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Communication Dans Un Congrès Année : 2022

A brief understanding of the chemiluminescence signature of premixed ammonia-air flames

Résumé

Ammonia has become one of the top contenders amongst other fuels in a conquest to reduce carbon emissions as it is a zero-carbon fuel, can be easily stored and transported and, has a high-octane rating which is favourable in spark-ignition engines. However, ammonia-air flames are characterized by low flame speeds leading to an early blow-off, low heat release and, narrow flammability limits. To enhance the combustion process, it is important to understand the inner flame structure and its response to change in equivalence ratio or even a perturbation in the flow. It is known that ammonia-air flames are thicker than most hydrocarbon flames. Studies on ammonia blended with methane and hydrogen flame structures are available in the literature. Determining the position of the highest heat release rate (HRR) is essential in industrial systems in order to characterize flame stability .Vigueras-Z ́u ̃niga et al. in their paper obtained chemiluminescence from various species which was used to study radical formation in high-temperature reactions for NH3/CH4 blends in swirl flows both experimentally and numerically and also to determine the location of the highest HRR. To the authors’ knowledge, no information on HRR is available for pure ammonia/air flames. The work presented here uses chemiluminescence of excited species and 1D Chemkin simulations of the counterpart non-excited species to compare the behaviour of these species and also, to determine possible HRR markers. The experiments were performed on a Bunsen burner at atmospheric conditions for φ = 0.9-1.4. The premixed laminar flame speed calculator of Chemkin-Pro was used to simulate 1D freely propagating ammonia-air flame. The kinetic scheme of Stagni et al. was used upon previous comparison and validation against experimental results among different kinetic schemes . Excited species of interest in this work for ammonia-air flames were identified as NH2* at 632 nm and NH* at 337 nm. The respective filters were used to obtain the chemiluminescence. The position of each species within the flame front has been determined by finding the distance of each of the species from the fresh gas surface. On choosing a position at which the strain rate for these flames can be considered as negligible; a comparison with the structure of simulated unstretched freely propagating flames was proposed. The 1D simulation provides the temperature evolution, the position of the maximum HRR, and the concentration of the non-excited species along the domain. The experimental and the numerical results can be superimposed. t was seen that both NH2* and NH* were quite close to their counterpart non-excited species which allows us to assume that both the excited species are formed mostly as a result of unre- active collisions. It was observed that the max HRR was in between both the excited species showing that the product of NH2* and NH* is a good indicator of determining the maximum HRR experimentally.
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Dates et versions

hal-03638868 , version 1 (12-04-2022)

Identifiants

  • HAL Id : hal-03638868 , version 1

Citer

Alka Karan, Guillaume Dayma, Christian Chauveau, Fabien Halter. A brief understanding of the chemiluminescence signature of premixed ammonia-air flames. Low-Carbon Combustion, the British and French sections of the Combustion Institute, Apr 2022, Cambridge, United Kingdom. ⟨hal-03638868⟩
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