Dual Catalyst Heating System for SCR Exhaust Aftertreatment
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Solution Overview
Problem
Existing diesel exhaust gas aftertreatment systems face inefficiencies at low temperatures, as the thermolytic-hydrolytic conversion of urea-based reducing agents is temperature-dependent and loses thermal energy before reaching the SCR catalyst, resulting in low conversion efficiency in urban traffic conditions.
Innovation Solution
A system with two catalyst devices and two heating devices is implemented, where the first heat device heats the exhaust gas at the inlet of the first catalyst device to reach operating temperatures, and the second heat device, coated with an SCR catalyst, further heats the exhaust gas downstream to ensure sufficient temperatures for the SCR reaction, allowing for rear-injection of the reducing agent onto a warm surface for enhanced decomposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the SCR catalyst is positioned downstream of other exhaust catalysts to achieve comprehensive exhaust treatment, then the exhaust gas temperature decreases due to thermal energy loss, but the SCR reaction efficiency deteriorates because the temperature falls below the optimal range
Solution Approach 1:
The exhaust treatment system is divided into multiple catalyst devices arranged in sequence (first catalyst device, second catalyst device, SCR catalyst). Each segment performs specific treatment functions, allowing the SCR catalyst to be positioned downstream while maintaining its temperature through the heating devices integrated with each catalyst segment.
Solution Approach 2:
The first and second heating devices are activated before the SCR catalyst reaches its operating temperature. The first heating device pre-heats the exhaust gas at the inlet of the first catalyst device, and the second heating device further heats the exhaust gas downstream, ensuring the SCR catalyst receives sufficiently hot exhaust gas for effective SCR reaction.
2Device complexity
If the reducing agent is injected further downstream at lower temperatures to simplify the system, then the injection system becomes simpler, but the decomposition efficiency of the reducing agent deteriorates
Solution Approach 1:
The feed device for injecting the reducing agent is positioned between the first and second catalyst devices, upstream of the SCR catalyst. The heating devices are activated in advance to create a warm environment for effective reducing agent decomposition and SCR reaction, eliminating the need to inject at lower temperatures downstream.
Solution Approach 2:
The first and second catalyst devices act as intermediaries between the reducing agent injection point and the SCR catalyst. These catalyst devices provide a controlled environment with sufficient temperature and catalytic activity to ensure complete reducing agent decomposition and effective SCR reaction before the treated exhaust reaches the SCR catalyst.
3Use of energy by stationary object
If the urea solution is injected at low temperatures to reduce heating energy consumption, then the energy consumption decreases, but the thermolytic-hydrolytic conversion efficiency deteriorates
Solution Approach 1:
The system dynamically adjusts the heating parameters (temperature, heating duration) based on the exhaust gas conditions and reducing agent injection requirements. The heating devices provide sufficient temperature for effective urea thermolytic-hydrolytic conversion only when and where needed, optimizing the balance between energy consumption and conversion efficiency.
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 configuration ensures immediate catalyst operation after engine start, increases exhaust gas temperature, and enhances the decomposition of nitrogen oxides, improving the overall efficiency of the SCR reaction by maintaining optimal temperatures and ensuring the reducing agent is effectively utilized by the SCR catalyst.
Implementation Method 1
a first heat device arranged at an inlet of the first catalyst device
Implementation Method 2
a second heat device arranged downstream of the first catalyst device
Implementation Method 3
selective catalytic reduction (SCR). In SCR, nitrogen oxides are reduced to water and nitrogen over a catalyst by the reducing agent ammonia
Implementation Method 4
the ammonia is introduced in the form of a urea solution (e.g., AdBlue) into the exhaust tract ahead of the SCR catalyst. If urea solution is introduced into the exhaust tract, ammonia and isocyanuric acid are formed from urea by thermolysis
Implementation Method 5
ammonia and isocyanuric acid are formed from urea by thermolysis, and then ammonia and carbon dioxide are formed from the isocyanuric acid by hydrolysis
Data Source
AI summary
Methods and systems are provided for an exhaust gas aftertreatment system for a combustion engine in a motor vehicle. In one example, the exhaust gas aftertreatment comprises at least two catalyst devices arranged in an exhaust tract, and a feed device for a reducing agent arranged between the two catalysts, and which furthermore comprises a first heat device at the inlet of the first catalyst and a second heat device downstream thereof, the system adapted for the reduction of nitrogen oxides.