SCR on Filter Regeneration via Hydrocarbon Dosing
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Solution Overview
Problem
Conventional exhaust aftertreatment systems for diesel engines face challenges in achieving stringent emission regulations for NOx and particulates, particularly due to the difficulty in removing NOx and the need for efficient regeneration of SCR on filter units, which requires precise temperature control and reductant management.
Innovation Solution
The system incorporates an oxidation catalyst, a selective catalytic reduction catalyst on filter, a hydrocarbon doser, and an aftertreatment controller that adjusts the dosing rate of hydrocarbons and reductants, including diesel exhaust fluid, to control temperature and regenerate the SCR on filter, using sensors to monitor and adjust parameters for optimal regeneration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reductant (DEF) is injected into the exhaust stream to enable SCR reactions, then NOx removal efficiency is improved, but reductant deposits form on the SCR on filter
Solution Approach 1:
The system performs periodic regeneration cycles where hydrocarbon dosing is activated to raise temperatures and burn off accumulated reductant deposits from the SCR on filter, alternating between normal SCR operation and regeneration modes to maintain system performance
Solution Approach 2:
The system changes operational parameters by dosing hydrocarbons upstream of the oxidation catalyst to temporarily raise exhaust temperature and shift the chemical environment, enabling oxidation of deposited reductant without affecting normal SCR reduction reactions
2Reliability
If the SCR on filter is regenerated by dosing hydrocarbons upstream of the oxidation catalyst, then reductant deposits are removed, but the oxidation catalyst outlet temperature must be precisely controlled
Solution Approach 1:
Temperature sensors monitor exhaust gas temperature at the oxidation catalyst outlet, and the aftertreatment controller adjusts hydrocarbon dosing rates in real-time to maintain temperature within the optimal regeneration window, preventing both incomplete regeneration and excessive temperature rise
Solution Approach 2:
The system dynamically adjusts multiple parameters including hydrocarbon dosing rate, oxidation catalyst outlet target temperature, and monitors temperature deviations to optimize regeneration while protecting downstream components
3Productivity
If hydrocarbon dosing rate is increased to accelerate regeneration, then regeneration speed is improved, but temperature control becomes more difficult
Solution Approach 1:
The hydrocarbon dosing system dynamically adjusts dosing rates based on real-time temperature feedback, increasing dosing during early regeneration phases and reducing it as target temperature is approached, enabling both rapid regeneration and precise temperature control
Solution Approach 2:
The aftertreatment controller continuously monitors temperature deviations and adjusts hydrocarbon dosing rates accordingly, reducing dosing when temperature approaches targets and increasing it when regeneration is incomplete, balancing speed and control
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 enables effective regeneration of the SCR on filter, improving NOx reduction and particulate management, thereby enhancing the system's ability to meet stringent emission standards while minimizing reductant deposits and optimizing system performance.
Implementation Method 1
DOCs reduce the amount of CO and HCs present in the exhaust gas via oxidation techniques
Implementation Method 2
SCR catalysts are configured to convert NOx (NO and NO2 in some fraction) into nitrogen gas (N2) and water vapor (H2O)
Implementation Method 3
The injected DEF spray is heated by the exhaust gas stream to vaporize the urea-water solution and trigger the decomposition of urea into NH3
Implementation Method 4
trigger the decomposition of urea into NH3
Data Source
AI summary
An exhaust aftertreatment system includes a diesel oxidation catalyst in exhaust gas receiving communication with an engine. A selective catalytic reduction catalyst on filter (SCR on filter) is positioned downstream of the diesel oxidation catalyst. A hydrocarbon doser is configured to inject hydrocarbons into a flow of the exhaust gas upstream of the diesel oxidation catalyst. A reductant doser is configured to inject reductant into the flow of the exhaust gas upstream of the SCR on filter and downstream of the diesel oxidation catalyst. An aftertreatment controller is operatively coupled to the hydrocarbon doser. The aftertreatment controller is configured to control a dosing rate at which the hydrocarbon doser injects hydrocarbons into the flow of the exhaust gas so as to cause regeneration of the SCR on filter.