Energy Environment

The UNREAL Project:

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

The UNREAL project aims to conduct molecular level studies on the various new particle formation mechanisms in engine exhaust from aircraft using different fuel compositions. This is particularly important in light of the aviation industry’s commitment to reduce the impacts of aviation on climate and air quality. The use of various sustainable aviation fuels (SAF) offers one possible means of accomplishing this.


  1. Identify the mechanism behind new particle formation (also known as volatile Particulate matter, VPM) in engine exhaust and whether there is a link to fuel composition.

  2. Establish a sampling protocol for vPM measurements that can be used in certification processes.

  3. Determine the effects of the fuel’s chemical composition on the physicochemical properties of vPM and non-volatile PM (nvPM).



A Combustion Aerosol Standard (CAST) Generator specially designed for use with aviation fuels is available at ONERA and used as an emission source. LISA lab’s CESAM atmospheric simulation chamber is used for the in-depth study of the formation of vPM and a Potential Aerosol Mass (PAM) flow reactor available at LSCE and operated in collaboration with INERIS are used to induce the formation of vPM using exhaust from the CAST.

The experimental resources available at ONERA and CESAM are used to characterise the emissions.

In addition, the chemical characterisation is conducted online by CERI EE (via an aerosol mass spectrometer, HR-ToF-AMS) and offline by PhLAM.

A series of theoretical simulations led by UTINAM provide a better understanding of the molecular mechanisms behind the formation of vPM.

The consortium is supplemented by Tampere University of Technology (TUT), which participates in characterising molecular clusters emitted by CAST via the Atmospheric Pressure Interface Time of Flight Mass Spectrometer (API-TOF).

Figure: Measurement campaign at LISA lab’s CESAM simulation chamber with CERI EE’s HR-ToF-AMS visible in the foreground.



IMT Nord Europe participated in the measurement campaign at the CESAM atmospheric simulation chamber in late 2020. Eight different fuels and mixtures were tested: a first set of fuels was used to test the effects of sulphur and aromatic content on particle formation, and a second set included jet A-1 fuel, 100% alternative fuel and a mixture of the two. Two types of experiments were conducted for this campaign.

Each experiment has two steps:

  1. CAST emissions are filtered to remove all soot particles, and only the emitted gases are injected into the chamber;
  2. after a first injection containing only gas, a second injection is conducted with the gases and soot particles.

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