Numerical Modelling and Experimental Characterization of a Pressure-Assisted Multi-Stream Injector for SCR Exhaust Gas After-Treatment

Abstract

Simulations for a pressure-assisted multi-stream injector designed for urea-dosing in a selective catalytic reduction (SCR) exhaust gas system have been carried out and compared to measurements taken in an optically accessible high-idelity low test rig. The experimental data comprises four different combinations of mass low rate and temperature for the gas stream with unchanged injection parameters for the spray. First, a parametric study is carried out to determine the importance of various spray sub-models, including atomization, spray-wall interaction, buoyancy as well as droplet coalescence. Optimal parameters are determined using experimental data for one reference operating condition. The model is subsequently applied to all operating conditions with unaltered parameters and validated by means of the measured droplet velocity ields, droplet diameter distributions and spray-tip propagations which have been characterized by means of Particle Image Velocimetry (PIV), Phase Doppler Anemometry (PDA) and shadow imaging. Finally, the model is used to investigate in detail phenomena characteristic of inclined sprays in cross-lows. Effects such as formation of vortices behind the spray core for low cross low velocities, greater entrainment of droplets at high low rates as well as wall ilm dynamics and the interaction of droplets also with the side walls are discussed in detail, highlighting the importance of the respective phenomena at the different operating conditions.

Experimental and numerical assessment of impingement and mixing of urea–water sprays for nitric oxide reduction in diesel exhaust

“…A constant injection velocity of 27.4 m/s was prescribed which was determined from the experiment. For secondary atomization, the model of KH-RT [28] has been activated, despite conclusions reached in [20] where it is reported that due to low Weber numbers secondary break-up is unlikely to occur. Based on the parametric study reported in [20], 'buoyancy' has been activated and the 'Bai' spray-wall interaction model, 'advanced' droplet collision model and film models are also applied in this work…”

“…Planar Mie scattering and PIV [29] as well as CFD simulations [20] have shown numerous effects of interest occurring off-center. To describe the spray transversal structure, the droplet size distribution analyzes all droplet data along the y-direction at given x-and z-coordinates.…”

“…The injector is located at [120, 0, 40] mm. A hexahedral mesh with local refinement has been used for which further details are given in [20], where a mesh sensitivity study has been carried out. Starting from recommendations put forward in [27], a cell size of 2 Â 1 Â 1 mm in axial, span-wise and vertical direction in the near nozzle region was found sufficient for this injection configuration in [20], which has also been used here.…”

“…Only few studies on SCR sprays in the presence of cross-flow are documented in the literature [14][15][16][17][18][19][20][21] and further understanding is crucial for further improvement of SCR injectors in view of stringent emission legislations.…”

Quasi 1D modeling of two-phase flow and deposit formation for urea-selective catalytic reduction systems

“…A UWS spray wall interaction also cannot be avoided in most SCR applications due to insufficient entrainment, slow evaporation and thermolysis, and the inertia of the droplets. It causes local cooling of the wall and a wall film will form if the wall temperature decreases below a critical temperature (Birkhold et al, 2006;Varna et al, 2014;Spiteri et al, 2015). Kuhnke et al (2004) and Abu-Ramadan et al (2012) divided the UWS spray impingement into four regimes based on the properties and energy of the droplet, and the wall surface condition.…”