Segmented Oxidation Catalyst for Diesel Exhaust Regeneration
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Solution Overview
Problem
Existing catalyst systems for diesel engine exhaust gas purification face challenges in maintaining efficiency and longevity during active regeneration of soot filters, particularly due to high temperature peaks that lead to premature aging and reduced conversion of hydrocarbons and carbon monoxide.
Innovation Solution
A catalyst system with two individual catalysts arranged closely, typically 2 to 30 mm apart, utilizing oxidation-active catalyst layers with noble metals on ceramic or metallic honeycomb bodies, and optionally zeolites, to optimize temperature distribution and composition for efficient hydrocarbon and carbon monoxide conversion, ensuring stable operation during active regeneration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If fuel is injected into the exhaust gas stream for active regeneration of the soot filter, then the exhaust gas temperature increases to ignite soot combustion, but high temperature peaks occur inside the oxidation catalyst leading to premature aging
Solution Approach 1:
The single oxidation catalyst is divided into two separate catalysts (first oxidation catalyst and second oxidation catalyst) arranged in series. The first catalyst handles hydrocarbon oxidation while the second catalyst handles nitrogen oxide oxidation, distributing the thermal load and preventing temperature peaks at any single catalyst location, thereby extending catalyst lifespan during active regeneration operations
2Temperature
If hydrocarbons are burned in the oxidation catalyst to heat exhaust gas for soot filter regeneration, then the exhaust gas temperature increases, but the conversion of hydrocarbons and carbon monoxide deteriorates with increasing operating time
Solution Approach 1:
The catalytic conversion function is segmented between two catalysts: the first oxidation catalyst primarily converts hydrocarbons and carbon monoxide, while the second oxidation catalyst primarily converts nitrogen oxides. This division of labor prevents the degradation of hydrocarbon and carbon monoxide conversion efficiency that would otherwise occur due to thermal aging from repeated regeneration cycles
Solution Approach 2:
Each catalyst is optimized for specific functions: the first oxidation catalyst is positioned to maximize hydrocarbon and carbon monoxide conversion, while the second oxidation catalyst is positioned to maximize nitrogen oxide conversion. This local optimization ensures that each catalyst operates within its optimal temperature and composition range, maintaining high conversion efficiency over time
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 system effectively slows down catalyst aging, maintaining better conversion efficiency of hydrocarbons and carbon monoxide, reducing emissions, and enabling reliable active regeneration of soot filters by heating exhaust gases to 500-700 °C, while minimizing temperature peaks and extending catalyst lifespan.
Implementation Method 1
at least two catalysts in a common converter housing, which are arranged one behind the other in the flow direction of the exhaust gas and at a distance from one another in the flow direction of the exhaust gas and which catalytically convert hydrocarbons and carbon monoxide in a lean exhaust gas
Implementation Method 2
an oxidation catalyst is arranged in front of the soot filter, which converts the nitrogen monoxide present in the exhaust gas into nitrogen dioxide
Implementation Method 3
fuel is injected into the exhaust gas stream upstream of the oxidation catalytic converter and burned on the oxidation catalytic converter, or the concentration of unburned hydrocarbons in the exhaust gas is increased by engine measures. The catalytic combustion in the oxidation catalytic converter must heat the exhaust gas by 200 to 400 °C to the soot ignition temperature
Implementation Method 4
the catalyst layer can also contain zeolites. To store hydrocarbons, the catalyst layer can also contain zeolites
Data Source
Figure 1~2
AI summary
Particle filters (6) for the removal of particulates from the exhaust gas of lean burn engines become blocked with the deposit of particulates with increasing operation time and must be regularly regenerated. It has been shown that a reliable operation of the particle filter is only possible when, from time to time, an active regeneration by increasing the exhaust gas temperature to the particulate ignition temperature is carried out. For this purpose, an oxidation catalyst (2) is normally arranged before the particle filter (6) and the exhaust gas temperature increased by catalytic combustion of additional injected fuel. The oxidation catalyst (2) is thus subjected to high thermal loads and hence ages rapidly. Surprisingly it has been shown that the aging of the oxidation catalyst (2) can be delayed when the same is divided into at least two separate catalysts and the separation between them is 2 to 30mm.