Numerical optimization of AdBlue-injection into the mixing section of SCR-systems

摘要

The selective catalytic reduction (SCR) of nitrogenous oxides is the most promising technique to meet prospective emission regulations of cars. Due to its toxic potential the reducing agent ammonia cannot be stored in a car, but it can be carried in the form of an urea-water-solution (UWS) which is injected into the hot exhaust gas and reacts in different sub-steps to ammonia. This formation of ammonia upstream the catalytic converter is a key factor for the efficiency of the entire SCR-process-chain. This study deals with the numerical optimization of the position and direction of the UWS-injection into the hot exhaust gas. For this purpose a numerical model was developed, which considers in contrast to previous surveys the loss of droplets' weight caused by evaporation and thermal decomposition. The model is able to determine the exact position of flying droplets, the droplets' velocity, the composition and its current temperature in a gas flow. Comparative investigations of coflow- and counter flow-injection, of centered or off-centered injection position of the UWS-injection system to avoid droplet/wall-contact are focused in this survey.