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Temporal temperature evolution of atmospheric pressure streamer discharge in air

The use of streamers for the ignition of fuels, also known as transient plasma ignition (TPI), has been shown in a variety of engines to improve combustion through decreased ignition delay and increased energy release relative to conventional spark ignition. The mechanisms behind these improvements, however, remain poorly understood. Of particular interest are the relative roles of thermal effects of the streamer afterglow compared to electronically excited species in initiating combustion. Here we report investigation of gas heating due to dissociation, relaxation, and recombination of active plasma species and present temperature measurements in the afterglow of the streamers by using a second probing discharge in conjunction with optical emission spectroscopy. Experimental results are presented and compared to modeling of the streamers. Future experiments are proposed to better understand the role of streamer kinetics in TPI.