Lean NOx Trap Regeneration via Cylinder Air-Fuel Cycling
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Solution Overview
Problem
Lean NOx traps in internal combustion engines face challenges in efficient regeneration, particularly when the exhaust gas temperature is below the optimum range, leading to increased NOx emissions and sulfur poisoning, which affects the engine's performance and emission control.
Innovation Solution
A method is introduced to operate a multi-cylinder lean burn engine in a lean NOx trap heating mode, where some cylinders are operated rich and others lean to increase the exhaust gas temperature to the optimum range for efficient regeneration, while minimizing fuel accumulation and oil dilution by alternating rich and lean combustion events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the engine is operated rich to increase exhaust gas temperature for LNT regeneration, then the temperature of the LNT increases to the optimum range, but NOx emissions increase suddenly because the catalyst materials are not active at low temperatures
Solution Approach 1:
The system performs preliminary heating of the LNT using a dedicated heating mode before initiating the NOx purge regeneration process. This preliminary action raises the LNT temperature to the optimum range (300-400°C) where catalyst materials become active, ensuring that when NOx purge is subsequently activated, the catalyst can immediately convert released NOx to N2 without sudden emissions increases.
Solution Approach 2:
The system dynamically switches between different operational modes (heating mode, purge mode, normal operation) based on real-time monitoring of LNT temperature and NOx storage levels. The heating mode operates with specific air-fuel ratios and durations that are dynamically adjusted to reach optimal temperature without excessive NOx emissions, then transitions to purge mode when temperature conditions are satisfied.
2Reliability
If the engine is operated rich for extended periods to regenerate the LNT, then the LNT regeneration is effective, but fuel accumulates in the engine leading to oil dilution
Solution Approach 1:
The system implements periodic heating cycles with controlled durations and intervals rather than continuous rich operation. The heating mode is activated only when LNT temperature and NOx storage conditions require it, and is deactivated after achieving regeneration or when temperature exceeds thresholds. This periodic approach limits fuel accumulation while maintaining effective LNT regeneration through targeted thermal cycles.
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 prevents sudden NOx emissions and sulfur poisoning, ensuring efficient NOx trap regeneration and reducing engine oil dilution, thereby maintaining emissions control and engine performance.
Implementation Method 1
operating the engine in a lean NOx trap heating mode in which at least one cylinder of the engine is operated rich of stoichiometric in order to increase the temperature of the lean NOx trap
Implementation Method 2
at least one cylinder of the engine is operated rich of stoichiometric in order to increase the temperature
Implementation Method 3
use a Lean NOx Trap (LNT) in the exhaust system for adsorbing NOx when the engine is run lean
Implementation Method 4
convert the stored NOx into N2 (nitrogen gas) during a NOx purge regeneration process in which the engine is run rich
Implementation Method 5
operating each cylinder with an alternating rich to lean air-fuel ratio pattern
Data Source
AI summary
Methods and systems are provided for regenerating a lean NOx trap. In one example, a method may include, responsive to an indication to regenerate a lean NOx trap (LNT), operating an engine with an overall rich air-fuel ratio to regenerate the LNT while minimizing fuel oil dilution by operating each cylinder of the engine with an alternating rich to lean air-fuel ratio pattern of two rich combustion events for every one lean combustion event across a plurality of engine cycles.