HC-Trap NOx-Trap Exhaust System Oxygen Management
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Solution Overview
Problem
Current exhaust emission reduction systems for gasoline-powered engines face challenges in effectively reducing non-methane hydrocarbons (nMHC) and nitrogen oxides (NOx) emissions, particularly during the cold start and light-off phases, due to insufficient oxygen availability during the hydrocarbon desorption process.
Innovation Solution
The implementation of an exhaust emission reduction system that combines a hydrocarbon (HC) trap with a nitrogen oxide (NOx) trap, along with a strategic lean running control unit, to extend the lean operation period and ensure sufficient oxygen supply during the HC desorption stage, utilizing a catalyzed HC-trap with platinum group metals and a NOx-trap configured to capture unconverted NOx for later reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a conventional three-way catalytic converter is used for exhaust purification, then CO, HC, and NOx can be converted simultaneously, but sufficient oxygen is not available during the HC desorption phase to ensure complete conversion
Solution Approach 1:
The system performs preliminary oxygen storage during the rich operation phase by having the oxygen storage component absorb excess oxygen from the exhaust gas. This stored oxygen is then released during the subsequent lean operation phase and HC desorption period, ensuring sufficient oxygen is available for complete HC conversion without requiring continuous rich operation.
Solution Approach 2:
The system dynamically changes the air-fuel ratio parameter over time, operating in alternating rich and lean cycles. During the lean phase, the oxygen storage component releases stored oxygen to maintain sufficient oxygen partial pressure during HC desorption, enabling complete oxidation of desorbed hydrocarbons even when the bulk exhaust is oxygen-deficient.
2Object-generated harmful factors
If the engine operates continuously in rich mode to ensure oxygen availability for HC conversion, then HC emissions are reduced, but fuel efficiency deteriorates and NOx emissions increase
Solution Approach 1:
The system employs periodic switching between rich and lean operation modes. During rich operation, the oxygen storage component is recharged with oxygen. During lean operation, the stored oxygen is released to support HC conversion during desorption. This periodic cycling achieves complete HC oxidation while maintaining overall fuel efficiency and accepting NOx for later reduction.
Solution Approach 2:
The system temporarily discards the ideal stoichiometric operation in favor of rich operation to charge the oxygen storage component, then recovers by using the stored oxygen during lean operation with HC desorption. This allows the system to achieve complete HC conversion during the critical desorption phase while operating predominantly in fuel-efficient lean mode overall.
3Object-generated harmful factors
If a longer lean operation period is implemented to extend oxygen supply during HC desorption, then HC conversion is improved, but NOx accumulation increases requiring larger storage capacity
Solution Approach 1:
The catalyst system is designed with multi-functional layers that simultaneously perform multiple functions: the oxygen storage component handles both oxygen storage for HC conversion and NOx storage, while the reduction catalyst layer handles both HC oxidation and NOx reduction. This multi-functionality allows extended lean operation for improved HC conversion without requiring separate, large-capacity NOx storage devices.
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 enhances the conversion of desorbed hydrocarbons into harmless products, effectively reducing overall HC emissions and meeting stringent emission standards by ensuring adequate oxygen availability during the desorption phase, thereby improving compliance with regulations such as LEVIII.
Implementation Method 1
a first/upstream TWC catalyst mounted in a position near the exhaust manifold and the engine compartment (the close-coupled position, CC), and a second/downstream TWC catalyst placed in a position either closely next to the first TWC catalyst (the second close-coupled position, CC2) or underneath the vehicle body (the underfloor UF or underbody UB position)
Implementation Method 2
The catalyst device facilitates the chemical reaction of different exhaust gas components, while forming non-hazardous products like carbon dioxide and water
Implementation Method 3
Components with such a capacity are generally referred to below as storage or trapping material components
Data Source
AI summary
Methods and systems are featured for reducing harmful exhaust gas components of combustion devices such as gasoline-powered combustion engines (e.g., predominately stoichiometric running engines). The methods and systems include an underbody combination of a hydrocarbon trap (HCT), suited for cold start hydrocarbon adsorption, as well as an associated NOx trap. The system is inclusive of a control unit for extending a lean exhaust condition reaching the desorbing HCT as to avoid a deficiency in oxygen during the time period of HCT desorption. The system is also inclusive of one or more TWCs as in one associated with the underbody HCT-NOx-trap combination and/or one positioned in a close coupled position. Platinum group metals as in Pd, Rh and Pt are also featured on one, two or all three of the HCT, NOx-trap, and TWC when present.