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).

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).