Audi is launching its TDI diesel initiative in the North American market in 2008 by putting its 3.0-liter TDI diesel with ultra-low emission system into production almost in parallel to its launch in Europe. The 3.0 TDI, which is California LEV II, US EPA Tier 2 Bin 5 compliant, will initially be available for the Audi Q7, and later for the new Audi A4.
The new Audi 3.0 TDI develops an output of 176 kW (236 hp) and 550 Nm (4046 lb-ft) of torque. New technologies optimize the combustion process in the V6: the common-rail piezo-electric injection system builds up 2,000 bar of pressure, while combustion cylinder sensors permit combustion processes to be controlled even more precisely.
High-efficiency exhaust gas recirculation and further optimized forced aspiration combine to help deliver low engine-out emissions.
The urea SCR exhaust aftertreatment system operates with AdBlue, small amounts of which are injected ahead of the DeNOx catalytic converter, and cuts emissions of NOx by up to 90%. The injection process is precisely timed, since for a high conversion rate it is important for the AdBlue solution and the gas flow reaching the entry surface in the converter to be continually matched.
The complete NOx aftertreatment system consists of the catalytic converter, the metering module and the AdBlue tank. The AdBlue solution has a freezing point of -11°C, so that both the active tank and the metering line and pump have to be heated at low outside temperatures. This function is activated automatically by temperature sensors.
Two NOx sensors measure the concentration of the oxides of nitrogen ahead of the diesel particulate filter and after the ultra-low emission system; system functions are also monitored by pressure and temperature sensors.
The AdBlue tank, like the fuel tank, is filled at the fuel filler flap. The reservoir volume of approximately 22.5 liters is divided between two tanks: the active tank below the fuel filler flap has a capacity of 7 litres, the passive tank under the floor holds 15.5 liters.
The AdBlue solution is added as a routine operation each time the car is serviced, without the customer having to take any action. Since consumption of the solution is very low, Audi can guarantee that the amount carried on the car will be sufficient from one workshop visit to the next. The system is rated to perform reliably for the car’s entire operating life.
The exhaust system is completed by two conventional catalytic converters, installed ahead of the ultra-low emission system. The oxidating converter transforms hydrocarbons and carbon monoxide into carbon dioxide and water. The diesel particulate traps particles in the gas flow and collects them in the structure of the filter.