$V_f$	flame spread rate [cm/s]
$x_p$	vertical length of pyrolysis zone [cm]
П	structure factor (the ratio of the side wall width to back wall width)
$x$	flame height (cm)
$\delta$	effective preheating zone length (preheating zone length subtracting vertical length of air gaps) (cm)
$V_p$	flame spread rate (advancement rate of total pyrolysis zone) (cm/s)
$V_{p,fuel}$	fuel spread rate (advancement rate of fuel pyrolysis zone) (cm/s)
$x_{air}$	total length of air gaps in preheating zone (cm)
ƒ	fuel coverage
${\delta }_l$	preheating zone length (cm)
$t_{ig}$	ignition time (s)
k	thermal conductivity $({\mathrm{Wm}}^{-1}{\mathrm{K}}^{-1}$)
ρ	density $({\mathrm{kg}\mathrm{m}}^{-3}$)
$c_p$	specific heat $({\mathrm{J}\mathrm{Kg}}^{-1}{\mathrm{K}}^{-1}$)
$T_{\mathrm{p}}$	pyrolysis temperature $(\mathrm{K}$)
σ	Stefan-Boltzmann constant $({\mathrm{W}}^2{\mathrm{m}}^{-4}{\mathrm{K}}^4$)
$T_f$	flame temperature $(\mathrm{K}$)
$Q^{*}$	dimensionless heat release rate
Lc	characteristic length $(\mathrm{cm}$)
$q_{conv}^{"}$	convective heat flux $({\mathrm{W}\mathrm{m}}^{-2}$)
$q_{rw}^{"}$	radiative heat flux $({\mathrm{W}\mathrm{m}}^{-2}$)
Abbreviations
PMMA	polymethyl methacrylate