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The 26 September 2022 at 14h00

PhD Defense : Jonathan WIRTZ : “Modelling the impact of fuel in aeronautical gas turbines”

Nathalie BROUSSET |  Conférence room - CERFACS - Toulouse |  

you tube link : https://youtu.be/nzu7fTK1yqU

Abstract :

The rise of climatic hazards, due to the human contribution, has led some governments and industries of the aeronautical sector to think about solutions to reduce combustion emissions. To create a less environmentally demanding aviation, electrical storage does not fill the power criteria and other promising fuels such as hydrogen require a change of the whole plane engine. Another short-run solution is the use of drop-in alternative fuel, which, despite some drawbacks, would reduce the emissions of the sector in the nearer future. The European H2020-JETSCREEN project, that funded this PhD, falls within this context. Indeed, the development of LES techniques and ARC development coupled with the rise of CPU resources has enabled precise kinetics to be used in turbulent combustion chambers. The main topic of this PhD is the development of a methodology to analyse a stabilised turbulent two-phase flow flame with complex chemistry and heat losses for three multi-component fuels : one conventional and two alternative fuels. Before the computation, questions on the chemistry and the evaporation properties of the fuels remain. At first, ARC mechanisms were developed and validated against the detailed mechanism, testifying the capability of the kinetic reduction code ARCANE to retrieve the chemical fuel sensitivities. Fuels were then analysed on every canonical cases concluding that the fuel composition had an influence on the global combustion but little on the pollutants. Furthermore, the simulation of 1D ARCs premixed flame explained why such complex kinetics need very few points in the flame front in order to give accurate results and underlined the prominent role of the flame foot and especially the fuel consumption that is monitoring the flame convergence. Second, evaporation properties comparisons led to results close to the experimental work of the DLR and retrieving the two-phase fuel sensitivities. Based on those results, a two-phase premixed flame was computed and the flame characteristic variables were found to depend on the degree of pre-evaporation. Furthermore, the spray counter-flow diffusion flame structure was investigated. The polydisperse two-phase flow initiating a change of the flame regime explained the exotic structure observed. Once those canonical analyses studied, the real combustion chamber simulation was tackled. Differences in terms of averaged solutions have then been drawn, showing the capability of the LES code, AVBP, to globally reproduce the experimental behaviour of those fuels whether for the dynamic quantities, the thermal fields or the two-phase flow properties. The comparison between a simple and a complex surrogate for Jet-A1 resulted in a similar stabilisation point, but a different flame structure, assessing the capability of the Takeno sensor to visualise the right flame regime. A lean blow-out methodology was suggested on the simple chemistry, starting by the evaluation of the characteristic timescales, key quantities for the transient flame evolution and followed by the right variable choice for the LBO detection. The LBO was detected slightly below the experimental value, following a flame stabilisation by hot gases process. Finally, the flame structure was compared for the three fuels and depicted differences in terms of flame structure mainly due to the evaporation properties that are impacting the thermal field and the local flame regime.
Jury : 
A. Vié – EM2C – Referee
D.J.E.M Roekaerts – TU Delft – Referee
N. Swaminathan – University of Cambridge – Member
A. Andreini – University of Florence – Member
A. Vincent-Randonnier – ONERA – Member
G. Exhilard – Safran Helicopter Engines – Invited Member
P. Le Clercq- DLR Stuttgart – Invited Member
B. Cuenot – CERFACS – Advisor
E. Riber – CERFACS – Co-advisor

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