Reverse Flow Hydrocarbon Trap for Cold Start Emissions
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Solution Overview
Problem
Conventional hydrocarbon traps fail to effectively retain hydrocarbons until the three-way catalyst reaches its light-off temperature during cold starts, resulting in poor hydrocarbon trap performance due to a temperature mismatch between the trapping material and the catalyst.
Innovation Solution
A reverse flow design hydrocarbon trap is implemented, where hydrocarbons desorbed from the trapping material encounter a higher temperature region within the trap, allowing the oxidative catalyst to convert a greater percentage of hydrocarbon emissions by reversing the exhaust gas flow and using high thermal conductivity and thermal mass materials to rapidly increase the temperature of the inlet end.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional layer configuration design of zeolite and three-way catalyst is used, then hydrocarbon trapping material can adsorb hydrocarbons at low temperatures, but hydrocarbons desorb before catalyst reaches light-off temperature resulting in poor conversion
Solution Approach 1:
The patent inverts the conventional layer configuration by placing the three-way catalyst layer below the hydrocarbon trapping material layer, creating a reverse flow path where exhaust gases first contact the trapping material and then flow upward through the catalyst layer. This inversion ensures that desorbed hydrocarbons immediately encounter the catalyst at higher temperatures for effective conversion.
Solution Approach 2:
The patent creates different thermal environments in different regions of the trap. The lower region contains the catalyst that operates at higher temperatures for conversion, while the upper region contains the trapping material that operates at lower temperatures for adsorption. This local differentiation of thermal conditions allows both functions to operate optimally simultaneously.
2Productivity
If hydrocarbon trapping material retains hydrocarbons until light-off temperature, then catalyst can convert hydrocarbons effectively, but trapping materials cannot retain all hydrocarbons until light-off temperature is reached
Solution Approach 1:
By inverting the layer configuration and reversing the flow direction, the patent ensures that hydrocarbons desorb in the upward flow and immediately encounter the hot catalyst layer below, converting them before they can escape. This resolves the retention issue by changing the spatial and temporal sequence of desorption and conversion.
3Device complexity
If conventional exhaust gas flow direction is used, then trap structure is simple, but desorbed hydrocarbons pass through trap before encountering catalyst at light-off temperature
Solution Approach 1:
The patent reverses the conventional flow direction by creating a dual-channel structure where exhaust enters the top channel, flows downward, then reverses direction in the intermediate channel, and flows upward through the outlet channel. This reverse flow path ensures desorbed hydrocarbons encounter the catalyst layer at the appropriate temperature and location.
Solution Approach 2:
The patent divides the exhaust flow path into multiple segments: a first channel for downward flow, an intermediate channel for flow reversal, and a second channel for upward flow. This segmentation allows the exhaust to follow a path that maximizes contact with both the trapping material and catalyst at optimal temperatures.
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 reverse flow design enhances hydrocarbon trap performance by ensuring that a higher percentage of hydrocarbons are converted to environmentally benign compounds, improving emissions reduction during cold starts.
Implementation Method 1
hydrocarbon emissions are adsorbed by the zeolite material during cold start
Implementation Method 2
conversion of hydrocarbons to water and carbon dioxide
Implementation Method 3
using high thermal conductivity and thermal mass materials to rapidly increase the temperature of the inlet end
Data Source
AI summary
A reverse flow hydrocarbon trap is provided that improves the conversion of hydrocarbons present in the exhaust gases of a vehicle to more environmentally benign compounds during cold engine starts. The trap includes a substrate having at least one exhaust gas passage therethrough, with the walls of the exhaust gas passage including a hydrocarbon trapping material and an oxidative catalyst. The substrate includes an inlet for hot exhaust gas from a vehicle engine and an outlet for the exhaust gas and further includes an inlet channel, an outlet channel, and an intermediate channel through which exhaust gas flows. The intermediate channel is oriented such that the flow of exhaust gas through the exhaust gas passage is reversed from the direction of flow in the inlet and outlet channels to improve the performance of the hydrocarbon trap.