High Speed Video Measurements with Water of a Planar Laser Illuminated Heated Tip Urea Injector Spray 2013-01-1073
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.
Recently, 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. 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
imaging work with an examination of the heated spray footprint and
side view using planar laser illumination (the results presented
here were measured using water as a substitute for AUS-32). The
spray structure change observed in the previously published
measurements is confirmed, and some preliminary quantification of
the change in the spray footprint is shown. An initial approach at
evaluating the sensitivity of spray-gas mixing models to the
observed spray structure changes is also discussed.