Exhaust Flow Passage Bend for Urea Hydrolysis
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The arrangement of the particulate filter upstream of the selective reduction catalyst in exhaust emission control devices prevents proper hydrolysis of urea water into ammonia before it reaches the catalyst, hindering effective NOx reduction in diesel engines.
Innovation Solution
Incorporating a bend in the exhaust gas flow passage between the urea water addition point and the selective reduction catalyst to refine the urea water's liquid particle size, ensuring proper hydrolysis into ammonia, along with an oxidation catalyst for particulate filter regeneration and an ammonia oxidizer to manage surplus ammonia.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the particulate filter is arranged upstream of the selective reduction catalyst, then the particulate filter can be effectively regenerated through fuel oxidation, but the urea water cannot be properly hydrolyzed into ammonia before reaching the catalyst
Solution Approach 1:
The flow passage is divided into distinct segments: a first passage section from the urea water addition means to the particulate filter, and a second passage section from the particulate filter to the selective reduction catalyst. This segmentation allows the urea water to be added upstream of the particulate filter while ensuring it reaches the selective reduction catalyst in a state suitable for hydrolysis, thus resolving the contradiction between filter regeneration efficiency and hydrolysis completeness.
Solution Approach 2:
The particulate filter serves as an intermediary element between the urea water addition point and the selective reduction catalyst. By positioning the urea water addition means upstream of the particulate filter and allowing the urea water to pass through or near the filter, the system enables both the regeneration function (through fuel oxidation on the filter) and the hydrolysis function (as urea water converts to ammonia in the flow passage) to occur simultaneously without interfering with each other.
2Productivity
If urea water is added upstream of the selective reduction catalyst, then NOx reduction can be achieved through ammonia reaction, but the urea water requires additional space and time for hydrolysis which conflicts with compact system design
Solution Approach 1:
The invention merges multiple functions into the flow passage structure: the passage not only transports exhaust gas from the engine to the selective reduction catalyst but also serves as the hydrolysis chamber for urea water conversion to ammonia. Additionally, the passage is configured to enable particulate filter regeneration through controlled fuel oxidation. By combining transport, hydrolysis, and regeneration functions into a single integrated flow path, the system achieves effective NOx reduction without requiring separate dedicated spaces for each function, thus maintaining compact design.
3Device complexity
If the flow passage is made straight and short for compact design, then device complexity is reduced, but the urea water cannot be properly hydrolyzed into ammonia
Solution Approach 1:
The urea water addition means is positioned upstream of the particulate filter in the flow passage, allowing urea water to be added to the exhaust gas stream before the exhaust gas reaches the selective reduction catalyst. This preliminary positioning ensures that the urea water has sufficient distance and time within the flow passage to hydrolyze into ammonia through contact with the exhaust gas, while still maintaining a compact overall structure. The upstream addition point provides the necessary preliminary action for complete hydrolysis without requiring an excessively long or complex passage.
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 enables effective hydrolysis of urea water into ammonia, facilitating NOx reduction and ensuring proper particulate filter regeneration while preventing ammonia discharge into the air.
Implementation Method 1
the urea water is decomposed into ammonia and carbon dioxide gas according to the following equation to thereby depurate NOx, well in the exhaust gas through reduction by ammonia on the catalyst. (NH2)2CO+H2O→2NH3+CO2
Implementation Method 2
by forming the one or more bends in the flow passage for guidance of the exhaust gas from the urea water addition means to the selective reduction catalyst, the urea water collides at the bend or bends to bring about refinement in liquid particle size of the urea water and thus effective mixing of the exhaust gas with the urea water
Implementation Method 3
the fuel is added to the exhaust gas upstream of the oxidation catalyst to bring about oxidation reaction of the added fuel (HC) during passing of the added fuel through the oxidation catalyst. The exhaust gas elevated in temperature by the reaction heat of the oxidation flows into the particulate filter arranged just behind so that temperature of a catalyst floor of the particulate filter is elevated to burn off the particulates
Implementation Method 4
a selective reduction catalyst incorporated in an exhaust pipe through which exhaust gas flow, said catalyst having a feature of selectively reacting NOx with a reducing agent even in the presence of oxygen
Data Source
AI summary
An exhaust emission control device is disclosed. The exhaust emission control device includes a particulate filter incorporated in an exhaust pipe to capture particulates in exhaust gas, a selective reduction catalyst arranged downstream of the particulate filter to selectively react NOx with ammonia, even in the presence of oxygen, and urea water addition means capable of adding urea water as reducing agent between the catalyst and the filter. The urea water addition means is arranged at an upstream end of a longest linear portion. At least one bend is formed in a passage which guides the exhaust gas from the urea water addition means to the selective reduction catalyst.