TOKYO - Joining the race to develop a filter to cleanse the sooty exhaust from diesel engines, a major issue in Japan, Toyota Motor Corp. has developed a system that both traps particulates and reduces nitrogen oxide.
Toyota plans to introduce its DPNR system, for Diesel Particulate-NOx Reduction, on its 2-ton Dyna and Toyoace trucks in 2003. However, the system cannot be retrofitted onto existing engines because it only works with common-rail diesels, a relatively new technology.
And it requires very low-sulfur fuel, a requirement that has thwarted other diesel-particulate reduction systems.
Toyota's system only works with fuel with a sulfur content of less than 50 parts per million, a level scheduled to become standard by 2003. For now, though, Japanese diesel fuel's sulfur content ranges as high as 500 ppm.
The DPNR system uses a simple and compact catalytic converter. At its heart is a newly developed fine-porous ceramic filter designed for use with lean-burn gasoline engines.
The system reduces levels of both soot and NOx by more than 80 percent compared to permitted levels under 1998 Japanese regulations. Those regulations are likely to be tightened considerably, but the exact timing and amount of the tightening are still being determined.
By alternately switching the direction of the exhaust gas flow in the catalytic converter, the system increases its ability to oxidize, or cleanse, particulates.
Japanese diesel-engine makers and users are under increasing pressure to reduce emissions. This is the result of rising public concern, and several lawsuits, over the adverse effects on health of particulates, as well as a high-profile campaign against diesel engines by the governor of the metropolitan Tokyo region.
In a draft report, a federal government panel set up to study the problem has recommended that all diesel-powered vehicles built before 1990 be banned. That recommendation is by no means final, but it illustrates how seriously the issue is viewed here.
In the 1990s, when both Europe and Japan tightened regulations on diesel emissions, European regulators focused on particulate matter, while their Japanese counterparts stressed the reduction of NOx. Now Japanese consumers and regulators are asking why Japanese diesels are pouring out more particulates than European trucks.