Zeolite-Protected NOx Adsorber for Cold Start Emissions
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Solution Overview
Problem
Existing engine exhaust aftertreatment devices are not catalytically active enough at low temperatures to effectively reduce hydrocarbon and NOx emissions, leading to fouling of NOx adsorbing materials and increased NOx emissions due to the presence of hydrocarbons and sulfur compounds.
Innovation Solution
A hydrocarbon and NOx trap system comprising a zeolite-based topmost layer to adsorb hydrocarbons and a NOx adsorbing material layer protected by the zeolite layer, supported by a monolithic substrate, which thermally releases adsorbed emissions once aftertreatment devices are warmed up, preventing fouling of the NOx adsorbing material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a three-way catalyst is directly exposed to exhaust gases during low temperatures, then NOx adsorption is achieved, but the catalyst is fouled by hydrocarbons and sulfur emissions
Solution Approach 1:
A hydrocarbon trap layer is introduced as an intermediary between the exhaust gas and the three-way catalyst. This trap layer selectively adsorbs hydrocarbons and sulfur compounds first, preventing them from reaching and fouling the catalyst, while allowing NOx to pass through to the catalyst for adsorption.
Solution Approach 2:
The exhaust aftertreatment system is segmented into two functional layers: a hydrocarbon trap layer for capturing hydrocarbons and sulfur, and a three-way catalyst layer for NOx adsorption. This segmentation allows each layer to perform its specific function without interference, resolving the fouling problem.
2Reliability
If a three-way catalyst is used for NOx adsorption at low temperatures, then some NOx reduction is achieved, but performance is inferior to lean NOx traps
Solution Approach 1:
The invention changes the operational parameters by controlling the temperature and composition of exhaust gases passing through each layer. The hydrocarbon trap operates at low temperatures to capture HC and S, while the three-way catalyst layer receives pre-conditioned exhaust that enhances its NOx adsorption performance, effectively optimizing its operation in the cold start regime.
3Productivity
If exhaust aftertreatment devices are used at low temperatures, then emissions treatment is attempted, but catalytic activity is insufficient
Solution Approach 1:
The hydrocarbon trap layer performs self-service by adsorbing hydrocarbons and sulfur compounds from the exhaust gas at low temperatures. This self-action prevents these substances from interfering with the catalyst and allows the system to function effectively without external intervention during cold start conditions.
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
Effectively reduces cold-start NOx emissions by adsorbing and thermally releasing hydrocarbons and NOx, enhancing the performance of engine emissions control beyond traditional lean NOx traps and preventing fouling of the NOx adsorbing material.
Implementation Method 1
a first, topmost layer, exposed to an exhaust gas flow path of exhaust gases from the engine, the first layer comprising a zeolite
Implementation Method 2
a second layer, covered by the top most layer, the second layer comprising a NOx adsorbing material
Implementation Method 3
a monolithic substrate, directly supporting the second layer and indirectly supporting the first layer, the substrate providing a substantially rigid structure of the trap
Data Source
AI summary
A hydrocarbon and NOx trap and related apparatus and methods for reducing cold-start NOx emissions from an engine are provided. In one embodiment a trap includes a first, topmost layer, exposed to an exhaust gas flow path of exhaust gases from an engine, the first layer comprising a zeolite, a second layer, substantially covered by the topmost layer, the second layer comprising a NOx adsorbing material and a monolithic substrate, directly supporting the second layer and indirectly supporting the first layer, the substrate providing a substantially rigid structure of the trap. In this way, engine emissions, such as NOx and hydrocarbons may be adsorbed over the exhaust trap at low temperature and then thermally released, limiting cold start emissions beyond engines that only include a lean NOx trap.