Lean NOx Trap Desulfurization Timing Control
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Solution Overview
Problem
Lean NOx traps (LNTs) in exhaust purification systems suffer from sulfur poisoning, which deteriorates their purification efficiency and requires desulfurization to maintain effectiveness, but existing methods lack precise timing for desulfurization and mode switching, affecting NOx purification and fuel efficiency.
Innovation Solution
A method is developed to determine the precise timing for desulfurization of LNTs by evaluating desulfurization feasibility and demand conditions, including temperature, H2S generation, and engine operation modes, allowing for mode switching between lean and rich modes to optimize desulfurization processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LNT is continuously operated in lean mode to maintain purification efficiency, then NOx adsorption capability is maintained, but sulfur accumulation increases and deteriorates LNT performance
Solution Approach 1:
The patent implements periodic switching between lean mode and rich mode operation. The controller alternates the air-fuel ratio between lean conditions (for NOx adsorption) and rich conditions (for desulfurization and regeneration), creating a cyclic operation that prevents sulfur accumulation while maintaining overall purification efficiency. This periodic action resolves the contradiction by preventing sulfur poisoning without continuously sacrificing NOx adsorption capability.
Solution Approach 2:
The patent changes the air-fuel ratio parameter dynamically between lean and rich states. By adjusting this critical parameter, the LNT operates in lean mode for NOx adsorption and switches to rich mode for desulfurization. This parameter change enables the system to alternate between maintaining purification efficiency and removing sulfur, resolving the technical contradiction between these two opposing requirements.
2Reliability
If desulfurization is performed frequently to remove sulfur, then LNT purification efficiency is maintained, but fuel consumption increases
Solution Approach 1:
The patent employs feedback control through sensors that monitor sulfur load, temperature, and other parameters. The controller uses this feedback information to determine the optimal timing for desulfurization operations. By base desulfurization timing on actual measured conditions rather than fixed schedules, the system performs desulfurization only when necessary, maintaining purification efficiency while minimizing fuel consumption penalties.
Solution Approach 2:
The patent performs preliminary assessment of desulfurization feasibility and demand conditions before initiating desulfurization mode. The controller evaluates whether desulfurization is actually needed based on sulfur load levels and operational conditions. This preliminary action prevents unnecessary desulfurization cycles, thereby maintaining purification efficiency when needed while avoiding unnecessary fuel consumption when sulfur levels are already acceptable.
3Use of energy by moving object
If mode switching timing is delayed to maintain lean mode operation, then fuel efficiency is improved, but sulfur accumulation accelerates and requires more aggressive desulfurization
Solution Approach 1:
The patent uses feedback from sulfur load sensors and operational condition monitoring to determine optimal mode switching timing. Rather than using fixed or delayed switching schedules, the controller continuously monitors sulfur accumulation and triggers mode switching when thresholds are reached. This feedback-based approach balances fuel efficiency considerations with the need to prevent excessive sulfur accumulation, resolving the contradiction between these two factors.
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 improves NOx purification efficiency, prevents unnecessary desulfurization, and enhances fuel economy by precisely controlling desulfurization timing and mode switching, thereby protecting the LNT and maintaining fuel efficiency.
Implementation Method 1
The LNT catalyst adsorbs the NOx contained in the exhaust gas when an air/fuel ratio is lean
Implementation Method 2
releases the adsorbed NOx and reduces the released nitrogen oxide and the nitrogen oxide contained in the exhaust gas when the air/fuel ratio is rich
Implementation Method 3
the NOx contained in the exhaust gas is reduced in the DeNOx catalyst through oxidation-reduction reactions with the reducing agents
Data Source
AI summary
A method of desulfurizing a lean NOx trap (LNT) of an exhaust purification system provided with the LNT and a selective catalytic reduction (SCR) catalyst includes determining whether a desulfurization feasibility condition of the LNT is satisfied, determining whether a desulfurization demand condition of the LNT is satisfied, and performing desulfurization of the LNT if both of the desulfurization feasibility condition of the LNT and the desulfurization demand condition of the LNT are satisfied, wherein the desulfurization of the LNT is performed by repeating a desulfurization lean mode and a desulfurization rich mode according to whether a mode switching condition due to a desulfurization temperature is satisfied and whether a mode switching condition due to generation of H2S is satisfied.