Biofuel blending reduces particle emissions from aircraft engines at cruise conditions

Abstract

Aviation-related aerosol emissions contribute to the formation of contrail cirrus clouds that can alter upper tropospheric radiation and water budgets, and therefore climate. The magnitude of air-traffic-related aerosol-cloud interactions and the ways in which these interactions might change in the future remain uncertain. Modelling studies of the present and future effects of aviation on climate require detailed information about the number of aerosol particles emitted per kilogram of fuel burned and the microphysical properties of those aerosols that are relevant for cloud formation. However, previous observational data at cruise altitudes are sparse for engines burning conventional fuels, and no data have previously been reported for biofuel use in-flight. Here we report observations from research aircraft that sampled the exhaust of engines onboard a NASA DC-8 aircraft as they burned conventional Jet A fuel and a 50:50 (by volume) blend of Jet A fuel and a biofuel derived from Camelina oil. We show that, compared to using conventional fuels, biofuel blending reduces particle number and mass emissions immediately behind the aircraft by 50 to 70 per cent. Our observations quantify the impact of biofuel blending on aerosol emissions at cruise conditions and provide key microphysical parameters, which will be useful to assess the potential of biofuel use in aviation as a viable strategy to mitigate climate change.

The Impact of Cloud Processing on the Ice Nucleation Abilities of Soot Particles at Cirrus Temperatures

“…If real aircraft aggregates behave like the propane flame soot studied here, the enhanced ice nucleation activity of such soot particles resulting from contrail processing could impact subsequent cirrus cloud formation. The caveat here is that the majority of aircraft emitted soot aggregates have diameters around 30 nm (Moore et al., ; Zhang et al., ). There is, however, some observational evidence of larger soot aggregates associated with aviation emissions (Petzold et al., ) and from contrail residuals (Petzold et al., ; Twohy & Gandrud, ).…”

Statistical analysis of contrail to cirrus evolution during the Contrail and Cirrus Experiment (CONCERT)

“…This increases the local relative humidity in the exhaust plume leading to the formation of contrails when the saturation with respect to liquid water is reached. In this case, soot and sulfate aerosols emitted by the aircraft (Moore et al, 2017) may act as condensation nuclei to form liquid droplets. Homogeneous ice nucleation of the liquid droplets can occur when the exhaust cools down through mixing with the ambient temperature, while preserving ice saturation.…”

Comparing parameterized versus measured microphysical properties of tropical convective cloud bases during the ACRIDICON–CHUVA campaign

“…We therefore estimate an uncertainty in particle size for particle diameters above 40 µm on the order of 13 to 15 %; the estimate is less for smaller particles. The instrument had been previously installed on HALO and the DLR Falcon aircraft during the campaigns ML-CIRRUS (The Midlatitude Cirrus; Voigt et al, 2017), ACCESS II (Alternative Fuel Effects on Contrails and Cruise Emissions; Moore et al, 2017), and DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa; Knippertz et al, 2015).…”

“…Another approach to estimating the number concentration of CCN that are expected to nucleate as droplets at cloud base is through the use of the κ-Köhler model (Petters and Kreidenweis, 2007). Based on a given dry aerosol particle size distribution (ASD), the κ-Köhler model with prescribed W b simulates the expansion and cooling of air, the resulting changes in relative humidity, the related hygroscopic growth of aerosol particles, and the further condensational growth of cloud droplets.…”