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Success stories Published on 26-Feb-2004

Title Cleaner diesel exhausts

A new kind of filter to remove smoke from the exhausts of diesel engines has been developed by an international team of scientists and engineers. Designed to meet the strict Euro 4 emission regulations that will come into effect in 2005, the filter employs a catalyst to burn out accumulated soot at lower temperatures than usual, minimising the effects on fuel consumption. Cars incorporating a refined version of the new filter are already in production, and the first models will be on sale early in 2004.

CRF’s Alfa 156 demonstrator. Within months of the end of the project, the filters were being incorporated into production vehicles.copyright Maurizio Maggiore
CRF’s Alfa 156 demonstrator. Within months of the end of the project, the filters were being incorporated into production vehicles.

© Maurizio Maggiore
Diesels are expected to make up half of all new cars sold in Europe by 2010. Their growing popularity is largely due to their superior fuel efficiency, which also means that they emit less carbon dioxide to the atmosphere than petrol engines. Although modern fuel-injection diesels are much cleaner than those of only a few years ago, they still have a reputation for being smokier than petrol engines. Euro 4, the new emission regulations coming into effect from 2005, will halve the permissible emissions of particulates and other pollutants, and have spurred manufacturers into making their diesel engines cleaner still.

To promote the environmentally friendly diesel, the European Commission has sponsored a cluster of projects known as DEXA (Diesel Exhaust Particulate Aftertreatment). They cover such topics as design and simulation of diesel exhaust systems, methods of measuring particulates, and research on ceramic materials for exhaust filters. One project, Art-Dexa (Advanced Regeneration Technologies), is concerned with developing a new filter to remove smoke from the exhaust.

“To achieve Euro 4 limits you can work on the combustion side by improving fuel injection, turbo-charging, or exhaust gas recirculation. But to reduce smoke emission you also need a filter,” explains Marco Pidria of Centro Ricerche Fiat (CRF), which coordinated the three-year project. “The filter collects about 99% of the carbon particulates, the black smoke, but after a certain time it becomes clogged,” he says. “So every 500 to 800 kilometres you have to increase the temperature inside the filter to burn out the collected carbon, transforming it into carbon dioxide.”

Maintenance-free filter
The prototype diesel exhaust filter that was tested on CRF’s Alfa 156 demonstrator. © Maurizio Maggiore
The prototype diesel exhaust filter that was tested on CRF’s Alfa 156 demonstrator.

© Maurizio Maggiore
Normally the filter temperature would need to be raised to 620-650°C by injecting fuel from the engine, but such high temperatures can greatly increase fuel consumption while the heating is in progress. Existing filters use a fuel additive to help clear out (or ‘regenerate’) the filter at lower temperatures, but the Art-Dexa team wanted a filter that would be completely self-contained and would not need regular maintenance to remove the ashes that are left by the additive.

So they decided to use a catalytic coating on the filter. “We focused on a catalysed filter to lower the regeneration temperature without a fuel additive. With a catalyst you can decrease the temperature to 550-600°C. Art-Dexa’s job was to select the best filtering media, and then the best catalyst.”

The team tested many different materials to see which was best at removing smoke particles from the exhaust fumes. “We investigated metallic felts, ceramic fibrous textile filters and monolithic filters made from silicon carbide and other materials,” Pidria says. Experts at the Aerosol and Particle Technology Laboratory (APTL) of the Centre for Research and Technology Hellas (CERTH) worked on the selection of materials and studied their filtration and regeneration behaviour with engine tests. “We found that a silicon carbide material developed by an external supplier is, to date, the most promising and best performing material for the particle filtering medium.” Obernosterer developed several fibrous textile filter materials and Clausthaler Umwelttechnik-Institut collaborated to characterise the support materials. Zeuna Stärker designed the container for the prototype filters.

Catalyst materials
The partners also screened several different catalyst materials, including some developed within Art-Dexa itself. They settled on three technologies – a noble metal formulation produced by Johnson Matthey, an innovative mixed-oxides formulation developed by APTL, and a perovskite-based technology from Politecnico di Torino. All three were scaled-up into full-sized filters.

Art-Dexa also examined the engine control strategies needed to make the engine and exhaust system work properly during the filter regeneration phase. “Experimental studies by FEV in Germany were really helpful in coming up with a solution that could be industrialised,” explains Pidria. “It was a very long and complex job. We had to develop a completely new engine management for regeneration driving.” The engine management also had to account for the accumulating particles in the filter, so APTL provided an algorithm for monitoring the amount of soot.

Both CRF and Renault constructed demonstrator cars equipped with the new technology, and found that the filter increased fuel consumption by less than 2%, a very acceptable figure. The project has been so successful that the research results have already been incorporated into production vehicles, only months after the project was completed in January 2003.

Pidria expects the first cars using a refined version of the new technology to go on sale early in 2004, especially in countries where there are tax incentives to buy cars with low emissions. “The numbers at the beginning will not be very high – probably fewer than 100 000 cars per year in 2004,” he notes. “But if you look ahead to 2009-2010, unless an unforeseen breakthrough comes along, I predict that 90% of diesel cars will have these filters. This is the only technology that meets Euro 4 and the forthcoming Euro 5 standard. To go into the US market you will need these filters. So this technology really is the key to developing new diesel engines.”

  • Title
    Advanced Regeneration Technologies for Diesel Exhaust Particulate Aftertreatment (ART-DEXA)
  • Reference
  • Programme
    FP5: Growth
  • Contact
    Marco Pidria
    Centro Ricerche Fiat
    Fax: +39 011 9083 666
  • Partners
    Aerosol and Particle Technology Laboratory (APT) / Centre for Research and Technology Hellas, Greece
    Centro Ricerche Fiat, Italy
    Clausthaler Umwelttechnik-Institut GmbH, Germany
    FEV Motorentechnik GmbH, Germany
    Johnson Matthey PLC, UK
    Obernosterer Strickstoffe GmbH, Austria
    Politecnico di Torino, Italy
    Renault Recherche et Innovation, France
    Zeuna Stärker GmbH & Co KG, Germany