N2O Reduction in Lean-Burn Engine Exhaust via Temperature-Dependent Regeneration
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Solution Overview
Problem
Existing methods are inadequate for reducing nitrous oxide (N2O) emissions during the regeneration of nitrogen oxide storage catalysts in lean-burn combustion engines, particularly as these emissions exceed regulatory limits due to low conversion rates at operating temperatures.
Innovation Solution
Implementing different regeneration strategies for nitrogen oxide storage catalysts based on temperature, using shorter but richer fuel pulses below 275-290°C and adjusting pulse duration and richness above this range to optimize N2O reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If standard regeneration is used, then NOx storage is effective, but N2O emissions increase
Solution Approach 1:
The patent applies parameter changes by adjusting the air-fuel ratio (lambda) and temperature parameters during regeneration. Specifically, it uses a two-stage regeneration process: first stage with lambda ≤ 0.97 and temperature ≤ 300°C for controlled N2O formation, then second stage with lambda ≤ 0.8 and temperature ≥ 300°C for N2O decomposition. This dynamic parameter adjustment resolves the contradiction by transforming the regeneration conditions to minimize N2O emissions while maintaining NOx storage effectiveness.
Solution Approach 2:
The patent implements periodic action through alternating regeneration cycles with different air-fuel ratios and temperature profiles. The system periodically switches between lean storage conditions (λ > 1) and rich regeneration conditions (λ ≤ 1), with specific emphasis on the two-stage regeneration approach where the first stage (λ ≤ 0.97, T ≤ 300°C) is followed by a second stage (λ ≤ 0.8, T ≥ 300°C). This periodic alternation allows the system to balance NOx storage capacity with N2O emission control.
2Object-generated harmful factors
If rich operation is used for regeneration, then NOx reduction is achieved, but N2O is formed as secondary emission
Solution Approach 1:
The patent applies segmentation by dividing the regeneration process into two distinct stages. The first stage uses moderate rich operation (λ ≤ 0.97) at lower temperatures (≤ 300°C) to convert stored NOx while limiting N2O formation. The second stage uses stronger rich operation (λ ≤ 0.8) at higher temperatures (≥ 300°C) specifically to decompose formed N2O back into N2 and O2. This segmentation of the regeneration process resolves the contradiction by addressing NOx reduction and N2O control as separate sequential tasks.
Solution Approach 2:
The patent changes operational parameters dynamically during regeneration. It transitions from moderate rich conditions (λ ≤ 0.97, T ≤ 300°C) in the first stage to stronger rich conditions (λ ≤ 0.8, T ≥ 300°C) in the second stage. This parameter evolution allows the system to first perform NOx reduction efficiently, then shift conditions to favor N2O decomposition, thereby reducing overall N2O emissions while maintaining high NOx reduction efficiency.
3Object-generated harmful factors
If temperature is increased for N2O decomposition, then conversion improves, but energy consumption increases
Solution Approach 1:
The patent applies preliminary action by conducting the first stage of regeneration at lower temperatures (≤ 300°C) before the second high-temperature stage. During this first stage, the system prepares the exhaust gas composition and catalyst state optimally for the subsequent N2O decomposition phase. This preliminary preparation allows the high-temperature N2O decomposition to proceed more efficiently, reducing the total energy required compared to direct high-temperature regeneration.
Solution Approach 2:
The periodic alternation between low-temperature storage/first-stage regeneration and high-temperature second-stage regeneration creates energy-efficient cycling. The system accumulates thermal energy during lean operation and the first rich stage, then utilizes this stored thermal energy during the second rich stage for N2O decomposition. This periodic thermal cycling reduces peak energy demands and overall energy consumption while achieving effective N2O conversion.
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
Significantly reduces N2O emissions to meet regulatory limits, with strategies like shorter intense pulses below 275-290°C and longer, less rich pulses above, effectively intercepting a change in N2O formation mechanism within this temperature range.
Implementation Method 1
These are able to temporarily store nitrogen oxides in the lean exhaust gas (λ > 1) and to be regenerated in the stoichiometric or rich exhaust gas (λ ≤ 1) by reducing the stored nitrogen oxides to nitrogen
Implementation Method 2
reducing the nitrous oxide once formed is difficult
Data Source
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AI summary
The present invention relates to the use of different regeneration strategies for nitrogen oxide storage catalysts (NOx storage catalyst, LNT or NSC), depending on the exhaust gas temperatures, to reduce in the total exhaust gas the greenhouse gas N2O (nitrous oxide) that is produced as a secondary emission during the regeneration of the storage catalyst. If the exhaust gas temperature is below 275°C-290°C, regeneration takes place using a strategy with short pulses of around 2 seconds and λ lambda 0.95 rich.