In the aviation sector, fuels derived from hydrotreated vegetable oils (HEFAa) are seen as an alternative to petroleum based Jet A-1b to reduce the environmental footprint of air transport. However, the use of these primarily paraffinic alternative fuels may generate problems related to circuit impermeability. To avoid this issue, a minimum aromatic content is needed, since aromatics are absorbed by polymer seals, ensuring their expansion. However, the quantity of these compounds needs to remain limited since they cause deposits and pollutant formation.
The optimization of the formulation of synthetic aviation fuels was the focus of the CAERc project. A dedicated experimental
research program was conducted on materials compatibility, thermal stability and oxidation resistance tests(1).
Using cutting-edge techniques, IFPEN’s teams thus investigated the various mechanisms involved in thermal and oxidation stability, also combining measurements on real fuels and model fluids. The latter were produced from Jet fuel formulation optimization.
Gasoline direct injection engines emit soot particles during rapid transients. This still poorly understood phenomenon is taken into account during new WLTCsa, aimed at more accurately reproducing real vehicle use.
High-resolution, digital flow simulations in the combustion chamber, capable, in particular, of resolving cycle-to-cycle variations, can be used to gain a better understanding of the mechanisms behind this soot formation. However, these simulations, based on LESb, are mastered on stabilized operating points(1), where they give relevant results, but they have never been carried out for transients.
Research conducted by IFPEN(2-3) in the ANR Astridec project demonstrated the relevance of LES for tackling this problem, via the first ever calculations involving 1D-3D code coupling. In particular, these simulations reproduced the impact of engine transients, i.e. engine speed variations (for example, acceleration between 1,000 rpm and 1,800 rpm in the figure), on the acoustics in the intake line, and thus on filling and aerodynamics in the combustion chamber.
Further work is now required to fine-tune the results, separating the average and fluctuating components of velocity ranges. To do this, research is focusing on two areas: obtaining a usable average based on several transients, and the implementation of specific after-treatment analyses, such as EMDd(4). LES resolution of instantaneous velocity ranges for three crankshaft angles, and for three transient cycles: cycle 4 (1,000 rpm), cycle 16 (1,400 rpm) and cycle 28 (1,800 rpm).
a - Hydroprocessed Esters and Fatty Acids.
b - Carburant utilisé dans l’aviation.
c - .Carburants alternatifs pour l’aéronautique, coordonné par IFPEN.
(1) A. Ben Amara, M.-H. Klopffer, B. Veyrat, L. Starck, International Congress and Expo on Biofuels & Bioenergy, August 29-31, 2016 Sao Paulo, Brésil.
(2) A. Ben Amara, M.-H. Klopffer, M. Alves Fortunato, L. Starck, Optimal jet fuel composition with stability and improved oxidation. Patent WO 2017/050687 A1.