ILASS – Europe 2014, 26th Annual Conference on Liquid Atomization and Spray Systems, 8-10 Sep. 2014, Bremen, Germany Analysis of the injection of urea-water-solution for automotive SCR systems: spray/exhaust-gas-interaction Jayesh Mutyal* 1 , Rana Faltsi 2 , Markus Braun 3 1 ANSYS India, Pune, India 2 ANSYS Inc., USA 3 ANSYS, Darmstadt, Germany *Corresponding author: jayesh.mutyal@ansys.com Abstract Selective Catalytic Reduction (SCR) is increasingly used to reach NOx emission levels which are unachievable in- cylinder. This technology sprays urea water solution (UWS) as reducing agent in exhaust system. This work focuses on evaporation and mixing modeling of the UWS using commercial CFD code ANSYS Fluent. A user subroutine is written to modify the rate determining multicomponent evaporation with two step urea vapor decomposition. The results are validated with experimental measurements. This numerical framework allows to simulate SCR system and to predict conversion efficiency and local distribution of the reducing agent. Introduction Emission norms are becoming tougher and therefore engine manufactures are exploring different ways to cut down tail pipe emissions. In recent years, lot of emphasis is on treating exhaust gases and SCR is becoming a preferred way to deal with NOx coming out from diesel engines [1]. In SCR system UWS is injected into the hot exhaust gases (See Fig1). Automotive SCR systems use a 32.5 % wt. solution of urea in water (also known AdBlue, Diesel Exhaust Fluid, or DEF). Injected liquid undergoes atomization, water vaporization and mixes with hot exhaust gases. At higher temperature urea undergoes thermolysis and hydrolysis to form ammonia and iso-cyanic acid described by eq 2 and 3 [2,3]. In presence of catalyst this ammonia reacts with NOx to produce CO2 and H2O [4,5]. Water vaporization from UWS spray, NH    CO  → NH    CO    + 6.9H  O  (1) Urea thermolysis and formation of ammonia and iso-cyanic acid, NH    CO    → NH    + HNCO  (2) Hydrolysis of iso-cyanic acid. HNCO  +    → NH    + CO   (3) Figure 1. Sketch showing mixture preparation and catalytic reduction process in SCR system.