SCR Dosing Control Using Weighing Factor for NOx Reduction
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Solution Overview
Problem
Selective catalyst reduction (SCR) devices face challenges in accurately reducing NOx emissions due to cross-sensitivity of sensors, leading to false positive feedback and excessive reductant introduction, resulting in unstable systems and waste.
Innovation Solution
A dosing control system that generates a resulting dosing command using a weighing factor applied to both lower and upper limit dosing commands, where the lower limit is based on emission requirements and the upper limit is constrained by maximum allowed NH3 slip, to optimize NOx reduction while minimizing reductant introduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback control is used to detect NOx and introduce reductant, then NOx reduction performance is improved, but false positive feedback occurs due to NH3 slip being read as NOx by the sensor
Solution Approach 1:
The patent introduces an intermediary calculation approach that separates the measurement of NOx from the direct sensor reading. By calculating the required reductant dose based on the difference between target and actual NOx levels, and using this to determine NH3 slip, the system creates an intermediary layer that filters out false positives from direct sensor readings while maintaining control accuracy.
Solution Approach 2:
The patent implements feedback control by continuously monitoring NOx levels and adjusting reductant dosing accordingly. The feedback loop uses the measured NOx concentration, compares it to target levels, and modifies the reductant dose to achieve the desired NOx reduction while compensating for NH3 slip effects.
2Reliability
If reductant dosing is increased to meet deNOx targets, then NOx reduction is improved, but reductant waste increases and system stability decreases
Solution Approach 1:
The patent dynamically adjusts the reductant dosing parameter based on real-time NOx measurements and calculated NH3 slip levels. By changing the dosing rate according to actual system conditions rather than using fixed high doses, the system achieves effective NOx reduction while minimizing reductant waste and maintaining stability.
Solution Approach 2:
The patent applies partial action by introducing reductant at optimized rates that are sufficient to meet NOx reduction targets but not excessive. The control algorithm calculates the minimum necessary reductant dose based on measured NOx levels and target reductions, avoiding both under-dosing and excessive dosing that would cause waste.
3Ease of manufacture
If electrochemical sensors are used to keep costs down, then system cost is reduced, but cross-sensitivity to NH3 causes false positive readings
Solution Approach 1:
The patent creates an intermediary calculation layer that compensates for the sensor's cross-sensitivity characteristic. By calculating NH3 slip separately and using it to adjust the NOx measurement interpretation, the system works around the sensor's limitation rather than trying to eliminate it, maintaining cost-effectiveness while improving accuracy.
Solution Approach 2:
The patent modifies the parameter interpretation by adjusting the NOx measurement based on calculated NH3 slip levels. The system changes how the sensor data is processed and interpreted, compensating for cross-sensitivity effects through parameter adjustment rather than requiring a more expensive sensor.
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 stabilizes the system by optimizing NOx reduction and reducing reductant waste, ensuring compliance with EPA dosing requirements while maintaining dosing economy and avoiding system instability.
Implementation Method 1
The introduced reductant reacts with the NOx to facilitate its reduction
Implementation Method 2
selective catalyst reduction (SCR) devices are used to introduce a reductant which reduces NOx generated in engine exhaust systems
Data Source
AI summary
An apparatus for introducing a reductant into an exhaust system is described. The apparatus includes a controller that generates a resulting dosing command used as an instruction to release an amount of reductant into the exhaust system. The controller includes a feedback control module that generates a weighing factor. The weighing factor is configured to be applied to a lower limit dosing command and configured to be applied to an upper limit dosing command, where the lower and upper limit dosing commands converted by the weighing factor are used by the controller to generate the resulting dosing command.