Close-Coupled SCR Catalyst for Low-Load NOx Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Large internal combustion engines face challenges in efficiently reducing nitrogen oxides (NOX) emissions during low-load conditions due to insufficient temperatures for the primary SCR catalyst, which is further downstream and may not reach activation temperatures, especially when idling or under low power output.
Innovation Solution
A close-coupled SCR catalyst is positioned upstream to receive high-temperature raw exhaust gases directly from the combustion chambers, with an upstream DEF injector introducing diesel exhaust fluid into the combustion chamber to ensure the SCR reaction occurs during low-load conditions, and a primary SCR catalyst is used during loaded conditions with a separate DEF injector for efficient NOX reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a primary SCR catalyst is positioned downstream in the exhaust system, then it can effectively treat exhaust gases during loaded conditions, but it cannot reach activation temperatures during low-load conditions
Solution Approach 1:
The exhaust aftertreatment system is segmented into two distinct SCR catalyst configurations: a close-coupled SCR catalyst positioned upstream for low-load conditions, and a primary SCR catalyst positioned downstream for loaded conditions. This segmentation allows each catalyst to operate in its optimal temperature range and fulfill its specific function, resolving the contradiction between reliability and temperature activation.
2Ease of operation
If DEF is introduced downstream at the primary SCR catalyst, then the system is simple to operate during loaded conditions, but it cannot effectively reduce NOX during low-load conditions due to insufficient temperature
Solution Approach 1:
The DEF injection system is made dynamic by implementing condition-based control logic that switches between two injection strategies: upstream DEF injection into the combustion chamber during low-load conditions to enable close-coupled SCR operation, and downstream DEF injection at the primary SCR catalyst during loaded conditions. This dynamic adaptation resolves the contradiction between ease of operation and reliability across different operating conditions.
3Reliability
If a close-coupled SCR catalyst is added upstream, then NOX reduction is effective during low-load conditions, but the device complexity increases
Solution Approach 1:
The close-coupled SCR catalyst is designed to serve multiple functions: it acts as the primary NOX reduction device during low-load conditions when downstream catalyst temperature is insufficient, and serves as a supplementary treatment stage during loaded conditions. This multi-functionality justifies the added complexity by providing reliable NOX reduction across the entire operating range.
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 configuration ensures effective NOX reduction during both low-load and loaded conditions by optimizing catalyst temperature and DEF introduction, enhancing the overall efficiency of the exhaust treatment system.
Implementation Method 1
a close-coupled selective catalytic reduction (SCR) catalyst that receives raw exhaust gases and reduces nitrogen oxides (NOX) to nitrogen (N2) and water (H2O) during a low-load condition
Implementation Method 2
an upstream DEF injector to selectively introduce DEF to the combustion chamber
Implementation Method 3
a primary SCR catalyst is used during loaded conditions with a separate DEF injector for efficient NOX reduction
Data Source
AI summary
A system for the treatment of exhaust gases from an internal combustion engine with a combustion chamber includes an upstream DEF injector disposed to introduce DEF to the combustion chamber and a close-coupled SCR catalyst downstream of and in close-coupled relation to the internal combustion engine. Downstream of the close-coupled SCR catalyst may be a primary SCR catalyst and a primary DEF injector. The system may operate to reduce NO2 in the close-coupled SCR catalyst during low-load conditions of the internal combustion engine and reduce NO2 in the primary SCR catalyst during loaded conditions.