Toyota is testing a system that it claims will drastically reduce nitrogen oxides and material emissions from diesel car engines.
It says its D-CAT process, which combines new catalyst technology with its existing high- pressure common rail diesels, can reduce NOx and particulates by 80 per cent simultaneously. This is well below new Euro IV regulations due to come into force in 2005 which limit particles to 0.005g/km and NOx to 0.08g/km. Toyota expects the system to remove one of the few remaining objections to diesel as a fuel.
The heart of the system is the DPNR (diesel particulate-NOx reduction system), a newly developed, highly porous ceramic filter coated with a catalyst originally developed for Toyota’s lean-burn petrol engines. This stores and reduces NOx, creating free oxygen, which is then used to oxidise particles.
The DPNR catalyst is mounted near the exhaust manifold, with a simple oxidation catalyst also further down the exhaust system to deal with carbon monoxide and unburnt hydrocarbons.
It complements Toyota’s second-generation common rail diesels which use exhaust gas recirculation to encourage low- temperature combustion, an important factor in reducing emissions at source.
Common rail technology is used by all the main manufacturers’ latest diesels. ‘Common rail’ refers to the high-pressure fuel line that feeds an individual electronically controlled fuel injector for each cylinder. Traditional diesels used mechanical injectors operated by bursts of pressure from the fuel pump. In common rail higher pressures, coupled with extremely fine injection nozzles and electronic control, allow more precise control of combustion and hence emissions.
Unlike other particle filters the DPNR catalyst does not require any maintenance during the life of the vehicle. However, it needs to run on ultra-clean diesel with less than 10ppm of sulphur, which is currently being introduced across Europe.
Toyota is undertaking European field trials with a fleet of 60 Avensis 2-litre diesels and says the cars will be evaluated by customers in a wide range of commercial activities.
If successful, the technology will be introduced from 2003. Toyota’s European diesel sales rose by 76 per cent in 2001 and have increased by 120 per cent in 2002 so far, on the back of an overall rise in Europe of 40 per cent and 54 per cent in the same periods.