NH3 Storage Correction in Selective Catalytic Reduction Systems
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Solution Overview
Problem
Existing selective reduction catalyst (SCR) systems face challenges in accurately estimating the amount of ammonia (NH3) stored, leading to inefficiencies in NOx reduction due to potential NH3 slip, where either insufficient or excessive NH3 can result in undesired emissions, making it difficult to optimize NH3 injection in vehicle exhaust systems.
Innovation Solution
A method is developed to correct the estimated amount of NH3 stored in the SCR using an observer system that adjusts based on indications of NH3 slip and SCR efficiency, utilizing NOx sensors positioned upstream and downstream of the SCR to optimize NH3 injection timing and quantity, thereby improving conversion efficiency and reducing emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the estimated amount of NH3 stored within the SCR is used for control actions, then NH3 injection can be adjusted, but the control actions may not perform as desired if the estimated amount deviates from the actual amount by more than a threshold amount
Solution Approach 1:
The patent implements a feedback mechanism where the estimated NH3 storage amount is continuously corrected based on actual NH3 slip measurements from sensors. The controller compares the estimated storage with actual slip conditions and adjusts future injection commands accordingly, creating a closed-loop system that improves estimation accuracy over time and ensures reliable control performance.
Solution Approach 2:
The patent replaces direct physical measurement of NH3 storage (which would require complex sensors capable of measuring ammonia concentration within the catalyst) with an estimation model that uses readily available NOx sensor data and injection commands. This substitution of measurement methodology enables accurate storage estimation without requiring specialized sensing hardware.
2Productivity
If insufficient amount of NH3 is present at the SCR, then NOx reduction efficiency decreases, but if excess NH3 is directed to the SCR, then NH3 may slip past the SCR
Solution Approach 1:
The system uses feedback from NH3 slip sensors downstream of the SCR to continuously adjust the estimated NH3 storage amount. When NH3 slip is detected, the estimator is corrected to reflect higher actual storage levels, which subsequently reduces the injection commands sent to the dosing device, thereby preventing excessive NH3 slip while maintaining adequate NOx reduction.
Solution Approach 2:
The patent dynamically changes the estimated NH3 storage parameter based on operating conditions and slip measurements. By adjusting the storage estimate in response to varying conditions (temperature, load, slip levels), the system optimizes the balance between maintaining sufficient NH3 for NOx reduction and preventing excess NH3 slip, effectively adapting to changing operational requirements.
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 enhances SCR conversion efficiency by optimizing NH3 injection, minimizing NH3 and NOx slip, reducing the frequency of refilling NH3 supplies, and lowering emissions by ensuring precise NH3 levels within the SCR, thus improving overall engine performance and environmental impact.
Implementation Method 1
Nitrogen oxides (e.g., NOx) contained in engine exhaust gases may be treated via a selective reduction catalyst (SCR) in the vehicle's exhaust system to form N2 and H2O. The SCR may co-operate with a reductant such as ammonia (NH3) to reduce the NOx.
Data Source
AI summary
A method for correcting an estimated amount of NH3 store within a SCR is described. In one example, SCR efficiency is determined from a NOx sensor output and the estimated amount of NH3 is corrected based on the SCR efficiency. Engine emissions may be reduced via improving the estimated NH3 storage level, at least during some conditions.