Virtual Ammonia Sensor for SCR Catalyst Control
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Solution Overview
Problem
Existing methods for determining the optimal amount of reducing agent to supply to an exhaust gas system, such as ammonia for NOx reduction in vehicle engines, are prone to inaccuracies due to hardware malfunctions and deviations, leading to increased NOx emissions and additional costs from using additional sensors.
Innovation Solution
A method utilizing relative magnitude-frequency analysis of NOx measurements downstream of a catalytic device to determine the reducing agent supply, eliminating the need for a physical ammonia sensor by using existing tail pipe NOx sensors and adjusting dosing based on calculated thresholds, thereby maintaining optimal ammonia levels and reducing emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an ammonia sensor is introduced to detect reducing agent supply level, then detection accuracy is improved, but system cost and complexity increase
Solution Approach 1:
The patent creates a virtual ammonia sensor by using the existing NOx sensor downstream of the SCR catalyst. Instead of installing a physical ammonia sensor, the system calculates ammonia storage level by copying and analyzing the NOx measurement data, thereby achieving ammonia detection functionality without additional hardware
Solution Approach 2:
The existing NOx sensor serves dual purposes: its primary function of monitoring NOx emissions and a secondary function of indirectly detecting ammonia storage level. The system makes the NOx sensor work for itself by utilizing its data to monitor ammonia supply, eliminating the need for dedicated ammonia sensing hardware
2Reliability
If an ammonia sensor is introduced to detect reducing agent supply level, then detection accuracy is improved, but warranty risks and part failure modes increase
Solution Approach 1:
By creating a virtual sensor that copies and processes existing NOx sensor data, the patent eliminates the physical ammonia sensor component that would be subject to failure. The virtual sensor exists as software logic rather than hardware, removing the associated failure modes and warranty risks
Solution Approach 2:
The patent uses NOx measurements as an intermediary to indirectly assess ammonia storage level. Instead of directly measuring ammonia (which requires a fragile sensor), the system measures NOx as a proxy, using it as a mediator to infer ammonia supply status without exposing the system to additional component failures
3Ease of operation
If absolute magnitude-frequency analysis is used to determine ammonia supply, then measurement simplicity is improved, but detection resolution deteriorates
Solution Approach 1:
Instead of analyzing the absolute magnitude of NOx signals, the patent inverts the approach by analyzing the relative magnitude-frequency characteristics. The system compares the frequency distribution of NOx measurements against expected patterns, thereby detecting ammonia supply issues through relative rather than absolute signal properties
Solution Approach 2:
The patent transitions from static absolute magnitude analysis to dynamic frequency-based analysis. By examining how NOx signal magnitudes vary in frequency over time, the system captures the dynamic behavior of the SCR catalyst, enabling higher detection resolution for ammonia supply status
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 provides a reliable and cost-effective means to detect ammonia insufficiency, adjust dosing, and maintain low NOx emissions, avoiding hardware-related issues and warranty risks while ensuring compliance with emissions regulations.
Implementation Method 1
The aftertreatment system or exhaust gas system usually includes a catalytic device such as a selective catalytic reduction (SCR) catalyst which is adapted to reduce the engine emitted pollutant NOx. In such an SCR catalyst nitrogen oxides react with a reducing medium in the form of ammonia (NH3) in a selective catalytic reduction reaction.
Implementation Method 2
One way to obtain the amount of ammonia to be supplied to the exhaust gas is to use an ammonia sensor.
Data Source
AI summary
A method for operating an exhaust gas system is provided. The method includes determining an amount of a reducing agent to be supplied to the exhaust gas of an engine and evaluating measurements which indicate a content of nitrogen oxides in the exhaust gas downstream of a catalytic device adapted to diminish the content of nitrogen oxides. A magnitude and a frequency of the measurements are taken into account in determining the amount of the reducing agent to be supplied. A plurality of measurements is captured during a predetermined period of time. A magnitude of a measurement captured within this period of time is related to a quantity derived from the respective magnitudes of the plurality of measurements. The related measurement is utilized to determine the amount of the reducing agent to be supplied. A control assembly for operating an exhaust gas system is also provided.