Partial-Flow Exhaust Gas Line Thermal Coupling for SCR Systems
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Solution Overview
Problem
Internal combustion engines, particularly lean-burn engines, face challenges in achieving quantitative reduction of nitrogen oxides using SCR catalytic converters due to varying operating conditions, which can lead to inefficient use of reducing agents and potential corrosion from backflow of ammonia and its by-products, affecting engine efficiency and material integrity.
Innovation Solution
A device and method that involve branching the exhaust gas flow into a partial and residual stream, with thermal coupling to a hot exhaust gas stream upstream of the turbocharger to ensure efficient decomposition of reducing agents, preventing backflow and corrosion, and utilizing a combination of catalysts and oxidation converters to optimize nitrogen oxide reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the partial exhaust gas flow is extracted close to the engine to operate the hydrolysis catalytic converter at high temperature, then the decomposition of reducing agent is improved, but exhaust gas can reverse flow direction into the engine block causing corrosion
Solution Approach 1:
The exhaust gas flow is divided into a partial flow and a main flow. The partial flow is extracted through a branch line to be heated separately and mixed back, allowing temperature control in the heating section without exposing the engine block to hot gases that could cause corrosion.
Solution Approach 2:
A mixing section is introduced as an intermediary between the heated partial exhaust gas flow and the main exhaust gas flow. This mixing section allows gradual temperature equalization and prevents direct contact of hot reducing agents with the engine block, thereby avoiding corrosion while maintaining decomposition efficiency.
2Reliability
If oxidation catalytic converter is arranged upstream of the reducing agent metering device to prevent backflow corrosion, then material integrity is improved, but engine efficiency deteriorates due to reduced charging group efficiency
Solution Approach 1:
The oxidation catalytic converter function is extracted from the main exhaust path and integrated into the heating section where hot exhaust gases naturally flow. This allows oxidation to occur in a dedicated zone without creating additional flow resistance in the main exhaust path, preserving charging group efficiency while still preventing corrosion.
Solution Approach 2:
The heating function and oxidation catalytic converter function are merged into a single heating section. The hot exhaust gas flow serves dual purposes: heating the partial flow for reducing agent decomposition and providing oxidation environment for preventing corrosion, eliminating the need for separate components that would reduce engine efficiency.
3Temperature
If thermal coupling is implemented to heat the partial exhaust gas flow, then reducing agent decomposition is improved, but thermal losses to the environment increase
Solution Approach 1:
The partial exhaust gas flow line is nested within or alongside the heating section through which hot exhaust gases flow. This nested arrangement maximizes thermal contact between the hot gases and the partial flow without requiring additional insulation or protective structures, efficiently transferring heat while minimizing environmental thermal losses.
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 approach ensures quantitative decomposition of reducing agents without significantly impairing engine efficiency, preventing corrosion, and enhancing nitrogen oxide reduction efficiency while minimizing thermal losses and maintaining engine performance.
Implementation Method 1
the partial-flow exhaust gas line is thermally coupled to at least one turbine line leading a hot exhaust gas stream to an exhaust gas turbine of an exhaust gas turbocharger
Implementation Method 2
quantitative decomposition of the reducing agent is ensured
Implementation Method 3
thermolysis occurs first, i. H. the thermal decomposition of urea
Implementation Method 4
SCR catalytic converter, wherein an exhaust pipe upstream of the SCR catalytic converter branches off
Implementation Method 5
at least one turbine line leading a hot exhaust gas stream to an exhaust gas turbine of an exhaust gas turbocharger
Data Source
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AI summary
The invention relates to a device and a method for cleaning an exhaust gas stream of an internal combustion engine, in particular a lean-burn internal combustion engine, with at least one SCR catalyst (3) arranged in an exhaust gas stream (2) of an internal combustion engine, wherein an exhaust gas line (8) upstream of the SCR catalyst (3) branches at a junction (7) into a partial-flow exhaust gas line (9) and into a residual-flow exhaust gas line (8'), wherein the partial-flow exhaust gas line (9) is coupled to a reducing agent metering device (12) for metering a reducing agent (13) into the exhaust gas partial flow (18) guided in the partial-flow exhaust gas line (9), and wherein the partial-flow exhaust gas line (9) and the residual-flow exhaust gas line (8') are joined upstream of the junction (7) and upstream of the at least one SCR catalyst (3) at an exhaust gas line (8").According to the invention, the partial-flow exhaust gas line (9) is thermally coupled to a turbine line (15) leading a hot exhaust gas flow (16) to an exhaust gas turbine (16) of an exhaust gas turbocharger (4).