CFD simulations of AdBlue spray in an exhaust pipe

Abstract

AdBlue systems treat exhaust gases from combustion engines. It utilises a urea spray and a catalyst in an exhaust pipe to reduce NOx emissions. The type of catalyst in this case is a Selective Catalytic Reduction, SCR. Development of these systems is of importance to the automotive industry with the continuously tightened emission standards. The development of the AdBlue systems often uses Computational Fluid Dynamics, CFD, to deal with the turbulent and multi-phase flow, however these are in many cases computationally expensive. The thesis deals with developing a CFD model that is reliable while still being computationally affordable. The simulation was made in the part of an exhaust pipe where the AdBlue was injected and the SCR catalyst was not accounted for. AdBlue was represented by water in the simulation. A Reynolds-Averaged Navier-Stokes solution, RANS, was used for the carrier phase, with a k 􀀀 " turbulence model. The relevance of other fluid dynamic models were also investigated and selected accordingly. For further evaluation of the droplet dynamics, a parametric study was made to investigate how the droplets are affected by different injection velocities and angles of injection. The CFD model was evaluated with regards to the theory and is considered reliable. Another conclusion is that a higher injection velocity results in a smaller mean droplet diameter and a smaller injection angle results in a wider droplet position distribution.