Renault announces new NOx trap features in new diesel catalytic converter

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Renault has announced a new anti-pollution treatment for diesel engines that is able to capture the nitrogen oxides (NOx) at the tailpipe while still performing the standard oxidization of unburnt carbons. This is good news because it opens one more door for the commercialization of diesel-powered Nissans stateside. The system will be available from September 2008 in France and Germany in private fleets of 2.0 dCi Renault Espaces, probably in the same engine developed for the Nissan X-Trail to be used for the G8 summit in Japan.

The new NOx trap works in two phases: It captures NOx for 10 minutes/10 km, obtaining a Ba(NO3)2 solution which can be safely transformed into N2. The latter is released to the atmosphere once the engine is working at a rich-burn mode which allows complete combustion. Compared to the AdBlue systems used by German automakers, this method is closer to Honda's D-CAT NOx trap. Find the complete explanation in the press release after the jump.

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[Source: Renault]

Renault's NOx Trap

The NOx Trap fits firmly with Renault's determination to reduce pollutant emissions. This chemical process captures harmful nitrogen oxides, then converts them into neutral gas. This post-combustion system will be available from September 2008 in France and Germany in private fleets of 2.0 dCi Renault Espaces. Renault has filed 36 patents for its NOx Trap.

The new NOx Trap with catalytic converter has a dual function:
- the traditional function of oxidising hydrocarbons (produced by partial combustion) and carbon monoxide (produced by partial combustion due to a lack of oxygen);
- the treatment of nitrogen oxide (produced by the combustion of diesel fuel at high temperatures).

How the NOx Trap works

The NOx Trap operates by capturing and storing NOx (for 10minutes/10km) then releasing it – a five-second process that vehicle occupants do not notice.

During the capture phase, the NOx Trap traps the nitrogen oxide contained in the exhaust gas on a porous carrier in the catalytic converter which is impregnated with chemicals – platinum, barium, rhodium. The platinum converts nitrogen oxide into nitrogen dioxide (NO2). The barium, which oxidises into barium oxide, traps and holds NO2 as part of an aqueous barium nitrate solution – Ba(NO3)2.

In the release phase, a chemical process known as reductive elimination purges the NOx Trap of the stored NOx, with the engine operating in rich-burn mode, i.e. when the air-fuel mixture has just enough air for complete combustion of the diesel. The nitrogen oxides are converted into neutral gases, mainly nitrogen. In this way the NOx Trap is regenerated and is ready to go on trapping more NOx.

To ensure the NOx Trap operates smoothly, additional (oxygen and heat) sensors are positioned at the intake manifold and on the tailpipe. The data they capture is transmitted over the controller area network to the ECU for managing the NOx Trap (deciding when to purge) and determining combustion modes (how to purge).

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