Abstract
AbstractDroplet impingement of urea water solution (UWS) is a common source for liquid film and solid deposits formed in the tailpipe of diesel engines. In order to better understand and predict wetting phenomena on the tailpipe wall, this study focuses on droplet spreading dynamics of urea water solution. Impingement of single droplets is investigated under defined conditions by high‐speed imaging using shadowgraphy technique. The experimental studies are complemented by numerical simulations with a phase‐field method. Computational results are in good agreement with experimental data for the advancing phase of spreading and the maximum and terminal spreading radius, whereas for the receding phase notable differences occur. For the maximum spreading radius, an empirical correlation derived for glycerol‐water‐ethanol mixtures is found to be valid for millimeter‐sized UWS droplets as well. A numerical simulation for a much smaller droplet however indicates that this correlation is not valid for the tiny droplets of UWS sprays in technical applications.
Highlights
Ammonia selective catalytic reduction (SCR) is an effective technology for removal of nitrogen oxides from the exhaust gas of diesel engines
In order to better understand and predict wetting phenomena on the tailpipe wall, this study focuses on droplet spreading dynamics of urea water solution
A perspective on the spreading behavior of much with the above radial size of the domain the sidewall is without smaller urea water solution (UWS) droplets is given by one numerical simulation
Summary
Ammonia selective catalytic reduction (SCR) is an effective technology for removal of nitrogen oxides from the exhaust gas of diesel engines. On the SCR catalyst downstream, ammonia will convert harmful NOx into non-pollutant nitrogen and water [5]. In this UWS-based SCR system, technical problems often arise under real driving conditions due to the incomplete conversion of the UWS spray into ammonia. A good understanding of wetting phenomena of single UWS droplets as central process in liquid film formation is needed. In spite of a large number of investigations as mentioned above using water and other model fluids, no studies are found on the wetting/spreading behavior of UWS droplets relevant to the SCR application. As a step to fill this gap, the present study combines experimental and numerical investigations of the orthogonal impact and subsequent spreading of a single UWS droplet on a flat surface. By one numerical simulation for a much smaller droplet, the validity of a suitable correlation identified for millimeter-sized UWS drops is tested for tiny droplets occurring in sprays of real SCR application
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