Exhaust Purification Urea Water Injection Control
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Solution Overview
Problem
The high temperature at the SCR catalyst in an exhaust purification system increases the speed of ammonia oxidation, leading to reduced ammonia usage for NOx reduction, resulting in excessive urea water consumption to maintain NOx purification performance.
Innovation Solution
An exhaust purification apparatus with an engine control device that adjusts urea water injection based on catalyst temperatures, implementing normal and decrease modes to optimize urea water supply, reducing consumption while maintaining NOx purification efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the catalyst temperature is high, then the oxidation reaction speed of ammonia increases, but the amount of ammonia available for NOx reduction decreases, leading to increased urea water consumption
Solution Approach 1:
The system performs preliminary action by injecting urea water before the high-temperature zone and using the DPF as a temporary storage medium. The urea water is hydrolyzed to generate ammonia in advance, and the ammonia is stored in the DPF during regeneration, making it available for NOx reduction when needed without requiring continuous high urea water injection rates.
Solution Approach 2:
The DPF serves as an intermediary between urea water injection and NOx reduction. It temporarily stores ammonia generated from urea water hydrolysis and releases it when needed, decoupling the timing of urea water injection from the timing of ammonia consumption for NOx reduction. This mediator function allows the system to overcome the mismatch caused by high-temperature oxidation.
2Reliability
If urea water injection amount is increased to maintain NOx purification performance at high temperature, then NOx purification efficiency is maintained, but urea water consumption increases
Solution Approach 1:
The system generates ammonia in advance by injecting and hydrolyzing urea water before the high-temperature zone, storing it in the DPF during regeneration. This preliminary generation and storage ensures sufficient ammonia is available for NOx reduction when temperature is high, maintaining purification performance without requiring proportionally high injection rates throughout operation.
Solution Approach 2:
The system changes the operational parameters by utilizing the DPF regeneration process to create favorable conditions for urea water hydrolysis and ammonia generation. By coordinating urea water injection with the regeneration phase, the system optimizes ammonia production timing and quantity, allowing effective NOx purification at high temperatures with reduced overall urea water consumption.
3Speed
If ammonia oxidation speed increases at high temperature, then ammonia is consumed faster, but this leads to ammonia slip and reduced efficiency
Solution Approach 1:
The DPF acts as an intermediary that temporarily stores ammonia generated from urea water hydrolysis. By storing ammonia in the DPF during regeneration and releasing it during normal operation, the system decouples ammonia generation from consumption, preventing both ammonia slip from rapid oxidation and ensuring efficient ammonia utilization for NOx reduction.
Solution Approach 2:
The system performs preliminary ammonia generation through urea water hydrolysis during DPF regeneration, storing the ammonia in advance. This preliminary action ensures ammonia is available when needed without requiring rapid oxidation that would cause slip, improving overall ammonia utilization efficiency while maintaining effective NOx purification.
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 apparatus effectively suppresses urea water consumption while maintaining NOx purification performance by optimizing urea water injection, reducing ammonia slip and improving drivability by preventing engine restart due to low urea water levels.
Implementation Method 1
The SCR catalyst generates ammonia (NH3) by hydrolyzing, on the catalyst, urea water supplied into the exhaust passage from the exhaust upstream side of the catalyst
Implementation Method 2
The SCR catalyst generates ammonia (NH3) by hydrolyzing, on the catalyst, urea water supplied into the exhaust passage
Implementation Method 3
the speed of the oxidation reaction of ammonia (NH3) proceeding secondarily with respect to the reduction reaction of the NOx by the ammonia (NH3) increases
Data Source
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AI summary
An exhaust purification apparatus includes: a urea water supplier that is configured to supply urea water into an exhaust passage in which exhaust discharged from an internal-combustion engine flows; a nitrogen oxide trapping catalyst that is disposed on an exhaust upstream side of the urea water supplier, the nitrogen oxide trapping catalyst that is configured to occlude nitrogen oxide contained in the exhaust under an oxidizing atmosphere, and is configured to reduce the nitrogen oxide under a reducing atmosphere; a selective reduction catalyst that is disposed on an exhaust downstream side of the urea water supplier, the selective reduction catalyst that is configured to reduce the nitrogen oxide contained in the exhaust by using as a reducing agent the urea water supplied from the urea water supplier; and a controller that is configured to control an amount of supply of the urea water supplied from the urea water supplier, and that has a normal mode and a decrease mode in which the amount of supply of the urea water supplied from the urea water supplier is suppressed compared with in the normal mode.