6 August 2003
Mercedes-Benz announced it will introduce diesel particulate filters (DPF) on a number of diesel car models starting this October. The filters will initially be available for the C-Class and E-Class models with the most popular 4 cylinder CDI engines (to date, 85% of C-Class and about 50% of E-Class diesel customers have opted for the 200 and 220 CDI engines). At the beginning of 2004, the 6 cylinder CDI engines in the E-Class and S-Class will be also equipped with DPFs. All DPF-equipped car models will also meet the Euro 4 (2005) emission standards.
The combination of EU 4 + DPF will be made available to customers at an additional price, which in the German market will be €580 (incl. VAT). In countries which provide tax benefits for EU 4 vehicles—currently Germany, the United Kingdom, Belgium, Sweden and the Netherlands—the additional cost would be reduced or cancelled when customers register such a vehicle for the first time.
Very limited technical information has been released on the DPF system. In contrast to the Peugeot filter, the Mercedes filer system does not utilize fuel additives for regeneration. The filter is regenerated by adjusting, in accordance with requirements, various engine control functions, such as fuel injection, intake-air throttle, exhaust gas recirculation and boost-pressure control. In this way, it is possible to increase the temperature of the exhaust gas to the point when the particulates accumulated in the filter are burned off. It is not yet clear if the DPF system utilizes a catalyst—either in the form of a catalyst coating or else as an NO2-forming precatalyst—to decrease the regeneration temperature requirement.
Mercedes also said that sulfur-free fuels and specially developed engine oils can extend the service life of the filter. However, fuel sulfur content requirements, if any, for using the filter were not specified.
In 1985, Mercedes was the first car manufacturer in the world to introduce particulate filter systems, which were fitted on its model 300D sold in the California market. After a brief period, the use of DPF technology was abandoned, mainly due to difficulties with controlling the filter regeneration. Modern diesel filter systems were made possible by advanced, active regeneration strategies which are integrated with electronically controlled engines and injection systems, such as the common-rail. First such advanced filter system, utilizing cerium-based fuel additive for regeneration, was introduced in May 2000 by the PSA Group on its Peugeot 607 2.2 HDi. Following the PSA Group, filters (with different regeneration principles) have been announced by an increasing number of manufacturers, including Renault, Toyota, and Mazda.
The Peugeot DPF system, which is offered as a standard equipment on a growing number of Peugeot, Citroen, and certain other car models with Peugeot diesel engines, remains the most widespread diesel particulate filter with over 500,000 units sold to date. Peugeot introduced the filter voluntarily and without receiving any tax benefit, as the fist generation of DPF-equipped Peugeot cars was not fully EU 4 compliant due to NOx emissions and DPF service interval requirements. The voluntary introduction of DPF-equipped, ultra-low PM emission cars was praised, among others, by German clean air authorities and environmental organizations, who often played it against German car makers who were reluctant to voluntarily introduce DPF technology. Widespread use of particulate filters in the coming years would indeed require voluntary action by the car makers, as the EU 4 limits can be met—at least in small and medium-sized cars—without the use of filters.
In its announcement, Mercedes-Benz emphasized the additive-free operation as the main advantage of its filter system. The use of additive results in gradual build-up of ash in the filter, which in turn can cause increased pressure drop, fuel economy loss, and requires added maintenance, says Mercedes. The Mercedes filter, in contrast, operates without additives and thus with no fixed change interval, remaining efficient over a “very high” (but unspecified) mileage.