Heated Urea Mixer Control for NOx Reduction Efficiency
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Solution Overview
Problem
Modern diesel engines face challenges in reducing NOx emissions, particularly at low exhaust temperatures where ammonia formation is insufficient, leading to inefficient NOx reduction and potential damage from urea crystallization, resulting in increased toxicity and environmental harm.
Innovation Solution
A controller system is introduced to manage and heat urea mixers using various energy sources, ensuring efficient formation of reductants by regulating the mixer temperature based on real-time engine and emission data, thereby enhancing NOx reduction efficiency and preventing urea crystallization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If urea-water solution is injected into exhaust pipes at low temperatures, then NOx reduction should occur, but urea crystallization occurs and ammonia formation is insufficient
Solution Approach 1:
The system pre-heats the urea-water solution before injection using a heater positioned upstream of the injection point. This preliminary heating action ensures the urea solution reaches a temperature above its crystallization point before entering the exhaust system, preventing crystal formation on injectors and in the exhaust pipe while maintaining readiness for NOx reduction
Solution Approach 2:
A heated carrier gas stream is introduced as an intermediary medium between the urea solution and the cold exhaust environment. The carrier gas, heated to a controlled temperature, transports the urea vapor into the exhaust stream, facilitating ammonia formation without direct contact between cold urea droplets and exhaust components that would cause crystallization
2Reliability
If exhaust temperature is increased to improve ammonia formation, then NOx reduction efficiency improves, but energy consumption increases
Solution Approach 1:
The system dynamically adjusts the heater power and carrier gas temperature based on real-time exhaust temperature measurements and engine operating conditions. By changing these parameters adaptively rather than maintaining constant high temperature, the system achieves sufficient ammonia formation efficiency while minimizing unnecessary energy consumption during transient or high-exhaust-temperature conditions
Solution Approach 2:
The heated carrier gas stream provides continuous thermal energy to the urea solution throughout the injection and vaporization process. This continuous heating action ensures steady ammonia formation without temperature fluctuations that would require additional energy input, maintaining efficient NOx reduction across varying engine loads
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 increases reductant formation and concentration at low temperatures, improving NOx reduction efficiency and preventing urea crystallization, thus reducing emissions and maintaining engine component integrity.
Implementation Method 1
the thermal energy of exhaust gas 4 is transferred to UWS droplets 8, raising the temperature of emerging UWS droplets 8
Implementation Method 2
A controller system is introduced to manage and heat urea mixers using various energy sources
Implementation Method 3
This, in turn, causes water to evaporate from UWS droplets 8
Implementation Method 4
urea to be converted into gaseous ammonia 12 (referred to hereinafter to be understood to also include isocyanic acid - an ammonia precursor)
Implementation Method 5
Reaction of ammonia 12 with noxious NOx species in a downstream SCR catalyst 14 converts the hazardous emissions into benign waste products of water and nitrogen (N2)
Data Source
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AI summary
The present invention discloses methods and devices for controlling a heated mixer, situated downstream of a Urea-Water Solution (UWS) injector, to reduce NOx emission in an exhaust system from combustion engines, wherein the exhaust system has a Selective Catalytic Reduction (SCR) catalyst situated downstream of the UWS injector and the heated mixer, Methods include: determining a NOx reduction efficiency of the SCR catalyst; evaluating at least one reductant Uniformity Index (UI) based on operating parameters of the exhaust system and a mixer power calculation map; and modifying a mixer temperature of the heated mixer by regulating power to the heated mixer based on at least one reductant UI in order to improve at least one reductant UI and/or improve the NOx reduction efficiency. Alternatively, the method further includes: detecting at least one potential improvement of at least one UI and/or the NOx reduction efficiency based on an increased ammonia mass.