Tenneco Automotive now is supplying passenger-car diesel PM (particulate matter) filters said to be 99.99% efficient. The PM filters are fitted for current-production Citroen C5 and Peugeot 406 models.

Although this may delight environmental regulators not bound by any requirement to consider the cost of complying with forthcoming PM emissions standards, the Tenneco filter will not be cheap.

The company says its filter unit for typical passenger-car application will carry an OE cost of $500. The resulting impact on vehicle list price is not known, but based on some estimates it could be in the $750 to $1,000 range.

Tenneco says the system is based on the use of a small amount of cerium held in a 150-ml tank. After soot builds up in the filter to a level detected by an increase in exhaust backpressure, a small amount of the cerium is released into the exhaust stream ahead of the filter, coincidental with a brief increase of fuel flow.

The added fuel, alone, increases exhaust gas temperature, but not to a level hot enough to combust the filter’s contained PM deposits; the cerium additive then decreases the temperature at which combustion of the deposits takes place. Without adding cerium, higher-temperature materials (at higher cost for the filter system) would be needed.

The result is depletion of the stored 150 ml of cerium and accumulation of ash resulting from combustion of the trapped PM. The cerium supply must be replenished and the filter element removed for external cleaning (effectively replaced with an already cleaned element) at about 50,000 miles (80,000 km). Tenneco tells Ward’s the current retail price of this service in Europe is about $650.

The company says in time it expects the service interval will increase to 75,000 miles (120,000 km) and the service cost will drop by 30% to 60%.

Although the initial and service costs are considerable, as more attention is devoted to diesel efficiency and diesels are applied to lighter-weight vehicles, the outlook improves for the Tenneco PM filter in the US.

But before U.S. light-vehicle diesels can make increased headway comes the question of how stringent upcoming oxides of nitrogen emissions standards will be met, and at what cost, for various sizes of diesel vehicles.