Adapting Reductant Amount for SCR NOx Control
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Solution Overview
Problem
Existing selective catalytic reduction systems for nitrogen oxides in vehicle exhausts face inefficiencies due to sensor dispersions and misinterpretation of ammonia and nitrogen oxides, leading to inadequate treatment and potential 'runaway' scenarios where excess ammonia is released.
Innovation Solution
A process that aligns and corrects the measurements of upstream and downstream nitrogen oxide sensors, adjusts the reducing agent injection based on these alignments, and accounts for system dispersions and catalyst aging to optimize NOx treatment efficiency, minimizing ammonia slip and ensuring accurate pollutant removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a selective catalytic reduction system is used to remove nitrogen oxides, then NOx treatment efficiency is improved, but sensor dispersions and misinterpretation of ammonia and nitrogen oxides lead to inadequate treatment and potential runaway scenarios
Solution Approach 1:
The patent segments the measurement and control process into distinct phases: a first alignment phase without reducing agent injection to establish baseline sensor readings, and a second alignment phase with substoichiometric injection to calibrate the control model. This segmentation allows each sensor to be calibrated independently under controlled conditions, resolving the contradiction by improving measurement precision through systematic calibration while maintaining NOx treatment efficiency.
Solution Approach 2:
The patent applies preliminary action by performing sensor alignment and calibration before normal operation. The first alignment of sensors is conducted without reducing agent injection to establish accurate baseline measurements, and the control model is pre-calibrated with alignment factors. This preliminary calibration prevents runaway scenarios and ensures reliable NOx treatment from the start of operation.
2Reliability
If the amount of reducing agent is increased to ensure complete NOx removal, then NOx treatment efficiency is improved, but excess ammonia is released into the environment
Solution Approach 1:
The patent implements feedback control by continuously monitoring downstream NOx levels with aligned sensors and adjusting the reducing agent injection amount accordingly. The control model, calibrated through the alignment process, provides accurate feedback on actual NOx removal efficiency, allowing the system to maintain complete NOx removal while minimizing excess ammonia injection and preventing ammonia slip.
Solution Approach 2:
The patent changes the operational parameters by introducing alignment factors that adjust the relationship between injected reducing agent amount and expected NOx removal. The substoichiometric injection approach during second alignment modifies the injection parameter to calibrate the system without creating excessive ammonia, and these calibrated parameters are then used in normal operation to balance NOx removal with ammonia emission control.
3Device complexity
If a nominal control with predetermined reducing agent amount is used, then system simplicity is maintained, but deviations from actual vehicle conditions lead to suboptimal performance
Solution Approach 1:
The patent applies preliminary action by pre-calibrating the control model with alignment factors during system installation or initial operation. This preliminary calibration adapts the nominal control parameters to the specific vehicle and sensor characteristics without requiring complex real-time adaptive control algorithms, thus maintaining system simplicity while improving reliability for the specific application.
Solution Approach 2:
The patent changes the control parameters by introducing vehicle-specific alignment factors that modify the nominal reducing agent injection amounts. These parameter adjustments account for deviations in sensor characteristics, exhaust flow rates, and catalytic converter performance for each specific vehicle, allowing the simple nominal control system to achieve optimal NOx treatment performance for the actual vehicle conditions.
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 process effectively corrects sensor dispersions and system inefficiencies, reducing ammonia slip and optimizing NOx treatment, thereby enhancing the overall efficiency and reliability of the selective catalytic reduction system.
Implementation Method 1
a selective catalytic reduction system having injection of reducing agent into the line
Implementation Method 2
The NH3 is stored in an SCR catalyst in order to reduce the NOx that are in the gases discharged by the exhaust line
Implementation Method 3
The liquid reducing agent decomposes to give gaseous ammonia, of chemical formula NH3
Data Source
AI summary
In a process for adapting an amount of reducing agent for a removal of nitrogen oxides from the gases in an exhaust line, a first alignment of the amounts of nitrogen oxides measured by upstream and downstream sensors is performed without injection of agent and with a catalyst of the system emptied of ammonia. A second alignment of the estimated reduction of nitrogen oxides with the measured reduction is performed by a difference between amounts of nitrogen oxides upstream and downstream during a substoichiometric injection of reducing agent without creating a store of ammonia in a catalyst of the system with a first correction of the amount of agent. A third alignment of an estimated efficiency of retaining nitrogen oxides with a efficiency measured by the sensors is performed, this third alignment taking place via a second correction of the amount of reducing agent injected as an adaptive correction.