In this project funded by the Bayerische Forschungsstiftung two fundamental investigations had been carried out: first a new N-rich liquid ammonia precursor solution based on guanidine salts had been completely characterized and secondly a new type of side-flow reactor for the controlled catalytic decomposition of aqueous NH3 precursor to ammonia gas has been designed, applied and tested in a 3 liter passenger car diesel engine.
Guanidine salts came into the focus due to the fact of a high nitrogen-content derivate of urea (
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 precursor 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.