Ammonia Uniformity to Predict NOx Reduction Efficiency in an SCR System

The automotive industry has been restricted by several regulations to reduce nitrogen oxide emissions from diesel engines. To adhere to the emission regulation, advanced engine technology aims to control oxygen access, compression, and ignition engine, while achieving both reduced fuel consumption and lowering unburnt HC, CO2, and CO levels. However, it is difficult to meet the NOx limits of the European standard (EURO VI) and American standard (US TIER 2 BIN 5). Selective catalytic reduction (SCR) with ammonia (NH3) has been successfully employed to remove NOx from diesel engines. However, uniform ammonia distribution is usually difficult to achieve. Therefore, a study on ammonia uniformity to predict NOx reduction efficiency in SCR systems is needed. The engine utilized in the experiment was turned on for a few minutes to obtain the desired temperature and airflow, and the simulation was performed using a commercial code of STAR-CCM+. This study was performed at engine operating conditions of 1500 rpm, 2000 rpm, and 3000 rpm; simulation was performed with a fixed pressure and velocity, as in the experiment, thus creating a similar turbulent swirl flow in the SCR system. Numerical results were validated using experimental results of ammonia concentration distribution.