Development of a Urea DeNOx Catalyst Concept for European Ultra-Low Emission Heavy-Duty Diesel Engines

Tests are carried out to assess the potential of using SCR DeNOx catalysis, for achieving ultra-low NOx emission levels with heavy-duty diesel engines. A prototype DeNOx catalyst system has been developed which consists of a moderately sized SCR catalyst, upstream of which urea is injected through a heat-shielded nozzle. Downstream of the SCR catalyst a low sulphate oxidation catalyst is used to ensure any ammonia slippage from the SCR stage is oxidized.

The system was tested on a standard 2-valve EURO 2 engine over several steady-state and transient test cycles currently under discussion for European use. Over these test cycles NOx emission values of about 2 to 2.5 g/kWh are accomplished, which are sufficient to fulfill future European heavy-duty NOx emissions legislation to be expected around the year 2005.