Large-activation-energy theory for premixed combustion under the influence of enthalpy fluctuations in the oncoming mixture Part II: applications

Enthalpy (fuel mass fraction and/or temperature) fluctuations in the oncoming mixture are known to have important impacts on premixed combustion and in particular on combustion instability. Theoretical modeling has primarily been following an empirical approach. In Part I of the present study, an asymptotically reduced first-principle theory was derived from the reactive Navier-Stokes equations by using large-activation-energy analysis (AEA). In Part II, the general formulation is applied to special cases in order to elucidate several key fundamental physical processes involved in the overall interaction between the flame, the hydrodynamics and the combustion-generated acoustic field. These include (a) linear response of flame to weak 3-D enthalpy disturbances, (b) sound generation by (1-D) enthalpy fluctuations, (c) parametric instability induced by enthalpy fluctuations, and (d) non-linear development of a flame under the combined influence of an enthalpy perturbation and its spontaneously emitted waves. None of these effects can be accounted for by the empirical modeling approach.