Exhaust Gas Purification System Urea Injection Control
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Solution Overview
Problem
Conventional exhaust gas purification systems experience excess urea injection and ammonia slip due to incorrect ammonia detection, leading to inefficient nitrogen oxide reduction and increased urea supply in lean nitrogen oxide trap catalyst systems, particularly under EU6d/RDE exhaust gas regulations.
Innovation Solution
The system incorporates a nitrogen oxide trap catalyst, urea injector, mixer, composite catalyst device, selective catalytic reduction device, and ammonia oxidation catalyst, along with a low-pressure exhaust gas recirculation system and nitrogen oxide detectors to control urea injection based on engine conditions, preventing excess urea and ammonia slip by optimizing urea injection timing and reducing ammonia oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a nitrogen oxide detector is used to detect nitrogen oxide concentration for controlling urea injection, then nitrogen oxide purification efficiency is improved, but ammonia is wrongly recognized as nitrogen oxide leading to excess urea injection and ammonia slip
Solution Approach 1:
The detection function is segmented into multiple specialized detectors: a first nitrogen oxide detector positioned before the LNT device to detect actual nitrogen oxide concentration for urea injection control, and a second nitrogen oxide detector (ammonia oxidation catalyst) positioned after the LNT device to detect ammonia concentration. This segmentation allows each detector to perform its specific function without interference, preventing ammonia from being wrongly detected as nitrogen oxide.
2Productivity
If urea injection amount is increased to ensure sufficient nitrogen oxide reduction, then nitrogen oxide purification is improved, but excess urea injection occurs causing ammonia slip at the SCR device
Solution Approach 1:
The system implements feedback control by using the first nitrogen oxide detector to continuously monitor nitrogen oxide concentration in real-time and adjusting urea injection amount accordingly. The control unit receives detection results and dynamically optimizes urea injection to match actual nitrogen oxide levels, preventing both insufficient and excessive injection. This feedback mechanism eliminates the need for over-injection while ensuring sufficient nitrogen oxide reduction.
3Adaptability or versatility
If the LNT device is used to absorb and store nitrogen oxide, then exhaust gas regulation compliance is improved, but ammonia generated during desorption causes detection errors and excess urea supply
Solution Approach 1:
The harmful ammonia generated during LNT desorption is extracted and treated separately from the main nitrogen oxide purification stream. An ammonia oxidation catalyst device is positioned after the LNT device to specifically oxidize ammonia, converting it to nitrogen and water. This extraction approach removes the source of detection errors before the exhaust reaches the SCR device, preventing ammonia from being mistaken for nitrogen oxide.
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 approach prevents excess urea injection, stabilizes nitrogen oxide purification, and extends urea refill cycles, ensuring efficient exhaust gas treatment and reduced ammonia emissions.
Implementation Method 1
a nitrogen oxide trap catalyst (lean NOx trap; LNT) device configured to absorb and store nitrogen oxide generated by a lean combustion of an engine
Implementation Method 2
reduce the nitrogen oxide into nitrogen by a reduction action
Implementation Method 3
a selective catalytic reduction (SCR) device disposed at the rear of the SDPF and configured to reduce the nitrogen oxide of the exhaust gas passing through the diesel particulate matter filter
Implementation Method 4
an ammonia oxidation catalyst (AOC) device disposed at the rear of the SCR device, configured to oxidize ammonia of the exhaust gas passing through the SCR device
Implementation Method 5
an ammonia oxidation catalyst (AOC) device disposed at the rear of the SCR device, configured to oxidize ammonia
Implementation Method 6
a urea injector disposed at a rear of the LNT device and configured to inject a urea aqueous solution inside an exhaust pipe
Data Source
AI summary
A controlling method of exhaust gas purification system to which a lean combustion engine is applied and an LNT device, a DPF or an SDPF, and an SCR device are provided includes detecting vehicle information and determining whether the vehicle information satisfies nitrogen oxide desorption condition of the LNT device; desorbing the nitrogen oxide until the nitrogen oxide of the LNT reaches predetermined reference amount through engine rich combustion when vehicle information satisfies the nitrogen oxide desorption condition of the LNT device; injecting urea to purify the nitrogen oxide after a first period after ending of desorption of the nitrogen oxide of the LNT; desorbing sulfide of the LNT through the engine rich combustion; and injecting urea to purify the nitrogen oxide after a second period after ending of desorption of the sulfide rich combustion of the LNT.