Air Injection for SCR Catalyst Activation in Exhaust Purification
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Solution Overview
Problem
Existing exhaust purification systems face challenges in accurately determining the regeneration timing of lean NOx traps and effectively reducing nitrogen oxides in exhaust gases, especially when the air/fuel ratio is lean or at high exhaust gas temperatures, leading to increased non-combusted fuel content and oxygen concentration requirements for SCR catalyst activation.
Innovation Solution
An exhaust purification system and control method that utilize multiple oxygen sensors and an air injection device to control oxygen concentration upstream and downstream of the SCR catalyst, allowing for precise regulation of air injection based on detected oxygen levels and lambda values to activate the oxidation-reduction reaction and enhance NOx reduction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the air/fuel ratio is rich to release absorbed NOx from LNT, then regeneration of LNT is enabled, but the oxygen concentration in exhaust gas decreases making it difficult to activate SCR catalyst
Solution Approach 1:
The exhaust purification system is divided into two functional sections: LNT for NOx absorption during lean operation and SCR catalyst for NOx reduction during rich operation. The air injection device is positioned specifically between the LNT and SCR catalyst to locally adjust oxygen concentration only where needed for SCR activation, without interfering with LNT regeneration process.
Solution Approach 2:
An air injection device is introduced as an intermediary component between the LNT and SCR catalyst. This device injects additional air to increase oxygen concentration in the exhaust gas specifically at the SCR catalyst inlet, mediating between the rich conditions needed for LNT regeneration and the oxygen requirements of the SCR catalyst.
Solution Approach 3:
The air injection device creates a localized oxygen-enriched zone at the SCR catalyst inlet, while the overall exhaust gas maintains rich conditions for LNT regeneration. This local quality adjustment allows the SCR catalyst to receive sufficient oxygen for activation without requiring the entire exhaust system to operate under lean conditions.
2Reliability
If multiple oxygen sensors and air injection device are added to control oxygen concentration, then SCR catalyst activation is improved, but system complexity increases
Solution Approach 1:
A second oxygen sensor is installed between the LNT and SCR catalyst to provide real-time feedback on oxygen concentration at the SCR inlet. The controller uses this feedback signal to dynamically control the air injection device, creating a closed-loop control system that automatically maintains optimal oxygen levels for SCR activation without manual intervention.
3Productivity
If air injection is used to increase oxygen concentration upstream of SCR catalyst, then NOx reduction efficiency is improved, but energy consumption increases
Solution Approach 1:
The air injection device operates periodically or intermittently rather than continuously, injecting air only when the SCR catalyst requires activation or when oxygen concentration drops below optimal levels. This periodic operation reduces energy consumption compared to continuous air injection, while still maintaining effective NOx reduction when needed.
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 improves the purification efficiency of nitrogen oxides by activating the oxidation-reduction reaction in the SCR catalyst, ensuring effective NOx removal even when the air/fuel ratio is rich, thereby optimizing the regeneration of lean NOx traps and reducing NOx emissions.
Implementation Method 1
a first oxygen sensor mounted on the exhaust pipe and disposed between the engine and the LNT, the first oxygen sensor configured to detect an oxygen amount in the exhaust gas exhausted from the engine
Implementation Method 2
a second oxygen sensor mounted on the exhaust pipe and disposed between the LNT and the SCR catalyst, the second oxygen sensor configured to detect the oxygen amount in the exhaust gas discharged from the LNT
Implementation Method 3
configured to reduce the NOx contained in the exhaust gas by passing through the LNT
Implementation Method 4
a selective catalytic reduction (SCR) catalyst mounted at the exhaust pipe downstream of the LNT and configured to reduce the NOx contained in the exhaust gas by passing through the LNT
Implementation Method 5
configured to absorb nitrogen oxide (NOx) contained in the exhaust gas at a lean air/fuel ratio
Implementation Method 6
to release the absorbed NO at a rich air/fuel ratio
Implementation Method 7
to reduce the nitrogen oxide contained in the exhaust gas or the released nitrogen oxide using a reductant including carbon or hydrogen contained in the exhaust gas
Implementation Method 8
an air injection device configured to selectively inject air to an inside of the exhaust pipe based on a control signal of the controller
Data Source
AI summary
The present disclosure provides an exhaust purification system including: an engine; a lean NOx trap (LNT) mounted on an exhaust pipe and enable to absorb nitrogen oxide (NOx) contained in an exhaust gas at a lean air/fuel ratio, or to release the absorbed NOx at a rich air/fuel ratio; a selective catalytic reduction (SCR) catalyst provided downstream of the LNT so as to reduce the NOx contained in the exhaust gas; a controller to perform denitrification (DeNOx) by using the LNT and/or the SCR catalyst based on a driving condition of the engine; a first oxygen sensor disposed between the engine and the LNT to detect an oxygen amount in the exhaust gas; a second oxygen sensor disposed between the LNT and the SCR catalyst to detect an oxygen amount in the exhaust gas exhausted from the LNT; and an air injection device selectively injecting air into the exhaust pipe.