DETERMINING THE AIR-FUEL RATIO OF A FOUR-STROKE INTERNAL COMBUSTION ENGINE FROM SPARK IGNITION VOLTAGE WAVEFORMS

摘要

The spark plug in a spark-ignition engine is in contact with the combustion processes and so is potentially useful as a sensor of combustion phenomena. This paper describes a statistical analysis of the time varying voltage at the spark plug to determine potential relationships to air-fuel ratio (AFR). Visual inspection of the graphed data indicates two likely metrics; the waveform's mean-square value and its relative phasing. Regression analysis reveals a linear relationship between the mean-square and AFR for small data sets. Subsequent investigation with large numbers of waveforms has demonstrated that this metric is not a sufficient indicator when isolated but may prove valuable as part of AFR measurement using multiple regression.