Cascaded NOx Control via SCR and LNT Coordination
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Solution Overview
Problem
Current methods for controlling nitrogen oxide emissions in internal combustion engines face challenges in efficiently managing reducing agent consumption and fuel economy, particularly due to varying pollutant emissions influenced by driving style and operating conditions, leading to potential ammonia slippage and increased fuel consumption.
Innovation Solution
A method involving a control device that measures nitrogen oxide levels, adjusts the introduction of reducing agents, regulates the regeneration of nitrogen oxide storage catalytic converters, and modifies engine operating modes to dynamically manage nitrogen oxide emissions through a cascaded control strategy involving nitrogen oxide sensors, SCR, and LNT systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If constant introduction of reducing agent is used to remedy high nitrogen oxide emissions, then nitrogen oxide emissions are reduced, but ammonia slippage increases and reducing agent consumption increases
Solution Approach 1:
The patent employs a feedback control mechanism where nitrogen oxide emissions are continuously monitored by a sensor in the exhaust stream. The control device adjusts the reducing agent injection rate based on the measured NOx levels, increasing injection when NOx is high and decreasing it when NOx is low, thereby optimizing reducing agent consumption while maintaining emission control
Solution Approach 2:
The system dynamically adjusts the reducing agent injection rate and LNT regeneration timing based on real-time operating conditions and measured nitrogen oxide levels. This dynamic control allows the system to adapt to varying driving styles and operating conditions, preventing both excessive reducing agent consumption and ammonia slippage
2Object-generated harmful factors
If LNT is regenerated more frequently to reduce nitrogen oxide emissions, then nitrogen oxide emissions are reduced, but fuel consumption increases
Solution Approach 1:
The control device monitors nitrogen oxide storage levels in the LNT and initiates regeneration operations proactively before the LNT becomes fully saturated. By performing preliminary regeneration actions based on predicted storage capacity and operating conditions, the system optimizes the timing of regenerations to minimize fuel consumption while maintaining effective NOx control
Solution Approach 2:
The system adjusts regeneration parameters such as the duration and intensity of rich-burn phases based on measured nitrogen oxide levels and storage capacity estimates. This parameter optimization ensures that regenerations are performed only when necessary and with minimal impact on fuel consumption
3Object-generated harmful factors
If fixed settings of internal combustion engine and exhaust-gas aftertreatment devices are used, then device complexity is reduced, but nitrogen oxide emissions vary considerably with driving style and operating conditions
Solution Approach 1:
The control device integrates multiple functions into a single control unit that manages both the SCR system (reducing agent injection) and LNT regeneration operations. This multi-functional approach coordinates emission control and storage catalyst management, achieving effective NOx control across varying operating conditions while avoiding the need for separate complex control systems
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 efficient control of nitrogen oxide emissions over a long operating period, minimizing reducing agent consumption and fuel usage while maintaining low emissions, by inter-coordinating the SCR, LNT, and engine operations.
Implementation Method 1
the LNT oxidizes the nitrogen monoxide (NO) contained in the lean exhaust gas to form nitrogen dioxide (NO2), and subsequently stores this in the form of nitrates
Implementation Method 2
For the removal of nitrogen oxides from the exhaust gas for temporary adsorption and subsequent conversion into nitrogen oxides, use is made of nitrogen oxide storage catalytic converters
Implementation Method 3
nitrogen oxides are reduced to form nitrogen with the aid of a reducing agent, generally ammonia, which is introduced in the form of an aqueous urea solution into the exhaust tract and is stored in the SCR catalytic converter
Implementation Method 4
the nitrogen oxides are reduced to form nitrogen with the aid of a reducing agent
Implementation Method 5
During the regeneration, the stored nitrogen oxides are desorbed again and are reduced, on catalytically active components of the LNT and with the aid of the rich exhaust-gas constituents (CO, HC), to form nitrogen
Data Source
AI summary
A method is provided for controlling nitrogen oxide emissions in the exhaust gas of an internal combustion engine by means of successive actuation of catalytic converters in the exhaust tract and of the internal combustion engine, wherein the catalytic converters or the internal combustion engine are actuated in succession if the actuation of a first device is not sufficient for reducing the nitrogen oxide emissions. An arrangement for carrying out the method is also provided.