Segmented Heated Urea Mixer for Low-Temperature SCR
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Solution Overview
Problem
At lower exhaust gas temperatures, the decomposition of aqueous urea to form ammonia for NOx reduction in diesel engines is inefficient, leading to poor NOx conversion rates and urea deposit formation in the exhaust system.
Innovation Solution
A segmented, heated urea mixer system is introduced, where elements within the exhaust gas flowpath can be independently heated by an external power source to optimize the catalytic reduction of NOx to nitrogen and water, using a controller to manage temperature based on sensor inputs and improve reductant uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If aqueous urea is injected into the exhaust gas stream for catalytic reduction of NOx, then NOx conversion is enabled, but the decomposition reaction does not take place at an appreciable rate at lower temperatures
Solution Approach 1:
The exhaust system is segmented into multiple zones with different temperature characteristics. The first exhaust system portion is heated to a first temperature to promote urea decomposition, while the second exhaust system portion operates at a lower second temperature for SCR catalysis. This segmentation allows each zone to operate at optimal temperatures for its specific function.
Solution Approach 2:
The first exhaust system portion performs preliminary heating and urea decomposition before the exhaust enters the second portion for SCR catalysis. This preliminary action ensures that ammonia and other reaction products are formed in advance, making the subsequent catalytic reduction more efficient at lower temperatures.
2Loss of energy
If urea decomposition is performed at lower temperatures, then energy consumption is reduced, but urea deposit formation occurs in the exhaust system
Solution Approach 1:
The exhaust system is divided into a first portion dedicated to heating and urea decomposition, and a second portion for SCR catalysis. By isolating the decomposition process in a separate heated zone, the system prevents urea deposits from forming in the cooler SCR catalyst area while still operating at lower overall temperatures.
Solution Approach 2:
Different portions of the exhaust system are maintained at different temperatures tailored to their specific functions. The first portion has elevated temperature to prevent urea deposition and promote decomposition, while the second portion operates at lower temperature for efficient SCR catalysis without deposit formation.
3Device complexity
If a single heated zone is used for both urea decomposition and SCR catalysis, then device complexity is reduced, but temperature control precision is insufficient for optimal performance
Solution Approach 1:
The exhaust system is segmented into functionally distinct first and second portions, each with independent temperature control. This allows precise control of temperature in the decomposition zone to optimize urea conversion, while separately controlling the SCR catalyst zone temperature for optimal catalytic performance.
Solution Approach 2:
Each exhaust system portion is designed with specific thermal characteristics optimized for its function. The first portion has higher temperature and different thermal management than the second portion, allowing each to operate at optimal conditions for its specific process while maintaining overall system efficiency.
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 solution enhances NOx reduction efficiency and prevents urea deposit formation by ensuring sufficient ammonia formation even at low temperatures, maintaining optimal SCR catalyst performance and reducing emissions.
Implementation Method 1
at least one of the elements being heatable by an external power source independent of another of the plurality of elements
Implementation Method 2
direct power from the external power source to at least one of the elements to increase or decrease a temperature of the one or more elements
Implementation Method 3
catalytic reduction of the NO by an SCR catalyst to form nitrogen and water
Implementation Method 4
which thermally decomposes to form ammonia, ammonia precursors, and carbon dioxide
Data Source
AI summary
A segmented, heated urea mixer and an exhaust system to control NOx emission from combustion engines comprising a plurality of elements, at least one element independently heatable by an external power source to a temperature above a temperature of another element. A method of using the exhaust gas mixer and an exhaust gas mixer system further comprising a controller is also disclosed.