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Urea SCR technology is the most promising technique to reduce NOx emissions from heavy duty diesel engines. 32.5wt% aqueous urea solution is widely used as ammonia storage species for the urea SCR process. The thermolysis and hydrolysis of urea produces reducing agent ammonia and reduces NOx emissions to nitrogen and water. However, the application of urea SCR technology has many challenges at low temperature conditions, such as deposits formation in the exhaust pipe, lack deNOx performance at low temperature and freezing below -12°C. For preventing deposits formation, aqueous urea solution is hardly injected into exhaust gas stream at temperature below 200°C. The aqueous urea solution used as reducing agent precursor is the main obstacle for achieving high deNOx performances at low temperature conditions. This paper presents a solid SCR technology for control NOx emissions from heavy duty diesel engines.

This paper describes the development of an exhaust Thermal Enhancer™ using an airless nozzle fuel system. The purpose of the Thermal Enhancer™ is to increase diesel engine exhaust gas temperatures to a level where catalytic heating can be used for Diesel Particulate Filter regeneration. The system can also be used to achieve adequate temperatures for NOx reduction, employing techniques such as Selective Catalytic Reduction. The Thermal Enhancer™ is used to increase exhaust gas temperatures at conditions that would otherwise be too cold for effective catalyst operation. These conditions include idle and low-load operation. The airless-nozzle fuel system is necessary for engines that do not have a compressed-air system. Performance data, including hydrocarbon slip as a function of Thermal Enhancer™ outlet temperature are presented at steady state conditions. Pressure loss as a function of engine speed indicates it is less than 1 kPa at the maximum exhaust flow rate.

Stringent emissions standards (Euro 6 and Tier2Bin5) lead to the use of nitrogen oxides (NOx) aftertreatment. One of the most widespread technical solutions able to meet these legislations is Urea Selective Catalytic Reduction (Urea SCR). A urea aqueous solution is introduced into the exhaust system in order to reduce NOx over SCR catalyst. Before reaching the catalyst, the aqueous solution has to be transformed into ammonia. Current serial applications need long distances (≻ 400 mm) from injection point to SCR catalyst and a mixer apparatus to ensure sufficient mixing between exhaust gas and ammonia. Because of this distance, SCR catalyst is located far from the engine. The light-off of the catalyst is penalized and therefore the efficiency of the SCR system is low. The purpose of this paper is to show a compact mixing device able to ensure mixing in a short distance (~ 75 mm).