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H. Smith, M. Zöchbauer, T. Lauer:
"Advanced Spray Impingement Modelling for an Improved Prediction Accuracy of the Ammonia Homogenisation in SCR Systems";
Talk: SAE 2015 World Congress, Detroit,Michigan, USA; 2015-04-21 - 2015-04-23; in: "Advanced Spray Impingement Modelling for an Improved Prediction Accuracy of the Ammonia Homogenisation in SCR Systems", (2015), ISSN: 0148-7191.

A fast preparation of the liquid urea water solution (UWS) is
necessary to ensure high conversion rates in exhaust aftertreatment
systems based on Selective Catalytic Reduction (SCR). Droplet wall
interaction is of major importance during this process, in particular
droplet breakup and the Leidenfrost effect. A deeper understanding of
the underlying mechanisms is a basic requirement to calibrate CFD
models in order to improve their prediction accuracy.
This paper presents a detailed literature study and discussion about
the major impact factors on droplet wall interaction. Measurements of
the Leidenfrost temperature were conducted and the corresponding
regimes classified based on optical observations. The pre- and
post-impingement spray was analysed using the laser diffraction
method. Further, the validity of spray initialisation based on
measurements at room temperature was verified. The Leidenfrost
effect, partial droplet evaporation, droplet breakup and evaporation at
the catalyst are the crucial aspects of impingement modelling. Their
implementation and calibration against measurement data is
presented. Sensitivity studies of single impact factors were carried
out based on two exhaust systems that are representative for the
spectrum of typical automotive applications. A set of operating points
was used that covers the whole range of typical operating conditions.
Finally, a best practice setup was derived and validated with
measured ammonia distributions.
With the help of the presented numerical and experimental
investigations the prediction accuracy of the simulated ammonia
homogenisation could be significantly increased for inherently
different exhaust pipe geometries.

http://dx.doi.org/10.4271/2015-01-1054