New catalyser for diesel vehicles

Japanese carmaker Toyota says it has developed a catalytic converter that should solve one of the worst environmental problems of diesel-engine vehicles: excessive emissions of particles and NO_X.

Diesel engines are more energy-efficient than petrol engines, which makes them more attractive in view of the pressure on carmakers to reduce vehicle emissions of CO₂. The environmental disadvantage, however (emissions of NO_X and particulate matter), has been difficult to overcome.

Toyota's new catalytic converter, called a DPNR, consists of a porous ceramic filter with surfaces coated with the catalytic metal platinum. In this new version, NO_X are caught and split into nitrogen and oxygen, with the further result that particles are also consumed by the free oxygen. During low or moderate acceleration the particles also become oxidized by the excess oxygen in the exhaust gases.

According to Toyota, this will reduce emissions of NO_X to less than 0.08 g/km, which will be the EU standard for petrol-driven vehicles in 2005 (diesels will be allowed to emit three times as much).

Particle emissions are said to be less than 5 mg/km. The EU allowance for 2005 will be five times as much. No other diesels on the market can come anywhere near Toyota in this regard.

The Toyota engine operates on a direct-injection system, or "common rail" variety, which is now becoming much more common. The need for tight engine control regulation means, however, that the system cannot be retrofitted on older vehicles. To prevent premature ageing of the catalyser, too, the fuel must have a low (maximum 50 ppm) sulphur content. Although such fuel will not be obligatory in the EU before 2005, it is already available in several countries.

Toyota is intending to test the catalyser, which is protected by 150 patents, before releasing it on the market. The cost will be about the same as for an ordinary type. The system will also be opportune for use with heavy vehicles when EU exhaust standards become tightened in 2005, and again in 2008.

Per Elvingson
Swedish NGO Secretariat on Acid Rain <www.acidrain.org>

For more information: <www.sae.org/automag/techbriefs/01-2001/techb3.htm>