LNT-TWC Exhaust Purification System Control
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Solution Overview
Problem
Existing exhaust gas purification systems, particularly those using lean NOx traps (LNT) and three way catalysts, face performance degradation at low temperatures and high flow rates, leading to inefficient nitrogen oxide purification, especially when the three way catalyst is positioned downstream of the LNT in internal combustion engines.
Innovation Solution
An exhaust gas purification system that includes an engine with an air-fuel ratio adjustor, a lean NOx trap (LNT), and a three way catalyst (TWC), where the air-fuel ratio is controlled to a stoichiometric ratio when the nitrogen oxide storage or purification performance of the LNT falls below predetermined levels, utilizing specific catalyst materials and a controller to optimize nitrogen oxide reduction and purification across varying engine conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a three way catalyst is added to the front of the LNT to improve low temperature nitrogen oxide purification, then nitrogen oxide purification at low temperature is improved, but nitrogen oxide storage performance deteriorates due to the three way catalyst being disadvantageous for adsorbing nitrogen oxides
Solution Approach 1:
The patent inverts the conventional TWC-LNT layout to LNT-TWC arrangement. By placing the LNT upstream and TWC downstream, the system prioritizes nitrogen oxide storage capability while utilizing the TWC for post-processing remaining NOx and other emissions, thereby resolving the contradiction between low-temperature purification and storage performance
Solution Approach 2:
The LNT acts as an intermediary component that pre-concentrates nitrogen oxides from the exhaust stream before the TWC. This intermediary function allows the TWC to operate more effectively on a concentrated NOx stream, improving overall purification efficiency without compromising storage capability
2Productivity
If rich operation is performed to improve nitrogen oxide purification, then nitrogen oxide reduction is enhanced, but nitrogen oxide purification performance deteriorates more than when LNT alone is applied due to operational limitations
Solution Approach 1:
The system dynamically switches between lean and rich operational modes based on real-time exhaust conditions and LNT saturation state. The controller adjusts air-fuel ratio and injection timing to optimize NOx purification while preventing LNT overload, thereby achieving both high productivity and operational adaptability
Solution Approach 2:
The system employs periodic rich pulses to regenerate the LNT and maintain its storage capacity. These periodic rich operations are strategically timed to prevent NOx breakthrough while minimizing impact on fuel consumption, balancing purification efficiency with operational flexibility
3Device complexity
If stoichiometric air-fuel ratio operation is limited only by high load condition criterion, then control simplicity is maintained, but LNT performance is compromised in transient and low speed low load conditions where temperature and flow conditions vary
Solution Approach 1:
The controller continuously monitors exhaust temperature, flow rate, and LNT saturation level to dynamically adjust air-fuel ratio and injection timing. This feedback mechanism ensures LNT operates within optimal temperature and flow ranges across all driving conditions, maintaining high purification performance without excessive control complexity
Solution Approach 2:
The system changes operational parameters (air-fuel ratio, injection timing, injection quantity) based on detected exhaust conditions. By adjusting these parameters in response to temperature and flow variations, the system maintains LNT performance across diverse operating conditions while avoiding overly complex control logic
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 system effectively reduces nitrogen oxide emissions, meets stringent EU6c and RDE emission regulations, improves fuel efficiency, and lowers manufacturing costs by avoiding the use of urea-based SCR systems, while maintaining high purification performance under all operating conditions.
Implementation Method 1
The LNT catalyst absorbs the NOx contained in the exhaust gas when air/fuel ratio is lean
Implementation Method 2
releases the absorbed NOx and reduces the released nitrogen oxide
Implementation Method 3
converting noxious gas containing carbon monoxide, hydrocarbon, and nitrogen oxide contained in the exhaust gas into harmless components through a redox reaction
Implementation Method 4
an engine that generates power by burning a mixture of air and fuel
Data Source
AI summary
An apparatus for purifying exhaust gas includes: an engine; an exhaust gas air-fuel ratio adjustor for adjusting an air-fuel ratio of the exhaust gas; a lean NOx trap (LNT) mounted on the exhaust pipe and generating ammonia or reducing nitrogen oxides or desorbed nitrogen oxides contained in the exhaust gas using a reducing agent including carbon monoxide, hydrocarbon, or hydrogen contained in the exhaust gas; a three way catalyst (TWC) mounted on the exhaust pipe at a rear end of the LNT, and converting noxious gas in the exhaust gas into harmless components through a redox reaction; and a controller controlling the air-fuel ratio of the exhaust gas to a stoichiometric air-fuel ratio when the nitrogen oxide storage or purification performance of the LNT is in the operating period of the engine less than a predetermined level.