Closed Gas Recycling Loop for SCR Catalyst Preheating
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Solution Overview
Problem
Conventional exhaust gas aftertreatment systems face challenges in controlling NOx emissions during cold starts, as the SCR catalyst requires a minimum temperature threshold to be effective, leading to uncontrolled NOx emissions until this temperature is reached, which can take significant time.
Innovation Solution
A closed gas recycling loop configuration is introduced to preheat SCR components, utilizing a heater and blower to recirculate exhaust gas within the system, reducing the time needed to reach the minimum operating temperature and enabling earlier reductant dosing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a conventional exhaust aftertreatment system is used without a closed gas recycling loop, then the system structure is simpler, but the time to reach minimum SCR operating temperature is significantly longer (e.g., 200 seconds)
Solution Approach 1:
The closed gas recycling loop performs preliminary heating of the exhaust gas and SCR catalyst before the main exhaust flow arrives. The blower circulates exhaust gas through the SCR catalyst and heater in advance, preheating components to reduce the time required to reach operational temperature after engine start.
Solution Approach 2:
The recycling loop acts as an intermediary system between the engine exhaust and the SCR catalyst. It uses a blower and heater as mediating components to actively transport and heat exhaust gas, delivering preheated gas to the SCR catalyst more quickly than passive exhaust flow alone.
2Object-affected harmful factors
If the SCR catalyst temperature is too low during cold start, then the system structure is simpler, but NOx emissions exceed target levels
Solution Approach 1:
The system converts the harmful cold exhaust gas into a beneficial preheating medium. By recycling the cold exhaust gas through the heater and SCR catalyst in a controlled loop, the system uses this otherwise wasted thermal energy to accelerate catalyst heating, transforming a harmful condition (cold gas causing high emissions) into a useful function (preheating to reduce emissions).
Solution Approach 2:
The system actively changes the temperature parameter of the exhaust gas by introducing a heater into the recycling loop. This allows the exhaust gas temperature to be elevated above what would occur in a conventional passive system, enabling the SCR catalyst to reach its operational temperature threshold more quickly and maintain effective NOx conversion.
3Productivity
If reductant dosing is delayed until minimum SCR temperature is reached, then the SCR system operates more efficiently, but the duration of uncontrolled NOx emissions is extended
Solution Approach 1:
The recycling loop performs preliminary heating action to reach the minimum SCR temperature threshold faster. This allows reductant dosing to commence earlier after engine start, reducing the duration of uncontrolled emissions while maintaining the efficiency requirement that dosing only begins when the catalyst reaches adequate temperature.
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 solution significantly reduces the time to achieve the minimum SCR operating temperature, thereby minimizing NOx emissions during cold starts and allowing for earlier and more efficient NOx conversion, compared to conventional systems.
Implementation Method 1
The system may recycle gas located in the exhaust system within a closed loop including a heater
Implementation Method 2
In an embodiment, a blower is included in the closed loop system to drive the recirculation of gas in the closed loop system
Data Source
AI summary
A recycling loop configuration of an exhaust gas aftertreatment system decreases a level of system-out NOx emissions of an engine. An apparatus including the configuration has an exhaust gas recycling system having a closed gas recycling loop system configured to heat gas circulating within the loop, and a blower for circulating gas within the loop. A method for operating the engine includes preheating at least one aftertreatment component of an exhaust gas aftertreatment system of the engine by exposing the component to heated gas circulating in a closed gas recycling loop.