Lean and dilute operation of modern spark-ignited (SI) gasoline engines demand unique, reliable, and robust ignition devices. Our previous study found that three different low-temperature plasma (LTP) igniters could extend stable lean ignition limits relative to a baseline inductor coil spark igniter (phi_plasma = 0.62, phi_spark = 0.67), which led to an associated increase in indicated thermal efficiency (ITE) as well as reduced nitrogen oxide (NOx) emission for low-load operating points. The present study compares ignition kernel development and flame propagation characteristics of these ignition systems in a single-cylinder, optically accessible, research engine for two speed/load operating points: 800 rpm/2 bar indicated mean effective pressure (IMEP) and 1300 rpm/3.6 bar IMEP. The fuel-air charge was diluted by either excess air or synthetic exhaust gas recirculation (EGR) until the corresponding dilution limit was identified for each igniter. The LTP igniters evaluated included: 1) radio frequency (RF) corona ignition, 2) RF barrier discharge ignition, and (3) nanosecond-pulsed (NP) barrier discharge ignition. The RF plasma ignition systems employed high-frequency AC voltages at a fixed \~1 MHz frequency, while the NP ignition system used positive DC pulses (\~10 nanoseconds) at 10 kHz. Secondary voltages and total pulse numbers for each system were adjusted to optimize ITE while avoiding breakdown transition that can lead to electrode erosion or insulator puncturing. Time-resolved flame kernel boundaries were identified via high-speed hydroxyl (OH\*) chemiluminescence imaging. It was found that each LTP igniter promoted faster early kernel growth rates relative to the spark igniter, which was attributed to a combination of larger initial kernel volumes and plasma-enhanced reaction rates at the earliest stages of flame kernel development.


Assessment of Spark, Corona, and Plasma Ignition Systems for Gasoline Combustion

Division / Sponsors: 
Internal Combustion Engine Division (ICED)

Paper Proceedings: https://asmedigitalcollection.asme.org/ICEF/ICEF2020/volume/84034

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