Improvement in Spark-Ignition Engine Fuel Consumption and Cyclic Variability with Pulsed Energy Spark Plug
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Conventional spark plugs ignite a fuel-air mixture via an electric-to-plasma energy transfer; the effectiveness of which can be described by an electric-to-plasma energy efficiency. Although conventional spark plug electric-to-plasma efficiencies have historically been viewed as adequate, it might be wondered how an increase in such an efficiency might translate (if at all) to improvements in the flame initiation period and eventual engine performance of a spark-ignition engine. A modification can be made to the spark plug that places a peaking capacitor in the path of the electrical current; upon coil energizing, the stored energy in the peaking capacitor substantially increases the energy delivered by the spark. A previous study has observed an improvement in the electric-to-plasma energy efficiency to around 50%, whereas the same study observed conventional spark plug electric-to-plasma energy efficiency to remain around 1%. It is postulated that improving this electric-to-plasma energy efficiency can result in improved 0-10% mass fraction burned duration and shorter 10%-90% mass fraction burned duration. Perhaps by improving these aspects of combustion, engine fuel consumption and cycle-to-cycle variability can also be improved. This article provides a summary of engine and vehicle data comparing the "pulsed energy" spark plug to a conventional fine-wire iridium spark plug. Vehicle data are reported from a high-performance sports car on the European drive cycle; fuel economy improvements up to 1.2% are reported with the use of the pulsed energy spark plug. Engine data include brake specific fuel consumption, pre-catalyst exhaust concentrations of hydrocarbons, carbon monoxide, and oxides of nitrogen, and in-cylinder pressure-based calculations of mass fraction burned profiles. Over several steady-state engine operating speeds and loads including an idle condition, the pulsed energy plugs show a 1% improvement in brake specific fuel consumption. Over the same speeds and loads without the idle condition, the pulsed energy plugs show a 0.6% improvement in brake specific fuel consumption. The article provides analysis to this improvement, and suggests it results mostly from a sooner flame development (0-10% burn duration) and shorter 10-90% burn duration observed with the pulsed energy spark plugs. Copyright 2012 SAE International.
