Lean-Rich Cycling for NOx Storage Catalysts
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Solution Overview
Problem
Existing methods for controlling nitrogen oxide emissions in combustion engines, particularly during high-load conditions, face challenges due to high exhaust gas temperatures and velocities, leading to 'nitrogen oxide breakthrough' and inefficiencies in storage capacity, and require complex reductant injection systems that are costly and cumbersome.
Innovation Solution
A method that adjusts the air/fuel ratio of a combustion engine in response to torque requests and ammonia loads, using a control unit with sensors to manage the engine's operating mode between rich and lean conditions, and includes a second nitrogen oxide storage catalyst downstream to capture escaped nitrogen oxides, thereby optimizing NOx storage and reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If reductant injection systems are used to control nitrogen oxide emissions during high-load conditions, then nitrogen oxide conversion is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent removes the reductant injection system from the exhaust aftertreatment architecture entirely. Instead of injecting reductant into the exhaust stream, the system relies on the LNT to store NOx during lean operation and subsequently reduce it to N2 during rich regeneration cycles, eliminating the need for separate reductant storage tanks, injection valves, and associated control systems.
Solution Approach 2:
The LNT is designed to perform multiple functions: it stores nitrogen oxides during lean operation, provides oxidation of CO and HC, and acts as the sole source of reductant through in-situ generation during rich regeneration. This multi-functionality replaces what would traditionally require separate components for NOx storage, reductant supply, and injection control.
2Object-generated harmful factors
If reductant injection systems are implemented for high-load nitrogen oxide control, then emission conversion efficiency improves, but manufacturing cost increases
Solution Approach 1:
The patent extracts and eliminates the expensive reductant injection subsystem, including reductant storage tanks, high-pressure injection valves, dosing pumps, and associated electronics. The system achieves NOx control using only the LNT and standard engine management components, dramatically reducing manufacturing costs.
Solution Approach 2:
The system uses inexpensive, readily available materials already present in the engine and LNT (fuel, air, catalyst substrates) to achieve NOx reduction, replacing expensive proprietary reductant injection systems. The regenerative process uses common engine operating modes (rich/lean cycling) rather than specialized expensive components.
3Loss of time
If the nitrogen oxide storage catalyst is positioned close to the engine, then response time to high-load conditions improves, but storage capacity is reduced due to high temperature and velocity
Solution Approach 1:
The LNT operates dynamically, switching between storage mode during lean operation and reduction mode during rich regeneration. This dynamic operation allows the close-coupled LNT to respond immediately to changing engine loads while maintaining effective storage capacity through temporal separation of storage and reduction functions.
Solution Approach 2:
The system uses periodic rich/lean cycling to manage the close-coupled LNT. During lean periods, the LNT accumulates NOx storage capacity; during brief rich periods, it reduces stored NOx to N2. This periodic operation allows the small close-coupled LNT to handle high-load conditions effectively despite its limited instantaneous storage capacity.
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 reduces nitrogen oxide emissions across all operating conditions, enhances fuel economy, and simplifies the system by eliminating the need for complex reductant injection systems, while maintaining efficient NOx conversion and storage.
Implementation Method 1
the LNT oxidizes the nitric oxide (NO) contained in the lean exhaust gas to nitrogen dioxide (NO2) and then stores it in the form of nitrates
Implementation Method 2
Nitrogen oxides formed in lean-mixture operation of a combustion engine can be stored in an LNT
Implementation Method 3
In the SCR, the stored ammonia is used to reduce nitrogen oxides to nitrogen under lean exhaust gas conditions
Implementation Method 4
the stored nitrogen oxides are desorbed again and are reduced to nitrogen over catalytically active components of the LNT
Implementation Method 5
during this process, the stored nitrogen oxides are desorbed again and are reduced to nitrogen over catalytically active components of the LNT with the aid of the rich exhaust gas constituents (CO, HC)
Implementation Method 6
the stored nitrates furthermore react with molecular hydrogen, which is formed under rich exhaust gas conditions owing to incomplete combustion of the fuel and also owing to reactions in the LNT, as a result of which ammonia is also produced during a regeneration
Data Source
AI summary
A method for controlling exhaust gas aftertreatment in an exhaust gas aftertreatment system having at least one nitrogen oxide storage catalyst and at least one catalyst for selective catalytic reduction is provided, wherein, in phases of a high load, a combustion engine is operated with a substoichiometric fuel/air mixture, and nitrogen oxides in the exhaust gas are reduced in the nitrogen oxide storage catalyst to ammonia, which is stored in the catalyst for selective catalytic reduction, and, when the storage capacity of the catalyst for selective catalytic reduction is exceeded, the combustion engine is operated with a superstoichiometric fuel/air mixture, thus allowing nitrogen oxides in the catalyst for selective catalytic reduction to be reduced by the stored ammonia.