Unveiling Nucleation mechanism in aiRcraft Engine exhAust and its Link with fuel composition – UNREAL

Within this proposal we plan to use the state-of-the-art Combustion Aerosol Standard (CAST) generator especially designed to work with aeronautic fuels available at ONERA as emission source. To study the formation of vPM in detail, we will use the atmospheric chamber CESAM available at LISA and a Potential Aerosol Mass flow Reactor (PAM) available at LSCE and operated in collaboration with INERIS (subcontract) to induce the formation of vPM from the exhaust of CAST. We will use the experimental means available at ONERA and CESAM to characterize the emissions. In addition, key chemical characterization will be performed by SAGE and PhLAM. To get a further insight into the molecular mechanism behind vPM formation, we will perform a series of theoretical simulations led by UTINAM. To complement the consortium, two foreign partners will participate on their own funds or by means of researcher exchanges: Tampere University of Technology (TUT), that will participate in the characterization of molecular clusters emitted by CAST though the Atmospheric Pressure Interface Time of Flight Mass spectrometry (API-toF), and the Spanish national institute for aerospace (INTA) that will collaborate offering its sampling line in the stack of their test bench to measure vPM formation in one of its standard measurement campaigns with a complete engine.

- A first measurement campaign was carried out at the CESAM chamber in February 2020.
- We found a link between the fuel hydrogen content and black carbon mass emitted in laboratory scale tests.
- We found that alternative fuel (AtJ SPK) produced 89% less black carbon than a standard jet fuel.
- We found that a blending standard jet fuel with 30% AtJ (maximum blend rate allowed in civil aviation) reduced black carbon emissions by 75%.


A second campaign in CESAM atmospheric chamber was done between 16/11 and 10/12. During this campaign a potential aerosol mass flow reactor was tested in parallel with CESAM chamber. WE tested up to 8 different fuels. A first set of 4 fuels to test the Impact of sulfur an aromatic content on particle formation, and a second text using a reference jet A1 fuel, a 100% alternative fuel and a blend of those two. For this campaign, two different kinds of experiments were done. In one case, emissions from CAST were filtered to remove all soot particles, and only emitted gases were injected in the chamber. In the second case, after the injection of only gases, a second injection with both, gas and soot particles were done.
The test in the first set of fuel, showed how particle formation was more intense for high sulfur fuels, nevertheless, even for the fuels with 4 ppm of sulfur, particle formation was observed. In the case of the second set of fuels, we found that the highest rates of new particle formation corresponded to the 100% alternative fuel, what is quite surprising, since this fuels does not have sulfur nor aromatic compounds.

During this project we have found the key role of fuel composition on emissions. We have identified different points that should be further investigated, and that, taking in to account the future use of alternative aviation fuel, will be crucial to investigate. There are different examples of potential future studies linked to this project. For example the use of PAM behind a complete aircraft engine, the study of the impact of atmospheric conditions on particle formation observed from different fuels. Study of Cruise altitude conditions. Eventually to design an experimento to study alternatives like hydrogen engines.

1. R Ciuraru, J Kammer, C Decuq, M Vojkovic, K Haider, Y Carpentier, F Lafouge, C Berger, M Bourdat-Deschamps, I K. Ortega, F Levavasseur, S Houot, B Loubet, D Petitprez, C Focsa, New particle formation from agricultural recycling of organic waste products, Nature partner journal climate and atmospheric sciences, in review
2 Dumitru Duca, Mostafiz Rahman, Yvain Carpentier, Claire Pirim, Adam Boies, Cristian Focsa,, Chemical characterization of size-selected nanoparticles emitted by a gasoline direct injection engine: impact of a catalytic stripper, FUEL, under review

3 1. I. K. Ortega, C. Focsa, J. F. Doussin, V. Riffault, S. Picaud, A. Albinet, V. Gros, T. Rönkkö, V. Archilla, UNREAL Project: Unveiling nucleation mechanism in aircraft engine exhaust and its link with fuel composition, Poster, European Aerosol Conference, Göthenburg (Suède), 25-30 août 2019.

