SCR Emissions Control System Controller
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Solution Overview
Problem
Current SCR systems face challenges in minimizing ammonia slip and optimizing NOx conversion due to transient engine conditions and the complexity of solving differential equations for real-time control, particularly when differentiating between NO and NO2 components.
Innovation Solution
A controller is introduced that calculates the initial amount of reduction agent by approximating the completion of specific SCR reactions before others, allowing for real-time adjustments to prevent ammonia slip and optimize NOx conversion, using a decoupled solution of differential equations that accounts for both NO and NO2 reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the amount of NH3 stored on the catalyst's surface is increased to maximize NOx conversion, then NOx conversion efficiency is improved, but NH3 slip increases and is released into the atmosphere
Solution Approach 1:
The system dynamically changes the amount of NH3 stored on the catalyst surface by adjusting reduction agent injection based on real-time engine operating conditions (temperature, load, speed). During transient low-load conditions, less NH3 is stored to prevent slip, while during steady-state high-load conditions, more NH3 is stored to maximize conversion efficiency.
Solution Approach 2:
The control system transitions from static NH3 storage to dynamic adjustment of NH3 storage levels. The model-based controller continuously calculates optimal NH3 storage amounts based on changing engine conditions, allowing the system to adapt between different operating states (transient vs. steady-state, low-load vs. high-load) to balance conversion efficiency and slip prevention.
2Object-generated harmful factors
If a model-based controller uses an internal model to calculate the proper amount of reductant required, then NH3 slip is reduced and NOx conversion is maintained, but computational complexity increases and real-time implementation becomes difficult
Solution Approach 1:
The patent transforms the complex differential equations into simplified algebraic equations by using pre-calibrated parameters and lookup tables. The model uses empirically determined parameters (reaction rates, heat transfer coefficients) that are calibrated once and then used in real-time calculations without requiring complex numerical solutions during operation.
Solution Approach 2:
The system performs preliminary calibration and model setup offline, where differential equations are solved and parameters are determined in advance. These pre-calculated parameters are then used during real-time operation, eliminating the need to solve complex differential equations on-the-fly and enabling real-time implementation with standard control units.
3Device complexity
If a single fictional reaction is used to lump NO and NO2 terms, then the number of reactions to solve is reduced, but the accuracy of DeNOx calculations decreases and extensive model calibration is required
Solution Approach 1:
The patent segments the DeNOx process into distinct reaction pathways for NO and NO2 rather than lumping them into a single fictional reaction. By maintaining separate rate equations and parameters for each nitrogen oxide component, the model accurately captures their different reaction kinetics and stoichiometry while still being computationally tractable through the use of simplified algebraic formulations.
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 effectively reduces ammonia slip and enhances NOx conversion efficiency by accurately calculating the reduction agent dosage in real-time, applicable to various engine configurations with minimal calibration, while maintaining compliance with stringent emissions standards.
Implementation Method 1
An SCR system works by releasing a reductant, such as ammonia (NH3), into the engine exhaust flow in the presence of a catalyst. The NH3 may be stored on the surface coating of the catalyst where it reacts with the NOx in the exhaust flow to create environmentally friendly products, such as nitrogen gas (N2) and water (H2O).
Implementation Method 2
The NH3 may be stored on the surface coating of the catalyst where it reacts with the NOx in the exhaust flow. Reaction (1) describes the ammonia adsorption/desorption from the catalyst.
Implementation Method 3
NH3 may also be desorbed from the catalyst and carried by the exhaust flow downstream of the catalyst to a location where the NH3 is released into the atmosphere. The NH3 desorption rate is strongly dependent on the catalyst's temperature.
Implementation Method 4
The oxidation catalyst may be a three-way catalyst or a diesel oxidation catalyst. The oxidation catalysts generally promote the oxidation of CO and hydrocarbons to CO2 and H2O.
Data Source
AI summary
An emissions control system is disclosed. The emissions control system may have an SCR device that receives a flow of exhaust. The emissions control system may also have an injector that introduces a reduction agent into the flow of exhaust at or upstream of a catalyst within the SCR device. The emissions control system may have a controller in communication with the injector, the controller being configured to calculate a first amount of the reduction agent by using an approximation that at least one of a plurality of SCR reactions must be completed before the remaining SCR reactions commence. The controller may also be configured to adjust the injector according to at least the first amount.