A novel test method for evaluating ammonia distribution in Selective Reduction Catalyst

NOx emissions control is one of the key factors to meet future emission regulations for internal combustion engines. NOx is controlled better by dosing urea, providing ammonia to Selective Reduction Catalyst (SCR). This study investigates ammonia distribution across SCR and introduces a new method for evaluating the ammonia uniformity index (UI) based on ammonia slip in a hot air rig, rather than traditional NOx conversion efficiency. Three silencer configurations were tested, each under four distinct operating points. For every operating point, an individual ammonia UI was calculated using the proposed method and then compared to the corresponding UI derived from NOx conversion. Ammonia concentrations were measured using a Fourier Transform Infra-Red spectroscopy (FTIR) analyzer, while a NOx sensor was also evaluated as an alternative as a simpler option for ammonia concentration measurement. Each test was repeated twice to assess the robustness and repeatability of the method. An automated probe moving device was developed and a control logic was framed to reduce manual intervention during the measurement phase. The proposed approach aims to provide a more direct and representative evaluation of ammonia distribution, with benefits in terms of emissions, cost, and testing time.