NOx Trap Ammonia Estimation via Mode-Specific Sensor Processing
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Solution Overview
Problem
Current NOx trap systems in internal combustion engines face challenges in accurately estimating nitrogen oxides (NOx) and ammonia (NH3) concentrations downstream, leading to overestimation of NOx levels and excessive ammonia emissions, which can violate strict emission standards and affect engine performance.
Innovation Solution
A method that uses engine operating mode-specific data processing by two sets of sensors to differentiate between nitrogen monoxide (NO) and nitrogen dioxide (NO2) and accurately estimate ammonia (NH3) levels, ensuring compliance with emission standards by adjusting ammonia dosage accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a downstream NOx sensor is used to measure nitrogen oxide concentration, then the treatment efficiency of the NOx trap can be monitored, but the sensor cannot distinguish between nitrogen oxides and ammonia, leading to overestimation of NOx levels
Solution Approach 1:
The measurement process is segmented into two distinct paths: a first processing path for rich operating mode that detects ammonia and subtracts its contribution, and a second processing path for lean operating mode that directly measures NOx. This segmentation allows the system to account for ammonia interference in rich mode while maintaining simple NOx measurement in lean mode.
Solution Approach 2:
The system changes the operating parameter (air-fuel ratio) between rich and lean modes, and accordingly changes the processing method applied to sensor data. In rich mode, ammonia detection and subtraction is applied; in lean mode, direct NOx measurement is used. This parameter-based approach allows accurate NOx estimation under varying engine conditions.
2Reliability
If the NOx trap is purged using rich air-fuel mixture to restore storage capacity, then nitrogen oxides stored in the trap are transformed into harmless molecules, but ammonia is produced as a byproduct which increases overall emissions
Solution Approach 1:
The system continuously monitors exhaust composition and uses this feedback to adjust the purging strategy. When ammonia buildup is detected during or after purging, the system can modify subsequent purging duration, frequency, or intensity to prevent excessive ammonia emissions while maintaining adequate NOx trap regeneration.
Solution Approach 2:
The NOx trap operates in periodic cycles of lean storage mode followed by rich purging mode. The system optimizes the duration and frequency of these periodic rich-mode purging events to balance NOx trap regeneration with ammonia emission control, preventing continuous purging that would generate excessive ammonia.
3Measurement precision
If the NOx sensor interprets ammonia as nitrogen oxides, then the overall amount of NOx is overestimated at the outlet, but this leads to excessive AdBlue injection which produces more ammonia
Solution Approach 1:
An intermediary computational process is introduced between the sensor measurement and the AdBlue injection control. This intermediary subtracts the ammonia contribution (detected during rich mode) from the total nitrogen species measurement, providing a corrected NOx value that accurately reflects actual nitrogen oxide levels and prevents excessive AdBlue injection.
Solution Approach 2:
The system performs preliminary ammonia detection and quantification during rich operating mode before returning to lean operation. This preliminary action allows the system to know the ammonia baseline and subtract it from subsequent measurements, preventing overestimation of NOx and subsequent excessive AdBlue injection.
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 precise estimation of NOx and NH3 concentrations, maintaining ammonia levels below regulatory limits, thereby ensuring effective treatment and compliance with emission standards while optimizing the use of reducing agents.
Implementation Method 1
a downstream NOx sensor placed downstream of the NOx trap to measure the concentration of nitrogen oxides (NOx)
Implementation Method 2
the NOx trap stores a portion of the NOx emitted by the engine with a certain efficiency
Implementation Method 3
reducing agents are introduced in the form of engine fuel into the exhaust gases to transform the nitrogen oxides (NOx) stored in the NOx trap into harmless molecules, notably nitrogen (N2) and water (H2O)
Implementation Method 4
SCR catalysts continuously reduce NOx by injecting a urea-based compound that is a precursor to ammonia (NH3)
Data Source
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AI summary
The invention relates to a method for estimating the quantity of nitrogen oxides and/or ammonia at the outlet of a NOx trap located in the exhaust line of an internal combustion engine. The method comprises: - a step of obtaining (E100) information on the richness of the air-fuel mixture; - a step of identifying (E200) the operating mode of the engine; - a first processing step (E300) of the data acquired by a first set of sensors if the engine is operating with a rich air-fuel mixture; or - a second processing step (E400) of the data acquired by a second set of sensors, if the engine is operating with a lean air-fuel mixture; - at the end of the first step (E300) or the second step (E400), an adjustment step (E500) of the quantity of ammonia, NH3, so that the quantity of ammonia, NH3, remains below a predefined limit threshold.