The role of differential diffusion during early flame kernel development under engine conditions – part II: Effect of flame structure and geometry

The Role of Differential Diffusion during Early Flame Kernel Development under Engine Conditions -- Part I: Analysis of the Heat-Release-Rate Response

“…This observation is consistent with the correlation between the fuel consumption rate and curvature that was previously shown for an n-heptane/air flame in the broken reaction zones regime [65] and the correlation between the consumption speed and curvature in Le = 1 flames located in the corrugated flamelet regime [62]. Correlations between the local heat release rate and flame structure/geometry are discussed in Part II of the present study [1]. For a visualization of differential diffusion effects during flame kernel development, refer dataset.…”

“…shown in Part II of the present study [1], turbulence detrimentally alters the flame structure by hydrodynamic strain, in addition to the unfavorable effect of large positive curvature on the heat release rate of Le > 1 flame kernels. It should be noted that I 0 quantifies the deviation of the actual flame displacement speed from the respective laminar burning velocity, which is in fact lower in case of Le = 1 (s 0 l,Le=1 /s 0 l,Le>1 = 0.84).…”

“…The macroscopic perspective based on the reduced flame representation in terms of a propagating front (cf. 1 in Fig. 2) enables a separate consideration of differential diffusion effects on I 0,rn (flame structure and the chemical source term) on the one hand, and on I 0,κ as well as Σ c,Ω (flame geometry) on the other hand.…”

“…Then, the heat release rate is considered from a micro-scale point of view to identify the parameters that characterize the coupling between ωc and turbulence/flame interactions in presence of differential diffusion. In Part II of the present study [1], the effect of the local flame structure and geometry on the mixture state (φ, h, Y H ) and source term ωc is quantitatively investigated by relating the behavior of flame kernels to corresponding planar turbulent flames and laminar reference solutions.…”

“…As the flame kernels grow in size, differences in the curvature distributions develop (cf. Part II [1]), which cause differences in heat release rate that feed back into the tangential strain term in Eq. ( 8).…”