NOx Trap Regeneration via Lean Desorption
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Modern diesel engines face challenges in efficiently regenerating nitrogen oxide traps due to increased fuel consumption, oil dilution, and limited regeneration conditions, which can lead to excessive NOx emissions and reduced trap effectiveness, especially when combined with selective reduction catalysts.
Innovation Solution
A method that calculates the mass of nitrogen oxides stored in the trap and initiates regeneration by checking conditions for a rich mixture operation or, if the catalyst is insufficient, uses a high temperature lean mixture desorption mode to reduce NOx, allowing regeneration without restrictive operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the engine switches to a rich mixture mode for nitrogen oxide trap regeneration, then the trap efficiency is restored by reducing stored NOx, but fuel consumption increases significantly
Solution Approach 1:
The invention changes the operating parameters of the catalyst by controlling the air-fuel ratio and temperature to enable NOx reduction under lean mixture conditions. Specifically, the catalyst is operated at temperatures above its light-off temperature with a controlled air-fuel ratio that allows fuel to act as a reducing agent without requiring a globally rich mixture, thereby reducing fuel consumption while maintaining trap regeneration effectiveness.
Solution Approach 2:
The invention introduces a catalyst as an intermediary component between the nitrogen oxide trap and the exhaust system. This catalyst facilitates the reduction of NOx by fuel under lean mixture conditions, acting as a mediator that enables the regeneration process without requiring the engine to operate in a rich mixture mode, thus avoiding the penalty of increased fuel consumption.
2Reliability
If additional fuel is injected late into the cylinders for trap regeneration, then nitrogen oxides are reduced, but engine oil dilution increases and lubricating properties degrade
Solution Approach 1:
The invention changes the operating parameters from late post-injection under rich mixture to controlled fuel injection under lean mixture conditions. The air-fuel ratio is maintained above stoichiometric while the catalyst temperature is controlled to enable NOx reduction, thereby preventing fuel from passing through the piston rings and diluting the engine oil, while still achieving trap regeneration.
Solution Approach 2:
The catalyst serves as an intermediary that enables NOx reduction through a different chemical pathway that does not require fuel to pass through the combustion chambers and piston rings. The catalyst facilitates the reaction between fuel and NOx in the exhaust stream, preventing the harmful side effect of oil dilution while maintaining regeneration effectiveness.
3Reliability
If regeneration is limited to specific engine speed and load ranges, then reliability is maintained, but the frequency and flexibility of regeneration are restricted
Solution Approach 1:
The invention changes the operating parameters enabled for regeneration from restricted speed-load ranges to broader operating conditions. By using a catalyst that can facilitate NOx reduction under lean mixture conditions across a wider range of temperatures and air-fuel ratios, the system allows regeneration to occur more frequently and under more diverse engine operating conditions while maintaining reliability.
4Productivity
If the catalyst operates at high temperature for selective reduction, then nitrogen oxide reduction efficiency increases, but the risk of NOx emissions increases if reduction is insufficient
Solution Approach 1:
The invention implements feedback control by continuously monitoring the air-fuel ratio and catalyst temperature to optimize the reduction process. The control system adjusts the fuel injection timing and quantity to maintain the catalyst at optimal temperature and air-fuel ratio conditions, ensuring efficient NOx reduction while preventing excessive emissions. This feedback mechanism allows the system to respond to changing operating conditions and maintain reliable NOx control.
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 regenerates the nitrogen oxide trap with reduced fuel consumption and broader operational flexibility, maintaining low NOx emissions by leveraging the selective reduction catalyst for post-treatment.
Implementation Method 1
the trap stores at least some of the NOx molecules emitted in the engine's combustion gases
Implementation Method 2
a catalyst for the selective reduction of nitrogen oxides
Implementation Method 3
the introduction, at the inlet of the nitrogen oxide trap, of unburned fuel into the combustion chambers of the engine has the effect of causing a reduction of the stock of NOx into harmless molecules (nitrogen N2 and water H2O)
Implementation Method 4
uses a high temperature lean mixture desorption mode to reduce NOx
Data Source
Figure 1
Figure 2
AI summary
The invention provides a method for regenerating a nitrogen oxide trap mounted in the exhaust system of a motor vehicle's internal combustion engine. The system also includes a catalyst for the selective reduction of nitrogen oxides downstream of the trap. According to the invention, the method comprises a first, conventional regeneration mode by nitrogen oxide reduction, in which the engine is set to a rich mixture, and a second regeneration mode by nitrogen oxide desorption, in which the trap temperature is rapidly and significantly increased, and engine fuel is introduced upstream of the trap. The engine is set to a richer mixture than usual, but still with a lean mixture. When the mass of nitrogen oxides in the trap reaches a regeneration threshold, the second mode is used when the selective nitrogen oxide reduction catalyst is sufficiently effective.The desorbed nitrogen oxides are thus reduced by the said selective nitrogen oxide reduction catalyst.