SCR Catalyst Ammonia Surface Coverage Estimation
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Solution Overview
Problem
Current SCR systems face challenges in accurately controlling ammonia storage on selective catalytic reduction (SCR) catalysts, leading to inefficiencies in NOx emission reduction due to slow urea doser dynamics and temperature-dependent ammonia storage assumptions, resulting in ammonia slip or excess NOx emissions during transient engine conditions.
Innovation Solution
The system employs a controller with modules to determine and control ammonia storage modes, using sensors and pre-calibrated tables to adjust reductant dosing based on SCR catalyst temperature and ammonia/NOx ratios, allowing for optimal ammonia surface coverage between 20% and 60% of the catalyst's capacity to manage transient conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If urea dosing is used to generate ammonia in SCR systems, then ammonia is available to reduce NOx emissions, but the slow physical dynamics of the urea doser cause ammonia slip or excess NOx emissions during transient engine conditions
Solution Approach 1:
The system performs preliminary action by storing ammonia on the SCR catalyst surface in advance before transient conditions occur. The control system monitors engine operating conditions and pre-loads the catalyst with ammonia during steady-state operation, so that when transient conditions arise, the stored ammonia is immediately available for NOx reduction without waiting for the slow urea dosing process.
Solution Approach 2:
The invention changes the physical state and location of ammonia storage from liquid urea in a dosing system to adsorbed ammonia on the catalyst surface. This parameter change transforms the system from relying on slow liquid dosing dynamics to utilizing fast surface adsorption/desorption kinetics, enabling rapid response to transient engine conditions.
2Quantity of substance
If SCR catalyst temperature is used to determine ammonia storage capacity, then the control system can manage ammonia storage, but the assumption of fixed storage capacity below a specified temperature leads to significant overestimation or underestimation of ammonia storage capacity
Solution Approach 1:
The invention applies dynamics by transitioning from a static, binary ammonia storage model (full/empty based on fixed temperature thresholds) to a dynamic, continuous model. The new system continuously updates ammonia surface coverage estimates based on real-time catalyst temperature, exhaust gas composition, and flow conditions, allowing the estimated storage capacity to dynamically adapt to changing operating conditions rather than relying on fixed assumptions.
Solution Approach 2:
The system implements feedback by continuously monitoring actual NOx conversion performance and ammonia slip emissions, then using this information to refine the estimated ammonia surface coverage. The control algorithm adjusts its estimates based on the difference between expected and actual system behavior, progressively improving measurement precision through closed-loop feedback from emissions sensors and performance data.
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 enhances NOx conversion efficiency while minimizing ammonia slip and reductant consumption, effectively regulating ammonia storage to maintain optimal conditions across varying engine operations.
Implementation Method 1
the inherent ammonia storage capacity of many SCR catalyst formulations
Implementation Method 2
selective catalytic reduction (SCR) systems, are utilized to convert NOx (NO and NO2 in some fraction) to N2 and other compounds. SCR systems utilize a reductant (e.g., diesel exhaust fluid (DEF), typically ammonia, and an SCR catalyst to convert the NOx
Implementation Method 3
Many systems utilize an alternate compound such as urea, that vaporizes and decomposes to ammonia before entering the SCR catalyst
Implementation Method 4
Many systems utilize an alternate compound such as urea, that vaporizes and decomposes to ammonia before entering the SCR catalyst
Data Source
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AI summary
Described herein are various embodiments of an apparatus, a system, and a method for reducing NOx emissions using ammonia storage on an SCR catalyst (164). For example, according to one embodiment, an apparatus for controlling an SCR system (160) of an internal combustion engine system (100) includes an ammonia storage module (210) and a reductant dosing module (220). The ammonia storage module determines an ammonia storage surface coverage (350) on an SCR catalyst of the SCR system and an ammonia compensation value (240) based on one of an excess ammonia flow rate (330) entering the SCR catalyst and an excess NOx flow rate (335) entering the SCR catalyst. The reductant dosing module generates a reductant dosing command (250) based on the ammonia compensation value.