Experimental investigation of urea-water sprays in selective catalytic reduction (SCR) systems
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 a
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Experimental investigation of urea-water sprays in selective catalytic reduction (SCR) systems
© Springer Fachmedien Wiesbaden 2015, M. Bargende, H.-C. Reuss, J. Wiedemann (Hrsg.), 15. Internationales Stuttgarter Symposium, Proceedings, DOI 10.1007/978-3-658-08844-6_65
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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. Key words: urea-SCR, spray, shadow imaging, Mie scattering, infrared thermography, single droplet evaporation
1 Introduction To comply with the stringent regulations as stated in Euro6, the NOx emissions of heavy-duty vehicles have to be reduced by up to 80%. Urea-SCR (selective catalytic reduction) is a promising technique to reduce NOx emissions without sacrificing engine efficiency. The introduction of the reducing agent urea plays a significant role on the reduction reactions. Many studies have been done so far on urea-SCR. The fluid dynamic behavior of a 6-hole SCR injector spray was reported by Spiteri et. al. [1]. UWS evaporation and spray/wall interaction were investigated in a hot air stream by Grout [2]. Musa [3] performed investigations on the evaporation characteristics of a single urea solution droplet. Castanet [4] specified the conditions of the impact regimes for water droplets onto a heated plate. However, combined studies of UWS sprays under exhaust gas flow conditions and the impact of urea-water droplet on a heated surface are scarce. The lack of knowledge hinders the optimization of mitigation of deposit formation and homogenous distribution of urea.
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Experimental investigation of urea-water sprays in selective catalytic reduction (SCR) systems In this work, infrared thermography was introduced to i
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