Exhaust Filter TWC Design for Euro 6 PM Reduction
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Solution Overview
Problem
Current exhaust systems for positive ignition engines face challenges in maintaining stoichiometric exhaust gas composition for efficient NOx reduction and particulate matter filtration, particularly under transient engine conditions, and in meeting stringent Euro 6 emission standards while minimizing backpressure.
Innovation Solution
The design of an exhaust system featuring a wall-flow filter with a ceramic porous substrate coated with a three-way catalyst washcoat, where the upstream TWC is less efficient to allow pollutants to slip through and generate an exotherm for increased filter temperature, effectively combusting particulate matter without the need for active interventions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional exhaust system with efficient TWC is used, then NOx reduction and pollutant conversion are improved, but filter temperature remains insufficient for effective particulate matter combustion
Solution Approach 1:
The patent intentionally allows the upstream TWC to be less efficient, converting the harmful effect of incomplete pollutant conversion into a beneficial source of unreacted hydrocarbons and CO. These slipped pollutants then serve as fuel for generating the exotherm needed to reach the filter light-off temperature, effectively transforming a deficiency into a useful resource for PM combustion
Solution Approach 2:
The patent changes the operational parameter of the upstream TWC from high efficiency to deliberately reduced efficiency. This parameter change allows sufficient pollutants to slip through to provide fuel for the exothermic reactions in the filter, while still maintaining adequate NOx reduction performance. The filter's pore size and catalyst loading are also optimized to work with this modified operational regime
2Object-generated harmful factors
If active interventions are used to increase filter temperature, then particulate matter combustion is improved, but system complexity and energy consumption increase
Solution Approach 1:
The patent enables the filter to be self-sustaining by designing the upstream TWC to provide just enough unreacted pollutants to fuel the exothermic reactions within the filter. Once the light-off temperature is reached, the filter maintains its own temperature through the heat released by PM combustion, eliminating the need for external heating systems or active intervention mechanisms
Solution Approach 2:
The system converts the harmful unreacted pollutants from the TWC into a beneficial fuel source for the filter. These slipped emissions, which would normally be considered a performance deficiency, become the necessary fuel to initiate and sustain the exothermic reactions that combust particulate matter without requiring additional energy input or complex control systems
3Object-generated harmful factors
If stringent Euro 6 emission standards are met, then pollutant conversion is improved, but backpressure increases
Solution Approach 1:
The patent applies different functional qualities to different parts of the exhaust system. The upstream TWC is designed with lower catalyst loading to allow pollutant slip, while the filter is designed with specific pore sizes (10-20 μm) and TWC washcoat loading (1.0-2.0 g/in³) to optimize PM combustion. This localized differentiation of functional requirements allows the system to meet Euro 6 standards without uniform increases in backpressure across the entire system
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 configuration reduces positive ignition engine particle number emissions by >30% at acceptable backpressure, ensuring compliance with Euro 6 standards and improving catalyst light-off efficiency.
Implementation Method 1
a three-way catalyst washcoat comprising a plurality of solid particles wherein the porous structure of the washcoated porous substrate contains pores of a second mean pore size
Implementation Method 2
oxidation of carbon monoxide to carbon dioxide, (ii) oxidation of unburned hydrocarbons to carbon dioxide and water
Implementation Method 3
reduction of nitrogen oxides to nitrogen and oxygen
Implementation Method 4
allow pollutants to slip through and generate an exotherm for increased filter temperature, effectively combusting particulate matter
Implementation Method 5
a wall-flow filter with a ceramic porous substrate having a plurality of inlet channels each having inlet surfaces and a plurality of outlet channels each having outlet surfaces
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
An exhaust system (10) for a vehicular positive ignition internal combustion engine (12) comprises a filter (20) for filtering particulate matter from exhaust gas emitted from the engine, which filter comprising a porous substrate having inlet surfaces and outlet surfaces, wherein the inlet surfaces are separated from the outlet surfaces by a porous structure containing pores of a first mean pore size, wherein the porous substrate is coated with a three-way catalyst washcoat comprising a plurality of solid particles wherein the porous structure of the washcoated porous substrate contains pores of a second mean pore size, and wherein the second mean pore size is less than the first mean pore size and a three-way catalyst washcoat disposed on a separate substrate monolith (18) located upstream of the filter, wherein a mass of three-way catalyst washcoat on the upstream substrate monolith is =75% of the total mass of three-way catalyst washcoat in the exhaust system.