SCR Mixer Urea Injector Angling for Deposit Mitigation
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Solution Overview
Problem
In diesel engine after-treatment systems, crystalline urea deposits form on surfaces within the mixing zone and on the urea injector mounting boss, leading to undesirable accumulation due to the current design of the urea injector and exhaust flow configuration.
Innovation Solution
The exhaust flow from the particulate filter is directed through separate passages with varying cross-sectional areas to create different velocities, and the urea injector is angled to direct the urea solution across the faster-moving exhaust flow, preventing significant wetting of the bottom wall and reducing deposit accumulation by leveraging the energy of the accelerated flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the urea injector nozzle is aimed at a right angle to the exhaust flow direction to spray across the entire exhaust flow, then the urea solution is distributed widely, but crystalline urea deposits accumulate on the bottom wall and mounting boss surfaces
Solution Approach 1:
Instead of aiming the nozzle at a right angle to spray across the exhaust flow, the invention inverts the approach by directing the nozzle at an acute angle (15-45 degrees) relative to the exhaust flow direction. This angular adjustment changes the spray trajectory so that urea solution is injected upstream and carried by the exhaust flow rather than being deposited directly on downstream surfaces, thereby preventing crystal accumulation while maintaining distribution effectiveness
Solution Approach 2:
The invention changes the critical parameter of nozzle aiming angle from 90 degrees (right angle) to an acute angle range of 15-45 degrees relative to the exhaust flow direction. This parameter modification fundamentally alters the spray pattern and urea solution trajectory, enabling the solution to be carried by the exhaust flow velocity field rather than settling on surfaces, thus resolving the deposit accumulation problem
2Area of stationary object
If the injector nozzle is positioned to spray across the entire exhaust flow, then coverage is maximized, but wetting of the bottom wall occurs leading to deposit formation
Solution Approach 1:
The exhaust flow itself serves as an intermediary carrier that transports the injected urea solution from the injection point to the SCR catalyst. By injecting upstream at an acute angle, the exhaust flow velocity field carries the urea solution through the mixing zone without allowing it to settle on the bottom wall, using the flow field as a medium to prevent harmful deposition while maintaining broad coverage
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 effectively mitigates the accumulation of crystalline urea deposits on surfaces and the injector mounting boss, ensuring efficient evaporation and dispersion of the urea solution, thereby optimizing the catalytic reduction process in the SCR catalyst.
Implementation Method 1
The transverse cross sectional areas of the respective passages are chosen to accelerate the exhaust flow leaving the particulate filter, with the lower passage preferably having a smaller transverse cross sectional area than the upper passage so that the flow that it conveys into the mixing zone enters the mixing zone at a greater velocity
Implementation Method 2
a urea injector is disposed downstream of a particulate filter to spray urea solution into a mixing zone where the urea is intended to completely evaporate and mix throughly with engine exhaust
Implementation Method 3
where the urea is intended to completely evaporate and mix throughly with engine exhaust that has been filtered by the particulate filter
Implementation Method 4
the mixture is directed across surfaces of an SCR catalyst where oxides of nitrogen (NOx) are chemically reduced via catalytic action
Data Source
AI summary
A device and method for catalytic reduction of NOx in gaseous products of combustion by directing the products of combustion through a particulate filter (32) and then into a mixing zone (28) through separate flow passages (34, 36) at respective velocities greater than that at which products of combustion leave the filter, by causing an injector (38) to introduce urea solution through a nozzle (40) aimed toward the mixing zone along a slant direction (42) to, and across, flow entering the mixing zone through a first (34) of the separate flow passages and ultimately toward a far wall (44) of the mixing zone relative to the nozzle while directing exhaust flow entering the mixing zone through a second (36) of the separate flow passages to enter the mixing zone between the first flow passage and far wall, and by directing flow leaving the mixing zone through an SCR catalyst (48).