Development of a 3rd Generation SCR NH ₃ -Direct Dosing System for Highly Efficient DeNOx 2012-01-1078

Due to the fact of temperatures above 240°C required for the complete residue-free decomposition to ammonia gas, a side flow reactor concept has been developed for controlled decomposition of the precursor solution. In addition, this reactor concept could be operated with various liquid ammonia precursors such as AUS32 or aqueous guanidinium formate. In this heated catalytic reactor, the decomposition is realized under controlled conditions independent of the main exhaust flow and operation conditions of the engine. NH₃ gas is produced in real-time and directly dosed to the main exhaust flow without any buffer. With a venturi nozzle setup the homogeneous mixing of the NH₃ gas into the exhaust flow is realized. Measurements in steady state and transient cycles show an up to 60% more efficient NOx reduction (DeNOx) on a standard SCR catalyst in comparison to a classical urea to exhaust dosing system. Specially for exhaust conditions below 200°C much higher efficiencies could be achieved by direct NH₃ gas dosing than with liquid AUS32 dosing.