The injection process of urea-water solution (AdBlue) determines initial conditions for reactions and catalysis and is fundamentally responsible for optimal operation of selective catalytic reduction (SCR) systems. The spray characteristics of four, commercially available, injectors (one air-assisted and three pressure-driven with different nozzle-hole configurations) are investigated with non-intrusive measuring techniques.
Injection occurred in the crossflow of a channel blowing preheated air in an exhaust duct similar configuration. The effect of several gas temperatures and flows on the spray propagation and entrainment has been extensively studied by shadow imaging. Shadow images, in addition, show that the spray of the pressure-driven injectors is only marginally affected by the gas crossflow. In contrast, the air assisted spray is strongly deflected by the gas, the effect increasing with increasing gas flow. Phase Doppler Anemometry (PDA) measurements delivered droplet size distributions and droplet velocities. Measurements have been performed in several locations near the opposed channel wall area. Sauter mean diameters of the droplets from the pressure-driven injectors are between 60-80μm while of the air assisted 20μm. Higher velocities have been associated with the larger droplets in the pressure-driven spray after the primary breakup while droplet velocities have been evenly distributed to all droplets sizes in the air-assisted spray.
