SCR Catalyst Control System for NOx Conversion and Ammonia Slip Management
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Solution Overview
Problem
Existing SCR catalyst control systems face challenges in managing nitrogen oxide emissions in passenger cars under transient conditions, particularly due to the lack of effective buffering capacity in vanadium-based catalysts and the complexity of modeling chemical reactions, which requires high calibration efforts and is sensitive to ammonia slip.
Innovation Solution
A control system that determines the required urea quantity based on the differential between target and stored ammonia in the SCR catalyst, using a model that accounts for NOx engine emission values, catalyst temperature, and physical characteristics, with closed-loop adjustments to manage ammonia slip and NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a chemical model of the SCR catalyst is implemented in the ECU to accurately control NOx conversion, then NOx conversion efficiency is improved, but the calibration work and calculation load become very high
Solution Approach 1:
The patent extracts only the essential parameters needed for SCR control (stored NH3 amount, catalyst temperature, NOx conversion efficiency) from the complete chemical model, implementing a simplified control strategy that achieves effective NOx conversion without requiring full chemical reaction modeling
Solution Approach 2:
The patent changes the control parameters from complex chemical reaction rates to simplified state variables (stored NH3 amount, catalyst temperature, conversion efficiency), making the control system more manageable while maintaining effectiveness
2Measurement precision
If multiple complex chemical reactions are modeled in slices along the catalyst length to obtain accurate SCR behavior, then measurement precision is improved, but the calculation load increases significantly
Solution Approach 1:
The patent extracts the essential behavior of the catalyst (NH3 storage and NOx conversion) without modeling every chemical reaction in detail, achieving sufficient accuracy with reduced computational requirements
Solution Approach 2:
The patent uses a partial model approach, capturing only the critical aspects of catalyst behavior (stored NH3, temperature, conversion efficiency) rather than modeling all chemical reactions, providing adequate control precision with lower calculation load
3Measurement precision
If NOx sensors are used for closed-loop control before and after the SCR catalyst, then control accuracy is improved, but the system becomes more complex due to NH3 sensitivity
Solution Approach 1:
The patent uses conversion efficiency as an intermediary parameter that relates the upstream and downstream NOx measurements, simplifying the control logic by focusing on the catalyst's performance rather than directly controlling absolute NOx levels at both points
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 system effectively maintains NOx conversion efficiency while minimizing ammonia slip by dynamically adjusting urea supply and NOx emissions, improving control accuracy and reducing calibration complexity.
Implementation Method 1
Selective Catalytic Reduction (SCR) catalysts remove nitrogen oxides (NOx), often the most abundant and polluting component in exhaust gases, through a chemical reaction between the exhaust gases, a reducing agent, and a catalyst
Implementation Method 2
Selective Catalytic Reduction (SCR) catalysts remove nitrogen oxides (NOx) through a chemical reaction between the exhaust gases, a reducing agent, and a catalyst
Implementation Method 3
typically urea, also known as carbamide ((NH2)2CO), which decomposes to ammonia (NH3) and carbon dioxide in the presence of water, oxygen and heat
Data Source
AI summary
A selective catalytic reduction (SCR) catalyst control system and method for an engine is disclosed. Urea injection to an SCR catalyst is determined based on an SCR catalyst model, which determines a value of stored NH3 in the SCR catalyst based on the NOx engine emission value, the SCR catalyst temperature, the quantity of urea supplied to the SCR catalyst and a pre-determined efficiency of conversion of NOx gases. A target value of stored NH3 and the value of stored NH3 in the SCR catalyst is then used to determine a stored NH3 differential, which is then used to calculate urea injection.