ISSN 0010-5082, Combustion, Explosion, and Shock Waves, 2018, Vol. 54, No. 3, pp. 284–293.
Pleiades Publishing, Ltd., 2018.
Original Russian Text
E.S. Markus, E.A. Kuznetsov, A.Yu. Snegirev.
Natural Buoyant Turbulent Diﬀusion Flame
near a Vertical Surface
E. S. Markus
, and A. Yu. Snegirev
Published in Fizika Goreniya i Vzryva, Vol. 54, No. 3, pp. 36–46, May–June, 2018.
Original article submitted August 25, 2017; revision submitted October 24, 2017.
Abstract: The structure and dynamics of a natural buoyant turbulent diﬀusion ﬂame near a
vertical surface with combustible gas exhaustion are numerically studied by using the FDS model
and computer code. The ﬂame is considered near the surface through which gaseous propylene
is injected with a prescribed ﬂow rate. Requirements are determined for the grid cell size in the
near-wall region, which ensure suﬃcient spatial resolution of the boundary layer structure. It is
shown that the predicted value of the total heat ﬂux at the surface agrees with the measured
results. Investigations of ignition and combustion of a vertical plate of non-charring thermoplastic
(polymethylmetacrylate) with allowance for the material pyrolysis reaction show that the ignitor
parameters determine the duration of the transient period, but weakly aﬀect the growth of the heat
release rate and the height of the pyrolysis region at the stage of developed burning. Signiﬁcant
eﬀects of the ignitor shape, size, and temperature, as well as lateral entrainment of air on the
velocity of the upward ﬂame spread rate over the plate surface and on the shape of the pyrolysis
front are revealed. The existence of critical parameters of the ignitor separating ﬂame decay from
developed burning is demonstrated. Three ﬂame spread regimes with diﬀerent pyrolysis front
shapes are identiﬁed.
Keywords: ﬁre modeling, material ﬂammability, turbulent diﬀusion ﬂame, pyrolysis, coupled
Natural buoyant turbulent diﬀusion combustion at
the vertical surface of a combustible material is an im-
portant mechanism of ﬁre development whose typical
feature is close interaction of the gas-phase ﬂame and
thermochemical decomposition (pyrolysis) of the solid
fuel. The theoretical analysis and numerical simulation
of the ﬂame spread rate over the combustible material
surface is challenging because its dynamics depends on
several factors: orientation of the material surface, di-
rection of ﬂame spread with respect to the external air
ﬂow, geometric parameters and turbulence level of the
ﬂow, material layer thickness, and combustible material
type. The combination of these factors determines the
Peter the Great St. Petersburg Polytechnic University,
St. Petersburg, 195251 Russia; email@example.com.
variety of regimes of ﬂame propagation over the com-
bustible material surface. Each of these factors was
studied experimentally, theoretically, and numerically
by many researchers; some of these investigations were
summarized, e.g., in [1, 2].
Of major interest is to predict the ﬂame spread
rate over the surface and the growth of the heat trans-
fer rate. The approaches currently used in practice can
be classiﬁed depending on the complexity of gas-phase
and solid-phase models and methods used to predict the
thermal feedback to the surface. In gas phase simula-
tions, the heat ﬂux at the surface is either prescribed
on the basis of empirical data [3–6] or calculated in nu-
merical simulations of the mass and heat transfer by
methods of computational ﬂuid dynamics [7–11].
The simplest solid-phase models are characterized
by explicit separation of the inert heating region and
pyrolysis region over the height of the material surface.
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