Fuel Enrichment Control for TWC NMHC Emission Reduction
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Solution Overview
Problem
Vehicle exhaust systems with three-way catalytic converters face challenges in reducing non-methane hydrocarbon emissions during fuel cut events, as they can lead to increased NMHC production due to oxygen accumulation, which is not effectively managed by conventional systems.
Innovation Solution
A control system with oxygen sensors and a controller that detects fuel shut-off events, determines accumulated gas flow, and initiates a fuel enrichment event with a rich fuel/air ratio for a predetermined duration, optimizing fuel enrichment levels and durations based on lookup tables to minimize NMHC emissions while maintaining NOx control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the engine is operated fuel rich to counter oxygen accumulation in the TWC during fuel cut events, then NOx reduction is maintained, but non-methane hydrocarbon emissions increase
Solution Approach 1:
The system performs preliminary actions by detecting the fuel shut-off event and calculating the accumulated gas flow through the TWC before initiating the fuel enrichment event. This preliminary measurement allows the controller to determine the exact duration and level of enrichment needed, preventing excessive NMHC formation while ensuring sufficient O2 consumption to maintain NOx reduction capability.
Solution Approach 2:
The system dynamically changes the fuel enrichment parameters (air/fuel ratio and duration) based on the calculated accumulated gas flow. By adjusting these parameters precisely, the system maintains the rich operation necessary for NOx reduction while limiting the enrichment duration to prevent NMHC emissions.
2Reliability
If conventional fuel enrichment events are used after fuel cut, then oxygen accumulation is addressed, but the enrichment duration is insufficient to fully consume stored oxygen
Solution Approach 1:
The controller calculates the accumulated gas flow through the TWC during the fuel shut-off event as a preliminary step. This calculation provides the exact data needed to determine the precise duration of the subsequent enrichment event, ensuring that the enrichment lasts long enough to consume all stored oxygen without unnecessary extension.
Solution Approach 2:
The system uses feedback from the O2 sensors to continuously monitor the oxygen consumption process. The controller adjusts the enrichment event duration based on the measured gas flow and oxygen levels, ensuring complete oxygen consumption while optimizing the time required.
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
The system effectively reduces non-methane hydrocarbon emissions during fuel enrichment events while maintaining nitrogen oxide emission control, by prolonging the reduced air/fuel ratio beyond typical enrichment event termination points, thereby minimizing undesirable emissions.
Implementation Method 1
The TWC is configured to oxidize carbon monoxide (CO) and unburnt hydrocarbons (HC) to produce carbon dioxide (CO2) and water (H2O)
Implementation Method 2
reduce nitrogen oxides (NOx) to nitrogen (N2)
Implementation Method 3
A three-way catalytic converter (TWC) is a specific type of catalyst that is typically implemented in exhaust systems
Implementation Method 4
one or more oxygen (O2) sensors disposed proximate to a three-way catalytic converter (TWC) in an exhaust system of the vehicle, the one or more O2 sensors each being configured to measure an O2 level of exhaust gas
Data Source
AI summary
A control system for an engine of a vehicle includes one or more oxygen (O2) sensors disposed proximate to a three-way catalytic converter (TWC) in an exhaust system of the vehicle, the one or more O2 sensors each being configured to measure an O2 level of exhaust gas produced by the engine, and a controller in signal communication with the one or more O2 sensors. The controller is programmed to detect a fuel shut-off (FSO) event where the engine ceases providing fuel to the engine, determine an accumulated gas flow through the TWC during the FSO event, determine the FSO event has ended, and initiate a fuel enrichment event for a predetermined duration where the engine is supplied with a fuel enrichment level having a rich fuel/air ratio. The fuel enrichment level and the predetermined duration are chosen to reduce non-methane hydrocarbon (NMHC) emissions while maintaining NOx emission control.