Exhaust Catalyst Reductant Control for NOx Emissions
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Solution Overview
Problem
The NOx conversion efficiency of a selective catalytic reduction catalyst decreases during particulate filter regeneration in exhaust-gas treatment systems, leading to increased NOx emissions due to higher temperature exhaust gases and potential unburned fuel introduction into the air intake.
Innovation Solution
A method and system that adjust the amount of particulate matter combusted and reductant supplied to the selective catalytic reduction catalyst based on the particulate filter's loading, with increased reductant supply during regeneration to maintain reaction efficiency and prevent NOx emissions, and exhaust gas recirculation control to manage unburned fuel and NOx levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a selective reduction catalyst is arranged downstream of a particulate filter to avoid poisoning, then catalyst reliability is improved, but during filter regeneration the high temperature exhaust gas causes decreased NOx conversion efficiency
Solution Approach 1:
The control unit increases the supply amount of reductant to the selective reduction catalyst in advance before filter regeneration occurs. This preliminary action ensures that sufficient reductant is available when high-temperature exhaust gas flows through the catalyst during regeneration, maintaining effective NOx reduction despite the temporary decrease in conversion efficiency.
Solution Approach 2:
The system dynamically changes the reductant supply parameter based on the filter regeneration state. By detecting regeneration conditions and adjusting the reductant supply amount accordingly, the system optimizes NOx conversion efficiency under varying temperature conditions while maintaining catalyst reliability downstream of the particulate filter.
2Productivity
If unburned fuel is introduced into the air intake during filter regeneration to combust particulate matter, then filter regeneration effectiveness is improved, but NOx emissions increase due to unburned fuel combustion
Solution Approach 1:
The system converts the potentially harmful effect of unburned fuel combustion into a beneficial process by intentionally introducing unburned fuel during filter regeneration. The increased reductant supply compensates for the temporary increase in NOx emissions, ultimately achieving both effective particulate matter removal and controlled emissions through the enhanced reduction reaction.
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 maintains NOx reduction efficiency during particulate filter regeneration by compensating for decreased catalytic activity and preventing NOx release into the atmosphere, even when NOx conversion efficiency is reduced, thereby minimizing emissions.
Implementation Method 1
a selective reduction catalyst in an exhaust passage from an engine for reducing NOx
Implementation Method 2
the ammonia is adsorbed into the selective reduction catalyst and reduces NOx to give nitrogen (N2) and water (H2O) by a denitrating reaction with NOx in exhaust gas
Implementation Method 3
a particulate filter in an exhaust passage to decrease a particulate matter such as soot contained in the emission
Implementation Method 4
combusting and removing a particulate matter from a particulate trap, which is referred to as filter regeneration, is executed by combusting unburned fuel
Implementation Method 5
The urea aqueous solution injected from the nozzle is thermally decomposed or hydrolyzed into ammonia by heat from exhaust gas
Implementation Method 6
The urea aqueous solution injected from the nozzle is thermally decomposed or hydrolyzed into ammonia by heat from exhaust gas
Implementation Method 7
the ammonia is adsorbed into the selective reduction catalyst and reduces NOx
Data Source
AI summary
A method of controlling a system having an internal combustion engine, a filter in an exhaust passage, a reduction catalyst downstream of said filter capable of reducing nitrate oxide contained in the exhaust gas with reductant supplied thereto is provided. The method may include, in a first mode, combusting a first amount of particulate matter trapped in said filter and supplying a first amount of reductant to said reduction catalyst when an amount of particulate matter trapped in said filter is less than a predetermined trapping amount (α). The method may further include, in a second mode, combusting a second amount of particulate matter that is greater than said first amount of particulate matter and supplying a second amount of reductant to said reduction catalyst when an amount of particulate matter trapped in said filter is equal to or greater than said predetermined trapping amount (α).