A range of modes/regimes appear in the premixed turbulent combustion, out of which the flamelet regime includes many technologically important flows. In that regime, the principal effect of turbulence is (i) to wrinkle the flame fronts, (ii) to greatly increase its surface area, and (iii) to increase in the overall burning rate (& propagation speed). Studies have found that turbulence can also affect the local flame structure.

Both the structure and propagation of laminar flame can be affected by curvature and divergence of the flow field (usually characterized by the "hydrodynamic strain rate" acting in the flame tangential plane). However, the sensitivity of a laminar flame to strain rate and curvature strongly depends on a third factor, namely Lewis number, a non-dimensional number that shows the relative molecular transport of heat and chemical species. For the flames with non-unity Lewis number i.e. with differential diffusion, both the parameters (together referred to as stretch rate) become very important.

For H2 (Le<1) combustion, due to a difference in the rate of diffusion, thermo-diffusive instability appears, represented by a cellular, wavy pattern as shown in the top figure.

In general, the relative balance between molecular diffusion of species and diffusion of heat is strongly affected by the local geometry of the flame front. The upstream bulges are enriched with reactants but give up more heat (called as regions with high local curvature, higher reaction rate and faster flame speed), where as the reactants start to deplete in the downstream bulges with local increment in thermal energy (regions of low curvature, decreased consumption rate of reactant and decreased propagation speed). Independent studies that show the effect of strain only (with out curvature) also offers similar conclusion.