Experimental characterization of electrostatic loss relevant to aviation nvPM sampling

Aircraft gas turbine engines produce Particulate Matter (PM) emissions that have been linked to human health and climate issues, leading to the introduction of regulatory sampling and measurement standards for nonvolatile PM (nvPM) by the International Civil Aviation Organization (ICAO). Due to the significant nvPM losses within the prescribed sampling systems, loss corrections are used. Currently, based on sampling assumptions, electrostatic losses are not included in the standardized loss tool, as it is estimated to account for less than 3% of the total nvPM loss. This study experimentally investigated electrostatic loss of unipolar, bipolar, and naturally charged salt, silver, and carbon black particles at sizes (4–150 nm) and through sampling tubes representative of aircraft nvPM sampling. A unipolar and bipolar charger, along with a tandem SMPS-CPC measurement methodology, were employed to explore the impacts of tube material, Reynolds Number, tube diameter, residence time, and particle charge state on electrostatic loss. Minimal electrostatic loss was measured for conductive stainless steel and extensively bedded-in (above 300 h) carbon-loaded PTFE. However, an additional loss of up to 50% was observed within new cPTFE (with approximately 30 min of bedding-in), attributed to precipitation in an electric field. Furthermore, it was found that electrostatic dispersion could cause significant additional losses at high concentrations of unipolar or bipolar asymmetrically charged particles. Therefore, further research is required to determine the charge state of aircraft nvPM across different aircraft engine conditions to determine if unquantified electrostatic loss could occur within the probe section of the sampling system.