Audi A8 3.0 TDI: First Luxury Saloon Car to EU4 and with Diesel Particulate Filter

Audi is to launch a diesel particulate filter for the luxury A8 3.0 TDI saloon in the first half of 2004. The system, available as an optional extra, requires no fuel additives and lasts the lifetime of the vehicle itself. Audi is exhibiting a prototype of this innovative technology at the 2003 Frankfurt Motor Show. Particulate filters will already become available in the medium term as an optional extra for all Audi model series with TDI engines.
The 233 bhp six-cylinder engine – the first production diesel engine to have piezo injectors – is now set to propel the Audi A8 into pole position as the most environmentally friendly luxury saloon.

The A8 3.0 TDI has quattro permanent four-wheel drive and 6-speed tiptronic as standard. Even without the particulate filter, it still undercuts all the limit values laid down in the EU4 emission standard, which are based on a variety of factors including particulate content.

The EU4 standard is an exceptionally stringent set of rules: compared with vehicles registered as new in 1988, in other words when the first European emissions legislation came into force, EU4 for example specifies a reduction of approximately 93 percent for particulate emissions from new vehicles. Audi’s engine developers were able to satisfy this requirement exclusively through internal modifications, for all this engine’s power. Effective optimisation of combustion prevents pollutants from occurring in the first place.

The 3.0 TDI thus represents a further milestone in the history of TDI engines as an exceptionally clean technology. This is reflected not only by the overtly economical way in which it uses diesel fuel, but also by its success at cutting the levels of all relevant emission components. The proof: a total of eighteen vehicle versions with TDI engines in the Audi range – with outputs extending from 61 to 233 bhp – already currently fulfil the EU4 standard.

Along with the launch of the particulate filter for the most powerful and also most advanced of these EU4-compliant TDI engines, Audi is now systematically building on its strategy of successfully cutting emissions. It is using a system that likewise exploits the most advanced state of the art: the “catalysed soot filter” (CSF for short), which has a filter coating containing precious metals and acting in two ways.

The passive regeneration process involves the slow, environment-protecting conversion of the particulates deposited in the catalytic converter into CO2. This process takes place within a temperature range of 350 – 500 degrees and occurs continuously without any special measures being required, predominantly when the car is being driven at motorway speeds.

Only if the car is used for any length of time at low loads, for instance in urban traffic, is the temperature of the exhaust gas actively raised to around 600 degrees every 1,000 to 1,200 kilometres, to prompt addition regeneration of the filter. One clear advantage of this approach is that fuel consumption is inflated only very marginally, thanks to the rarity of the active regeneration phases.

As well as the A8 3.0 TDI, Audi is exhibiting another diesel model at the Frankfurt Motor Show that undercuts the EU4 limit values and is fitted with a diesel particulate filter: the A4 2.0 TDI is powered by a new two-litre, four-cylinder diesel engine.

This engine reduces particulate emissions by means of a filter system that uses a catalytically active additive. This organometallic compound is added to the fuel, thus reaching the filter along with the particulates. The active oxidation of the particulates takes place there at temperatures in excess of 500 degrees. The additive ash needs to be cleaned from the filter at intervals of approximately 120,000 kilometres.