Experimental characterization of the electrostatic charge of aircraft engine emissions using conventional and sustainable fuels

Aircraft gas turbines engines produce ions through chemiionization thought to result in electrostatically charged engine exhaust emissions. Most combustion systems generate a symmetrical bipolar charge distribution. However, due to high temperatures and pressures in aviation combustors, associated fast residence times, and high post-flame temperatures, aircraft emissions have been predicted to exhibit an asymmetrical bipolar charge distribution. It is thought this asymmetry tends toward a positive polarity, resulting from an increase in post-flame thermal ionization. This study employed an Electrostatic Precipitator and a Scanning Mobility Particle Sizer to determine the charged fraction, and an electrometer to determine the mean charge per particle of aircraft emissions. Three aircraft engines were assessed across a number of powers for conventional and sustainable aviation fuels. In agreement with previous theoretical studies, the measured emissions were found to be charged, resulting in up to 58.1% of the emissions being charged, which correlated with engine power. The charge distribution of aircraft emission was observed to be asymmetrical, tending toward positive polarities at higher powers (combustor temperatures). Along with power, it was noted that particle size was a key parameter driving the charge. As such, a fuel dependence was found, whereby emissions produced by JetA-1 typically carried 11–17% more charge compared to SAF for similar conditions, which was attributed to the reduced particle sizes in SAF emissions. Differences in charge was observed between the different engines; however, variations in the respective emissions sampling systems may have contribute to the findings, resulting in uncertainties associated with dynamical unsteady charging.