Exhaust Gas Purification System Cylinder Flow Uniformity
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Solution Overview
Problem
The uneven flow distribution of exhaust gas across the cross-section of a three-way catalyst in an internal combustion engine's exhaust system leads to variations in air-fuel ratios, making it difficult to maintain effective NOx reduction during air fuel ratio dither control, potentially decreasing the overall NOx removal rate.
Innovation Solution
By setting the cylinder with the lowest degree of uniformity in flow speed distribution as the rich cylinder and maintaining other cylinders as lean cylinders, the air fuel ratio dither control ensures that exhaust gases flow uniformly across the three-way catalyst, preventing shifts in air-fuel ratios and enhancing NOx reduction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If air fuel ratio dither control is performed to raise three-way catalyst temperature, then HC and CO oxidation functions and NOx reduction function are promoted, but uneven flow distribution causes air fuel ratio variations that decrease NOx removal rate
Solution Approach 1:
The patent applies local quality by switching specific cylinders (e.g., odd-numbered or even-numbered cylinders) between lean and rich operations in a predetermined pattern. This creates localized variations in exhaust gas composition that, when combined with flow distribution characteristics, ensures uniform air fuel ratio across the three-way catalyst cross-section, maintaining reliable NOx removal while enabling temperature rise through dither control.
2Quantity of substance
If exhaust gas flow is allowed to distribute naturally according to flow speed distribution, then exhaust gas flows into three-way catalyst, but uneven distribution causes air fuel ratio shifts that reduce NOx reduction efficiency
Solution Approach 1:
The patent implements local quality by assigning different operational modes (lean or rich) to specific cylinders based on their position and exhaust flow characteristics. This predetermined switching pattern compensates for natural flow distribution unevenness, ensuring that air fuel ratio variations are distributed uniformly across the three-way catalyst cross-section, thereby maintaining reliable air fuel ratio uniformity while preserving adequate exhaust gas quantity.
3Temperature
If cylinders are switched between lean and rich operations in air fuel ratio dither control, then three-way catalyst temperature rises, but this causes oxygen storage and release that creates air fuel ratio variations
Solution Approach 1:
The patent applies periodic action by implementing cyclic switching between lean and rich operations in specific cylinders according to a predetermined pattern. This periodic dither control creates controlled air fuel ratio variations that promote oxygen storage and release cycles in the three-way catalyst, raising catalyst temperature while the structured periodicity ensures uniform air fuel ratio distribution across the catalyst cross-section.
Solution Approach 2:
The patent implements local quality by selectively switching specific cylinders (e.g., odd-numbered or even-numbered) between lean and rich modes rather than all cylinders simultaneously. This localized periodic action creates controlled air fuel ratio variations in specific regions that, when combined with exhaust flow distribution, result in uniform overall air fuel ratio across the three-way catalyst, maintaining composition stability while enabling temperature rise.
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 stabilizes the air-fuel ratio distribution, reducing the likelihood of NOx reduction rate decreases and maintaining effective NOx removal within the three-way catalyst during air fuel ratio dither control.
Implementation Method 1
when the exhaust gas of the rich air fuel ratio is supplied to the three-way catalyst, HC and CO in the exhaust gas are oxidized by the oxygen held in the three-way catalyst. The temperature rise of the three-way catalyst will be promoted by the heat of oxidation of HC and CO at this time.
Implementation Method 2
during the execution of the air fuel ratio dither control, not only the HC and CO are oxidized, but also the NOx in the exhaust gas is reduced, in the three-way catalyst.
Data Source
AI summary
When the air fuel ratio dither control is carried out, an air fuel ratio of a mixture in each of one or more lean cylinders and one or more rich cylinders is controlled so that an average value of an air fuel ratio of exhaust gas flowing into the three-way catalyst becomes a predetermined target exhaust gas air fuel ratio. At this time, the air fuel ratio dither control is carried out by setting, as the one or more rich cylinders, at least a cylinder for which a degree of uniformity of the flow speed distribution of exhaust gas, which is a degree of uniformity of the flow speed distribution of exhaust gas discharged from that cylinder on a cross section of the three-way catalyst, is the lowest in the cylinder group of an internal combustion engine.