Integrated LNT-DPF Catalyst for Continuous Soot Oxidation
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Solution Overview
Problem
Existing emissions control systems for diesel and lean-burn gasoline engines face challenges in effectively reducing nitrogen oxides (NOx) and soot emissions, particularly in achieving continuous and fuel-efficient regeneration of soot-trapping capacity while providing sufficient ammonia to selective catalytic reduction (SCR) systems.
Innovation Solution
The integration of a diesel particulate filter (DPF) with a lean nitrogen-oxide trap (LNT) catalyst, where NOx is reduced to ammonia on the LNT catalyst and then flowed to an SCR catalyst, allowing for concurrent soot oxidation and NOx reduction, with adjustments in air-to-fuel ratio and duration based on soot accumulation to optimize reductant supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If an LNT catalyst is used to trap and reduce NOx, then NOx emissions are controlled, but ammonia supply to SCR system is insufficient and soot regeneration is not continuous
Solution Approach 1:
The patent combines LNT catalyst with DPF substrate to create an integrated system where NOx trapping and soot filtration occur simultaneously. The LNT catalyst is applied directly onto the DPF substrate, enabling both functions in a single component rather than separate systems.
Solution Approach 2:
The integrated LNT/DPF system performs multiple functions: trapping NOx during lean operation, storing it, reducing trapped NOx to ammonia during rich operation, filtering soot particles, and enabling continuous soot oxidation through controlled rich/lean cycling. This multi-functionality resolves the contradiction by making the system productive for both NOx control and continuous soot regeneration.
2Loss of substance
If periodic high-temperature regeneration is used for DPF, then soot is removed, but fuel efficiency decreases and ammonia supply to SCR is interrupted
Solution Approach 1:
The system uses periodic rich/lean operation cycles to enable controlled soot oxidation. During rich periods, the LNT catalyst reduces trapped NOx and generates active oxygen that oxidizes soot at lower temperatures. During lean periods, normal exhaust flow continues. This periodic action replaces continuous high-temperature regeneration, improving fuel efficiency while maintaining soot removal capability.
Solution Approach 2:
The system changes operational parameters (air-to-fuel ratio) between rich and lean states to control the reduction and oxidation processes. By adjusting the richness duration and timing, the system optimizes both soot oxidation rate and ammonia generation, enabling continuous low-temperature soot regeneration without sacrificing fuel efficiency.
3Quantity of substance
If rich operation is extended to provide more ammonia to SCR, then ammonia supply improves, but soot oxidation capability is reduced
Solution Approach 1:
The system uses feedback control to adjust rich operation duration based on ammonia sensor readings downstream of the SCR catalyst. When ammonia levels are sufficient, rich operation is reduced to prioritize soot oxidation. When ammonia levels drop, rich operation is extended to replenish ammonia supply. This feedback mechanism dynamically balances ammonia generation and soot oxidation requirements.
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 enhances NOx emission control, enables continuous, fuel-efficient soot regeneration, and provides ammonia to the SCR system, improving overall emissions management compared to standalone LNT systems.
Implementation Method 1
reducing trapped nitrogen oxides to ammonia on an LNT catalyst
Implementation Method 2
oxidizing soot accumulated on the LNT catalyst
Implementation Method 3
oxidizing soot accumulated on the LNT catalyst
Implementation Method 4
a selective catalytic reduction (SCR) catalyst may be used to destroy NOx by reacting it with a nitrogenous reducing agent
Data Source
AI summary
A method for controlling emissions from an engine includes reducing trapped nitrogen oxides to ammonia on an LNT catalyst while concurrently oxidizing soot accumulated on the LNT catalyst, and, flowing the ammonia so formed to an SCR catalyst.