Exhaust Mixing Device Flow Guide for Urea Deposit Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing mixing devices for exhaust gas from combustion engines face issues with urea deposits, which can clog the doser and lead to service stops, especially under high NOx emissions, and require effective mixing of aqueous urea solutions with exhaust gas to reduce nitrogen oxides.
Innovation Solution
A mixing device with a flow guide configured as a splitting baffle upstream of the dosing unit, creating a gap between the flow guide and the casing side wall, where clean exhaust gas accelerates and washes over the dosing unit area, preventing urea deposits and enhancing mixing uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mixing device uses a corner region configuration to divert exhaust gas flow, then effective mixing of urea solution and exhaust gas is achieved, but urea deposits form on the side wall near the dosing unit opening
Solution Approach 1:
The exhaust gas flow is segmented into two separate streams by the flow guide: a first exhaust gas stream that bypasses the dosing unit area and a second exhaust gas stream that flows through the gap between the flow guide and side wall. This segmentation prevents urea-laden recirculating flow from contacting the side wall near the dosing unit, eliminating deposit formation while preserving the corner region's mixing effectiveness.
2Device complexity
If the flow guide is positioned downstream of the dosing unit opening, then the device structure is simpler, but urea spray hits the side wall causing deposit formation
Solution Approach 1:
The flow guide is positioned upstream of the dosing unit opening to perform preliminary action by directing the second exhaust gas stream through the gap before the recirculating urea spray can reach the side wall. This preemptive flow direction prevents urea deposits from forming on the side wall and dosing unit mounting area.
3Object-generated harmful factors
If the second exhaust gas stream flows through the gap between the flow guide and side wall, then urea deposits are prevented, but additional flow path complexity is introduced
Solution Approach 1:
The second exhaust gas stream serves a dual function: it maintains the primary exhaust flow path while simultaneously acting as a protective flow that washes over the side wall near the dosing unit opening. This self-service approach prevents urea deposits without requiring additional active components 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
Significantly reduces urea deposits, lowers repair costs, and improves the uniformity of ammonia distribution at SCR-catalyst substrates, while maintaining low back pressure and being cost-effective with minimal redesign efforts.
Implementation Method 1
a gap for the second exhaust gas stream is formed between the flow guide and a side wall of the casing, in which the opening for the dosing unit is located
Implementation Method 2
When the aqueous urea solution is fed into the exhaust gas, ammonia (NH3) forms upon the hydrolysis of urea in the hot exhaust gas
Implementation Method 3
This ammonia reacts with the nitrogen oxides (NOx) that are present in the exhaust gas in a selective catalytic reduction (SCR) reaction
Implementation Method 4
improves the uniformity of ammonia distribution at substrates of an SCR-catalyst arranged downstream of the mixing device
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
The invention relates to a mixing device (18) for mixing exhaust gas from a combustion engine of a vehicle with a solution (20) for lowering the content of nitrogen oxides in the exhaust gas. The mixing device (18) comprises a casing (24) with an exhaust inlet (30), an exhaust outlet (32) and a corner region (40) in which an exhaust gas flow is diverted towards the exhaust outlet (32). The corner region (40) has an opening (26) for a dosing unit. The mixing device (18) comprises a flow guide (48) arranged within the casing (24). The flow guide (48) is configured to divide a total of the exhaust gas flow into a first exhaust gas stream and a second exhaust gas stream. A gap (54) for the second exhaust gas stream is formed between the flow guide (48) and a side wall (22) of the casing (24). In the side wall (22) the opening (26) for the dosing unit is located. An end region (56) of the flow guide (48) is arranged upstream of the opening (26) for the dosing unit.