  Various flame tracking techniques are often used in hydrodynamic simulations.
Their use is indispensable when resolving actual scale of the flame is
impossible. We show that parameters defining "artificial flame" propagation
found from model systems may yield flame velocities several times distinct from
the required ones, due to matter expansion being ignored in the models.
  Integral effect of material expansion due to burning is incorporated into
flame capturing technique (FCT) [Khokhlov(1995)]. Interpolation formula is
proposed for the parameters governing flame propagation yielding 0.2% accurate
speed and width for any expansion (and at least 0.01% accurate for expansions
typical in type Ia supernova explosions.) Several models with simple burning
rates are studied with gas expansion included. Plausible performance of the
technique in simulations is discussed. Its modification ensuring finite flame
width is found. Implementation suggestions are summarized, main criterion being
the scheme performance being insensitive to expansion parameter (thus absence
of systematic errors when the burning progresses from inner to outer layers);
in this direction promising realizations are found, leading to flame structure
not changing while flame evolves through the whole range of densities in the
white dwarf.
