Ammonia Mass Flow Determination Between SCR Converters
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Solution Overview
Problem
In SCR catalytic converter systems, ammonia slip occurs due to reduced storage capacity during load steps, leading to inefficiencies in nitrogen oxide reduction and potential emission limit exceedances, especially when only one ammonia-releasing dosing valve is used upstream of the first SCR catalytic converter.
Innovation Solution
A method to determine the mass flow of ammonia between two SCR catalytic converters using signals from NOx sensors positioned between and downstream of the converters, allowing for the separation of ammonia and nitrogen oxide signals and calculation of ammonia mass flow, which can correct modeled levels and minimize deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a second SCR catalytic converter is added to absorb ammonia slip, then ammonia slip is reduced, but device complexity and cost increase
Solution Approach 1:
The patent introduces a computational intermediary (control unit with algorithms) that processes sensor signals to determine ammonia mass flow. This virtual intermediary enables monitoring and control of ammonia slip without adding physical hardware like a second SCR converter, thus resolving the contradiction between reducing harmful emissions and maintaining system simplicity.
2Ease of manufacture
If only one dosing valve is used, then cost is reduced, but ammonia storage capacity is insufficient during load steps
Solution Approach 1:
The patent implements a feedback mechanism where sensor signals from downstream of the first SCR converter are continuously monitored. The control unit uses this feedback to determine ammonia mass flow and adjust the dosing valve operation in real-time, enabling one dosing valve to effectively manage ammonia storage and delivery during load transitions without requiring additional hardware.
Solution Approach 2:
The system uses the existing downstream sensor signals to self-determine ammonia mass flow and storage status. The control algorithm automatically adjusts dosing based on this self-generated information, eliminating the need for additional dosing valves or sensors while maintaining adequate ammonia storage capacity.
3Ease of operation
If NOx sensor signals are used directly, then measurement is simple, but ammonia and nitrogen oxide signals cannot be distinguished
Solution Approach 1:
The control unit acts as a computational intermediary that receives the combined NOx sensor signal and applies algorithms to separate ammonia and nitrogen oxide components. This virtual separation enables precise ammonia measurement using the existing simple sensor infrastructure, resolving the contradiction between measurement simplicity and precision.
Solution Approach 2:
The patent replaces physical separation methods (which would require complex hardware) with computational signal processing. The control unit uses mathematical algorithms to separate the overlapping sensor signals, substituting mechanical/physical separation with an electronic/computational approach that maintains simplicity while achieving precision.
4Duration of action of moving object
If SCR catalytic converters are installed close to the engine, then warm-up time is reduced, but ammonia storage capacity is compromised at operating temperature
Solution Approach 1:
The patent implements dynamic control of the dosing valve based on real-time sensor feedback and ammonia mass flow determination. The system adapts dosing rates according to changing operating conditions, enabling the first SCR converter to maintain adequate ammonia storage capacity even at operating temperature by precisely controlling when and how much ammonia is introduced, thus compensating for the reduced thermal storage capacity of closely-mounted converters.
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 method enhances the accuracy of ammonia mass flow determination, improving nitrogen oxide reduction efficiency and ensuring compliance with emission limits by accurately accounting for ammonia slip and storage behavior in the SCR catalytic converter system.
Implementation Method 1
the NOx sensor disposed between the two SCR catalytic converters in such SCR catalytic converter systems reacts cross-sensitively to ammonia in any case, and therefore ammonia from an ammonia slip at the first SCR catalytic converter is also measured in addition to the nitrogen oxides that are not reduced in the first SCR catalytic converter
Implementation Method 2
The efficiency of a SCR catalytic converter depends on the temperature thereof, on the space velocity of the exhaust gas and very decisively on the level of the ammonia absorbed at the surface thereof
Implementation Method 3
Selective catalytic reduction (SCR) by means of ammonia or ammonia-releasing reagents represents a promising method for reducing nitrogen oxides in oxygen-rich exhaust gases
Data Source
AI summary
A method for determining a mass flow of ammonia between two SCR catalytic converters disposed one after the other in an SCR catalytic converter system in an exhaust system, which comprises only one reduction agent dosing unit upstream of the first SCR catalytic converter, characterized in that the determination is carried out from the signal of a NOx sensor disposed between the two SCR catalytic converters and the signal of a NOx sensor disposed downstream of the second SCR catalytic converter.