Gas Deflector Shield for Urea Injector Deposit Prevention
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Solution Overview
Problem
Urea deposits form and accumulate in the exhaust system of diesel engines, leading to blockages and reduced NOx conversion efficiency in SCR aftertreatment systems, particularly in recessed surfaces like the dosing injector boss, due to exhaust gas recirculation and temperature variations.
Innovation Solution
A system with a gas deflector creating a pressure differential to divert exhaust gas and form a gas shield around the urea injector, reducing recirculation and deposit formation, including a bypass flow passage and collector to direct exhaust gas around the injector outlet, and a mixing device to ensure proper spray distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a urea dosing injector is installed in the exhaust passage, then NOx conversion efficiency is improved, but urea deposits form and accumulate in recessed surfaces like the dosing injector boss
Solution Approach 1:
A gas deflector is introduced as an intermediary component between the exhaust flow and the injector boss cavity. This deflector redirects the exhaust gas flow to create a protective gas shield that prevents urea spray from entering and accumulating in the recessed boss cavity, thereby eliminating the harmful deposit formation while maintaining injector functionality
Solution Approach 2:
The harmful recirculation flow pattern within the boss cavity is extracted and redirected through the bypass flow passage. By providing an alternative flow path that bypasses the recessed area, the system removes the condition that leads to deposit accumulation while preserving the necessary exhaust flow for NOx conversion
2Reliability
If the injector is positioned to minimize exposure to high temperatures, then injector protection is improved, but exhaust gas recirculation into the cavity increases deposit formation
Solution Approach 1:
The gas deflector serves as a mediator that decouples the relationship between injector positioning and deposit formation. It allows the injector to remain in its protected position within the boss cavity while the deflector actively manages the exhaust flow to prevent recirculation and deposit accumulation in the recessed area
3Object-generated harmful factors
If mixing devices are used to reduce deposits, then deposit formation is reduced, but device complexity increases
Solution Approach 1:
The system utilizes the existing exhaust gas flow itself to create the protective gas shield, rather than introducing external complex mixing devices. The exhaust flow automatically redirects through the bypass passage and forms the shield around the injector, achieving deposit prevention through self-organizing flow dynamics
Solution Approach 2:
The solution employs pneumatic principles by using pressure differential created in the bypass flow passage to drive exhaust gas through the system. This natural pressure-driven flow creates the gas shield without requiring mechanical moving parts or complex control systems
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 gas shield significantly reduces urea deposit formation and accumulation, maintaining NOx conversion efficiency and engine power by preventing recirculation and ensuring consistent exhaust flow around the injector.
Implementation Method 1
A pressure differential is thereby formed that allows a portion of the exhaust gas flow to be diverted through the bypass flow passage to form a gas shield for the liquid reductant spray
Implementation Method 2
a bypass flow passage configured to divert a portion of exhaust flow from the exhaust passage, the bypass flow passage having an inlet in the higher pressure zone upstream of the deflector, and a collector in fluid communication with the bypass flow passage, the collector having one or more openings for allowing the bypassed portion of exhaust to flow out of the collector openings into the exhaust gas stream to form a gas shield for the liquid reductant spray
Implementation Method 3
The gas shield created may also serve to decrease recirculation of exhaust gas near the injector outlet, such as in an injector boss cavity, to reduce liquid reductant deposit formation and accumulation
Implementation Method 4
an aqueous urea solution is often stored onboard in a urea tank and injected via a urea injector into the vehicle exhaust, where the injected urea decomposed into ammonia (NH3) and carbon dioxide (CO2)
Implementation Method 5
The ammonia generated is then absorbed onto a surface of a downstream SCR catalyst, where it reacts with the NOx in the exhaust for conversion to nitrogen and water
Implementation Method 6
Urea solution is often injected into the vehicle exhaust in form of an atomized spray
Implementation Method 7
The increased exhaust gas temperature may enable removal of urea deposits from the floor and the ceiling surfaces
Data Source
AI summary
Systems and methods are provided for injecting liquid reductant into an engine exhaust. An example system includes a gas deflector positioned upstream of an injector where the gas deflector is configured to create a high pressure zone upstream of the deflector and a low pressure zone downstream of the deflector surrounding the injector outlet. A bypass flow passage diverts exhaust flow from the high pressure zone upstream of the deflector to allow the bypassed portion of exhaust to flow into the exhaust gas stream to form a gas shield for a liquid reductant spray from the injector. In this way, it is possible to reduce deposit formation and accumulation in the exhaust system.