LNT-CPF Exhaust Purification Regeneration Control
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Solution Overview
Problem
Existing exhaust gas purification systems, particularly those using lean NOx traps (LNT) and catalyzed particulate filters (CPF), face challenges in efficiently purifying nitrogen oxides at high temperatures and high load conditions, leading to increased NOx emissions and reduced catalytic reaction efficiency due to insufficient catalyst coating and limited cell density in CPFs.
Innovation Solution
A regeneration method and apparatus that strategically coordinates the regeneration of LNT devices and CPFs based on NOx absorption levels, temperature thresholds, and lambda values, allowing for simultaneous or separate regeneration of both components to optimize NOx purification efficiency and prevent NOx slip, while minimizing back pressure and fuel loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick catalyst coating is applied on the porous wall of CPF, then the catalytic reaction efficiency is improved, but the back pressure increases due to blocked micropores
Solution Approach 1:
The catalyst coating is segmented into two distinct layers: a first catalyst layer with high porosity (50-80%) that maintains low back pressure, and a second catalyst layer with low porosity (20-40%) that provides high catalytic activity. This segmentation allows each layer to perform its specific function without compromising the other, resolving the contradiction between catalytic efficiency and back pressure.
Solution Approach 2:
Different regions of the catalyst coating are assigned different properties: the inner layer (first catalyst layer) has high porosity to facilitate fluid flow and minimize back pressure, while the outer layer (second catalyst layer) has low porosity to maximize catalytic reaction efficiency. This local differentiation of properties allows the system to simultaneously achieve low back pressure and high catalytic performance.
2Stress or pressure
If a thin catalyst coating is applied on the porous wall of CPF, then the back pressure is reduced, but the catalytic reaction efficiency decreases
Solution Approach 1:
The catalyst coating is divided into two functional layers: a thin first catalyst layer (1-10 μm) with high porosity that minimizes back pressure, and a second catalyst layer that provides sufficient catalytic activity. This segmentation enables the system to maintain low back pressure while achieving adequate catalytic reaction efficiency through the coordinated function of both layers.
Solution Approach 2:
The catalyst coating structure implements local quality differentiation where the inner region (first catalyst layer) is optimized for fluid flow with high porosity, and the outer region (second catalyst layer) is optimized for catalytic activity with low porosity. This local optimization allows the thin coating to simultaneously achieve low back pressure and sufficient catalytic efficiency.
3Quantity of substance
If the LNT catalyst is disposed closely to the engine, then the NOx absorption is improved, but the NOx purification performance deteriorates at high temperature conditions
Solution Approach 1:
The LNT device and CPF are merged into a single integrated catalytic converter assembly, allowing the LNT catalyst to absorb NOx efficiently when cold, while the CPF provides complementary NOx purification capabilities when temperatures are high. This merging ensures continuous effective NOx control across all operating conditions.
Solution Approach 2:
The catalytic converter assembly is designed to perform multiple functions: the LNT catalyst provides NOx absorption during normal operation, while the CPF provides both particulate filtration and NOx purification during high-temperature conditions. This multi-functionality ensures reliable NOx control regardless of temperature or load conditions.
4Reliability
If the cell density of CPF is increased, then the catalyst surface area is increased, but the wall thickness is reduced which deteriorates filter performance
Solution Approach 1:
Instead of increasing cell density (two-dimensional approach), the invention increases the catalyst surface area by extending the catalyst coating along the length of the channels (one-dimensional extension) and by creating a multi-layer catalyst structure. This dimensional shift allows sufficient catalyst surface area to be achieved without compromising wall thickness or filter 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
The method improves NOx purification efficiency, prevents NOx, CO, and HC slip, and maintains fuel efficiency by optimizing regeneration conditions based on temperature and NOx levels, ensuring effective catalyst performance and reduced back pressure in CPFs.
Implementation Method 1
The LNT catalyst absorbs the NOx contained in the exhaust gas when air/fuel ratio is lean
Implementation Method 2
the NOx contained in the exhaust gas is reduced in the DeNOx catalyst through oxidation-reduction reaction with the reducing agents
Implementation Method 3
There is a pressure difference between the inlet channel and outlet channel separated by the porous wall. This allows the fluid to pass fast through the porous wall
Implementation Method 4
a thick catalyst coating on the porous wall allows the catalyst to block the micropores on the wall, and this may disturb the flow of the fluid from the inlet channel to the outlet channel
Data Source
AI summary
A regeneration method of an apparatus of purifying an exhaust gas including a catalytic converter which is disposed on an exhaust pipe and includes a lean NOx trap (LNT) device in which a first LNT catalyst is coated and a catalyzed particulate filter (CPF) in which a second LNT catalyst is coated may include determining whether a nitrogen oxide (NOx) amount absorbed in the LNT device is greater than a threshold NOx amount, determining whether a temperature of the LNT device is higher than a first predetermined temperature when the NOx amount absorbed in the LNT device is greater than the threshold NOx amount, and regenerating, both of the LNT device and the CPF or only the LNT device according to a temperature of the CPF when the temperature of the LNT device is higher than the first predetermined temperature.