Exhaust NOx Sensor Signal Separation for Ammonia and Nitrogen Oxide Quantification
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Solution Overview
Problem
Current exhaust gas sensors in gasoline engines are unable to accurately distinguish between ammonia and nitrogen oxide emissions, especially under varying oxygen levels and catalyst core temperatures, which is problematic for meeting stringent Euro 7 emissions standards.
Innovation Solution
A method that involves modeling ammonia and nitrogen oxide emissions using specific models and a separation algorithm, which processes the signal from an exhaust NOx sensor to separate and quantify tailpipe ammonia and NOx emissions, taking into account catalyst temperature, air-fuel ratio, and engine parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a nitrogen oxide sensor is used to monitor exhaust emissions, then nitrogen oxide emissions can be detected, but the sensor also detects ammonia due to cross-sensitivity, making it difficult to distinguish between the two emissions
Solution Approach 1:
The sensor signal is segmented into separate ammonia and nitrogen oxide components through a separation algorithm. The total sensor signal S_total is divided into S_NH3 (ammonia component) and S_NOx (nitrogen oxide component) based on stoichiometric relationships and oxygen content measurements, allowing distinct quantification of each emission type despite cross-sensitivity
Solution Approach 2:
An oxygen sensor (lambda sensor) is introduced as an intermediary measurement device to provide additional information about the exhaust gas composition. This intermediary measurement enables the separation algorithm to distinguish between ammonia and nitrogen oxide signals by detecting oxygen content variations that correlate with different emission scenarios
2Ease of operation
If a simple interpretation model based on oxygen content is used, then ammonia and nitrogen oxide signals can be separated, but cold start conditions and other influencing factors are not taken into account
Solution Approach 1:
The system performs preliminary detection and identification of cold start conditions through the control device before applying the separation algorithm. During cold start phases, the system recognizes that aftertreatment components are not yet effective and adjusts the evaluation accordingly, ensuring reliable emission monitoring from the outset rather than relying on post-processing corrections
Solution Approach 2:
The evaluation model transitions from a static simple interpretation to a dynamic adaptive system. The control device continuously monitors multiple parameters including oxygen content, engine operating conditions, and catalyst temperature, adjusting the separation algorithm's behavior based on current operational state to maintain reliability across varying conditions
3Device complexity
If the exhaust gas aftertreatment components are not yet effective during cold start, then emissions cannot be properly monitored, but the simple model does not account for this limitation
Solution Approach 1:
The system performs preliminary detection and identification of cold start conditions through the control device before applying the separation algorithm. During cold start phases, the system recognizes that aftertreatment components are not yet effective and adjusts the evaluation accordingly, ensuring reliable emission monitoring from the outset rather than relying on post-processing corrections
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 allows for precise monitoring and separation of ammonia and nitrogen oxide emissions, enabling effective compliance with future emissions standards and improving the accuracy of exhaust gas aftertreatment system performance.
Implementation Method 1
sensors for detecting nitrogen oxides, with which systems for the selective, catalytic reduction of nitrogen oxides are controlled or regulated, are known in particular from the exhaust aftertreatment of diesel engines. However, such nitrogen oxide sensors have a cross sensitivity to ammonia, so that a nitrogen oxide sensor installed in the exhaust system detects both ammonia and nitrogen oxides.
Implementation Method 2
In gasoline engines, exhaust gas purification takes place in a known manner via a three-way catalytic converter
Data Source
AI summary
A method for evaluating a sensor signal of an exhaust NOx sensor, which is disposed downstream of a three-way catalytic converter in an exhaust system of a spark ignition internal combustion engine. An ammonia factor is modeled downstream of the three-way catalytic converter using an ammonia formation model. A NOx emission is modeled in the exhaust system downstream of the three-way catalytic converter using a NOx model. The modeled ammonia emissions and the modeled NOx emission are separated by a separation algorithm using the sensor signal of the exhaust NOx sensor. The separation algorithm provides quantitative information about the tailpipe ammonia emissions and the tailpipe NOx emissions of the spark ignition internal combustion engine. An engine control unit and an internal combustion engine for carrying out such a method are also provided.