Catalysed Soot Filter with Front-End DOC for Diesel Regeneration
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Solution Overview
Problem
Diesel engines face challenges in achieving reliable passive regeneration of particulate filters due to limited exhaust gas temperatures, especially under conditions like extended idling or slow urban driving, which can lead to PM buildup, particularly in light-duty diesel engines.
Innovation Solution
A catalysed soot filter with a diesel oxidation catalyst (DOC) located at the front end, combined with engine management to provide sufficient NOx or HC, promoting passive oxidation of soot in oxygen and active regeneration by retaining heat within the filter, thereby improving the efficiency of both processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a catalysed soot filter is used to enable passive regeneration at lower temperatures, then soot combustion can occur at 300-400°C, but passive regeneration is unreliable under extended idling or slow urban driving conditions due to insufficient exhaust gas temperatures
Solution Approach 1:
The patent combines a catalysed soot filter (CSF) with a diesel oxidation catalyst (DOC) into a single integrated filter assembly. The DOC is positioned upstream within the same filter structure, allowing both catalytic functions to work together. This merging enables the system to reliably achieve passive regeneration by combining the low-temperature soot combustion capability of the CSF with the oxidation capabilities of the DOC, even under challenging driving conditions like extended idling or slow urban driving where exhaust temperatures would otherwise be insufficient.
2Productivity
If active regeneration techniques are used to introduce increased amounts of unburned fuel into the exhaust gas, then PM combustion is promoted in the CSF, but the system complexity increases with separate DOC positioning and engine management techniques
Solution Approach 1:
The patent integrates the DOC functionality directly within the filter structure rather than positioning it as a separate upstream component. This merging reduces the number of separate exhaust system components and simplifies the overall system architecture while maintaining the ability to perform active regeneration by introducing unburned fuel into the exhaust gas for enhanced PM combustion.
Solution Approach 2:
The integrated filter assembly performs multiple functions simultaneously: it acts as both a particulate filter for soot collection and a catalytic converter for fuel oxidation and soot combustion. This multi-functionality eliminates the need for separate DOC and CSF components, reducing system complexity while maintaining high PM combustion efficiency during active regeneration events.
3Loss of energy
If the filter material has high porosity to allow exhaust gas flow, then pressure drop is reduced, but thermal mass is decreased making it harder to retain heat for regeneration
Solution Approach 1:
The patent specifies filter materials with porosity in the range of 40-70% and mean pore diameters of 5-40 μm, optimizing the balance between gas flow and thermal mass. This parameter optimization ensures sufficient porosity to maintain acceptable pressure drop for exhaust gas flow while retaining enough thermal mass within the filter walls to store and retain heat generated during regeneration, facilitating sustained soot combustion.
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 enables efficient passive and active regeneration of the filter, reducing PM buildup and maintaining effective emissions control across varying driving conditions, with improved thermal mass retention and reduced energy losses for heating, thus meeting stringent emission standards.
Implementation Method 1
a diesel oxidation catalyst (DOC) located in a zone on the front end of the filter for oxidising carbon monoxide (CO), hydrocarbons (HC) and nitrogen monoxide (NO)
Implementation Method 2
which filter comprising a diesel oxidation catalyst (DOC) located in a zone on the front end of the filter... with a bulk volumetric heat capacity of at least 0.50 J cm−3 K−1 at 500° C.
Implementation Method 3
to combust particulate matter (PM) in the filter
Implementation Method 4
combustion of PM in oxygen occurs at 550-600° C.
Data Source
AI summary
A diesel engine includes an exhaust system having a particulate filter made from a porous material having a mean pore diameter of from 5 μm to 40 μm, a porosity of at least 40% and a bulk volumetric heat capacity of at least 0.50 J cm−3 K−1 at 500° C. The filter includes a diesel oxidation catalyst (DOC) located in a first catalyst zone on the front end of the filter and at least one catalyst zone located downstream thereof, for oxidizing carbon monoxide, hydrocarbons and nitrogen monoxide. The engine includes engine management means, in use, to provide continuously or intermittently an exhaust gas having sufficient nitrogen oxides or hydrocarbon and/or an exhaust gas of sufficiently high temperature to combust particulate matter. The platinum group metal (PGM) loading in the first catalyst zone is greater than the total PGM loading in the at least one downstream catalyst zone.