Diesel particulate filters and SCR systems combined

Diesel particulate filters reduce the particulate emission of commercial vehicle engines to a minimum. And they control the nitrogen oxide emissions by means of selective catalytic reduction (SCR). Therefore nothing was more obvious to the Eberspächer development engineers than to combine both methods. The result is a trend-setting system which reduces both the particulates and the nitrogen oxide emissions by more than 90%.

First cleaning phase: Oxidation catalytic converter and particulate filter

At first the exhaust gases flow through the oxidation catalytic converter. This converts the hydrocarbons and the carbon monoxide into carbon dioxide and water. In addition a part of the nitrogen monoxide (NO) is oxidised to form nitrogen dioxide (NO2).

In the downstream particulate filter the NO2 reacts with the trapped particulates to form NO and CO2. The deposits are reduced - the system regenerates. The catalytic layer of the particulate filter then converts the NO arising in combustion of the particulates back into NO2, so that new particulate fuel is available.

So that optimum filter regeneration is possible at low operating temperatures, this "passive" system is coupled with an active process (for example fuel after-injection).

Second cleaning phase: SCR catalytic converter

After the exhaust gas flows through the filter unit, it passes into the SCR catalytic converter. The nitrogen oxides are removed here. For this purpose a precisely metered amount of urea is injected into the exhaust gas - controlled by the latest electronic control systems. This urea decomposes to form ammonia and carbon dioxide. The ammonia reacts on the catalytic converter with the nitrogen monoxide and the nitrogen dioxide of the exhaust gas. Nitrogen and water remain behind. A really clean thing!