Close-Coupled SCR Ammonia Storage for Cold Start NOx Control
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Solution Overview
Problem
Diesel engines face challenges in controlling NOx emissions during the cold start phase due to the inefficiency of existing emissions aftertreatment systems at temperatures below 200°C, which fail to meet stringent greenhouse gas and ultra-low NOx regulations.
Innovation Solution
A method to evaluate and optimize the ammonia storage capacity of a selective catalytic reduction (SCR) unit in an emissions aftertreatment system by operating the system at steady-state conditions, dosing diesel exhaust fluid upstream of a close-coupled SCR unit, and adjusting operation parameters based on the evaluated ammonia storage capacity to control NOx emissions effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the SCR catalyst is located close to the engine to shorten heat-up time, then the cold start emissions control is improved, but the ammonia storage capacity is reduced due to catalyst aging
Solution Approach 1:
The system performs preliminary ammonia storage in the close-coupled SCR catalyst before the cold start phase begins. By pre-loading the catalyst with ammonia during warm operation, the system ensures that sufficient ammonia is available immediately when cold start occurs, eliminating the need to wait for heat-up while maintaining effective NOx reduction from the beginning of cold start.
Solution Approach 2:
The close-coupled SCR catalyst acts as an intermediary between the engine exhaust and the downstream SCR system. It temporarily stores ammonia and provides it during cold start when the downstream SCR is not yet operational, mediating the gap between engine emissions and aftertreatment effectiveness.
2Productivity
If high levels of ammonia are stored in the SCR unit to achieve high NOx emissions control during cold start, then the emissions control effectiveness is improved, but the system complexity increases due to additional DEF dosing systems
Solution Approach 1:
The close-coupled SCR catalyst performs multiple functions: it acts as a traditional SCR catalyst for NOx reduction during warm operation, serves as an ammonia storage device during cold start, and functions as a buffer between the engine and downstream aftertreatment. This multi-functionality eliminates the need for separate cold start DEF dosing systems.
Solution Approach 2:
The patent merges the ammonia storage function with the close-coupled SCR catalyst that is already positioned near the engine for heat-up purposes. By combining ammonia storage and NOx reduction functions in a single component, the system avoids adding separate DEF dosing hardware while achieving effective cold start emissions control.
3Ease of operation
If the EAS operates at temperatures below 200°C during cold start, then the engine can start in cold conditions, but the emissions control effectiveness deteriorates
Solution Approach 1:
The system changes the operational parameters of the close-coupled SCR catalyst by maintaining it at higher temperatures through proximity to the engine, while the downstream SCR operates at lower temperatures during cold start. The close-coupled SCR's temperature parameter is optimized for ammonia storage and rapid release, enabling effective emissions control despite the cold start conditions in the downstream system.
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 enables effective NOx emissions control during the cold start phase, ensuring compliance with stringent regulations by optimizing ammonia storage and usage in the SCR unit, thereby improving the overall efficiency of the emissions aftertreatment system.
Implementation Method 1
the storage capacity of the catalyst decreases... Understanding the ammonia storage capacity of the SCR catalyst is valuable
Implementation Method 2
selective catalytic reduction (SCR) catalyst within an SCR bed of an EAS attains optimal temperature for NOx reduction
Data Source
AI summary
The present disclosure describes methods for evaluating ammonia storage capacity of a close-coupled SCR unit while remaining compliant with prescribed emissions limits, methods of controlling an emission aftertreatment system including multiple SCR units and emission management systems for a vehicle including an internal combustion engine and an emission aftertreatment system that includes two or more SCR units.