Experimental Fluid Dynamic Investigation of Urea–Water Sprays for Diesel Selective Catalytic Reduction–DeNOx Applications

Abstract

The injection process of urea−water solution determines initial conditions for reactions and catalysis and is fundamentally responsible for optimal operation of selective catalytic reduction (SCR) systems. In this study, injection and spray atomization characteristics of a pressure driven injector were investigated in varying crossflow conditions using shadow imaging, Mie scattering, and particle image velocimetry (PIV). Spray angle and tip propagation are described. Processed images characterize spray density and mass distribution. Velocity fields from PIV analyses indicate the entrainment of droplets in the spray. This is shown to be primarily dependent on the injection momentum ratio, in accordance with previous literature. The presence of a vortex pair is clearly evidenced at low gas flow momentums. Results indicate that fluid mechanic differences between the spray and gas flow are insufficient to induce substantial secondary breakup and interact extensively with the bulk of the spray. Spray wall impingement remains unavoidable; therefore, sufficient mixing lengths or devices are required for urea decomposition.

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

“…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.…”

“…Newer studies still rely heavily on experimental data gathered in the before-mentioned instances and only recently data has been available on entrainment, mixing, evaporation and impingement [19,22,23]. The study presented in [19] experimentally investigated spray density across a wide range of conditions, while in [22,24] droplet evaporation has been studied.…”

“…The study presented in [19] experimentally investigated spray density across a wide range of conditions, while in [22,24] droplet evaporation has been studied.…”

Experimental investigation of urea-water sprays in selective catalytic reduction (SCR) systems

“…al. [1]. UWS evaporation and spray/wall interaction were investigated in a hot air stream by Grout [2].…”

“…In this work, infrared thermography was introduced to investigate the heat transfer characteristics of the spray wall impingement on the basis of previous experiments, [1]. In addition, a single droplet evaporation test rig which allows the determination of the boiling regimes and the wetting conditions of UWS droplet was newly built.…”