Exhaust Gas Flow Guide for Urea Precipitation Control
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Solution Overview
Problem
Existing methods for reducing NOx emissions in diesel engine exhaust gases, such as the SCR technique, face challenges with urea precipitation in exhaust gas passages due to low surface temperatures, insufficient vaporization time, and bends in the passage, leading to reduced efficiency and increased maintenance needs.
Innovation Solution
A method that divides the exhaust gas flow into a centre flow and an edge flow, with the reactive substance fed into the centre flow, utilizing a flow guide with blades to create a spiral edge flow that prevents urea from colliding with the passage walls, ensuring even mixing and efficient vaporization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the reactive substance is sprayed into the exhaust gas flow from the side of the exhaust gas passage, then the mixing of the reactive substance with exhaust gas is improved, but the reactive substance collides with the walls of the exhaust gas passage causing precipitation
Solution Approach 1:
The exhaust gas flow is divided into a center flow and an edge flow. The reactive substance is injected only into the center flow, which is separated from the wall regions by the edge flow. This segmentation prevents direct contact between the reactive substance and the exhaust gas passage walls, eliminating precipitation while maintaining mixing efficiency.
Solution Approach 2:
Different regions of the exhaust gas flow are given different functions: the center flow region is designated for reactive substance injection and mixing, while the edge flow region serves as a protective barrier that prevents wall contact. This local differentiation of flow regions optimizes both mixing and precipitation prevention.
2Temperature
If the distance between the injection site and the catalyser is increased to ensure vaporisation, then the vaporisation of urea is improved, but the engine structure becomes more complex and space requirements increase
Solution Approach 1:
The edge flow is created in advance to establish a protective barrier before the reactive substance is injected. This preliminary structuring of the flow ensures that subsequent injection and vaporisation processes occur without wall contact, eliminating the need for extended passage lengths or complex routing to prevent precipitation.
Solution Approach 2:
The invention uses fluid dynamic principles to create a spiral edge flow that acts as a protective barrier. By manipulating the exhaust gas flow patterns through pneumatic means rather than mechanical barriers, the system achieves effective precipitation prevention without adding mechanical complexity or increasing space requirements.
3Quantity of substance
If the exhaust gas flow is set in rotation motion to improve mixing, then the distribution of reactive substance is improved, but the reactive substance still collides with the walls causing precipitation
Solution Approach 1:
The rotating exhaust gas flow is segmented into a center flow and an edge flow. The reactive substance is injected into the center flow, which is protected from wall contact by the edge flow. This segmentation allows the benefits of rotational mixing while preventing the harmful wall collisions that cause precipitation.
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 approach significantly reduces urea precipitation, maintains engine efficiency, and allows for more flexible exhaust gas passage design, improving the overall cleaning efficiency and reducing maintenance requirements.
Implementation Method 1
an edge flow rotating and advancing around the centre flow
Implementation Method 2
Under the influence of the heat of the exhaust gas the water in the urea/water mixture is vaporised and the urea is disintegrated into ammonia
Implementation Method 3
which reacts in the SCR catalyser with the nitrogen oxides. Pure nitrogen and water is generated as a final result of the reaction
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 2c~2d
AI summary
In the method a substance is fed into the exhaust gas flow flowing in the exhaust gas passage (10), which substance reacts with harmful compounds in the exhaust gas, whereby compounds are generated, which are less harmful for the environment. The reactive substance can be urea. The exhaust gas flow is with the aid of a flow guide (50) divided into two parts: a centre flow (20) flowing in the centre of the cross-section of the exhaust gas passage and an edge flow (22) circulating and advancing around the centre flow. The reactive substance is fed into the centre flow. The flow guide has a first passage part and a second passage part. The first passage part is fitted to form a centre flow from the exhaust gas passing through it in the centre of the exhaust gas passage and the second passage part is fitted to form an edge flow surrounding the centre flow from the exhaust gas passing through it. The first passage part is an inner duct (52) and the second passage part has at least one blade (54) for steering the exhaust gas into a motion circulating the inner duct. The flow guide can comprise several blades, which are placed symmetrically around the inner duct. The flow guide comprises a casing, inside which the inner duct and the blades are placed.