Municipal vehicles and delivery vans are often driven for only short distances in city centres. Under these driving conditions, they do not achieve the exhaust gas temperatures required to cut nitrogen oxide emissions effectively with conventional SCR systems (selective catalytic reduction).
Emitec’s E-SCR® system cleans the exhaust gas of diesel vehicles and reduces harmful nitrogen oxides in inner-city traffic. The system can be retrofitted to older vehicles to meet the stricter European air quality objectives for urban areas.
The E-SCR® system is essentially a small emission control factory that consists of an electrically heated catalytic converter, a tank for the reducing agent AdBlue and a dosing unit. A control unit with temperature and NOx sensors ensures that the system operates efficiently. After the engine starts, the electrically heated catalytic converter raises the temperature of the exhaust gas to the required level. The temperature sensor then sends a signal to activate the SCR system. An aqueous urea solution is injected directly onto the heated catalytic converter. The solution evaporates on the hot surface and forms ammonia, which is used by the SCR catalytic converters to break down the nitrogen oxides into harmless nitrogen and water. The injected amount is adjusted by NOx sensors located in front of and behind the system. The heated catalyst is shut down when the engine produces sufficiently hot exhaust gas. During longer breaks when the engine is not running or idling, the heated catalytic converter is activated again by the temperature sensors, as required.
SCR catalytic converters with electric heating reach their operating temperature (light-off range) almost two minutes faster after an engine cold start. The system keeps temperatures at a constant level while the engine is idling or switched off. This reduces NOx emissions in inner-city traffic by over 90%.
This system is mostly used in heavy duty trucks and starts to be applied in light duty vehicles. Do you think it is preferable to use a NOx trap instead of SCR from a cost perspective for light duty vehicles? What about urea supply in cities?