This paper reports the ignition temperature and emissivity of heterogeneous materials characterised by high void fraction of between 0.92 and 0.94 and composed of loose particles of shredded grass and paper, planed wood, shredded plastic bags, as well as sugar and bread, with about 95 % of the particles (by mass) of less than 50 mm in size. These materials reflect a typical composition and void fraction of so-called refusederived fuels (RDF), which are obtained from municipal solid waste, then

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... ensified and combusted for energy recovery. An infrared pyrometer, with a spectral response range of 8 to 14 µm, recorded the surface temperature of the surrogate RDF, prior to the onset of the flaming combustion, in a stand alone mass loss calorimeter operated at 20 and 45 kW m -2 . The overlapping spectral ranges of the pyrometer and the radiator heater necessitated the development of a practical methodology to obtain the actual surface temperature from the apparent measurements, which included the effect of the reflected radiation. In addition to surface temperatures (292 -325 °C for 20 kW m -2 and 250 -294 °C for 45 kW m -2 ), in this contribution, we estimate the actual emissivities (0.95 -0.98) of the materials from the intensity of the reflected radiation. NOMENCLATURE c constant that accounts for view factor, surface area and pyrometer response Greek E energy reaching the pyrometer (kW m -2 ) α Absorptivity E α energy emitted (W m -2 ) ε emissivity within spectral range 8-14 µm E γ energy reflected (W m -2 ) ε guess pyrometer emissivity selected by operator q ʹ′ ʹ′  heat flux (W m -2 ) γ reflectivity T a extrapolated apparent temperature (K) σ Stefan-Boltzmann constant (W m -2 K -4 ) T 0 initial sample temperature (K)