Numerical investigation on the role of a mixer on spray impingement and mixing in channel cross-stream airflow

Abstract

The present study numerically investigates the influence of introducing a spin-type mixer and different angular orientations of the mixer blades on the spray-wall interaction and mixing, following cross-stream injection of a pulsed spray into airflow in a circular duct. This is relevant to the Selective Catalytic Reduction system in diesel engines for exhaust gas after-treatment. The spin-type static mixer is located downstream of the injector and generates a swirling airflow in the duct. All simulations were carried out using ANSYS Fluent V18.0. The standard k–ω model is used to simulate the turbulent continuous phase flow, while the discrete phase model is employed to track the spray droplets. The Taylor Analogy Breakup and Kuhnke wall film models are adopted to model droplet breakup and wall-film formation, respectively. First, the swirling airflow characteristics without spray injection are validated against in-house particle image velocimetry measurements. Second, the spray computations are compared with the experiment. Overall, good agreement between simulation and experiment is achieved. Furthermore, the choice of water and urea water solution injection liquid on the in-channel spray characteristics is also studied. The main focus of the present work is on the study of the influence of spin mixer clocking on the post-impingement spray evolution, droplet redistribution and mixing, and wall-film characteristics. The results show that the choice of the angular orientation of the mixer governs the extent of droplet deposition and splashing on the mixer blades and, as a result, strongly influences the spatial uniformity of droplets and ammonia species at the channel exit.