SCR Catalyst NOx Conversion Efficiency Control
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Solution Overview
Problem
Diesel engines face challenges in reducing nitrogen oxides (NOx) and particulate matter (PM) emissions, with existing methods impacting fuel efficiency and requiring frequent regeneration of diesel particle filters (DPFs).
Innovation Solution
A system and method that monitor and adjust NOx conversion efficiency in real-time using an SCR catalyst, allowing for increased NOx concentration in the exhaust to improve fuel economy and reduce PM by promoting oxidation, while also optimizing engine parameters like EGR flow and ammonia storage to maintain emissions compliance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If cooled exhaust gas recirculation (EGR) is used to lower NOx emissions, then NOx emissions are reduced, but fuel consumption increases
Solution Approach 1:
The system dynamically adjusts EGR rate parameters based on real-time SCR catalyst efficiency monitoring. When SCR efficiency is high, EGR rate is reduced to improve fuel economy; when SCR efficiency drops, EGR rate is increased to maintain NOx emission compliance. This dynamic parameter adjustment resolves the contradiction by optimizing the trade-off between emission control and fuel consumption.
Solution Approach 2:
The control system implements closed-loop feedback by continuously monitoring SCR catalyst efficiency and using this information to adjust EGR rate. The feedback mechanism allows the system to adapt EGR strategy based on actual catalyst performance, thereby reducing fuel consumption while maintaining emission compliance throughout the catalyst's life cycle.
2Object-generated harmful factors
If diesel particle filter (DPF) is used to reduce PM emissions, then PM emissions are reduced, but the filter requires frequent regeneration
Solution Approach 1:
The system performs preliminary oxidation of particulate matter using SCR-generated ammonia before the DPF becomes fully loaded. By proactively reducing PM accumulation through ammonia-based oxidation in the SCR catalyst, the system extends the time between required high-temperature regeneration events, thereby extending DPF regeneration intervals while maintaining PM emission reductions.
Solution Approach 2:
The SCR catalyst acts as an intermediary that oxidizes PM using stored ammonia, preventing PM from accumulating in the DPF. This intermediary oxidation process reduces the frequency and severity of required DPF regeneration events, extending regeneration intervals while maintaining effective PM control.
3Object-generated harmful factors
If SCR catalyst efficiency is maximized to meet emissions targets, then NOx conversion is improved, but fuel economy deteriorates
Solution Approach 1:
The system applies partial EGR action based on actual SCR efficiency needs rather than maintaining maximum EGR rates continuously. By monitoring SCR conversion efficiency in real-time, the system applies only the necessary amount of EGR to achieve emission compliance, avoiding excessive EGR that would harm fuel economy. This partial action approach maintains adequate NOx conversion while improving fuel efficiency.
Solution Approach 2:
The control system dynamically adjusts EGR rate based on real-time SCR catalyst efficiency monitoring. As the catalyst ages and efficiency changes, the system adapts EGR strategy accordingly - reducing EGR when catalyst performance is high and increasing EGR when performance degrades. This dynamic adjustment resolves the contradiction by optimizing the balance between maintaining NOx conversion efficiency and preserving fuel economy throughout catalyst operation.
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 fuel economy and extends DPF regeneration intervals by leveraging the performance margin of high SCR efficiency, reducing fuel consumption and maintaining emissions compliance without increasing tailpipe NOx emissions.
Implementation Method 1
The SCR process reduces NOx to diatomic nitrogen (N2) and water (H2O) using a catalyst and anhydrous ammonia (NH3) or aqueous NH3
Implementation Method 2
The SCR process reduces NOx to diatomic nitrogen (N2) and water (H2O)
Implementation Method 3
a diesel oxidation catalyst (DOC) to reduce HC, CO and soluble organic fraction (SOF) of PM in diesel exhaust
Data Source
AI summary
A method of controlling an internal combustion engine and exhaust system having an SCR, and engine and exhaust system including an SCR, described herein, monitors, in real time, NOx conversion efficiency of an exhaust flow output by the internal combustion engine through the SCR. A determination is made as to whether the monitored NOx conversion efficiency exceeds a predetermined target conversion efficiency, such as a target based on a predetermined allowable amount of NOx emission. While the monitored NOx conversion efficiency exceeds the predetermined amount, the NOx concentration level in the exhaust flow is increased by an amount based on the difference in the monitored conversion efficiency and the predetermined target conversion efficiency. Another method and engine and exhaust system provided herein tracks an amount of ammonia stored on a catalyst of the SCR based on a feed-forward calculation of injected urea based on engine out NOx mass flow and reduction efficiency of the SCR catalyst based on a temperature of the SCR catalyst, and operates the engine and exhaust system in a NOx-rich mode in which an EGR fraction command is adjusted, based on the tracked amount of stored ammonia, to decrease an amount of EGR gas entering an intake of the internal combustion engine and thereby reduce ammonia stored on the SCR catalyst.