Ademe, the French Agency for the Environment and Energy Resources, has given a glowing endorsement to the new particulate filter PSA Peugeot Citroen is using with its common rail turbodiesel engines for passenger vehicles.

In an 18-month study of a fleet of Peugeot 607 taxicabs, the agency found that the cars had as little particulate in the exhaust as a gasoline engine, yet they produce 20% less carbon dioxide.

“For the 607 taxis using the filters, the level of emissions was far below the limits fixed by the Euro 3 norms, and the filters continued to perform to 80,000 km (50,000 miles), when they need to be renewed,” Ademe says. “The diesel motor with particle filter is thus equivalent to a gasoline engine in terms of particulate emission.”

Peugeot has fitted the filters to the 2L and 2.2L common rail diesels in its 607 since it was launched in 1999 and has since fitted the filters with those engines in the 406, 307 and 807. By 2005, PSA plans to have the filter in all its diesel-powered cars, and it has been awarded a number of environmental prizes in Europe.

European particulate emissions regulations for 2008 will be 0.025 g/km — and with the filter, the PSA engines emit 0.001 g/km, says a spokeswoman.

The government study, which cost about $600,000, agreed that the filters treat all sizes of particles. The study involved buses, delivery trucks and garbage trucks, as well as the cars.

Filters available on the aftermarket for the heavy vehicles provided satisfactory results on trucks and buses but not on garbage trucks, says Ademe. Because garbage trucks move slowly and stop often, exhaust temperatures don't get high enough to burn out the particles, so the filters get clogged and become ineffective, the agency says.

In the Peugeots, particulates trapped by the filter are burned off by a higher exhaust temperature, which is dictated at intervals by the engine management system. Thus, accommodation for the filter's process must be integrated into the engine management software.

The Ademe study says the PSA filters work continuously to the 50,000-mile limit. PSA says that when old filters are removed, the substrates are recycled in a factory built for the purpose.

Since Ademe concludes PSA's particulate filters are effective and reliable, the next challenge for diesel engine makers must be to make a treatment system for oxides of nitrogen (NOx) to work in harmony with the particle filter. Although diesels produce low carbon dioxide emissions, they create an excess of NOx.