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

publication date

  • January 2012

start page

  • 1813

end page

  • 1825

issue

  • 2

volume

  • 37

international standard serial number (ISSN)

  • 0360-3199

electronic international standard serial number (EISSN)

  • 1879-3487

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 sphericosymmetrical flame balls are investigated with the objective of providing analytic expressions for critical combustion conditions in ultra-lean hydrogen-oxygen mixtures diluted with N-2 and water vapor. If attention were restricted to planar premixed flames, then the lean-limit mole fraction of H-2 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 one-step 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...

keywords

  • hydrogen; flammability limit; ultra-lean combustion; reduced chemistry; flame balls