Abstract
Engine research community interest in the Radio-Frequency corona-based ignition systems is currently gaining in importance mainly due to their capability to ensure robust combustion at challenging operating conditions such as very lean mixture and/or high EGR dilution. The benefits of Corona low-temperature plasma foster the early flame development thanks to combustion precursors production and to a more energetic and volumetric discharge, resulting in a larger amount of involved mixture. The corona discharge generates ionizing waves, named streamers, whose temporal and spatial variability in orientation, length and branching can affect the combustion onset and, therefore, the engine cycle-to-cycle variability. In this work, the discharge natural luminosity of a RF corona igniter, characterized by four tips electrodes, was recorded in an optically accessible engine via high-speed camera detection. A preliminary statistical analysis of the spatial and temporal streamer variability was performed by operating in motored conditions. Four different engine speeds and two different loads were explored in order to deeply investigate the streamer behaviour at diverse engine operating conditions. A comparison between a motored and a lean operating condition is also proposed to analyse, at a specific engine speed, the mixture influence on the streamers propagation before the start of the combustion.
Highlights
Internal Combustion Engines (ICEs) are forced to decrease the amount of pollutant emissions and fuel consumption while maintaining high performance [1,2]
According to the operating conditions (Table2), it was necessary to determine, case by case, the right IT value in order to maintain the start of discharge as fixed around pch=6bar
This work reports an analysis of the discharge natural luminosity of a RF corona igniter characterized by four tips electrodes in an optically accessible engine via high-speed camera detection
Summary
Internal Combustion Engines (ICEs) are forced to decrease the amount of pollutant emissions and fuel consumption while maintaining high performance [1,2]. Spark ignition (SI) engines actual trends to obtain a cleaner and more efficient combustion are focusing on innovative strategies such as water injection, turbocharging, high exhaust gas recirculation (EGR) dilution, and/or lean combustion [3,4,5] At these operating conditions, where high released energy is required for mixture ignition, conventional spark plugs have shown its limits in obtaining robust combustion onsets with low cycle-to-cycle variability [6]. CSI discharge is based on the production of a strong electric field amplified through needles/ tips to generate filaments, named streamers [14] These ionization waves propagate from the device-tips to the counter-electrode represented by the engine walls or by piston head, resulting in a larger amount of involved mixture [15]. Temporal and spatial variability of the streamer in orientation, branching and length can affect the combustion onset and, the engine cycle-to-cycle variability [19]
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