P. Durbetaki et al., NUMERICAL STUDY OF RADIATIVE IGNITION OF PYROLYSING SOLID FUELS, International journal for numerical methods in fluids, 20(6), 1995, pp. 507-522
A numerical model of radiative ignition of pyrolysing solid fuels is d
eveloped. The model is one-dimensional and transient. The following me
chanisms are simultaneously accounted for: (i) the surface heat and ma
ss transport, (ii) the surface oxidation chemical reaction, (iii) the
in-depth pyrolysis, (iv) the gas-phase heating by absorption of the ra
diation and by heat conduction/convection from the solid surface, and
(v) the gas-phase chemical reaction. The solutions are obtained numeri
cally with the method of lines. Using lignite and bituminous coal for
the simulations, the results confirm that the pyrolysis products absor
b a significant amount of the external radiation. Predictions of the i
gnition times show that both the surface ignition time and the gas-pha
se ignition time decrease rapidly with increasing radiation intensitie
s. A good agreement between predictions and experiments is obtained. A
sensitivity analysis is also carried out with the key kinetic paramet
ers. This analysis establishes an upper limit for surface and pyrolysi
s activation energies and a lower limit for gas-phase activation energ
y. Within these limits, the radiative ignition of coals appears as an
integration of two consecutive ignition modes: the surface ignition oc
curs first, which is then followed by the gas-phase ignition. Beyond t
hese limits, the single gas-phase ignition mode is the only ignition m
ode to prevail.