This content is not included in
your SAE MOBILUS subscription, or you are not logged in.
Experimental Analysis of SCR Spray Evolution and Sizing in High-Temperature and Flash Boiling Conditions
Abstract:
In the last years, new stringent emission legislation in terms of nitrogen oxides (NOx) has been leading to a massive development of advanced after-treatment systems for diesel engines. Among them, selective catalytic reduction (SCR) technology has proved to be an effective approach for NOx reduction in a wide range of engine operating conditions. In SCR systems, the interaction between diesel exhaust fluid (DEF) and hot exhaust gas is crucial to promote the chemical reactions through which ammonia is produced. Hence, a proper matching between the exhaust pipe architecture and the DEF spray is mandatory for obtaining an adequate SCR efficiency, especially in close-coupled configurations and moderate exhaust gas temperature conditions. To this end, significant benefits could be derived via appropriate SCR injector thermal management, as the spray structure is significantly influenced by the DEF temperature upstream of the injector nozzle.
In this article, the results of a spray analysis campaign carried out on a prototype DEF dosing system are presented. The goal of this research is to investigate the influence of both air and DEF temperature upon spray structure and atomization. In a previous investigation, preliminary tests were carried out using a hot flow bench (HFB) in order to perform spray evolution and SCR system efficiency analyses in realistic flow rate and temperature conditions. In the current investigation, a deeper analysis was carried out individually controlling DEF and test vessel air temperature, with the spray evolving in quiescent hot conditions. Mie scattering and Schlieren spray images were simultaneously acquired in order to investigate both liquid and vapor spray phase evolution, in order to perform a characterization of spray global structure. In the same conditions, a dedicated test campaign was carried out to perform drop sizing analysis. Some of the most significant results are discussed, along with their possible effects in real exhaust system applications.