SCR Injection Sleeve Thermal Decoupling
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Solution Overview
Problem
Existing SCR injection devices face challenges in maintaining the injector at a low temperature during operation due to direct contact with hot exhaust gas and heat conduction from the exhaust pipe, leading to aging of the reducing agent and potential corrosion, which affects the robustness and dosing accuracy.
Innovation Solution
The SCR injection device employs a thin-walled sleeve element with a high length-to-thickness ratio as a heat flow restrictor and a non-positive connection to the holding structure, combined with thermal insulation and a heat-conducting body, to minimize heat conduction from the exhaust pipe to the injector, thereby preventing overheating and ensuring robust construction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the injector is positioned close to the hot exhaust pipe for optimal reducing agent introduction, then the dosing accuracy is improved, but the injector temperature increases leading to reducing agent aging and corrosion
Solution Approach 1:
A sleeve element is introduced as an intermediary component between the exhaust pipe and the injector. This sleeve has a thin-walled connecting section with high length-to-thickness ratio that acts as a heat flow restrictor, thermally decoupling the injector from the hot exhaust pipe while maintaining close positioning for optimal dosing accuracy
Solution Approach 2:
The sleeve element is segmented into distinct functional sections: a shield section facing the exhaust pipe for thermal protection, a thin-walled connecting section for heat restriction, and a holding structure for injector mounting. This segmentation allows each section to optimize its specific function while working together to resolve the temperature-dosing accuracy contradiction
2Measurement precision
If the injector is positioned close to the hot exhaust pipe, then the dosing accuracy is improved, but the robustness of the injector decreases due to temperature stress
Solution Approach 1:
The sleeve element serves as a thermal intermediary that protects the injector from direct heat exposure. By positioning the injector close to the exhaust pipe through this thermal barrier, the system achieves both high dosing accuracy and improved injector robustness against temperature stress and corrosion
Solution Approach 2:
The sleeve element provides beforehand thermal cushioning to the injector by absorbing and restricting heat flow from the exhaust pipe. This protective barrier is in place before the injector is exposed to thermal stress, preventing reducing agent aging and maintaining injector robustness
3Temperature
If thermal insulation is added between the exhaust pipe and injector, then the injector temperature is reduced, but the device complexity increases
Solution Approach 1:
The sleeve element merges multiple functions into a single component: it provides thermal insulation through its thin-walled connecting section, mechanically holds the injector via the holding structure, and shields the injector from direct exhaust gas contact. This integration reduces device complexity compared to separate insulation components while achieving effective temperature reduction
4Ease of manufacture
If a metal sleeve element is used instead of ceramic, then the manufacturing cost is reduced and service life is improved, but the heat conduction increases
Solution Approach 1:
The metal sleeve element incorporates local quality variations through its different sections: the thin-walled connecting section has high length-to-thickness ratio for heat restriction, while the shield section provides structural protection. This local differentiation allows the use of cost-effective metal material while maintaining low heat conduction to the injector through the optimized connecting section geometry
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 effectively reduces the aging of the reducing agent, enhances the injector's temperature robustness, and prevents boiling, ensuring accurate dosing without the need for active cooling systems, while maintaining a simple and cost-effective manufacturing process.
Implementation Method 1
the conduction of heat across the sleeve element is reduced by virtue of the fact that this has an elongated, thin-walled connecting section which forms a kind of 'heat flow restrictor' and through which the heat has to flow
Implementation Method 2
The flow of heat across the sleeve element to the heat sink is further reduced if thermal insulation is arranged between the heat sink and the connecting section
Data Source
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AI summary
An SCR-injection unit (18) comprises an injector (30), a sleeve element (20) for fixing the injector (30) to a flange (16) of an exhaust gas pipe (12), and a cooling body (64). According to the invention, the sleeve element (20) has an elongated thin-walled connecting section (34), one axial end of which is non-positively connected to the flange (16) of the exhaust gas pipe (12) and the other axial end of which is non-positively connected to a supporting structure (36) for the injector (30).