Segmented Mixing Device for Exhaust Gas Urea Injection
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Solution Overview
Problem
Conventional mixing systems for exhaust gases after-treatment, such as those using swirl boxes, are inefficient in achieving complete chemical decomposition and mixing of urea with exhaust gases, leading to solid deposits on pipe walls, which reduces engine efficiency and can cause operational issues.
Innovation Solution
A mixing system comprising a first mixing device with a peripheral portion creating a swirl along the pipe wall to prevent fluid deposition and a second mixing device downstream that creates a central swirl to enhance mixing and decomposition, reducing backpressure and solid deposits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional swirl box is used to mix urea with exhaust gases, then mixing is achieved to some extent, but solid deposits still form on the pipe wall and backpressure is generated
Solution Approach 1:
The mixing device is segmented into a peripheral portion with blades that create peripheral swirl and a central portion that creates central swirl, allowing different regions of the flow to be mixed separately and then combined, effectively preventing deposits while maintaining mixing efficiency
Solution Approach 2:
Different portions of the mixing device have different functions: the peripheral portion creates peripheral swirl to prevent wall deposits, while the central portion creates central swirl to enhance mixing in the core flow region, optimizing both functions simultaneously
2Productivity
If a conventional swirl box is used to mix urea with exhaust gases, then mixing is achieved to some extent, but backpressure is generated reducing engine efficiency
Solution Approach 1:
The mixing device is segmented into peripheral and central portions that operate independently with different swirl patterns, allowing efficient mixing without requiring a bulky overall structure that would generate excessive backpressure
Solution Approach 2:
The peripheral portion creates peripheral swirl that is sufficient to prevent wall deposits without requiring excessive mixing intensity throughout the entire flow, thereby reducing unnecessary backpressure while maintaining effective mixing
3Reliability
If a long swirl box is used to achieve complete chemical decomposition of urea, then decomposition is improved, but the device becomes bulky and requires design adjustments of surrounding parts
Solution Approach 1:
The mixing device is segmented into functional zones (peripheral and central portions) that achieve complete decomposition within a compact length, eliminating the need for a long bulky swirl box while maintaining reliable chemical decomposition
Solution Approach 2:
The device changes flow parameters locally by creating peripheral and central swirls with different characteristics, enhancing decomposition efficiency within a shorter overall length rather than requiring extended pipe length
4Ease of operation
If urea is injected at an angle with respect to exhaust gases flow direction, then injection is achieved, but solid deposits form on the exhaust pipe wall opposite the injection point
Solution Approach 1:
The peripheral portion of the mixing device creates peripheral swirl that acts as a preliminary protective action, preventing the injected fluid from wetting and depositing on the pipe wall before deposition can occur
Solution Approach 2:
The mixing device performs preliminary mixing and swirl generation immediately after injection, creating protective flow patterns that prevent wall contact and deposition of the injected fluid
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 system effectively prevents solid deposits on the pipe surface, improves the decomposition and mixing of urea with exhaust gases, and reduces backpressure, leading to enhanced engine efficiency and longer pipe service life.
Implementation Method 1
a first mixing device positioned inside the pipe upstream from the injection inlet; wherein the first mixing device includes a peripheral portion comprising blades capable of creating a peripheral swirl along the pipe wall
Implementation Method 2
a second mixing device positioned inside the pipe downstream from the injection inlet, said second mixing device including a central portion comprising blades capable of creating a swirl inside the pipe
Implementation Method 3
the first mixing device is designed to generate turbulence mostly in the peripheral part of the pipe inner volume. For example, immediately downstream from the first mixing device, the turbulent kinetic energy of the fluid flowing in the pipe is at least ten times higher in the peripheral part than in the central part of the pipe inner volume
Implementation Method 4
Ammonia is introduced in the form of urea in an aqueous solution from which ammonia is obtained through hydrolysis
Data Source
AI summary
A mixing system includes a pipe having a longitudinal axis, in which exhaust gases can flow in a flow direction, a nozzle designed to inject a fluid inside the pipe from an injection inlet arranged in the pipe wall, according to an injection direction, a first mixing device positioned inside the pipe upstream from the injection inlet, the first mixing device including a peripheral portion including blades capable of creating a peripheral swirl along the pipe wall, and a central portion designed to create substantially no turbulence, and a second mixing device positioned inside the pipe downstream from the injection inlet, the second mixing device including a central portion including blades capable of creating a swirl inside the pipe.