Heated SCR Mixer Elements Prevent Urea Deposits
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Solution Overview
Problem
Existing exhaust gas mixer systems for selective catalytic reduction (SCR) in internal combustion engines face challenges with solid urea deposits forming at low temperatures, which hinder NOx reduction efficiency, especially during engine start-up and coasting operations.
Innovation Solution
A mixer with resistance heating elements, configured as turbine blades, is used to directly heat the exhaust gas stream with electricity, preventing and melting off deposits, ensuring optimal distribution of the reducing agent and maintaining efficient NOx reduction even at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional mixers are used for distributing reducing agent in exhaust gas, then the distribution can be improved, but solid deposits form on mixer elements at low temperatures
Solution Approach 1:
The mixer elements are designed with electric heating capability to change the temperature parameter of the exhaust gas stream. By heating the mixer elements to above 132°C (urea melting point), the system prevents urea from solidifying and depositing on the mixer surfaces, thereby eliminating the harmful deposit formation while maintaining the mixing function.
Solution Approach 2:
The patent replaces the purely mechanical mixing system with an electro-thermal assisted system. Electric heating elements are integrated into the mixer structure, substituting the need for complex mechanical anti-deposit mechanisms with a simpler thermal field approach that prevents deposit formation through controlled heating.
2Productivity
If AdBlue is injected into exhaust gas for SCR reaction, then NOx reduction is achieved, but exhaust gas temperature decreases due to cold injection
Solution Approach 1:
The mixer elements perform preliminary heating of the exhaust gas stream before the gas enters the SCR catalyst. By pre-heating the gas and mixer elements to sufficient temperatures, the system ensures that the subsequent SCR reaction can proceed efficiently even when the engine is cold or operating at low temperatures, thus maintaining NOx reduction productivity.
Solution Approach 2:
The electric heating elements apply preliminary anti-action against the temperature decrease caused by cold AdBlue injection. By actively heating the exhaust stream in the mixer, the system counteracts the cooling effect of the injected AdBlue, preventing temperature from dropping below the threshold required for effective SCR operation.
3Reliability
If mixer elements are heated to prevent deposits, then deposit formation is prevented, but additional energy consumption occurs
Solution Approach 1:
The mixer elements serve multiple functions simultaneously: they perform the mechanical mixing of exhaust gas and reducing agent, and they also function as heating elements through integrated electric resistance heating. This multi-functionality reduces the need for separate heating devices, thereby minimizing additional energy consumption while ensuring deposit-free operation.
Solution Approach 2:
The mixer elements are designed to self-heat through integrated electric heating elements, eliminating the need for external heating systems. The heating function is built into the mixer structure itself, allowing the system to serve its own heating needs without requiring additional energy-intensive external heating apparatus.
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 enables uniform distribution of the reducing agent across the catalyst surface, prevents deposit formation, and allows NOx reduction at low exhaust gas temperatures, enhancing the efficiency of the SCR reaction and reducing emissions, especially during cold engine operations.
Implementation Method 1
The mixer elements are adapted for direct electrical heating with an electric current flowing through them due to their electrical resistance
Implementation Method 2
The melting point of dry urea is at 132° C. The lower the exhaust gas temperatures, the more unwanted solid deposits form
Data Source
AI summary
The invention relates to a mixer for a device for selective catalytic reduction of exhaust gases from internal combustion engines. The mixer comprises a structure of mixer elements through which the mixture of exhaust gas and reducing agent is to flow. The mixer elements have an electric current flowing through them for electrical heating due to the electrical resistance thereof. The invention further relates to a device for selective catalytic reaction of exhaust gases from an internal combustion engine having an exhaust gas pipe leading to a mixer according to the invention and having a reducing agent pipe which is connected to a reservoir for reducing agent and which opens into the exhaust gas pipe in the flow direction upstream of the mixer, and a catalyst in the flow direction downstream of the mixer.