous wall. They are burned off at intervals dependent on the way the vehicle has been driven. This burn-off process is initiated by deliberately retarding the post-injection of fuel into the engine, which causes the exhaust gas temperature to briefly rise dramatically.
Audi’s first TDI with a particulate filter was the 3.0 TDI, introduced in 2004. Since the spring of 2006 the brand with the four-ring emblem has installed this technology as standard equipment in all TDI models. The latest developments are particulate filter with a SCR coating, which additionally convert the NOx.