Bypass Catalyst Diagnostic for Cold Start Emissions
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Solution Overview
Problem
Conventional engine exhaust aftertreatment systems face challenges in achieving low tailpipe emissions immediately after a cold engine start due to low catalyst conversion efficiency, which is often addressed by increasing light-off temperatures at the cost of backpressure, durability, longevity, and complexity.
Innovation Solution
A light-off catalyst bypass system with a bypass catalytic converter and valve that reroutes exhaust gas directly to a bypass catalyst located close to the cylinder head, allowing for rapid heating and efficient conversion of harmful constituents, accompanied by a diagnostic method using oxygen sensor signals to monitor and ensure the bypass catalyst's functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the catalyst is positioned downstream in the main exhaust system, then the system structure is simpler, but the catalyst cannot reach light-off temperature quickly enough after cold start
Solution Approach 1:
The exhaust system is segmented into a main path and a bypass path with separate catalysts. The bypass catalytic converter is positioned close to the cylinder head to achieve fast light-off during cold start, while the main catalytic converter handles normal operation. This segmentation allows each catalyst to be optimized for its specific function without compromising the other.
Solution Approach 2:
A bypass valve is introduced as an intermediary component to control the flow path of exhaust gas. The valve selectively directs exhaust gas through the bypass passage to the bypass catalyst during cold start conditions, and redirects flow to the main catalyst when operating temperature is achieved, enabling flexible system configuration.
2Speed
If the bypass catalytic converter is positioned close to the cylinder head, then light-off temperature is achieved faster, but exhaust system backpressure increases
Solution Approach 1:
The system dynamically adjusts the exhaust flow path based on operating conditions. During cold start, the bypass valve opens to route exhaust through the bypass catalyst close to the cylinder head for fast heating. Once light-off is achieved, the valve closes to redirect flow through the main exhaust system, minimizing backpressure during normal operation.
Solution Approach 2:
The bypass valve operates periodically, switching between open and closed states based on engine temperature and catalyst light-off status. This periodic action allows the system to optimize for fast light-off during cold start, then transition to low backpressure operation during steady-state conditions.
3Productivity
If the bypass catalytic converter is used during cold start, then emissions conversion efficiency improves, but the catalyst durability and longevity are reduced
Solution Approach 1:
The catalyst system is segmented into two functional units: the bypass catalytic converter optimized for cold start performance with fast light-off, and the main catalytic converter optimized for durability during normal operation. This segmentation allows each catalyst to be designed for its specific operational regime, reducing overall system degradation.
Solution Approach 2:
The bypass catalyst is selectively deactivated (discarded from service) after the engine reaches operating temperature and the main catalyst becomes effective. The system then recovers by redirecting exhaust flow to the main catalyst, which is better suited for sustained operation. This prevents the bypass catalyst from undergoing excessive thermal cycling and degradation.
4Object-generated harmful factors
If conventional catalyst systems are used, then system longevity is maintained, but tailpipe emissions remain high during cold start
Solution Approach 1:
The bypass catalytic converter performs preliminary emissions conversion during cold start before the main catalyst reaches light-off temperature. By positioning the bypass catalyst close to the cylinder head and using it selectively during cold start conditions, harmful emissions are converted early in the engine operation cycle, reducing tailpipe emissions during the critical cold start period.
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 enables extremely fast catalyst light-off, high conversion efficiency, and reduced degradation of the main catalyst by selectively deactivating the bypass catalyst after light-off, thereby improving tailpipe emissions and extending the lifespan of the emissions system.
Implementation Method 1
a bypass catalytic converter configured to selectively receive exhaust gas from the internal combustion engine
Implementation Method 2
a controller in signal communication with an oxygen sensor disposed downstream of the bypass catalytic converter
Data Source
AI summary
An engine system includes an internal combustion engine, a main exhaust aftertreatment system with a main catalytic converter, and a light-off catalyst bypass system with a bypass passage and a bypass catalytic converter. An emissions control system includes a controller in signal communication with an oxygen sensor disposed downstream of the bypass catalytic converter. The emissions control system performs a diagnostic of the bypass catalytic converter, by the controller, including (i) monitoring signals from the downstream oxygen sensor for a predetermined time period during an engine cold start condition, (ii) determining a curve plotting oxygen content at the downstream oxygen sensor over the predetermined time period, based on the signals from the downstream oxygen sensor, (iii) calculating an accumulated area under the curve over the predetermined time period, and (iv) comparing the calculated accumulated area to a predetermined threshold to determine if the bypass catalytic converter has failed.