Exhaust Recirculation for Catalyst Heating
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Solution Overview
Problem
Internal combustion engines emit more harmful emissions during cold-start and low load conditions due to inefficient aftertreatment devices, which do not reach full efficiency until the engine exhaust gas heats the catalyst to a reaction temperature.
Innovation Solution
An exhaust gas recirculation method that diverts exhaust gas from downstream of the aftertreatment device to upstream, allowing it to be treated again and heat the catalyst, combined with controlling the volume and pressure of the recirculated gas to enhance heat transfer and engine torque during idling and partial load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the aftertreatment device is used to treat exhaust gas during cold-start conditions, then emissions control is attempted, but the catalyst does not reach reaction temperature and conversion efficiency is low
Solution Approach 1:
The system performs preliminary heating action by recirculating hot exhaust gas through the catalyst before normal operation begins. The recirculation system activates during cold-start conditions to preheat the catalyst, ensuring it reaches reaction temperature faster and improves conversion efficiency before the engine enters normal operating range.
Solution Approach 2:
The recirculated exhaust gas acts as an intermediary heat transfer medium. Hot exhaust gas is diverted through a recirculation path that contacts the catalyst exterior surfaces, transferring thermal energy to the catalyst and enabling it to reach operating temperature without directly exposing the catalyst to cold incoming exhaust.
2Temperature
If exhaust gas is recirculated through the aftertreatment device, then the catalyst is heated faster, but the system complexity increases
Solution Approach 1:
The recirculation system uses existing exhaust gas flow and the same aftertreatment device for multiple purposes: normal emissions treatment and catalyst heating. The recirculated exhaust gas serves dual function as both the heating medium and the treatment target, eliminating the need for separate heating equipment and reducing overall system complexity.
Solution Approach 2:
The exhaust system serves itself by using its own hot exhaust gas to heat the catalyst. The recirculation path allows the exhaust gas to contact the catalyst exterior surfaces and transfer heat, enabling the system to self-heat without external energy input or additional heating components.
3Temperature
If recirculated exhaust gas contacts the exterior surfaces of the aftertreatment device, then heat transfer to the catalyst is enhanced, but pressure loss in the exhaust system increases
Solution Approach 1:
The recirculation system creates a localized heat transfer zone where exhaust gas contacts only the exterior surfaces of the aftertreatment device housing, not the entire exhaust path. This localized approach concentrates heat transfer where needed while minimizing interference with the main exhaust flow and reducing overall pressure loss.
Solution Approach 2:
The system uses pneumatic principles to manage exhaust gas flow through the recirculation path. By controlling pressure differentials and utilizing exhaust gas momentum, the system directs flow through the heat transfer cavity without requiring additional pumping power, thereby minimizing pressure loss while maintaining effective heat transfer.
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 method reduces vehicle emissions by quickly and uniformly heating the catalyst, improving conversion efficiency and reducing emissions during cold-start and low load conditions, while also increasing engine torque requirements.
Implementation Method 1
channeling the recirculated gas into a cavity of a housing that encloses the aftertreatment device, the cavity defined between interior surfaces of the housing and exterior surfaces of the aftertreatment device, wherein at least some of the recirculated exhaust gas within the secondary exhaust gas stream contacts the exterior surfaces of the aftertreatment device
Data Source
AI summary
Methods and systems are provided for recirculation of an engine exhaust gas. The system includes an engine, an exhaust system configured to channel exhaust gas from the engine to an outlet, an aftertreatment device, an exhaust recirculation system configured to divert at least some of the exhaust gas as recirculated exhaust gas from a first position in the exhaust system downstream of the aftertreatment device, through a housing enclosing the aftertreatment device, and to a second position in the exhaust system upstream of the aftertreatment device, wherein the recirculated exhaust gas is combined with the exhaust gas at the second position, a controller configured to, by a processor, selectively operate the exhaust recirculation system to control the exhaust recirculation system to divert the exhaust gas and thereby cause the recirculated exhaust gas to be treated with the aftertreatment device more than once.