Flammability conditions for ultra-lean hydrogen premixed combustion based on flame-ball analyses

Fernández Tarrazo, Eduardo and Sánchez Pérez, Antonio Luis and Liñán Martínez, Amable and Williams, F.A. (2012). Flammability conditions for ultra-lean hydrogen premixed combustion based on flame-ball analyses. "International Journal of Hydrogen Energy", v. 37 ; pp. 1813-1825. ISSN 0360-199. https://doi.org/10.1016/j.ijhydene.2011.10.037.

Description

Title: Flammability conditions for ultra-lean hydrogen premixed combustion based on flame-ball analyses
Author/s:
  • Fernández Tarrazo, Eduardo
  • Sánchez Pérez, Antonio Luis
  • Liñán Martínez, Amable
  • Williams, F.A.
Item Type: Article
Título de Revista/Publicación: International Journal of Hydrogen Energy
Date: November 2012
ISSN: 0360-199
Volume: 37
Subjects:
Faculty: E.T.S.I. Aeronáuticos (UPM)
Department: Motopropulsión y Termofluidodinámica [hasta 2014]
Creative Commons Licenses: Recognition - No derivative works - Non commercial

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Abstract

It has been reasoned that the structures of strongly cellular flames in very lean mixtures approach an array of flame balls, each burning as if it were isolated, thereby indicating a connection between the critical conditions required for existence of steady flame balls and those necessary for occurrence of self-sustained premixed combustion. This is the starting assumption of the present study, in which structures of near-limit steady sphericosym-metrical flame balls are investigated with the objective of providing analytic expressions for critical combustion conditions in ultra-lean hydrogen-oxygen mixtures diluted with N2 and water vapor. If attention were restricted to planar premixed flames, then the lean-limit mole fraction of H2 would be found to be roughly ten percent, more than twice the observed flammability limits, thereby emphasizing the relevance of the flame-ball phenomena. Numerical integrations using detailed models for chemistry and radiation show that a onestep chemical-kinetic reduced mechanism based on steady-state assumptions for all chemical intermediates, together with a simple, optically thin approximation for water-vapor radiation, can be used to compute near-limit fuel-lean flame balls with excellent accuracy. The previously developed one-step reaction rate includes a crossover temperature that determines in the first approximation a chemical-kinetic lean limit below which combustión cannot occur, with critical conditions achieved when the diffusion-controlled radiation-free peak temperature, computed with account taken of hydrogen Soret diffusion, is equal to the crossover temperature. First-order corrections are found by activation-energy asymptotics in a solution that involves a near-field radiation-free zone surrounding a spherical flame sheet, together with a far-field radiation-conduction balance for the temperature profile. Different scalings are found depending on whether or not the surrounding atmosphere contains wáter vapor, leading to different analytic expressions for the critical conditions for flame-ball existence, which give results in very good agreement with those obtained by detailed numerical computations.

More information

Item ID: 33570
DC Identifier: http://oa.upm.es/33570/
OAI Identifier: oai:oa.upm.es:33570
DOI: 10.1016/j.ijhydene.2011.10.037
Official URL: http://www.sciencedirect.com/science/article/pii/S0360319911023962
Deposited by: Biblioteca ETSI Aeronauticos
Deposited on: 19 Jan 2015 11:03
Last Modified: 19 Jan 2015 11:03
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