Combustion Stability Indicator for Engine Torque Transients
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Solution Overview
Problem
Existing methods for determining combustion stability in spark-ignition internal combustion engines, particularly during transient conditions, are imprecise due to overestimation of the coefficient of variation (COV) of the Mean Indicated Pressure (MIP), leading to inefficiencies and increased pollutant emissions.
Innovation Solution
A method that calculates the coefficient of variation (COV) of the ratio of Mean Indicated Pressure (MIP) to the product of fuel injected and engine efficiency, using a Bayesian estimator to determine a confidence interval, thereby improving accuracy during torque transients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the coefficient of variation (COV) of Mean Indicated Pressure (MIP) is used to determine combustion stability, then combustion stability can be assessed, but during transient conditions the COV overestimates instability due to torque variations
Solution Approach 1:
The patent changes the parameter used for combustion stability assessment from raw MIP COV to a normalized ratio: (MIP COV) / (1 + k * torque variation). This parameter transformation eliminates the overestimation of instability during transients while maintaining sensitivity to actual combustion quality variations, resolving the contradiction between measurement precision and reliability during transient conditions.
Solution Approach 2:
The patent introduces an intermediary correction factor that mediates between the raw MIP COV measurement and the actual combustion stability. This correction factor, based on torque variation and a constant k, acts as a mediator that adjusts the COV value to account for transient effects, thereby improving both measurement precision and reliability during transient operation.
2Loss of energy
If lean-burn conditions are implemented to reduce fuel consumption, then thermodynamic efficiency increases, but combustion stability decreases
Solution Approach 1:
The patent implements a feedback mechanism that continuously monitors combustion stability through the corrected COV indicator and adjusts engine operating parameters accordingly. When combustion instability is detected under lean-burn conditions, the system can modulate fuel injection, air-fuel ratio, or ignition timing to restore stability, enabling the engine to operate at optimal lean conditions while maintaining reliable combustion.
3Object-generated harmful factors
If exhaust gas recirculation (EGR) rate is increased to reduce emissions, then thermodynamic efficiency improves, but combustion instability increases
Solution Approach 1:
The patent employs a feedback control system that monitors combustion stability indicators and adjusts EGR rate accordingly. By continuously measuring the corrected COV and comparing it against stability thresholds, the system can modulate EGR injection to maintain optimal combustion stability while maximizing emission reduction benefits, resolving the contradiction between emission control and combustion stability.
Data Source
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AI summary
The present invention relates to a method for determining a combustion stability indicator that determines the VOC variation coefficient of a ratio of the indicated mean pressure (PMI) divided by the product of the injected fuel quantity (Qinj) and the efficiency η of the engine.