Multi-Injector SCR Mixer for Diesel DEF Deposit Reduction
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Solution Overview
Problem
High diesel exhaust fluid (DEF) injection rates required for low NOx emission compliance increase the risk of solid deposit formation in selective catalytic reduction (SCR) systems, especially during cold starts and low load conditions, which hampers SCR mixer functionality and increases back pressure and DEF consumption.
Innovation Solution
A compact SCR device with multiple DEF injectors strategically placed to distribute the DEF dosing between two or more locations within the SCR mixer, enhancing liquid film evaporation rates through increased heat transfer and reducing the risk of solid deposit formation by increasing the wall wetting area and film thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high DEF injection rates are used to meet low NOx emission requirements, then NOx reduction efficiency is improved, but the risk of solid deposit formation increases
Solution Approach 1:
The patent divides the single DEF injection function into multiple injectors positioned at different locations within the SCR mixer. This segmentation allows the total DEF dosing rate to be distributed across multiple injection points, reducing the liquid film thickness at each location while maintaining the total NOx reduction capacity. The multiple injectors prevent excessive liquid accumulation that would otherwise lead to solid deposit formation.
Solution Approach 2:
The patent applies different injection characteristics at different locations within the SCR mixer. Each injector is positioned to target specific zones, creating locally optimized DEF distribution patterns. This local quality approach ensures that areas prone to liquid accumulation receive appropriate dosing while maintaining overall system effectiveness for NOx reduction.
2Productivity
If high DEF dosing rates are applied, then NOx emission compliance is improved, but wall wetting area increases leading to solid byproduct formation
Solution Approach 1:
By segmenting the DEF injection across multiple injectors positioned at different locations and angles, the patent distributes the total dosing rate over a larger cumulative surface area. This prevents excessive liquid film thickness at any single wall location, reducing the formation of solid byproducts while maintaining the required total DEF injection rate for NOx compliance.
3Object-affected harmful factors
If multiple DEF injectors are installed at different locations, then solid deposit formation is reduced, but device complexity increases
Solution Approach 1:
The patent combines multiple DEF injectors into a single SCR mixer assembly, integrating them into one unified device. This merging approach allows the system to benefit from multiple injection points for reduced solid deposit formation while maintaining a compact, integrated structure that minimizes overall system complexity compared to separate injection systems.
Solution Approach 2:
The SCR mixer is designed to serve multiple functions: it houses multiple DEF injectors for optimized dosing distribution, provides mixing functionality for exhaust gases and DEF vapor, and acts as a flow distribution manifold. This multi-functionality reduces the need for separate components, thereby managing device complexity while achieving the benefits of multiple injectors.
4Productivity
If DEF liquid film thickness is increased for higher dosing rates, then NOx reduction capacity is improved, but evaporation rate decreases leading to solid deposits
Solution Approach 1:
The patent segments the DEF injection into multiple streams at different locations, which prevents the formation of excessively thick liquid films at any single point. Thinner liquid films evaporate more rapidly, and the segmentation ensures that the total dosing capacity is maintained while improving evaporation rates across all injection zones, thereby reducing solid deposit formation.
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 multi-injection system effectively reduces the risk of solid deposit formation, improves ammonia distribution, and maintains SCR system efficiency by promoting higher DEF evaporation rates and reducing back pressure.
Implementation Method 1
enhancing liquid film evaporation rates through increased heat transfer
Implementation Method 2
enhancing liquid film evaporation rates through increased heat transfer
Implementation Method 3
a swirl plate disposed in the chamber and oriented about a portion of the outlet opening
Implementation Method 4
reducing the risk of solid deposit formation by increasing the wall wetting area and film thickness
Data Source
AI summary
A compact SCR device is provided for use with a diesel exhaust fluid (DEF) injection system having multiple injectors for providing diesel exhaust fluid to exhaust gas to reduce NOx emissions. The DEF injectors are disposed in the close coupled SCR mixer. A first injector injects into a chamber of the mixer with sidewardly oriented impingement plates having openings. A second injector radially spaced and offset has a different angle from the first injector for injecting DEF into the SCR mixer. A swirl plate forces the exhaust gas in the flow path to turn and exit through an outlet opening. An inlet opening for the mixer is aligned transversely near the first injector and is offset from the outlet opening. Thus, upon entering the compact SCR mixer, the exhaust gas must change direction and passes by at least one injector and impingement plates having flaps and openings before exiting the mixer.