20 December 2001
A milestone in the development of SCR NOx reduction system for European truck manufacturers was announced by TNO Automotive and Engelhard Corporation. In cooperation with two unnamed European truck manufacturers, the TNO/Engelhard urea SCR catalyst system has entered a field testing stage on heavy-duty trucks. After installation of the catalyst system the trucks meet Euro-4 NOx requirements (3.5 g/kWh effective 2008) and approach Euro-5 NOx requirements (2 g/kWh effective 2008). The truck manufacturers are performing a one-year field test in order to evaluate the technical feasibility of this technology for future application.
Two long haul trucks have been equipped with a selective catalytic reduction (SCR) catalyst for the reduction of nitrogen oxide (NOx) emissions. The catalyst has replaced the silencer. A water/urea solution is injected at the catalyst inlet in order to activate the reduction process. The heat in the exhaust transforms the urea into gaseous ammonia (NH3), which reacts with exhaust NOx over the catalyst. In the ideal SCR process, the reaction products include only the harmless nitrogen and water.
NOx emissions were reduced by around 80% over the ESC (European Stationary Cycle) and around 70% over the ETC (European Transient Cycle). The actual NOx levels are around 1.5 g/kWh for the ESC and around 2 g/kWh for the ETC. This means that the engines meet Euro-4 NOx requirements and approach the Euro-5 NOx requirements. Hydrocarbons were reduced by more than 90%.
SCR technology makes it possible to reduce the fuel consumption of the engine without affecting performance. In comparison with other technologies, the engine can be operated with advanced injection timing and optimized for low fuel consumption. The overall economic effect of the SCR depends on the price ratio of diesel fuel and urea. According to TNO, an actual economic benefit of SCR compared to other technologies is likely.
This newly developed technology is being tested on the two trucks performing their normal duties. One of the trucks has now driven over 150,000 km in about one year without significant problems. A NOx conversion test in the course of the year has shown the same NOx conversion as with new catalysts. Moreover the SCR system has not affected the reliability of the truck operation. The results of these field tests will be used to determine the next steps in the development of this technology. The commercialization of this system will need another few years of further development and, importantly, will require that urea distribution and fueling infrastructure be created.
Source: TNO Automotive