General Motors Europe (GME) is launching a new, maintenance-free diesel particulate filter (DPF) system for its Vauxhall and Opel-branded cars, which needs no additives and is claimed to avoid other disadvantages of conventional systems.

Performance, fuel consumption and CO2 emissions remain at levels similar to operation without a filter thanks to an intelligent regeneration strategy.

The after-treatment system, including a pre-catalyst close to the engine and an oxidation catalyst, is designed to reduce all exhaust emissions, especially hydrocarbons (HC) and carbon monoxide (CO).

The DPF-system makes its production debut early next year on GME’s Vectra and [Vectra derivative] Signum lines with the new 1.9-litre CDTi Ecotec engine, which will be unveiled at the Frankfurt motor show in September.

The new diesel particulate filter consists of a honeycomb-like, ceramic core made of silicon carbide, perforated by microscopic channels.

Exhaust gases pass through the channel walls, on which the particulates collect and these must be burned off regularly, to prevent the filter from exceeding back-pressure limits.

But instead of using additives in the fuel for the regeneration process, GME has chosen to apply a precious metal coating to the filter substrata and inject additional quantities of fuel, to raise the exhaust temperature to the necessary 600 degrees Celsius.

This requires an injection system with flexibility under all engine-load conditions, since the system must operate not only under full-load, but also when the car is driven on short journeys.

To meet these demands, GME will use the latest common rail direct-injection system that allows constant and precise control of the fuel-injection process (e.g. amount, pressure).

Another advantage of the system is that regeneration occurs at irregular intervals, according to the way the car is driven.

For instance, the combustion of the filtered particulates, and thus the additional injection of fuel, only takes place when the build-up of particulates has caused sufficient back pressure in the filter. Unnoticed by the driver, the process is controlled via pressure and temperature sensors in the DPF-unit.

Located between the pre-catalyst near the engine and the particulate filter is an oxidation catalytic converter under the floor, which reduces the HC and CO emissions with the help of the oxygen in the diesel emissions.

Oxides of nitrogen (NOx) emissions are also lowered to meet the Euro 4 standard which is due to come into force in 2006.