SCR-Technology

The SCR technique is the only procedure which enables simultaneously a reduction of exhaust emissions and also an optimization of the engine regarding performance and fuel consumption.

Functionality

During the SCR procedure the high emissions of NOx, which originate during an efficient combustion of the engine, are treated post-engine in a catalytic converter.

For this procedure, the reduction agent AdBlue®, a non-toxic and odourless urea solution in an accurately defined concentration and of highest quality, is necessary.

The exactly defined dose of AdBlue® is sprayed through a nozzle into the stream of exhaust, where it is first subject to hydrolysis, and then causes the transformation of the nitrogen monoxide (NOx) into nitrogen (N) and water (H2O) in the catalytic converter.

The SCR technology, assured with a good future, allows the EURO 5 parameters, valid since 2008 to be reached

Set-Up of a Catalytic Converter

The SCR catalytic converter consists of catalytic active transitory metal connections, such as titanium dioxide, vanadium pentoxide and Wolframoxide, which are fixed onto ceramic carriers. The transformation of NOx in this catalytic converter depends on the actual number of active cells, and especially on the size of the pores in the ceramic carrier.

The permanent functioning of the SCR catalytic converter is consequently highly dependent on the quality of the AdBlue®. The fine pores and active cells can be physically blocked, and inevitably deactivated, which would lead to the destruction of the SCR catalytic converter. In that case the entering nitrogen monoxide could not be sufficiently transformed into nitrogen and water, which would have as result the transgression of the EURO 4 and EURO 5 limit values, and consequently high costs.

Possible excess ammoniac, formed in a pre-catalytic converter through the hydrolysis of AdBlue® and hot exhaust gas is re-transformed in a back-end oxidation converter. With this, there is no danger of poisonous ammoniac escaping into the environment.

® Registered trademark of the automobile industry association (VDA)

With the exhaust gas norm Euro 5, valid from October 2008 for heavy vehicles, the emission of nitrogen monoxide is lowered by 90% in comparison to 1990; the following Euro 6 norm will reduce this by 97%. The presently valid Euro 4 norm has resulted in the decrease of nitrogen monoxide emission by 80% and of particle emission by 95% as compared to 1990.

The German automobile industry is well-prepared for this emission decrease. Already commercial vehicles are equipped with the SCR technology (Selective Catalytic Reduction) which uses the additional operating supply AdBlue®. SCR and AdBlue® are the forerunners in vehicle technology when it comes to decreasing the emission of pollutants - especially nitrogen monoxide - in diesel fuelled commercial vehicles. The SCR process is effected by adding an ammoniac admixture to the exhaust. The ammoniac is added in form of AdBlue®, whose trademark is registered by the automobile industry association (VDA). Today there are already 44 licensees worldwide for AdBlue®.

In Europe today, already over 300.000 commercial vehicles are equipped with SCR and AdBlue®. This number increases by ca. 25,000 commercial vehicles per month worldwide. On the way to a worldwide application, the SCR system is spreading also in the USA and Japan. With this technology, the commercial vehicle once again demonstrates its role as a forerunner; after proving itself in heavy commercial vehicles, the SCR technology commences to be applied in light commercial vehicles as well as cars.

Technologies for Future Emission Standards

Function Principle of the SCR Technology

The engine is optimized to the point where few soot particles, but on the other hand a consciously high amount of nitrogen monoxide develop during combustion.

The reduction agent AdBlue® is sprayed into the exhaust stream.

As a result of the high exhaust temperature, the AdBlue® is hydrolyzed to ammoniac and CO2.

With the help of the ammoniac, the nitrogen monoxide on the surface of the catalytic converter reacts to become nitrogen and water, natural components of our atmosphere.

Effect of the SCR catalytic converter

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How does the SCR exhaust after-treatment work?