Modeling the kinetic and thermal interaction of UWS droplets impinging on a flat plate at different exhaust gas conditions. Politecnico di Milano

Format:

Book

Conference/Event

Author/Creator:

Nappi, Antonello, author.

Contributor:

Della Torre, Augusto

Dimopoulos Eggenschwiler, Panayotis

Montenegro, Gianluca

Onorati, Angelo

Conference Name:

15th International Conference on Engines & Vehicles (2021-09-12 : Capri, Italy)

Language:

English

Physical Description:

1 online resource cm

Place of Publication:

Warrendale, PA SAE International 2021

Summary:

With the introduction of the Euro 6dTemp emissions standards Selective Catalytic Reduction (SCR) has confirmed its role as a cost effective and efficient method for the reduction of NOx emissions in Diesel engines. This technology uses ammonia as a reducing agent to convert NOx to gaseous nitrogen in a catalyst. To achieve the best catalyst efficiency, ammonia must be delivered to the catalyst with the right concentration (to avoid ammonia slip) and with a uniform distribution. To achieve these objectives, most SCR systems inject a Urea Water Solution (UWS) in a mixing unit system placed before the catalyst, to improve the uniformity of the ammonia distribution. The UWS injected in this form interacts with the walls of the exhaust manifold and of the mixing unit. This interaction is used to improve the evaporation of the UWS, but it can lead to rapid cooling of the walls where impingement occurs, leading to the formation of liquid film with the possibility of formation of solid deposits. To avoid the formation of such deposits, the usage of CFD has become a fundamental tool during the design of the SCR unit. An accurate description of the spray behaviour, both from a kinematic and thermal standpoint is therefore fundamental. To achieve this, the authors have implemented in OpenFOAM a model for the spray wall interaction capable of predicting the kinematic and thermal evolution of the spray, and have coupled this model with a Conjugate Heat Transfer (CHT) model of the solid walls, thus allowing the prediction of wall film formation on the mixer surfaces. Inside this CHT framework, the three way coupling between the bulk gas region, solid region and film region is achieved through the use of a fictitious buffer region, used to transfer the source terms used to perform the linking of the three distinct regions and to evaluate the heat flux between film and solid region. To perform the validation of the model, simulations are performed using as reference experimental measurements performed in a test rig at EMPA labs (Switzerland). The temperature on the back of a thin metal plate is measured with infrared thermometry with multiple injections performed during one test session. This allows the author to capture the transition in boiling regimes at typical temperature ranges of SCR systems. The predicted temperatures and time gradient and extension of liquid film pools are compared with the ones obtained from the experimental measurements, showing the capabilities of the framework

Notes:

Vendor supplied data

Publisher Number:

2021-24-0079

Access Restriction:

Restricted for use by site license