Wall-Flow Catalyst Density Ratio for Stop-Start Stability
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Solution Overview
Problem
Eco-friendly vehicles with energy-saving systems, such as hybrid engines and stop-start systems, experience unstable exhaust gas temperatures due to frequent engine stops and starts, leading to intermittent degradation of exhaust gas purification performance in conventional wall-flow-type exhaust gas purification catalysts.
Innovation Solution
A wall-flow-type exhaust gas purification catalyst with a substrate and two catalytic layers, where the first catalytic layer is located near the exhaust inlet and the second near the outlet, with a coating density ratio of 1.01 to 1.4, ensuring high pressure loss at the second layer, promoting heat retention and increased contact opportunities for purification, even at unstable temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional wall-flow-type exhaust gas purification catalyst is used, then the catalytic layer can be simplified, but the exhaust gas purification performance degrades intermittently when the engine stops and starts
Solution Approach 1:
The catalytic layer is divided into a first catalytic layer in the entrance cell and a second catalytic layer in the exit cell, with the second layer having higher coating density to create higher pressure loss. This segmentation allows the exhaust gas flow to be controlled and directed through the first catalytic layer during engine stop-start conditions, maintaining purification performance while keeping the overall structure relatively simple.
Solution Approach 2:
The second catalytic layer is designed with higher coating density than the first catalytic layer, creating localized differences in pressure loss. This local quality enhancement in the exit cell region ensures that exhaust gas preferentially flows through the first catalytic layer during transient conditions, thereby maintaining effective purification without requiring complex structural modifications throughout the entire catalyst.
2Temperature
If the coating density of the second catalytic layer is increased to control exhaust gas flow, then pressure loss increases, but the warm-up performance and heat retention are improved
Solution Approach 1:
The coating density of the second catalytic layer is optimized to be 1.01 to 1.4 times that of the first catalytic layer. This parameter change creates sufficient pressure loss difference to control exhaust gas flow direction during engine stop-start conditions, thereby improving heat retention and warm-up performance while limiting the increase in overall pressure loss to an acceptable range.
Solution Approach 2:
Instead of making the second catalytic layer significantly denser than the first, a moderate ratio (1.01 to 1.4) is applied. This partial action approach provides enough pressure loss differentiation to achieve the desired flow control and heat retention effects without excessively increasing the overall pressure loss that would harm engine performance.
3Stress or pressure
If the first catalytic layer is made shorter to reduce pressure loss, then exhaust gas flows more freely, but the contact time with the catalytic material is reduced
Solution Approach 1:
The catalytic function is segmented between two layers with different characteristics. The first catalytic layer in the entrance cell has lower coating density and shorter length to minimize pressure loss and maximize flow rate. The second catalytic layer in the exit cell has higher coating density to create pressure loss differential. This segmentation allows each layer to optimize its function independently.
Solution Approach 2:
The first catalytic layer serves as a flow-optimized version with lower coating density, while the second catalytic layer serves as a pressure-loss-optimized version with higher coating density. By having both layers present, the system copies the benefits of both extreme designs without requiring the entire catalytic structure to compromise between the two opposing requirements.
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 catalyst maintains excellent catalytic activities and purification performance even when the engine stops and restarts, ensuring stable exhaust gas treatment and reduced pressure loss, enhancing the efficiency of NOx reduction and overall exhaust gas purification.
Implementation Method 1
upon contact between the exhaust gas and the catalytic layer (catalytic metal), the exhaust components are purified (detoxified)
Implementation Method 2
passes through micro pores of the porous partition wall
Data Source
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AI summary
Provided is an exhaust gas purification catalyst capable of stably maintaining and exhibiting excellent catalytic performance. This invention provides an exhaust gas purification catalyst 10 comprising a wall-flow-type substrate, a first catalytic layer 261 and a second catalytic layer 262. The first catalytic layer 261 is provided to an internal portion of a partition wall 26 in contact with an entrance cell 24. The second catalytic layer 262 is provided to an internal portion of a partition wall 26 in contact with an exit cell 25. The ratio (D2/D1) of the coating density D2 of the second catalytic layer 262 to the coating density D1 of the first catalytic layer 261 is 1.01 to 1.4.