Bypass Catalyst Diagnostic for Fast 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, often requiring faster 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 redirects exhaust gas directly to the bypass catalyst during cold starts, allowing rapid heating and efficient conversion of harmful constituents, while a diagnostic method monitors oxygen sensor signals to determine the bypass catalyst's health and adjust operations accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the catalyst light-off temperature is increased to achieve faster light-off, then the conversion efficiency during cold start is improved, but the exhaust system backpressure increases and durability decreases
Solution Approach 1:
The exhaust aftertreatment system is segmented into two separate catalytic converters: a light-off catalyst positioned upstream for cold start emissions control, and a main catalytic converter for normal operation. This segmentation allows each catalyst to be optimized for its specific function, with the light-off catalyst designed for rapid light-off without compromising the main catalyst's durability and backpressure characteristics.
2Productivity
If a light-off catalyst bypass system is added to improve cold start emissions, then conversion efficiency during cold start is improved, but device complexity increases
Solution Approach 1:
A bypass valve is incorporated into the light-off catalyst bypass system, allowing it to dynamically switch between two states: directing exhaust through the light-off catalyst during cold starts, and bypassing it once the main catalyst is operational. This dynamic control enables the system to adapt to different operating conditions, improving cold start emissions without permanently increasing complexity.
3Object-affected harmful factors
If the bypass catalyst is continuously activated to maintain emissions control, then emission compliance is improved, but precious metal usage increases and aging accelerates
Solution Approach 1:
The light-off catalyst bypass system operates periodically rather than continuously. The bypass valve activates the light-off catalyst only during cold start conditions when emissions control is most critical, and deactivates it once the main catalyst reaches operating temperature. This periodic operation reduces precious metal consumption and minimizes aging while maintaining emission compliance during the most vulnerable operating phase.
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 selective deactivation of the bypass catalyst, reducing precious metal usage and minimizing aging, thereby improving emission system efficacy and compliance with emissions standards.
Implementation Method 1
allowing rapid heating and efficient conversion of harmful constituents
Implementation Method 2
efficient conversion of harmful constituents
Implementation Method 3
monitoring, by the controller, signals from the downstream oxygen sensor for a predetermined time period
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) determining a number of times the curve crosses a predetermined setpoint over the predetermined time period, and (iv) comparing the number to a predetermined threshold to determine if the bypass catalytic converter has failed.