Throwing a Glance at Nonvolatile PM Emissions from Unregulated Aircraft Engines: Particle Mass, Number and Particle Size Distributions

Emissions of aircraft turbine engines are regulated by the International Civil Aviation Organization (ICAO). For nearly 40 years, ICAO Annex 16, Volume 2 has been defining standards for the maximum emissions of visible smoke (smoke number, SN) and gaseous pollutants (NOx, CO, and HC). As air traffic increases and so do environmental impacts of aviation, emission standards need to evolve. Therefore, in 2020, a new non-volatile particulate matter (nvPM) emission standard will come into force, limiting nvPM mass and number. This standard will retire the SN standard for large engines. Yet, aircraft engines with rated thrust <26.7 kN are still only certified for SN, mainly because reduction of e.g. gaseous emissions would not be cost effective, and because engines with a thrust <26.7 kN are only a minor contributor to the global aviation emissions. Nevertheless, certain regional airports may have a dominant traffic contribution from business aviation, reason why it is important to evaluate nvPM emissions of such engines, which are largely unknown.

In this work, we present nvPM emission characteristics of two small in-production turbofan engines used on business jets. We performed the emission measurements using the Swiss Mobile Aircraft Emission Measurement System (SMARTEMIS) on engines installed on aircraft. A cruciform multi-point probe provided representative exhaust samples. To cope with thermophoretic and diffusion losses, we performed a loss correction for both nvPM mass and number. As for widely used large jet engines with thrust >26.7 kN, exhaust characteristics are reported at ICAO landing-take-off cycle thrust settings. Using a common large airliner engine as a comparison, we show that the nvPM emission characteristics of the three engines significantly differed: Maxima of nvPM mass appeared either at take-off or medium trust, while nvPM number emissions peaked at either low or high thrust settings. Mean particle sizes grew with increasing thrust for all engines regardless of the location of the maximum nvPM mass and number emissions. These results therefore highlight the need for a deeper investigation of emission characteristics of small unregulated turbine engines. Only then, a holistic contribution to quantitative studies of local air quality and global atmospheric processes can be performed.