Lean NOx Trap Regeneration via Six-Stroke Rich Exhaust Pulses
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Solution Overview
Problem
Internal combustion engines operating on a six-stroke cycle face challenges with increased nitrogen oxide emissions (NOX) and compatibility with other technologies, despite offering advantages like reduced emissions and improved fuel efficiency.
Innovation Solution
The implementation of a lean nitrogen oxide trap (LNT) in the exhaust system, controlled by a fuel injector to manage fuel rates and produce stoichiometric lean and rich conditions, temporarily trapping NOX and regenerating the trap by releasing adsorbed nitrogen oxides during rich exhaust conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a six-stroke cycle is implemented with a second combustion event, then fuel efficiency is improved and soot combustion is enhanced, but nitrogen oxide emissions increase
Solution Approach 1:
The exhaust treatment system is segmented into multiple functional components: a lean nitrogen oxide trap (LNT) for NOX storage, a diesel oxidation catalyst (DOC) for oxidation reactions, and a selective catalytic reduction (SCR) catalyst for NOX conversion. This segmentation allows each component to specialize in specific emission treatment functions, effectively reducing NOX emissions while maintaining the six-stroke cycle's fuel efficiency benefits
Solution Approach 2:
A urea injection system is introduced as an intermediary substance to facilitate NOX reduction. The urea is injected into the exhaust stream and converted to ammonia, which then acts as a reducing agent in the SCR catalyst to convert NOX into nitrogen and water vapor. This intermediary approach enables effective NOX reduction without compromising the combustion efficiency gains from the six-stroke cycle
2Object-generated harmful factors
If a lean nitrogen oxide trap is used to reduce NOX emissions, then emission compliance is improved, but system complexity increases
Solution Approach 1:
The exhaust treatment system merges multiple functions into an integrated after-treatment train: the LNT stores NOX during lean operation, the DOC performs oxidation of CO and hydrocarbons, and the SCR catalyst converts NOX using urea-derived ammonia. This merging of functions into a coordinated system achieves comprehensive emission reduction while managing complexity through systematic integration rather than isolated components
Solution Approach 2:
The LNT operates in periodic cycles of NOX storage during lean combustion phases and regeneration during rich combustion phases. The controller periodically manages fuel injection to create rich conditions that regenerate the LNT by reducing stored NOX. This periodic action allows the system to handle NOX emissions dynamically without requiring continuously complex active control mechanisms
3Object-generated harmful factors
If fuel injection is increased to produce rich exhaust conditions for LNT regeneration, then NOX reduction is improved, but fuel consumption increases
Solution Approach 1:
Instead of maintaining continuously rich conditions, the system applies partial excessive fuel injection only during periodic LNT regeneration phases. The controller monitors LNT storage capacity and triggers rich-mode fuel injection only when regeneration is needed, rather than maintaining elevated fuel injection continuously. This partial application of excessive fuel minimizes overall fuel consumption while achieving necessary LNT regeneration to maintain NOX reduction performance
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 NOX emissions by temporarily trapping them in the LNT during lean conditions and releasing them during regeneration, improving engine efficiency and compliance with emission regulations.
Implementation Method 1
a lean nitrogen oxide trap (LNT) disposed in the exhaust system that can temporarily trap nitrogen oxides in the exhaust gasses
Implementation Method 2
The controller also periodically introduces fuel at a second fuel rate to produce a rich air/fuel mixture in the combustion chamber during a second time period
Data Source
AI summary
An internal combustion engine operates on a six-stroke combustion cycle including a first compression stroke, a first power stroke, a second compression stroke, and a second power stroke. A first fuel charge is introduced to a combustion chamber of the engine at a first fuel rate during the first compression and/or first power stroke to produce lean exhaust gasses. A second fuel charge is also introduced to the combustion chamber during the second compression and/or second power stroke to normally produce lean exhaust gasses. Periodically, the second fuel charge can be increased to a second fuel rate to produce stoichiometric rich exhaust gasses. A lean nitrogen oxide trap can be disposed in an exhaust system associated with the engine to temporarily trap nitrogen oxides. Once saturated, the LNT can be periodically regenerated by production of the rich exhaust gasses.