Modified Lean NOx Trap for Cold Start Emissions
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Solution Overview
Problem
Current exhaust gas treatment systems are inefficient in reducing NOx emissions during the cold start period of internal combustion engines, as they require temperatures above 180°C for effective NOx conversion, which can increase CO2 emissions and are not effective below 200°C.
Innovation Solution
A modified lean NOx trap (LNT) system with a first layer containing a NOx adsorbent component and platinum group metals, and a second layer comprising a diesel oxidation catalyst zone and a NO oxidation zone, along with an ammonia-selective catalytic reduction (NH3-SCR) catalyst, which stores NOx at temperatures below 200°C and releases it at higher temperatures, and a urea injection system for further NOx conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current urea based SCR systems are used for NOx conversion, then high temperature NOx conversion efficiency is improved, but low temperature NOx conversion efficiency deteriorates
Solution Approach 1:
The exhaust system is segmented into three functional zones: a first LNT for low-temperature NOx storage, a second LNT for intermediate temperature storage, and an SCR catalyst for high-temperature conversion. This segmentation allows each component to operate in its optimal temperature range, resolving the contradiction between high-temperature efficiency and low-temperature adaptability.
Solution Approach 2:
The second LNT acts as an intermediary between the first LNT and the SCR catalyst. It receives stored NOx from the first LNT at lower temperatures and releases it to the SCR catalyst at higher temperatures, enabling smooth transition across temperature ranges and improving overall system adaptability.
2Reliability
If heating strategies are used to achieve low temperature NOx storage and conversion, then NOx conversion during cold start is improved, but CO2 emissions increase
Solution Approach 1:
The first LNT is designed to autonomously store NOx during cold start conditions without requiring external heating. The catalyst formulation and structural design enable passive NOx storage at low temperatures, eliminating the need for CO2-intensive heating strategies while maintaining cold start conversion capability.
3Device complexity
If a single-layer LNT is used, then device complexity is reduced, but NOx storage and release performance across different temperatures deteriorates
Solution Approach 1:
The LNT is divided into multiple layers with distinct functions: the first layer optimized for NOx storage at low temperatures, the second layer for intermediate temperature storage, and the third layer for NO release. This segmentation improves performance across different temperature ranges while maintaining manageable structural complexity through systematic design.
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
The system effectively reduces NOx emissions during cold start conditions while maintaining good CO oxidation activity and resistance to deactivation by sulfation, improving NOx conversion efficiency and reducing CO and HC emissions.
Implementation Method 1
NOx adsorbent component
Implementation Method 2
diesel oxidation catalyst zone
Implementation Method 3
oxidation catalyst
Implementation Method 4
NO oxidation zone
Implementation Method 5
oxidation catalyst
Implementation Method 6
ammonia-selective catalytic reduction (NH3-SCR) catalyst
Implementation Method 7
selective catalytic reduction
Data Source
Figure 1
Figure 2
AI summary
An exhaust system for treating an exhaust gas from an internal combustion engine is disclosed. The system comprises a modified lean NOx trap (LNT), a urea injection system, and an ammonia-selective catalytic reduction catalyst. The modified LNT comprises a first layer and a second layer. The first layer comprises a NOx adsorbent component and one or more platinum group metals. The second layer comprises a diesel oxidation catalyst zone and an NO oxidation zone. The diesel oxidation catalyst zone comprises a platinum group metal, a zeolite, and optionally an alkaline earth metal. The NO oxidation zone comprises a platinum group metal and a carrier. The modified LNT stores NOx at temperatures below about 200°C and releases at temperatures above about 200°C. The modified LNT and a method of using the modified LNT are also disclosed.