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Ammonia, the carbon-free fuel of the future? Numerical study of the flame structure and emissions of NH3 / H2-Air flames

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Required Education : Master or Engineering school
Start date : 1 February 2021
Mission duration : 6 mois
Deadline for applications : 31 December 2020
Salary : 650 euros/month

Description

Following a recent report from IEA [1], the replacement of standard carbon fuels with hydrogen is actually considered as one of the most promising technical solution to achieve cleaner combustion inside energy (gas turbines) and transport (internal combustion and aero engines) systems. Indeed, hydrogen offers no emissions of HC and CO2, and it Is characterized by a high flammability which helps the stabilization of leaner flames. Nevertheless, the use of non-negligible quantity of H2 leads to difficulties in terms of combustion performances and safety. Hydrogen leaks may happen promoting explosions. These safety issues are a major constraint not only for the combustion systems but also for the transport and storage of this very flammable fuel.
For these reasons, researchers have focused their attentions to find materials that feature the highest potential hydrogen storage capacity complying with these security issues. Methane (or natural gas) offers clear advantages in terms of energy capacity but it is poorly integrated in a low-carbon scenario. A valid carbon-free alternative is Ammonia (NH3)[2]. It is not a very reactive gas and it provides liquefaction at relatively low pressures and atmospheric temperature with an ease of transportation in a pre-existing infrastructure. Furthermore, technically speaking ammonia could be also directly used as a fuel in the combustion chambers avoid H2 re-conversion costs. Nevertheless, to this scope two are the main challenges: (1) the low reactivity limits pure NH3/Air flames[3]. It is then of interest to explore flame resulting from ammonia/hydrogen blends, where the pure H2 is use as booster of the combustion process [4]. (2) A second problem linked to ammonia combustion is linked to NOx emissions. Ammonia/H2 blends generate high NO emissions, especially if high quantity of H2 is used in the mixture as a consequence of increase of flame temperature [5].

Project program

Hence, the goal of this internship will be to numerically characterized the structure and NOx emission levels of flames generated by different blends of ammonia/H2-air. In this context, first of all canonical flame simulations (premixing and diffusion) will be carried out using the open-source chemical kinetics software CANTERA. Then a LES (Large Eddy Simulation) simulation of a turbulent NH3 / H2-Air flame from the literature will be carried out using AVBP, the combustion code developed at Cerfacs.

The internship program is hereafter detailed:

  •  Bibliography study and training on numerical combustion, CANTERA and AVBP;
  • 1D simulations in CANTERA of premixed and diffusion ammonia/H2-Air flames using detailed chemical mechanisms. Validation with measurements found in literature. Study of the impact of H2 on flame structure and NOx level emissions.
  • Derivation and validation of a reduced chemical mechanism to be used in LES simulations. This will be performed with the Cerfacs tool ARCANE (https://chemistry.cerfacs.fr/en/arcane/).
  • LES simulation with AVBP (https://www.cerfacs.fr/avbp7x/) and validation of a full-3D turbulent NH3/H2-Air flame. [6]

Références
[1] IEA, “The Future of Hydrogen – Seizing today's opportunities,” 2019.
[2] T. Vegge, A. Klerke, H. Christensen, K. Nørskov, and T. Vegge, “Ammonia for hydrogen storage : challenges and opportunities †,” vol. 18, no. 20, 2008.
[3] X. Han, Z. Wang, M. Costa, Z. Sun, Y. He, and K. Cen, “Experimental and kinetic modeling study of laminar burning velocities of NH 3 / air , NH 3 / H 2 / air , NH 3 / CO / air and NH 3 / CH 4 / air premixed flames,” Combust. Flame, vol. 206, pp. 214–226, 2019.
[4] R. C. da Rocha, M. Costa, and X. S. Bai, “Chemical kinetic modelling of ammonia/hydrogen/air ignition, premixed flame propagation and NO emission,” Fuel, vol. 246, no. February, pp. 24–33, 2019.
[5] E. C. Okafor et al., “Towards the development of an efficient low-NOx ammonia combustor for a micro gas turbine,” Proc. Combust. Inst., vol. 37, no. 4, pp. 4597–4606, 2019.
[6] X. Zhu, A. A. Khateeb, T. F. Guiberti, and W. L. Roberts, “NO and OH* emission characteristics of very-lean to stoichiometric ammonia-hydrogen-air swirl flames,” Proc. Combust. Inst., vol. 000, pp. 1–8, 2020.

Contacts: send a complete CV to:

laera@cerfacs.fr, riber@cerfacs.fr