Air-Fuel Ratio Control for Lean Combustion Stability
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Solution Overview
Problem
Conventional air-fuel ratio control systems for lean-burn engines face challenges in stabilizing combustion while reducing NOx emissions, as they often lead to misfiring and combustion fluctuations when the lean degree exceeds a certain limit, and may incorrectly detect deteriorating combustion states due to high sensitivity in fluctuation thresholds.
Innovation Solution
An air-fuel ratio control device that sets a target air-fuel ratio and adjusts it based on the actual NOx concentration, using a lean combustion determination unit, a target NOx setting unit, and a correction unit to optimize NOx emission and stabilize combustion by increasing or decreasing the lean degree of the air-fuel ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the lean degree of air-fuel ratio is increased to reduce NOx emissions, then NOx emission is reduced, but combustion stability deteriorates and misfiring occurs
Solution Approach 1:
The control device uses a NOx concentration detection unit to continuously monitor actual NOx levels and feeds this information back to the correction unit. The correction unit adjusts the target air-fuel ratio based on the deviation between actual and target NOx concentrations, creating a closed-loop feedback system that dynamically optimizes the lean degree to reduce NOx while maintaining combustion stability.
Solution Approach 2:
The system dynamically changes the air-fuel ratio parameter based on operating conditions and NOx measurements. The correction unit modifies the target air-fuel ratio within a predetermined range, adjusting the lean degree as a variable parameter to achieve optimal balance between NOx reduction and combustion stability across different engine operating points.
2Measurement precision
If high sensitivity is used to detect combustion fluctuation, then combustion state detection is improved, but erroneous detection of deterioration occurs
Solution Approach 1:
The system uses feedback from NOx concentration measurements to verify combustion state changes. Rather than relying solely on sensitive fluctuation detection that may produce false positives, the feedback mechanism cross-validates detected changes against actual NOx levels, confirming whether perceived combustion deterioration is real or erroneous before triggering corrective action.
Data Source
AI summary
An air-fuel ratio control device sets a target air-fuel ratio and performs an air-fuel ratio control based on the target air-fuel ratio for an engine of a spark ignition type. The air-fuel ratio control device includes a lean combustion determination unit that determines whether a lean combustion is performed in the engine at the target air-fuel ratio, the target air-fuel ratio being set leaner than the theoretical air-fuel ratio; a target NOx setting unit that sets a target NOx concentration according to an operation state of the engine; an acquisition unit that acquires an actual NOx concentration detected by using a NOx concentration detection unit in an exhaust passage of the engine; and a correction unit that corrects the target air-fuel ratio based on the target NOx concentration and the actual NOx concentration when determination is made that lean combustion is performed.