DEF Nozzle Converging-Diverging Flow Path for SCR Atomization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing spray nozzle assemblies for injecting reductant solutions into exhaust gas paths in exhaust treatment systems suffer from incomplete mixing of air and liquid, leading to suboptimal atomization, evaporation, and spatial uniformity, which impairs NOx conversion efficiency in SCR processes.
Innovation Solution
The proposed solution involves a diesel exhaust fluid (DEF) nozzle design with a unique configuration of conduits and mixing chambers, where a first conduit defines a flow path that feeds into a first mixing chamber, and a second conduit surrounds the first conduit to form a second flow path that communicates with the first mixing chamber, optimizing the ratio of mixing chamber length to transverse gap width for enhanced mixing and atomization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pressurized air is used to internally atomize liquid in the spray nozzle, then atomization is achieved, but mixing of air and liquid streams is incomplete
Solution Approach 1:
The patent merges the air and liquid flow paths into a single mixing chamber where the flows are combined before exiting through a common outlet. The air supply passage and liquid supply passage both communicate with the mixing chamber, allowing complete mixing of the two streams, which resolves the contradiction by achieving thorough mixing without requiring complex multi-chamber structures.
Solution Approach 2:
The patent introduces a transverse mixing component that adds a lateral dimension to the flow interaction. By designing the air and liquid flows to mix in a transverse direction within the mixing chamber rather than only axially, the patent enhances mixing efficiency and atomization quality while maintaining a relatively simple overall structure.
2Ease of manufacture
If a multi-piece nozzle configuration is used, then manufacturing flexibility is improved, but assembly time and manufacturing cost increase
Solution Approach 1:
The patent combines multiple functional components into a single integrated nozzle assembly. The mixing chamber, air supply passage, liquid supply passage, and outlet are all formed as one piece, eliminating the need for separate components and assembly operations. This resolves the contradiction by maintaining manufacturing flexibility through integrated design while completely eliminating assembly time and reducing manufacturing cost.
3Ease of operation
If non-atomized reductant is injected, then injection simplicity is maintained, but evaporation is incomplete and NOx conversion efficiency is impaired
Solution Approach 1:
The patent performs preliminary atomization and mixing of the reductant with air before the reductant enters the exhaust stream. The mixing chamber pre-mixes the reductant solution with pressurized air, creating a finely atomized mixture that enhances evaporation and reaction efficiency. This resolves the contradiction by maintaining simple injection operation while dramatically improving NOx conversion efficiency through preliminary mixing and atomization.
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
This design achieves improved mixing and atomization of the DEF with the exhaust gas, leading to enhanced NOx conversion efficiency in the SCR process, while also simplifying the nozzle structure to reduce manufacturing costs and complexity.
Implementation Method 1
A flow area of the second flow path decreases from an inlet of the second flow path to a throat, and the flow area of the second flow path increases from the throat to an outlet of the second flow path
Implementation Method 2
The injected reductant may thermally decompose into ammonia (NH3), react with NOx and other exhaust constituents on the surface of an SCR catalyst
Implementation Method 3
the injected reductant may thermally decompose into ammonia (NH3), react with NOx and other exhaust constituents on the surface of an SCR catalyst
Data Source
AI summary
A diesel exhaust fluid (DEF) nozzle includes a first conduit, an outlet of the first conduit defining an inlet of a first mixing chamber; and a second conduit disposed around the first conduit, an outer surface of the first conduit and an inner surface of the second conduit defining a second flow path therebetween. A flow area of the second flow path decreases from an inlet of the second flow path to a throat, and increases from the throat to an outlet of the second flow path. The inner surface of the second conduit defines a peripheral wall of the first mixing chamber, and a peripheral wall of a second mixing chamber, the first flow path and the second flow path being in fluid communication with the second mixing chamber via the first mixing chamber.