Urea Injector Mixing Pipe for Exhaust Gas Homogeneity
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Solution Overview
Problem
Existing exhaust gas post-treatment devices face challenges in ensuring sufficient mixing of urea aqueous solution with exhaust gas and preventing the solution from attaching to the inner walls of the exhaust pipe, leading to inadequate ammonia production and potential crystallization, which can result in nitrogen oxide purification deficiencies and increased fuel consumption.
Innovation Solution
A reducing agent aqueous solution mixing device is designed with an exhaust pipe featuring an elbow section, a mixing pipe with peripheral openings, and an inner pipe, where the urea solution is injected into the elbow section and mixed with exhaust gas, which then flows into the inner pipe, allowing efficient heating and dispersion, thereby preventing attachment to the pipe walls and optimizing ammonia production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the distance between the injector and the reducing catalyst unit is short, then the device complexity is reduced, but the urea aqueous solution is not sufficiently mixed with the exhaust gas and attaches as droplets to the inner wall of the exhaust pipe
Solution Approach 1:
The patent employs a nested pipe structure where an inner pipe is disposed within the exhaust pipe. The inner pipe serves as a dedicated channel for injecting and mixing the urea aqueous solution with exhaust gas, while the exhaust pipe carries the main exhaust flow. This nesting allows sufficient mixing distance and volume within a compact overall footprint, resolving the contradiction between short device length and adequate mixing efficiency.
Solution Approach 2:
The invention introduces a radial dimension for mixing by injecting the urea aqueous solution through the inner pipe wall into the annular space between the inner pipe and exhaust pipe. This radial injection creates turbulence and enhances mixing in three dimensions, achieving thorough mixing within a shorter axial distance than conventional single-dimension mixing approaches.
2Productivity
If the exhaust gas temperature is high, then the decomposition of urea aqueous solution into ammonia is enhanced, but the reducing agent aqueous solution may attach and crystallize on the inner wall of the exhaust pipe
Solution Approach 1:
The nested pipe structure creates an annular mixing zone where the urea aqueous solution is injected and rapidly mixed with exhaust gas. This confined annular space ensures uniform heating and prevents the solution from contacting the cooler outer exhaust pipe wall, eliminating the condition for crystallization while maintaining high decomposition efficiency through exposure to hot exhaust gas.
Solution Approach 2:
The inner pipe acts as an intermediary structure that mediates between the injected urea aqueous solution and the exhaust gas flow. It provides a controlled environment for mixing and heating, isolating the solution from direct contact with the exhaust pipe wall during the critical mixing phase, thereby preventing crystallization while enabling efficient decomposition.
3Reliability
If a double-nested pipe structure is used to prevent attachment, then the mixing efficiency is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent implements a practical nested pipe structure where the inner pipe is positioned within the exhaust pipe at a specific distance from the injector. This configuration achieves the attachment prevention function with a relatively simple structural arrangement that can be manufactured using conventional piping techniques, balancing manufacturing ease with functional effectiveness.
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 configuration ensures effective mixing and decomposition of the urea solution into ammonia, reducing the risk of attachment and crystallization, enhancing nitrogen oxide reduction and maintaining engine efficiency by minimizing back pressure and fuel consumption.
Implementation Method 1
The inner pipe is heated by the exhaust gas, and accordingly, the urea aqueous solution can be inhibited from attaching as droplets to the inner wall of the inner pipe
Implementation Method 2
the urea aqueous solution is thermally decomposed by the exhaust gas and ammonia is thereby obtained
Implementation Method 3
Turbulence is herein generated within the mixing pipe by causing the exhaust gas to flow into the mixing pipe through the openings of the mixing pipe. With use of the turbulence of the exhaust gas, dispersion of the urea aqueous solution is promoted
Data Source
AI summary
A reducing agent aqueous solution mixing device includes an exhaust pipe, an injector, a mixing pipe and an inner pipe. The exhaust pipe includes an elbow part having a curved portion, and a linear part disposed downstream of the elbow part. The injector is disposed outside the curved portion and injects the reducing agent aqueous solution towards the linear part. The mixing pipe is disposed inside the elbow part to surround the reducing agent aqueous solution injected from the injector. The mixing pipe includes a plurality of openings on its outer peripheral surface. The inner pipe is disposed downstream of the mixing pipe and spaced apart from an outlet portion of the mixing pipe and from an inner wall of the linear part to allow the exhaust gas to flow through the inside of the inner pipe and along the outer periphery of the inner pipe.