Numerical modeling of urea water based selective catalytic reduction for mitigation of NOx from transport sector

• The upcoming Euro 6 norm demands a high reduction in NOx emissions from vehicles.
• The most promising technology in this field is selective catalytic reduction (SCR).
• Distribution of ammonia for SCR is influenced by the spray/wall interaction.
• Numerical simulation of the spray and the wall film formation was conducted.
• Developed mathematical models show satisfactory agreement with experimental data.

Various environmental regulations put ever stringent requirements on the automotive industry as a part of solution to the problem of global warming and climate change. In Europe, the upcoming Euro 6 standard that will come into force on September 1, 2014 demands reduction in NOx emissions from cars and vehicles intended for transport by more than 50% compared to the current standard. The urea-water-solution (UWS) based selective catalytic reduction (SCR) is currently the most promising method for fulfilling these requirements. In principle, the UWS spray is injected into a hot exhaust gas stream preceding the SCR catalyst and ammonia is generated through series of chemical reactions. Then, the generated ammonia acts in various deNOx reactions as a reductant.This paper investigates application of numerical modeling in the area of environmentally friendly technology of mobile SCR as a green engineering measure to reduce pollution in the road transport sector. Within this work the mathematical model of surface tension has been developed and compared to analytical expression for isothermal droplet spreading. Furthermore, this model was incorporated into the wall film module of the commercial computational fluid dynamics code FIRE for description of urea-water-solution injection into hot exhaust gases of diesel engine and compared to experimental data. Results of the conducted numerical study support the feasibility of commercial application of the presented model.