A study of flame dynamics and structure in premixed turbulent planar NH3/H2/air flames

Author:

Tamadonfar Parsa1ORCID,Karimkashi Shervin1ORCID,Kaario Ossi1ORCID,Vuorinen Ville1

Affiliation:

1. Department of Mechanical Engineering, School of Engineering, Aalto University, Espoo, Finland

Abstract

Ammonia (NH3) has received considerable attention as a near future carbon-free synthetic fuel due to its economic storage/transportation/distribution, and its potential to be thermally decomposed to hydrogen (H2). To promote the low burning velocity and heat of combustion of ammonia, one viable option is to enrich pure ammonia with hydrogen. In this study, two quasi direct numerical simulations (quasi-DNS) with detailed chemistry and the mixture-averaged transport model are examined to study stoichiometric planar ammonia/hydrogen/air flames under decaying turbulence. The reactants temperature and pressure are set to 298 K and 1 atm, respectively. The initial turbulent Karlovitz number is changed from 4.3 to 16.9, implying that all the test conditions are located within the thin reaction zones combustion regime. The results indicate that the density-weighted flame displacement speed ([Formula: see text]), on average, is higher than the unstrained premixed laminar burning velocity ([Formula: see text]) value for both test cases. This suggests that the flame elements propagate faster than their laminar flame counterpart. With increasing the Karlovitz number, the turbulent burning velocity and the wrinkled flame surface area increase by about 35%. Furthermore, the mean flame stretch factor defined as the ratio of the turbulent to the laminar burning velocity divided by the ratio of the wrinkled to the unwrinkled flame surface area is equal to 1.08. This indicates that the local flamelet velocity value, on average, is higher than the unstrained premixed laminar burning velocity. In addition, the results show that the mean value of the local equivalence ratio for the turbulent conditions is higher than its laminar counterpart due to the preferential diffusion of hydrogen and turbulent mixing. Furthermore, the net production rate of hydrogen is shown to be negatively correlated with the flame front curvature suggesting that the local burning rate is intensified in positively curved regions.

Funder

Academy of Finland

Publisher

SAGE Publications

Subject

Mechanical Engineering,Ocean Engineering,Aerospace Engineering,Automotive Engineering

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