Exhaust Aftertreatment Catalyst Light-Off via Cylinder Segmentation
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Solution Overview
Problem
The efficiency of engine exhaust gas after treatment systems is temperature-dependent, and existing methods fail to quickly reach the threshold temperature after a cold engine start, leading to reduced catalyst efficiency and increased tailpipe emissions.
Innovation Solution
The system operates engine cylinders with a rich air-fuel ratio continuously to deliver heat flux to the exhaust gas after treatment system, while others operate with a lean air-fuel ratio to oxidize hydrocarbons, thereby accelerating catalyst temperature increase, maintaining an overall stoichiometric air-fuel ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the engine operates with a rich air-fuel ratio to deliver heat flux to the exhaust gas after treatment system, then the catalyst reaches light-off temperature faster, but the engine emissions increase due to incomplete combustion
Solution Approach 1:
The engine cylinders are divided into two groups: one group operates with a rich air-fuel ratio to generate heat flux for the exhaust gas after treatment system, while the other group operates with a lean air-fuel ratio to oxidize hydrocarbons. This segmentation allows simultaneous achievement of fast catalyst light-off and reduced engine emissions by balancing incomplete combustion in rich cylinders with oxidation in lean cylinders.
Solution Approach 2:
Different air-fuel ratios are applied to different cylinder groups based on their local function: rich air-fuel ratio for heat generation in the exhaust system, and lean air-fuel ratio for hydrocarbon oxidation. This local quality differentiation enables each cylinder group to perform its specific function optimally while contributing to the overall emission reduction goal.
2Object-generated harmful factors
If the engine operates with a lean air-fuel ratio to oxidize hydrocarbons, then the engine emissions decrease, but the exhaust gas temperature is insufficient to reach the catalyst light-off temperature
Solution Approach 1:
The engine cylinders are segmented into two functional groups: one group operates lean to oxidize hydrocarbons and reduce emissions, while the other group operates rich to generate the necessary heat flux for catalyst light-off. This segmentation resolves the contradiction by allowing each group to specialize in its function while the combined exhaust stream achieves both emission reduction and sufficient temperature.
Solution Approach 2:
The exhaust streams from rich and lean cylinder groups are merged in the exhaust system. The rich exhaust provides heat flux for catalyst light-off, while the lean exhaust provides oxygen for hydrocarbon oxidation. By merging these complementary exhaust streams, the system achieves both high temperature for catalyst activation and low emissions through hydrocarbon oxidation.
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 reduces the time for the catalyst to reach the light-off temperature, enhancing catalyst efficiency and reducing engine emissions without increasing system costs.
Implementation Method 1
operating at least one engine cylinder with a rich air-fuel ratio continuously for a plurality of engine cycles... to deliver heat flux to an exhaust gas after treatment system
Implementation Method 2
operating at least one engine cylinder with a lean air-fuel ratio continuously for the plurality of engine cycles... to oxidize hydrocarbons contained in exhaust gases
Data Source
AI summary
Methods and systems are provided for improving efficiency of an exhaust gas after treatment system of a vehicle. In one example, a first group of engine cylinders is operated with a rich air-fuel ratio continuously while a second group of engine cylinders is operated with a lean air-fuel ratio continuously. The rich and lean exhaust gases from the two groups of engine cylinders may be oxidized within an exhaust gas after treatment system to improve catalyst efficiency.