van Vuuren, N. and Sayar, H., "High Speed Video Measurements of a Heated Tip Urea Injector Spray," SAE Technical Paper 2012-01-1747, 2012, doi:10.4271/2012-01-1747.
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 automotive exhaust aftertreatment systems.One of these technologies comprises a catalyst that facilitates the reactions of ammonia (NH₃) with the exhaust nitrogen oxides (NOx) to produce nitrogen (N₂) and water (H₂O). This technology is referred to as Selective Catalytic Reduction (SCR). The ammonia is delivered by a separate fluid supply and injection system to the exhaust in the form of AUS-32 (Aqueous Urea Solution), and is also known under its commercial name of AdBlue® in Europe, and DEF - Diesel Exhaust Fluid - in the USA.The development and application of current production AUS-32 injection systems typically rely on spray diagnostics techniques that were implemented for the gasoline port injector. These data are often obtained under standard room temperature conditions. These data are then used as initial conditions for Computational Fluid Dynamics (CFD) simulations.Up until the present, there had been only limited information about urea injector spray quality as the fluid temperature in the injector increased to typical hot levels in the exhaust-mount urea injection applications. This paper presents results 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 results show substantial structural differences in the static spray between room temperature conditions, and conditions where the fluid temperature is approaching and exceeding 100°C. There are also noticeable differences in the post injection phase, which are typically not taken into account by the CFD community, but which could have a significant impact on mixing calculations and prediction of deposits behavior.The high-speed video imaging setup and results for various spray configurations are described in this paper. The implications for better understanding of spray-gas mixing and deposits formation are also discussed.