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

Abstract

Urea-SCR (selective catalytic reduction) is currently the state-of-the-art NOx reduction technique for Diesel engines. The main challenges for the implementation of mobile urea-SCR systems include rapid decomposition and homogeneous distribution of urea and the mitigation of deposit formation. A key affecting these performance factors is the injection of the urea-water solution (UWS). However, urea-water sprays under exhaust flow conditions have not been studied extensively so far.The present study is a comprehensive analysis of the behavior of the UWS spray. The investigation was conducted with a 3-hole commercial SCR injector. The spray properties under exhaust flow conditions are described by non-intrusive optical techniques: shadow imaging and Mie scattering. The spray cooling effect on the exhaust channel wall is analyzed based on the temporal and spatial evolution of the wall temperature using infrared thermography. This work is also complemented with the investigation of the specific behavior of UWS droplet during the wall impact over a wide range of temperatures and urea concentrations. This fundamental study provides information on the characteristics of UWS droplets evaporation time, the boiling regimes and the wetting conditions, which enhances the understanding of the wall impingement of urea-water sprays.

Fluid Dynamic Comparison of AdBlue Injectors for SCR Applications

“…This can be detrimental for the SCR systems operation. In [32] we have shown that the local cooling effect is strong, while under certain low conditions the local wall temperature fells below 100°C leading to permanent liquid ilm formation.…”

“…Based on extensive investigations [28,32] we can conclude that the sprays from pressure-driven injectors are hitting the opposed wall always at the same location, regardless of the low properties.…”

“…This phenomenon prevents the formation of a large uniied liquid pool on the opposed channel wall. Nevertheless, the liquid pool forming on the opposed wall is substantial [32]. This can be detrimental for the SCR systems operation.…”

“…The inluence of two different injectors on the NOx conversion of an SCR catalyst was investigated in [31]. The temperature evolution on the exhaust gas duct being hit by the urea water spray has being also investigated [32].…”

Review of Improving the NOx Conversion Efficiency in Various Diesel Engines fitted with SCR System Technology

“…The wall surface conditions may also be used as a parameter to help the urea droplets break apart and become finer droplets [45][46][47]. Spray-wall impingement occurs as a result, and spray cooling occurs throughout the injection period [48][49][50][51]. Spray cooling creates a liquid film which is the precursor to the formation of solid deposits [52,53].…”