Analysis of Global Shape and Sizing of Urea-Water Sprays in a Hot Air Flow Tunnel for the Development of SCR Systems

摘要

In the present paper, the results of an experimental campaign aiming at the analysis of an urea-water solution (UWS) injection system are presented. UWS is used as reductant agent to control NO_x emissions in the exhaust of automotive Diesel engines. In this research, a UWS dosing system was tested in a hot air flow tunnel, developed to investigate the spray behaviour in operating conditions similar to those present in Diesel exhaust systems, while allowing an adequate optical access for both spray imaging and Phase Doppler Anemometry (PDA) measurements. The present research activity is divided into three parts. In the first one, PDA measurements were conducted in order to get reliable data about spray velocity and droplets sizing, varying the temperature of the air flow UWS is injected in. In the second part, an imaging technique was adopted to visualize the spray global characteristics, such as the spray spreading and the UWS mass distribution in the pipe. In the third part of this work, the same imaging technique was used to focus the attention on small portions of the spray, to achieve an indirect measurement of droplets diameter thanks to a noncommercial image post-processing software.