The effect of transitioning to sustainable aviation fuels on contrails and climate (SAFice)
Lead Research Organisation:
University of Leeds
Department Name: School of Earth and Environment
Abstract
Contrail cirrus clouds, that evolve from line-shaped clouds that form in the wake of aircraft in the middle and upper troposphere, are an important part of the climate impacts of aviation. The increasing use of sustainable aviation fuels (SAFs) may not only reduce CO2 emissions but is also thought to have the advantage of shorter-lived contrails. However, to quantitatively predict the magnitude of this benefit we need to improve our fundamental understanding of contrail formation and the emission of ice-forming particles from the use of different SAFs and SAF-blends.
The link between ice crystals number, crystal size and emitted aerosol. The radiative properties and lifetime of contrail cirrus are strongly affected by the number concentration of ice-forming particles in the engine exhaust. Contrails form when ambient air and exhaust plumes mix resulting in a supersaturation with respect to water where liquid water can condense on particles. At temperatures below homogeneous freezing (~-38°C), these droplets almost instantly freeze and then grow into ice crystals. If the background atmosphere is supersaturated with respect to ice, then these crystals continue to grow forming a persistent contrail. The fewer aerosol that are emitted the fewer ice crystals that can form, the larger these crystals grow, the more rapidly they sediment and the shorter the lifetime of the contrail, thus reducing the fraction of the atmosphere containing contrails.
The overarching goal of SAFice is to quantify the change in the contrail radiative effect on transitioning to sustainable aviation fuels from standard fossil Jet A1 fuel. This will be achieved through:
1. Probing experiments: Aerosol chamber and PINE (Portable Ice Nucleation Experiment) measurements in Leeds to examine the competition between non-volatile soot and lubrication oil, as well as between aircraft emissions and proxies of background atmospheric aerosol.
2. Gas turbine experiments: Experiments in Sheffield to examine the contrail-ice-forming potential of turbine exhaust using a range of SAFs and blends making use of an aircraft turbine engine and our PINE instrument. This will be much more detailed than could ever be achieved flying aircraft.
3. Global contrail simulations: Define new parameterisation based on the laboratory data and use them to quantify contrail properties and radiative effects with a range of SAF usage scenarios.
This is timely because we are at the cusp of the transition to SAF (with the first 100% SAF trans-Atlantic flight having taken place in Nov '23) and we need to understand the impact of this transition. The newly opened Translational Energy Research Centre (TERC) has developed a state-of-the-art facility comprising a turbine engine (APU) that has been shown to run on SAF fuels as well as having the connections to SAF producers and end users through the SAF clearing house. In Leeds we have developed an instrument for quantifying the concentration of ice forming particles - PINE. In Imperial we have developed modelling tools (pycontrails) which require our basic experimental input to make predictions of the effect of the switch to SAF on global contrail cirrus radiative properties. The team have also recently published the first ever study on the role of lubrication oil droplets in contrail formation and collaborated on the first 100% SAF flight operated by Virgin Atlantic, where TERC was used to measure changes in particle emissions resulting from the SAF used for the flight.
The link between ice crystals number, crystal size and emitted aerosol. The radiative properties and lifetime of contrail cirrus are strongly affected by the number concentration of ice-forming particles in the engine exhaust. Contrails form when ambient air and exhaust plumes mix resulting in a supersaturation with respect to water where liquid water can condense on particles. At temperatures below homogeneous freezing (~-38°C), these droplets almost instantly freeze and then grow into ice crystals. If the background atmosphere is supersaturated with respect to ice, then these crystals continue to grow forming a persistent contrail. The fewer aerosol that are emitted the fewer ice crystals that can form, the larger these crystals grow, the more rapidly they sediment and the shorter the lifetime of the contrail, thus reducing the fraction of the atmosphere containing contrails.
The overarching goal of SAFice is to quantify the change in the contrail radiative effect on transitioning to sustainable aviation fuels from standard fossil Jet A1 fuel. This will be achieved through:
1. Probing experiments: Aerosol chamber and PINE (Portable Ice Nucleation Experiment) measurements in Leeds to examine the competition between non-volatile soot and lubrication oil, as well as between aircraft emissions and proxies of background atmospheric aerosol.
2. Gas turbine experiments: Experiments in Sheffield to examine the contrail-ice-forming potential of turbine exhaust using a range of SAFs and blends making use of an aircraft turbine engine and our PINE instrument. This will be much more detailed than could ever be achieved flying aircraft.
3. Global contrail simulations: Define new parameterisation based on the laboratory data and use them to quantify contrail properties and radiative effects with a range of SAF usage scenarios.
This is timely because we are at the cusp of the transition to SAF (with the first 100% SAF trans-Atlantic flight having taken place in Nov '23) and we need to understand the impact of this transition. The newly opened Translational Energy Research Centre (TERC) has developed a state-of-the-art facility comprising a turbine engine (APU) that has been shown to run on SAF fuels as well as having the connections to SAF producers and end users through the SAF clearing house. In Leeds we have developed an instrument for quantifying the concentration of ice forming particles - PINE. In Imperial we have developed modelling tools (pycontrails) which require our basic experimental input to make predictions of the effect of the switch to SAF on global contrail cirrus radiative properties. The team have also recently published the first ever study on the role of lubrication oil droplets in contrail formation and collaborated on the first 100% SAF flight operated by Virgin Atlantic, where TERC was used to measure changes in particle emissions resulting from the SAF used for the flight.
