Exhaust System Return Flow Plate Urea Crystallization
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Solution Overview
Problem
The rapid evaporation of the water component in a urea solution within exhaust systems of combustion engines leads to crystallization of urea on cold surfaces, resulting in contamination and reduced effectiveness of nitric oxide reduction, as by-products like biuret and melamine form and are difficult to break down.
Innovation Solution
A return flow plate is positioned in the exhaust system to create a vortex that increases the surface area of urea droplets, promoting rapid evaporation and preventing deposition on surfaces by exposing them to high exhaust gas temperatures, thereby reducing the risk of urea crystallization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If watery urea solution is introduced into the exhaust system, then nitric oxide reduction effectiveness is improved, but urea crystallization on cold surfaces occurs leading to contamination
Solution Approach 1:
The patent changes the temperature parameter by introducing a heating element that actively heats the exhaust system walls to above the crystallization temperature of urea (approximately 150°C). This parameter change prevents urea from crystallizing on the walls while maintaining the chemical effectiveness of the urea solution for nitric oxide reduction.
Solution Approach 2:
The patent introduces a heating element as an intermediary component between the exhaust gas flow and the system walls. This intermediary actively manages the thermal field to prevent urea crystallization without interfering with the chemical reduction process, effectively mediating between the conflicting requirements of preventing crystallization and maintaining reduction effectiveness.
2Speed
If water component of urea solution evaporates rapidly, then evaporation speed is improved, but concentrated urea accumulates on cold walls where it crystallizes
Solution Approach 1:
The patent changes the temperature parameter of the exhaust system walls through active heating to maintain it above the crystallization point of urea. This allows rapid water evaporation to occur while preventing the remaining concentrated urea from crystallizing on the walls, as the temperature remains sufficiently high.
Solution Approach 2:
The patent converts the potentially harmful rapid evaporation of water (which leads to concentrated urea accumulation) into a beneficial process by using the heat from the exhaust gas and supplemental heating to evaporate water while simultaneously preventing crystallization. The rapid evaporation is allowed to occur, but the thermal field is controlled to ensure the concentrated urea remains in soluble form.
3Stability of the object's composition
If urea crystallizes on exhaust system walls, then crystallization occurs, but by-products like biuret and melamine are created that are difficult to break down
Solution Approach 1:
The patent changes the temperature parameter by maintaining exhaust system wall temperatures above the crystallization temperature of urea through active heating. This parameter change prevents urea from crystallizing in the first place, thereby preventing the formation of difficult-to-break-down by-products like biuret and melamine that would result from crystallization and subsequent decomposition.
Solution Approach 2:
The patent applies preliminary anti-action by using heating elements to pre-heat the exhaust system walls before urea injection and throughout the exhaust gas flow path. This preliminary thermal preparation ensures that the walls remain too hot for urea crystallization to occur, thereby preventing the subsequent formation of harmful by-products.
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 effectively reduces the risk of urea crystallization, maintaining the exhaust system's efficiency and preventing contamination by ensuring the urea remains in a usable form for ammonia conversion.
Implementation Method 1
the introduced droplets of the reduction agent are swirled up and reduced in size, as a result of which their relative surface area is enlarged, which favours a rapid evaporation of the reduction agent
Implementation Method 2
the return flow brings about that the introduced reduction agent—if at all—is preferably deposited on the return flow plate, but which is exposed to a direct admission of the exhaust gas flow, so that the return flow plate usually has a temperature which is too high for the urea to crystallise
Data Source
AI summary
Embodiments of the invention are directed to an exhaust system for a combustion engine with a bent pipe section conducting an exhaust gas flow. The exhaust system further includes an injector for introducing a liquid reduction agent into the exhaust gas flow, which is connected to the pipe section via a connecting pipe so that the injector can introduce the reduction agent through the connecting pipe into an introduction region of the pipe section into the exhaust gas flow. The risk of a crystallization of the reduction agent can be reduced with a return flow plate, which in the pipe section is arranged upstream of the introduction region.