Multi-Stage Mixing Elements for Aftertreatment Reductant Distribution
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Solution Overview
Problem
The existing mixing systems in aftertreatment systems for reducing NOx in exhaust gases face issues with reductant particle deposition, leading to increased back pressure and reduced NOx conversion efficiency due to improper mixing and distribution within the mixing tube.
Innovation Solution
A multi-stage mixing system with a series arrangement of mixing elements, including flow convergent, flapper, and swirl mixers, strategically positioned to break up and evaporate reductant, ensuring uniform mixing and minimizing deposit formation by optimizing the distance and orientation of each element within the mixing tube.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a mixing element is placed inside the mixing tube to increase turbulence and improve reductant distribution, then mixing effectiveness is improved, but reductant particles collect on the mixing element surface forming solid deposits
Solution Approach 1:
The mixing tube is divided into multiple sections with mixing elements positioned at specific locations. The mixing elements are segmented into multiple discrete components rather than a single continuous structure, allowing exhaust gas to flow through and around them, reducing surface area for deposit accumulation while maintaining mixing effectiveness.
Solution Approach 2:
The mixing elements are positioned to utilize three-dimensional space within the mixing tube, creating turbulence through spatial arrangement rather than relying on large surface areas. The elements are strategically placed at different heights and radial positions to maximize mixing while minimizing deposit formation on any single surface.
2Productivity
If reductant is injected into the exhaust gas flow, then NOx conversion is improved, but back pressure on the engine increases due to deposit formation
Solution Approach 1:
The mixing elements are positioned upstream of the SCR catalyst to pre-mix the reductant with exhaust gas before it reaches the catalyst. This preliminary mixing action ensures uniform distribution of reductant, improving NOx conversion efficiency while the optimized element geometry prevents excessive pressure buildup.
Solution Approach 2:
The mixing elements are designed with specific geometric parameters including optimized dimensions, spacing, and angular orientations. These parameters are carefully selected to generate sufficient turbulence for effective mixing while maintaining pressure drop within acceptable limits, preventing excessive back pressure on the engine.
3Length of stationary object
If a single mixing element is used to achieve mixing within a short length, then system compactness is improved, but deposit formation increases and mixing uniformity decreases
Solution Approach 1:
Instead of using a single large mixing element, the system employs multiple smaller mixing elements distributed along the mixing tube. This segmentation allows the exhaust gas to mix with reductant in multiple stages, achieving uniform mixing distribution over a compact length while each individual element maintains a small surface area to reduce deposit formation.
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 achieves improved NOx conversion and reduced ammonia slip by ensuring thorough and uniform mixing of reductant with exhaust gases, minimizing deposit formation, and maintaining engine performance.
Implementation Method 1
A mixing element is affixed inside the mixing tube so that increased turbulence and improved distribution of the reductant within the exhaust gases may be achieved within a short length of the mixing tube
Implementation Method 2
A multi-stage mixing system with a series arrangement of mixing elements, including flow convergent, flapper, and swirl mixers, strategically positioned to break up and evaporate reductant, ensuring uniform mixing and minimizing deposit formation
Data Source
AI summary
A mixing system for an aftertreatment system is disclosed. The mixing system includes a mixing tube. The mixing tube is provided in fluid communication with an exhaust conduit. The mixing system also includes a reductant injector positioned at an injection location on the mixing tube. The mixing system further includes a mixer assembly positioned downstream of the injection location. The mixer assembly includes a plurality of mixing elements provided in a series arrangement, such that each of the plurality of mixing elements is provided downstream of one another.