SCR Sensor Calibration During Engine Overrun Cut-Off
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Solution Overview
Problem
Existing methods for acquiring accurate nitrogen oxide and ammonia values in internal combustion engines with SCR catalytic converters face challenges due to sensor aging and cross-sensitivity issues, leading to inaccuracies in urea injection control.
Innovation Solution
A method that calibrates nitrogen oxide and ammonia sensors during the overrun cut-off phase, combining signals to adjust characteristic curves and account for zero offsets, and uses a urea injection system to manage ammonia drift, ensuring precise measurement of nitrogen oxide and ammonia values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If nitrogen oxide sensors and ammonia sensor are used continuously in normal operation, then measurement data is obtained, but sensor aging effects cause zero offset drift and measurement inaccuracy
Solution Approach 1:
The patent implements periodic calibration during overrun cut-off phases, where the engine operates without fuel injection. During these periodic intervals, the nitrogen oxide sensors and ammonia sensor are calibrated by exposing them to known reference concentrations (zero offset conditions), thereby resetting their baseline measurements and compensating for aging effects without requiring continuous interruption of normal operation.
Solution Approach 2:
The patent performs preliminary calibration of sensor zero offsets during overrun cut-off phases before returning to normal operation. By calibrating the sensors in advance during these natural engine cycles, the system prepares accurate baseline measurements that will be used during subsequent normal operation, ensuring measurement precision without real-time intervention.
2Reliability
If urea injection is increased to reduce nitrogen oxides, then SCR conversion efficiency improves, but ammonia slip increases causing measurement interference and secondary pollution
Solution Approach 1:
The patent employs feedback control by continuously monitoring ammonia concentrations downstream of the SCR catalytic converter using ammonia sensors. When ammonia slip is detected, the control system adjusts urea injection rates to optimize the balance between nitrogen oxide reduction efficiency and ammonia emission control, creating a closed-loop control system that responds to actual operating conditions.
Solution Approach 2:
The patent changes operational parameters by adjusting urea solution concentration and injection timing based on engine load and temperature conditions. During high-load operation, higher urea injection rates are used to maintain SCR efficiency, while during low-load or cold operation, injection rates are reduced to minimize ammonia slip, thereby adapting the system to different operating regimes.
3Measurement precision
If nitrogen oxide sensor is placed downstream of SCR catalytic converter to measure conversion efficiency, then SCR performance monitoring is enabled, but sensor cross-sensitivity to ammonia causes measurement errors
Solution Approach 1:
The patent introduces ammonia sensors as intermediary measurement devices that specifically detect ammonia concentrations downstream of the SCR converter. By using ammonia sensors with selective sensitivity, the system can distinguish between nitrogen oxide signals and ammonia interference, allowing accurate calculation of SCR conversion efficiency by comparing upstream and downstream nitrogen oxide levels while compensating for ammonia presence.
Solution Approach 2:
The patent segments the measurement function by using separate nitrogen oxide sensors upstream and downstream of the SCR converter, combined with dedicated ammonia sensors. This segmentation allows the system to independently measure nitrogen oxide conversion and ammonia slip, then combine these measurements to calculate true SCR efficiency without cross-interference affecting the overall measurement accuracy.
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 reduces sensor aging effects, improves measurement accuracy, and enables effective control of urea injection, enhancing the precision of nitrogen oxide and ammonia value acquisition in internal combustion engines.
Implementation Method 1
a nitrogen oxide sensor arranged downstream of the SCR catalytic converter and designed to generate a nitrogen oxide signal which indicates a nitrogen oxide value
Implementation Method 2
an ammonia sensor arranged downstream of the SCR catalytic converter and designed to generate an ammonia signal which indicates an ammonia value
Implementation Method 3
SCR (selective catalytic reduction) catalytic converters, which are used to reduce nitrogen oxides in the exhaust gases
Implementation Method 4
the nitrogen oxides (NO, NO2) are preferably reduced, while undesired secondary reactions
Implementation Method 5
urea is injected into the exhaust gas upstream of the SCR catalytic converter, which urea subsequently at least partially decomposes into ammonia
Data Source
AI summary
A method for acquiring a corrected nitrogen oxide and/or corrected ammonia value in an internal combustion engine by determining that the engine is in an overrun cut-off phase, interrupting an injection of urea, acquiring a nitrogen oxide reference value from a nitrogen oxide reference signal generated by a nitrogen oxide sensor and acquiring an ammonia reference value from an ammonia reference signal generated by an ammonia sensor, and acquiring a corrected nitrogen oxide value from a nitrogen oxide signal generated by the nitrogen oxide sensor during normal operation of the engine, taking into account the nitrogen oxide reference value, and acquiring a corrected ammonia value from an ammonia signal generated by the ammonia sensor during normal operation of the engine, taking into account the ammonia reference value.