Virtual Ammonia Sensor for SCR Exhaust Systems
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Solution Overview
Problem
Current SCR systems for nitrogen oxide reduction in vehicle exhausts face challenges in discriminating between residual nitrogen oxides and ammonia slips, leading to inefficient urea usage and increased ammonia emissions due to lack of specific ammonia concentration sensors and high computational burdens.
Innovation Solution
A method utilizing existing nitrogen-oxide sensors to create a 'virtual ammonia sensor' through defining a reference function and processing it using Fourier transform and frequency filtering, allowing discrimination between nitrogen oxides and ammonia without additional sensors or excessive computational operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a specific ammonia-concentration sensor is installed downstream of the SCR system, then ammonia slips can be directly detected and discriminated from nitrogen oxides, but the device complexity and cost increase significantly
Solution Approach 1:
The patent creates a virtual ammonia sensor by processing the output signal of an existing nitrogen oxide sensor through Fourier transform and frequency filtering. This virtual sensor copies the detection function for ammonia without requiring physical ammonia sensors, thereby maintaining measurement precision while avoiding the complexity and cost of additional hardware sensors.
Solution Approach 2:
The patent replaces the need for physical ammonia concentration sensors with a signal processing system. By substituting mechanical/sensor-based detection with computational methods (Fourier transform and frequency filtering), the system achieves ammonia detection capability without the complexity of additional sensor hardware.
2Measurement precision
If complex signal processing methods are used to discriminate ammonia from nitrogen oxides, then discrimination accuracy improves, but computational burden increases excessively
Solution Approach 1:
The patent extracts the ammonia signal component from the mixed sensor output by identifying and removing the characteristic low-frequency harmonics associated with ammonia slips. This extraction approach achieves discrimination accuracy by isolating the relevant signal component without requiring excessively complex computational processing of the entire signal spectrum.
Solution Approach 2:
The patent changes the parameter domain from time-domain signal analysis to frequency-domain analysis using Fourier transform. This parameter transformation enables effective discrimination of ammonia from nitrogen oxides by exploiting frequency characteristics, achieving high accuracy while maintaining computational efficiency through targeted frequency filtering rather than complex full-signal processing.
3Reliability
If the nitrogen oxide sensor detects high concentrations without ammonia discrimination, then the system responds by increasing urea injection, but this leads to increased ammonia slips due to system saturation
Solution Approach 1:
The patent implements a feedback mechanism where the virtual ammonia sensor continuously monitors ammonia slips and provides real-time information to the control system. This feedback enables the system to adjust urea injection rates dynamically, preventing over-injection that would cause ammonia saturation and emissions, thereby maintaining reliable nitrogen oxide abatement while minimizing harmful ammonia releases.
Solution Approach 2:
The patent applies preliminary anti-action by detecting ammonia slips before they lead to system saturation and excessive emissions. The virtual sensor provides advance warning of ammonia accumulation, allowing the control system to preemptively reduce urea injection and prevent the harmful effect of ammonia oversaturation and subsequent emissions.
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
Effectively identifies ammonia slips and adjusts urea injection to improve nitrogen oxide reduction efficiency, reducing ammonia emissions and preventing system saturation, while avoiding computational overloads and the need for additional sensors.
Implementation Method 1
a first selective-catalytic-reduction element, the SCRoF, in an over-floor position (typically in the engine compartment of the vehicle), and a second selective-catalytic-reduction element, the SCRuF, in an under-floor position
Implementation Method 2
defining a reference function and processing it using Fourier transform and frequency filtering
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
Described herein is a method for detecting the occurrence of ammonia slips downstream of an exhaust-gas after-treatment line comprising at least one selective-catalytic-reduction nitrogen-oxide treatment element (SCRoF, SCRuF), which uses urea, wherein the after-treatment line comprises a first sensor (S1) upstream of said at least one selective-catalytic-reduction nitrogen-oxide treatment element (SCRoF, SCRuF), and a second sensor (S2) downstream of said at least one selective-catalytic-reduction nitrogen-oxide treatment element (SCRoF, SCRuF). The method enables processing of the temporal signal associated to a reference function so as to identify the occurrence of ammonia slips, and estimate the amount thereof, without carrying out computationally burdensome transform operations.