Double-Walled Exhaust Routing for Cold-Start Reactant Mixing
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Solution Overview
Problem
Existing exhaust systems for internal combustion engines struggle to efficiently mix exhaust gas and reactants, particularly during cold start phases, leading to deposit formation and incomplete catalytic reactions.
Innovation Solution
A double-walled exhaust system design featuring a helically structured inner pipe within an outer pipe, ensuring reactant vaporization on the inner pipe surface, which heats up quickly, and promoting mixing by splitting the exhaust gas flow into inner and outer swirl flows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the reactant is delivered into the exhaust gas routing component during cold start phase, then the catalytic reaction can be initiated, but the reactant contacts the cold outer pipe surface causing deposit formation and incomplete vaporization
Solution Approach 1:
The exhaust gas routing component is segmented into an outer pipe and an inner pipe, creating separate flow paths. The inner pipe isolates the reactant from the cold outer pipe surface, preventing deposit formation while allowing catalytic reaction to occur in the exhaust gas stream.
Solution Approach 2:
The inner pipe acts as an intermediary structure that separates the reactant delivery zone from the cold outer pipe surface. It provides a thermal barrier that prevents the reactant from contacting the cold surface while still allowing the exhaust gas to carry the reactant to the catalytic converter.
2Productivity
If the exhaust gas flow is used directly for reactant vaporization, then mixing can occur, but during cold start the exhaust gas is insufficient to rapidly vaporize the reactant completely
Solution Approach 1:
By segmenting the exhaust gas flow into inner and outer streams, the system creates a concentrated hot flow path through the inner pipe that rapidly vaporizes the reactant. This segmented approach intensifies the heat transfer to the reactant during the critical cold start period.
Solution Approach 2:
The helical geometry of the inner pipe changes the flow parameters of the exhaust gas, creating swirl and enhancing heat transfer coefficients. This parameter change accelerates the vaporization process during cold start when time is critical.
3Ease of manufacture
If a straight inner pipe is used, then the structure is simple, but the mixing of exhaust gas and reactant is insufficient
Solution Approach 1:
The inner pipe is designed with a helical curvature instead of a straight configuration. This curvature induces swirl flow in the exhaust gas and reactant mixture, significantly enhancing mixing efficiency while maintaining a relatively simple manufacturing process for a bent pipe structure.
Solution Approach 2:
The helical inner pipe adds a rotational dimension to the otherwise linear flow path. This dimensional change from straight to helical creates centrifugal forces and swirl that dramatically improve mixing without requiring complex multi-component mixing devices.
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
Ensures rapid and uniform mixing of exhaust gas and reactants, reducing deposit formation and enhancing catalytic reaction efficiency, especially during cold starts, thereby minimizing untreated emissions.
Implementation Method 1
The reactant can be efficiently vaporized on the inner surface of the inner pipe, which is surrounded by exhaust gas and therefore heats up relatively quickly even at the start of an internal combustion engine.
Implementation Method 2
The inner pipe extends in a helical fashion in the direction of a straight longitudinal axis of the inner pipe. By providing the inner pipe and the internal volume it creates, contact between the reactant, which is to be mixed with and vaporized by the exhaust gas, and the outer pipe, which is comparatively cold and heats up only slowly
Implementation Method 3
The inner pipe extends in a helical fashion in the direction of a straight longitudinal axis of the inner pipe. When the inner pipe rests against the outer pipe along a connecting line that is spirally wound around the longitudinal axis of the inner pipe, the portion of the exhaust gas flowing through the outer volume is forced onto a spiral flow path, thereby promoting the mixing of these exhaust gas flows
Data Source
Figure 1
Figure 2a~2c
AI summary
An exhaust system for an internal combustion engine comprises at least one exhaust gas treatment unit (14), an exhaust gas routing component (12) leading to the at least one exhaust gas treatment unit (14), and a reaction agent delivery unit (18) for delivering reaction agent (R) into the exhaust gas routing component (12). The exhaust gas routing component (12) comprises an outer pipe (20) and, in a length section (B) between the reaction agent delivery unit (18) and the exhaust gas treatment unit (14), an inner pipe (22), wherein an outer volume (24) through which exhaust gas (A) flows is provided between the outer pipe (20) and the inner pipe (22), and an inner volume (26) through which exhaust gas (A) flows is provided in the inner pipe (22).