van Vuuren, N., "High Speed Video Measurements of a High Temperature Urea Injector Spray - Comparison of Spray Evolution in Water and AUS-32," SAE Technical Paper 2013-01-2527, 2013, doi:10.4271/2013-01-2527.
The recent implementation of new rounds of stringent nitrogen oxides (NOx) emissions reduction legislation in Europe and North America is driving the introduction of new exhaust aftertreatment systems, including those that treat NOx under the high-oxygen conditions typical of lean-burn engines.One increasingly common solution, referred to as Selective Catalytic Reduction (SCR), comprises a catalyst that facilitates the reactions of ammonia (NH3) with the exhaust nitrogen oxides (NOx) to produce nitrogen (N2) and water (H2O). It is customary with these systems to use 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.Current production AUS-32 injection systems typically rely on technologies previously developed for gasoline port fuel injection systems. Spray data (patternator data, particle size measurements, etc.) for these injectors are typically obtained under standard room temperature conditions.In recent months, results were 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. The imaging included microscopic views of the spray in the proximity of the injector tip (using AUS-32), and also macroscopic side and footprint investigations using water. Those results showed substantial structural differences in the spray between room temperature conditions, and conditions where the fluid temperature approached and exceeded 100° C.The results presented in this paper follow up on the previous macroscopic imaging work with an examination of the heated spray with planar laser illumination using AUS-32 as the test medium. The global spray structure changes observed in the previously published H2O measurements are confirmed, and some comparisons of the spray evolution with the different media are presented. Notable differences in the spray evolution and structure between the media are discussed.