The recent implementation of new rounds of stringent nitrogen oxides (NOx) emissions reduction legislation in Europe and North America is driving the expanded use of exhaust aftertreatment systems, including those that treat NOx under the high-oxygen conditions typical of lean-burn engines.
One of the favored aftertreatment solutions is referred to as Selective Catalytic Reduction (SCR), which comprises a catalyst that facilitates the reactions of ammonia (NH3) with the exhaust nitrogen oxides (NOx). It is customary with these systems to generate the NH3 by injecting a liquid aqueous urea solution, typically at a 32% concentration of urea (CO(NH2)2). The solution is referred to as AUS-32, and is also known under its commercial name of AdBlue® in Europe, and DEF - Diesel Exhaust Fluid - in the USA. The urea solution is injected into the exhaust and transformed to NH3 by various mechanisms for the SCR reactions.
Understanding the spray performance of the AUS-32 injector is critical to proper optimization of the SCR injection system.
Results were previously presented from high-speed video imaging of an AUS-32 injector spray simulating the hot conditions at the injector spray exit for an exhaust injection application. These results were obtained while injecting into room temperature ambient air. Those results showed substantial structural differences in the spray between room temperature fluid conditions, and conditions where the fluid temperature approached and exceeded 100° C. However, it was unknown whether certain aspects of the observed spray behavior were the result of the room temperature ambient environment.
The spray investigations results presented in this paper follow up on the previous macroscopic imaging work with an examination of the heated spray injected into a hot air flow environment representative of a light-duty vehicle exhaust system. The test facility concept and operation is described. The overall global spray structure changes observed in the previously published room temperature air measurements are confirmed. Specific differences in the spray evolution are also observed. Quantifications of the spray penetration and spray atomization are presented. The implications of the observed spray behavior for vehicle exhaust applications are discussed.