Double-Swirl Mixing Device for Urea Atomization in SCR Systems
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Solution Overview
Problem
Conventional SCR systems face issues with urea deposition, insufficient atomization, and uneven mixing with exhaust gas, leading to unstable NOx reduction reactions and reduced conversion efficiency due to urea crystal formation during low load conditions in diesel vehicles.
Innovation Solution
A double-swirl mixing device comprising a tapered mixer with swirl plates and fan-type blades is introduced, where the tapered mixer rotates exhaust gas to prevent urea deposition and the fan-type blades enhance airflow to improve mixing and prevent urea crystal formation by reducing contact between urea and the mixing tube wall.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional mixing devices are used, then the structure is simple, but urea deposition and crystal formation occur leading to unstable operation
Solution Approach 1:
The mixing device is segmented into multiple functional components: a tapered mixing tube divided into fast-swirl section and slow-swirl section, multiple swirl plates at different positions and angles, and a fan-type blade. This segmentation allows each component to perform a specific function in the urea atomization and mixing process, improving reliability through specialized functionality.
Solution Approach 2:
The mixing device employs dynamic swirl motion through multiple swirl plates that create rotating airflow at different speeds and directions. The tapered geometry and angled swirl plates generate dynamic centrifugal forces that continuously move urea droplets away from walls, preventing deposition and crystal formation, thus ensuring stable operation.
2Manufacturing precision
If high-speed rotating airflow is used to atomize urea, then atomization is improved, but urea droplets land on the rear end of the mixing tube causing crystal formation
Solution Approach 1:
The tapered mixing tube geometry transitions from a narrow inlet to a wider outlet, adding a dimensional gradient that modifies airflow patterns. This dimensional change creates a expanding flow field that reduces centrifugal force intensity downstream, preventing urea droplets from landing on the mixing tube wall and forming crystals while maintaining good atomization.
Solution Approach 2:
Instead of using a straight cylindrical mixing tube, the invention inverts the conventional approach by using a tapered geometry with smaller inlet and larger outlet. This inversion of the typical flow path geometry allows the airflow to expand and decelerate gradually, reversing the harmful effect of high-speed droplet impact on the tube wall.
3Productivity
If urea is jetted into exhaust gas, then NOx reduction is achieved, but insufficient mixing and decomposition occur resulting in side products
Solution Approach 1:
The mixing device performs preliminary atomization and mixing actions before the urea-exhaust gas reaction. The swirl plates and fan blade pre-mix the urea spray with exhaust gas, creating a more uniform mixture that promotes complete decomposition and reduces side products, thereby improving both productivity and reaction stability.
Solution Approach 2:
The invention replaces simple mechanical injection with a more sophisticated fluid dynamic system using swirl plates and tapered geometry. This mechanical-substitution approach uses rotational flow fields and pressure gradients to enhance mixing and decomposition efficiency, leading to better NOx reduction performance and reaction stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents urea crystal formation, ensures uniform mixing, and enhances NOx reduction efficiency by efficiently atomizing and distributing urea within the exhaust gas, stabilizing the operation of diesel vehicles.
Implementation Method 1
The function of the tapered swirl plates is to rotate the entered exhaust gas at high speed
Implementation Method 2
to warp and take away the jetted urea
Implementation Method 3
part of the airflow flows through the fan-type blades, which accelerates the flowing and rotating of airflow near the wall surface of the mixing tube
Implementation Method 4
timely takes away the urea liquid film that is thrown on the wall surface of the mixing tube under the action of strong swirling function
Data Source
AI summary
An engine and a double-swirl mixing device thereof are provided. The double-swirl mixing device includes a mixing tube configured to mix exhaust gas with urea, a tapered mixer including a tapered tube having an outlet end extending into the mixing tube, and a plurality of tapered swirl plates which are arranged along a circumferential direction on a side wall of the tapered tube, and a fan-type blade arranged at the outlet end of the tapered tube, and a diameter of an inlet end of the tapered tube is smaller than a diameter of the outlet end of the tapered tube.