Hybrid Engine Transition Control for NOx Blow-By Suppression
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Solution Overview
Problem
In hybrid systems with three-way catalysts, switching from lean burn to stoichiometry operation leads to a significant blow-by of NOx due to the deterioration of the catalyst's purification function caused by excess oxygen during lean burn operation, resulting in increased NOx emissions.
Innovation Solution
A control device that switches the engine operation from lean burn to rich and then to stoichiometry, implementing intake air restriction and fuel cut to reduce oxygen in the exhaust gas, thereby recovering the catalyst's NOx purification function and minimizing NOx blow-by.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the engine operation is switched from lean burn to stoichiometry directly, then the emission control is simplified, but the three-way catalyst purification function deteriorates due to excess oxygen, causing significant NOx blow-by
Solution Approach 1:
The patent applies preliminary action by performing a fuel cut and intake air restriction before switching from lean burn to stoichiometry operation. This reduces the oxygen concentration in the exhaust gas in advance, preventing the deterioration of the three-way catalyst's purification function and avoiding subsequent NOx blow-by. The fuel cut is executed at a timing that ensures oxygen reduction occurs before the operation mode switch.
Solution Approach 2:
The patent segments the transition process into distinct phases: a first period with fuel cut and intake air restriction to reduce oxygen, followed by a second period where the operation switches to stoichiometry. This segmentation allows controlled management of oxygen levels and catalyst conditions during the transition, preventing harmful NOx emissions while maintaining emission control effectiveness.
2Object-generated harmful factors
If a fuel cut is performed before switching to rich operation, then oxygen in the exhaust gas is reduced, but the engine output is temporarily decreased
Solution Approach 1:
The patent applies dynamics by making the fuel injection amount variable based on the operating phase. During the first period, fuel injection is reduced or cut off to lower exhaust oxygen. During the second period, fuel injection is increased to achieve rich operation. This dynamic adjustment optimizes the balance between reducing catalyst oxygen exposure and maintaining engine output at different transition stages.
Solution Approach 2:
The patent changes the fuel injection parameter dynamically: reducing or cutting fuel during the first period to reduce exhaust oxygen, then increasing fuel during the second period to achieve rich operation and restore engine output. This parameter change strategy allows temporary power reduction to be accepted in exchange for preventing severe NOx blow-by, which would have much greater environmental impact.
3Object-generated harmful factors
If intake air restriction is performed during the transition period, then the amount of intake air is reduced, but the combustion stability may be affected
Solution Approach 1:
The patent applies preliminary action by implementing intake air restriction before the rich operation phase begins. This pre-restriction limits the amount of air available for combustion during the subsequent rich operation, thereby controlling and reducing NOx generation. The restriction is removed after the transition is complete, allowing normal combustion to resume.
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
The solution effectively suppresses NOx blow-by during stoichiometry operation by reducing oxygen in the catalyst and limiting NOx generation during the rich operation phase, maintaining stable combustion and adhering to emission regulations.
Implementation Method 1
Some hybrid systems have a three-way catalyst in the exhaust system of the engine
Implementation Method 2
a fuel cut for cutting fuel to the engine is performed
Implementation Method 3
an intake air restriction for restricting an amount of intake air to the engine is performed
Data Source
AI summary
When switching an operation state of an engine in a hybrid system from a lean burn operation to a stoichiometry operation, the lean burn operation is once switched to a rich operation and then switched to the stoichiometry operation. During a period from before switching to the rich operation to after switching to the rich operation, an intake air restriction for restricting an amount of intake air to the engine is performed. As a result, the amount of intake air is made smaller than when the intake air restriction is not performed. Further, during the period in which the intake air restriction is performed before switching to the rich operation, a fuel cut for cutting fuel to the engine is performed.