Effect of a Spark Aider Fuel Additive on the Misfire Characteristics of a Spark Ignition Engine

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Abstract
Certain fuel additives known as “spark-aiders” are known to increase early flame development rates and reduce cyclic variation in spark-ignition engines and to lead to improvements in driveability characteristics in vehicles. In this work we report the effects of such an additive—a potassium compound —on the misfire characteristics of a single cylinder engine running on iso-octane. During the tests we monitored average early flame travel time and cyclic variation using a laser-based technique for flame speed measurement and also the current-voltage characteristics of the spark. We also studied the implications of changing the strength of the spark electrically by changing the supply voltage lo the coil. The additive leads to an extension of the lean limit and the reduction in the misfire frequency when the engine operates in the misfire mode; average early flame travel time and cyclic variations as well as the spark glow voltage arc reduced and spark duration is extended. Similar results are obtained when plug electrodes arc directly coaled with potassium sulphate. Changing the coil supply voltage from 5 V lo 12 V, leads to a longer spark duration and improvements in the misfire characteristics but apparently does not change the actual energy supplied to the mixture by the spark in the critical, early combustion phase since it docs not noticeably improve flame development. These studies help in understanding how spark aiders improve engine operation and further support the view that spark aiders act by depositing low electron work function material on the spark plug electrodes, thus improving the efficiency of the spark.