Overview of SCR System Mixing Devices

Without good distribution, the SCR system will be prone to increased DEF consumption, decreased NOx reduction, and increased NH3 slip (Fig. 15.18). Although Fig. 15.18 shows a comparison between a no mixer scenario and to an SCR system with a mixer, the trend will remain true for a system with an optimized mixing solution compared to one without an optimized mixing solution. Therefore, it is important that care is taken when determining a mixer for an application as well as how the mixer is implemented. 

A primary concern with mixing devices is the increase in backpressure associated with implementing a mixing device. The trade-oflf between mixing efficiency and backpressure are key factors in designing the decomposition tube. 

Mixer placement is not only limited to reducing the potential for impingement on the exhaust pipe, but it also needs to meet the backpressure, velocity, and species uniformity targets. To do this effectively, the engine conditions need to be understood. The primary engine outputs that need to be considered are exhaust mass flow 

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