Exhaust Purification Catalyst Sulfur Poisoning Mitigation
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Solution Overview
Problem
The exhaust purification system of internal combustion engines faces a challenge where sulfur content in exhaust gas adsorbs on the surface of catalyst precious metals, reducing their activity and oxygen storage ability, leading to decreased effectiveness in removing unburned HC, CO, and NOX.
Innovation Solution
An exhaust purification system that employs a control device to alternately control the average air-fuel ratio between rich and lean settings across multiple cylinders, ensuring at least one cylinder operates at a rich air-fuel ratio, and adjusts these ratios based on the output of downstream air-fuel ratio sensors to maintain optimal oxygen storage and catalyst activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the average air-fuel ratio is controlled to a lean air-fuel ratio to improve fuel efficiency, then fuel consumption is reduced, but the catalyst precious metal activity drops due to sulfur content adsorption
Solution Approach 1:
The control device performs periodic inter-cylinder air-fuel ratio control where the air-fuel ratio of at least one cylinder is switched between rich and lean states in a periodic manner. This periodic rich-state operation prevents sulfur from permanently adsorbing on the catalyst precious metal surface, thereby maintaining catalyst activity while allowing overall lean operation for fuel efficiency.
Solution Approach 2:
The control device dynamically changes the air-fuel ratio parameter of specific cylinders between rich and lean states based on catalyst temperature and sulfur content conditions. By adjusting this critical parameter periodically, the system prevents sulfur poisoning of the catalyst while maintaining overall fuel efficiency through predominant lean operation.
2Use of energy by moving object
If the average air-fuel ratio is controlled to a lean air-fuel ratio to improve fuel efficiency, then fuel consumption is reduced, but the oxygen storage ability of the exhaust purification catalyst drops
Solution Approach 1:
The control device implements periodic inter-cylinder air-fuel ratio control that alternates between rich and lean states. During rich-state operation, the exhaust gas provides reducing conditions that help regenerate the oxygen storage capacity of the catalyst by releasing stored oxygen, thereby maintaining oxygen storage ability while allowing overall lean operation for fuel efficiency.
3Reliability
If inter-cylinder air-fuel ratio control is performed to maintain catalyst activity, then the control complexity increases, but this is necessary to prevent sulfur poisoning
Solution Approach 1:
The control device applies different air-fuel ratio control strategies to different cylinders based on their individual operating conditions and catalyst exposure. Specifically, it controls the air-fuel ratio of at least one cylinder differently from others, creating local quality differences in the exhaust gas composition to prevent sulfur poisoning while maintaining overall system efficiency.
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 effectively suppresses the decline in catalyst precious metal activity and oxygen storage ability, enhancing the system's capability to remove unburned HC, CO, and NOX from exhaust gases.
Implementation Method 1
an exhaust purification catalyst which is arranged in an engine exhaust passage and which can store oxygen
Implementation Method 2
sulfur content is adsorbed or stored on the surface of the catalyst precious metal which is carried on the carrier of the exhaust purification catalyst
Data Source
AI summary
An exhaust purification system of an internal combustion engine which has a plurality of cylinders is comprised of an exhaust purification catalyst, a downstream side air-fuel ratio sensor, and a control device which controls the average air-fuel ratio of the exhaust gas and the combustion air-fuel ratios of the cylinders. The control device performs average air-fuel ratio control where it alternately controls the average air-fuel ratio between the rich air-fuel ratio and the lean air-fuel ratio and inter-cylinder air-fuel ratio control where it controls the combustion air-fuel ratios of the cylinders so that the combustion air-fuel ratio becomes the rich air-fuel ratio at least at one cylinder among the plurality of cylinders even when the average air-fuel ratio is controlled to the lean air-fuel ratio by average air-fuel ratio control. In average air-fuel ratio control, the average air-fuel ratio is controlled so that the lean shift amount when controlling the average air-fuel ratio to the lean air-fuel ratio becomes smaller than the rich shift amount when controlling the average air-fuel ratio to the rich air-fuel ratio.