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The reduction of NOx-emissions from diesel engines is crucial for the fulfilment of environmental standards. Selective catalytic reduction (SCR) is an effective way to achieve very low tailpipe NOx-emission levels. For an efficient after treatment system, a homogeneous distribution of gaseous ammonia across the catalytic surface is essential. Therefore, a detailed understanding of the impingement of the injected urea water solution (UWS), its evaporation and transformation to gaseous ammonia is of vital importance. Due to the complex physics of the impingement process, the simulation of SCR systems with computational fluid dynamics (CFD) relies upon empirical models known as impingement maps. In the current study a droplet chain generator was used to investigate single droplet impingement of UWS. The impingement events were filmed with a high speed camera and then analysed with respect to impingement velocity and droplet diameter as well as droplet Weber-number.

The pressure drop across the aftertreatment systems directly affects the fuel economy as a function of the flow characteristics and also the soot loading in the case of the Diesel particulate filter. However, the relative position of this system with respect to the turbine has an additional effect which is dependent on the influence of the turbine expansion ratio. When the DPF is placed upstream of the turbine, its pressure drop is not affected by the multiplicative effect of the turbine expansion ratio to set the exhaust manifold pressure. This work concentrates on the analysis of the influence that the aftertreatment pressure drop has on the engine performance depending on the DPF soot loading and the location of the aftertreatment with respect to the turbine. The interaction with the turbocharger and the EGR operation is also analyzed taking as reference a two stage turbocharger heavy duty Diesel engine.

The use of particulate filters (DPF) has become in recent years the state of the art technology for the reduction of soot aerosol emissions for light, medium and heavy duty Diesel vehicles. However, the effect of the system location on engine performance is a key aspect that should be studied. In the present work a numerical study has been carried out with the objective to analyze the effect on the engine performance of an innovative DPF placement upstream of the turbine. This study has been performed by means of the gas dynamic simulation of a two-stage turbocharged heavy duty Diesel engine, which has been previously modeled from experimental data obtained under steady state conditions. The original DPF has been divided into two monoliths for the case of the pre-turbo DPF configuration. Three cylinders discharge in each of these monoliths and after the filtration the flow is driven towards the high-pressure turbine and the EGR system.