4 2. I.K. Ortega, M.Cazaunau, J. Duplissy, R. Barrellon-Vernay , A. Bergé, A. Berthier,E. Pangui, D. Delhaye, C. Di Biagio,M. Sicard, Y. Carpentier, B. Raepsaet,F. Ser, M. Kulmala , C. Focsa, and J.F. Doussin, Starting the quest for aeronautic bananas: First UNREAL project campaign at the CESAM atmospheric chamber, European Aerosol Conference, Aachen (Germany), 2020

5 Antoine Berthier, David Delhaye, Ismael K. Ortega, Mickael Sicard et Cristian Focsa, impact de la composition du carburant sur les emissions aeronautiques, ASFERA anual meeting, Paris, 2020

Aviation is actually one of the strongest growing transport sectors, and this trend is predicted to continue. Currently, aviation represents 2% of global CO2 emissions, but is expected to grow up to 3% by 2050. While this amount is small compared with other industry sectors, such as energy production and ground transport, these industries have viable alternative energy sources currently available. For example, the power generation industry can turn to wind, hydro, nuclear and solar technologies to produce electricity with low CO2 emissions. In the case of aviation, while solar and electric aircrafts are being researched, they are still a long way from commercial versions due to aviation need for high power-to-weight ratio and globally compatible infrastructure. Therefore, the aviation industry has identified the development of biofuels as one of the major tools to tackle its emissions.

Aviation emissions are not limited to greenhouse gases like CO2 or water but include as well other gases like nitrogen oxides (NOx) or sulfur oxides (SOx) and volatile and non-volatile particulate matter (vPM and nvPM respectively). nvPM is defined as particles present in the engine exhaust at temperatures higher than 350°C and consists essentially in soot particles produced by the incomplete combustion of the fuel. vPM is formed by nucleation from gaseous precursors in the cooling exhaust gas downstream the combustor, when the concentration of preexisting particles has decreased, favoring homogeneous nucleation versus heterogeneous one (absorption of gases onto preexisting particles). Sulfuric acid formed in the engine exhaust seems to be linked to the formation of vPM. However, the amount of sulfur present in the fuel converted to sulfuric acid in the exhaust is too small to explain the amount of vPM observed. Chemi-ions and organic compounds emitted by the engine are one of the most suitable candidates to explain the formation of vPM in the engine exhaust, but the molecular mechanism behind this phenomenon is still unknown.

The main objectives of this project are:

1) To determine the mechanism behind vPM formation in the engine exhaust and if there is a link with fuel composition
2) To establish a sampling protocol for vPM measurements that can be used in certification processes
3) To determine the impact of fuel chemical composition on the physico-chemical properties of vPM and nvPM

Within this proposal we plan to use the state-of-the-art Combustion Aerosol Standard (CAST) generator especially designed to work with aeronautic fuels available at ONERA as emission source. To study the formation of vPM in detail, we will use the atmospheric chamber CESAM available at LISA and a Potential Aerosol Mass flow Reactor (PAM) available at LSCE and operated in collaboration with INERIS to induce the formation of vPM from the exhaust of CAST. We will use the experimental means available at ONERA and CESAM to characterize the emissions. In addition, key chemical characterization will be performed by SAGE and PhLAM. To get a further insight into the molecular mechanism behind vPM formation, we will perform a series of theoretical simulations led by UTINAM. To complement the consortium, two foreign partners will participate as well: Tampere University of Technology (TUT), that will participate in the characterization of molecular clusters emitted by CAST though the Atmospheric Pressure Interface Time of Flight Mass spectrometry (API-toF), and the Spanish national institute for aerospace (INTA) that will collaborate offering its sampling line in the stack of their test bench to measure vPM formation in one of its standard measurement campaigns with a complete engine.