DOC and HC-SCR Exhaust System for Fast Light-off
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Solution Overview
Problem
Internal combustion engines, such as diesel engines, face challenges in reducing nitrogen oxide (NOx) emissions efficiently, as conventional selective catalytic reduction (SCR) systems often require high temperatures and take time to reach light-off temperatures, leading to incomplete NOx emission reduction.
Innovation Solution
The system incorporates a diesel oxidation catalyst (DOC) with hydrocarbon injection for thermal management, a hydrocarbon-selective catalytic reduction unit (HC-SCR) downstream, and an ammonia SCR close-coupled to the turbocharger, utilizing hydrocarbon slip and unconverted NOx and NH3 to enhance NOx reduction, with the DOC configured to reach light-off temperature in under 30 seconds and generate a hydrocarbon slip with a carbon to NOx ratio of 3 to 6.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional SCR systems are used, then NOx emission reduction is attempted, but the system takes time to reach light-off temperature and requires high temperatures for effective operation
Solution Approach 1:
The patent applies preliminary action by placing the DOC upstream of the SCR system to pre-heat the exhaust gas and perform initial NOx reduction before the main SCR catalyst operates. This preliminary thermal management action reduces the time required for the SCR system to reach its light-off temperature by starting the heating and reduction process earlier in the exhaust flow path.
Solution Approach 2:
The patent segments the NOx reduction process into multiple stages: first through the DOC which performs partial NOx reduction and thermal management, then through the HC-SCR unit, and finally through the ammonia SCR catalyst. This segmentation allows each component to operate at optimized temperatures and functions, reducing the overall time to achieve effective NOx reduction while maintaining lower light-off temperature requirements.
2Productivity
If high temperatures are used for SCR operation, then NOx conversion efficiency improves, but the system complexity and energy consumption increase
Solution Approach 1:
The patent changes the temperature parameters across different stages of the NOx reduction process. The DOC operates at lower temperatures to perform thermal management and partial reduction, while subsequent stages operate at progressively higher temperatures optimized for each specific function. This parameter change strategy achieves high overall NOx conversion efficiency without requiring the entire system to operate at maximum temperature, thereby reducing complexity and energy consumption.
Solution Approach 2:
The patent introduces an intermediary HC-SCR unit between the DOC and the ammonia SCR catalyst. This intermediary unit facilitates the transition between different temperature zones and reduction mechanisms, enabling efficient NOx conversion at moderate temperatures before the final ammonia SCR stage, thus reducing the overall system complexity and energy requirements compared to a single high-temperature SCR system.
3Object-generated harmful factors
If conventional SCR systems are used, then NOx reduction is implemented, but emission standards are not fully met
Solution Approach 1:
The patent implements continuous NOx reduction action through multiple sequential stages: the DOC continuously performs thermal management and partial NOx reduction, the HC-SCR unit continuously converts hydrocarbons and NOx, and the ammonia SCR catalyst continuously reduces remaining NOx. This continuity of useful action ensures consistent and reliable NOx reduction throughout the exhaust flow, achieving stricter emission standards more reliably than conventional single-stage SCR systems.
Solution Approach 2:
The patent merges multiple NOx reduction mechanisms into a single integrated system: oxidation-catalyzed thermal management in the DOC, hydrocarbon-selective catalytic reduction in the HC-SCR unit, and ammonia-based SCR in the final catalyst stage. This merging of functions allows the system to address different aspects of NOx reduction simultaneously, achieving higher reliability in meeting emission standards through combined actions rather than relying on a single reduction mechanism.
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 reduces NOx emissions more effectively than conventional systems by quickly reaching light-off temperature and utilizing hydrocarbon slip for enhanced NOx conversion, achieving higher conversion efficiency without supplemental energy.
Implementation Method 1
promoting oxidation of at least one of hydrocarbons and carbon monoxide
Implementation Method 2
converting hydrocarbons and nitrogen oxide compounds to diatomic nitrogen and ammonia
Implementation Method 3
hydrocarbon-selective catalytic reduction unit
Implementation Method 4
ammonia SCR catalyst is configured to receive exhaust gas from the turbocharger
Implementation Method 5
producing diatomic nitrogen
Data Source
AI summary
A vehicle system includes a diesel oxidation catalyst. The vehicle system includes a hydrocarbon-selective catalytic reduction unit located downstream of the diesel oxidation catalyst. The hydrocarbon-selective catalytic reduction unit is configured to receive exhaust gas from the diesel oxidation catalyst. The vehicle system includes a turbocharger located downstream of the hydrocarbon-selective catalytic reduction unit. The turbocharger is configured to receive exhaust gas from the hydrocarbon-selective catalytic reduction unit.