Lean NOx Trap Control Method for Residual Nitrogen Oxide Purification
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Solution Overview
Problem
Conventional control systems for lean nitrogen oxide traps (LNTs) and passive selective catalytic reduction (pSCR) systems fail to minimize residual nitrogen oxides (NOx) and optimize ammonia (NH3) generation, leading to incomplete NOx regeneration and reduced purification performance, due to reliance on lambda sensor readings affected by oxygen detachment.
Innovation Solution
A control method that introduces NOx into a regeneration process, converts the engine mode to an enriched fuel condition, and extends the enriched mode based on lambda sensor comparisons and LNT temperature, delaying the termination of NOx regeneration to maximize NH3 generation and oxygen emission without additional equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the enriched mode is terminated when lambda sensor values become identical, then the control system operates efficiently with existing sensors, but residual NOx remains in the LNT and NH3 generation is insufficient
Solution Approach 1:
The control method introduces a pre-set time delay after the lambda sensors indicate equal values before terminating the enriched mode. This preliminary extension ensures that residual NOx is fully converted to NH3, compensating for the sensors' inability to detect complete regeneration due to oxygen detachment effects.
Solution Approach 2:
The system uses the existing lambda sensors and natural chemical reactions within the LNT to determine regeneration completion, avoiding additional sensors or equipment. The time-based extension leverages the self-catalytic conversion of NOx to NH3 within the LNT structure.
2Reliability
If the enriched mode duration is extended to minimize residual NOx, then NH3 generation increases, but fuel consumption increases due to prolonged enriched operation
Solution Approach 1:
The control method optimizes the enriched mode duration by introducing a specific time delay parameter (e.g., 0.5-2 seconds) after lambda sensor equalization. This parameter-based approach extends the mode just enough to maximize NH3 generation while minimizing unnecessary fuel consumption, avoiding both premature termination and excessive extension.
3Measurement precision
If additional sensors or equipment are installed to accurately detect NOx regeneration completion, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The system utilizes the existing lambda sensors and the inherent chemical properties of the LNT to determine regeneration completion. By measuring oxygen concentration changes through the lambda sensors and applying a time delay, the system achieves accurate NOx conversion detection without requiring additional NOx-specific sensors or complex equipment.
Solution Approach 2:
The control unit acts as an intermediary, processing the lambda sensor signals and applying the time delay algorithm to infer NOx regeneration status. This software-based intermediary compensates for the limitations of the lambda sensors without requiring direct NOx measurement hardware.
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 minimizes residual NOx, enhances NH3 generation, and improves NOx purification performance by extending the enriched mode until optimal conditions are met, ensuring complete regeneration and increased oxygen utilization.
Implementation Method 1
reduce the NOx into nitrogen (N2) by means of a reduction reaction
Implementation Method 2
store NOx in an LNT in a general driving mode, in which oxygen is plentiful
Implementation Method 3
NH3 reacts with NOx that slipped through the LNT to generate N2 which is then removed
Data Source
AI summary
A control method for improving nitrogen oxide purification performance (NOx) includes starting NOx regeneration, comparing first and second lambda values measured at first and second lambda sensors in a control unit, checking the lean NOx trap (LNT) temperature, and measuring a second time that has elapsed after the first and second lambda values are found to be the same, and checking whether the second time is greater than or equal to a predetermined time when it is observed that the temperature of the LNT is greater than or equal to the predetermined temperature value.