Exhaust Gas Control Catalyst Periodic Air-Fuel Ratio Switching
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Solution Overview
Problem
Existing exhaust gas control apparatuses for internal combustion engines face challenges in efficiently removing particulate matter (PM) from filters while maintaining emission quality, as they often rely on secondary air supply at rich air-fuel ratios, which limits the reactivity of NO2 with PM.
Innovation Solution
The apparatus incorporates an oxygen supply device and an electronic control unit that regulate the oxygen supply to alternately vary the air-fuel ratio of exhaust gas flowing into the particulate filter between rich and lean ratios, enhancing the reactivity of NO2 with PM and improving PM removal efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If secondary air is supplied at rich air-fuel ratio to remove PM from filter, then PM removal is achieved, but NO2 reactivity with PM is limited
Solution Approach 1:
The patent applies periodic action by alternating between rich air-fuel ratio operation (to generate NO2 through fuel-rich combustion) and lean air-fuel ratio operation (to supply oxygen and enable PM combustion). This periodic switching creates cycles where NO2 is generated during rich phases and then reacts with PM during lean phases, significantly enhancing PM removal efficiency compared to continuous rich operation.
Solution Approach 2:
The patent changes the air-fuel ratio parameter dynamically between rich and lean states. During rich operation, the air-fuel ratio is controlled to be richer than stoichiometric to maximize NO2 generation. During lean operation, the air-fuel ratio is controlled to be leaner than stoichiometric to provide excess oxygen for PM combustion. This parameter modulation optimizes both NO2 availability and PM removal rate.
2Quantity of substance
If lean air-fuel ratio exhaust gas is continuously supplied to increase NO2, then NO2 availability improves, but NO passes through filter without reacting with PM
Solution Approach 1:
The patent uses periodic switching between rich and lean air-fuel ratios to overcome the limitation of continuous lean operation. During rich phases, NO2 is generated in abundance. During subsequent lean phases, the accumulated NO2 reacts with PM while excess oxygen is available. This periodic approach ensures both NO2 availability and effective PM combustion, whereas continuous lean operation allows NO to pass through unreacted.
Solution Approach 2:
The patent applies preliminary action by generating NO2 during the rich air-fuel ratio phase before transitioning to the lean phase. This pre-generation of NO2 ensures that when the lean phase begins and oxygen becomes available for PM combustion, the reactive NO2 is already present in the exhaust gas, enabling immediate and efficient PM removal.
3Productivity
If rich air-fuel ratio is maintained to supply fuel for PM combustion, then PM burning rate increases, but NO2 generation is insufficient
Solution Approach 1:
The patent resolves this contradiction by periodic switching: during rich phases, fuel is supplied to generate NO2 through fuel-rich combustion; during lean phases, the same fuel-rich exhaust gas (containing generated NO2) is combined with excess oxygen to enable rapid PM combustion. This temporal separation of NO2 generation and PM combustion functions optimizes both processes.
Solution Approach 2:
The patent segments the exhaust gas treatment process into distinct functional phases: a rich phase dedicated to NO2 generation and a lean phase dedicated to PM combustion with oxygen supply. This segmentation allows each phase to optimize its specific function without interfering with the other, thereby achieving both sufficient NO2 availability and high PM burning rate.
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 reduces emission deterioration while effectively removing PM from the filter, as the alternating air-fuel ratios optimize the presence of NO2, enhancing the combustion of PM.
Implementation Method 1
an exhaust gas control catalyst (20) disposed in an exhaust passage of the internal combustion engine, the exhaust gas control catalyst having a catalytic function
Implementation Method 2
the secondary air reacts with unburnt fuel contained in the rich air-fuel ratio exhaust gas on the filter to raise the temperature of the filter, with the result that the PM is burnt and removed
Implementation Method 3
the NO2 is caused to flow into the filter, and PM deposited on the filter is burnt with the NO2
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
An exhaust gas control apparatus includes an exhaust gas control catalyst (20) disposed in an exhaust passage, a filter (24) disposed downstream of the catalyst, a secondary air supply device (25) configured to supply secondary air into exhaust gas flowing into the filter at a location downstream of the catalyst in an exhaust gas flow direction, and an electronic control unit (31). The electronic control unit is configured to, when a temperature of the catalyst is higher than or equal to an activation temperature and an air-fuel ratio of exhaust gas emitted from an engine body (1) is a rich air-fuel ratio, cause the supply device to supply secondary air into exhaust gas while periodically increasing or reducing the air such that the air-fuel ratio of exhaust gas flowing into the filter alternately varies between rich and lean air-fuel ratios.