  The influence of equivalence ratio on preferential diffusion effects and the
resulting changes in the distributions of major species and their reaction
rates have been analysed based on 2D simulations of lean ${\mathrm{H_2}}$-air
laminar premixed flames, at $\phi=0.4$ and $0.7$. The enhancements of burning
rate, flame surface area, and stretch factor increase with decreasing
equivalence ratio with the increase in stretch factor particularly prominent
when the burning rate and flame area are evaluated based on normalised mass
fraction variation of ${\mathrm{H_2}}$. The preferential diffusion effects have
been demonstrated to lead to significant deviations of mass fractions of major
species and their reaction rates from the corresponding 1D unstretched laminar
premixed flame solution and local variations of equivalence ratio. This
tendency is particularly strong for ${\mathrm{H_2}}$ among all the major
species. Moreover, mass fractions of ${\mathrm{O_2}}$ and ${\mathrm{H_2O}}$ are
found to assume super-adiabatic values at the super-adiabatic temperature zones
and this trend is particularly strong for the $\phi=0.4$ case. It has been
demonstrated that the deviations of major species mass fractions and their
reaction rates from their corresponding 1D unstretched laminar premixed flame
values arise principally due to preferential diffusion effects induced by
relative focussing/defocussing of species and heat at the positively and
negatively curved regions with the nature of the deviations being opposite to
each other depending on the sign of the curvature. The variations of normalised
species mass fractions of $\mathrm{O_2}$ and $\mathrm{H_2O}$ are found to be
significantly affected by the local equivalence ratio within the 2D laminar
flame with $\phi=0.4$ but these effects weaken with an increase in global
equivalence ratio.
