Natural gas is increasingly used as a clean fuel. In many industrial combustion systems, such as industrial furnaces and boilers, a large portion of heat is transferred by radiation. The use of natural gas in such industrial systems leads to a decrease in radiative heat transfer. The addition of solid reactant particles into flame is widely proposed in the literature as a method to enhance radiation from non-luminous flames, with a preponderance of research on hydrogen flame. The present study explores how the injection of pulverized anthracite coal particles into natural gas diffusion flame, as a non-luminous one, affects the thermal and radiative properties of natural gas. A novelty of our research method is the exploitation of yellow chemiluminescence of soot particles together with infrared photography to locate radiative particles and discover their qualitative distribution. The IR filter used in our technique was tested with Thermo Nicolet Avatar 370 FTIR Spectrometer for its spectral transmittance to be determined. The results indicate that the injection of coal particles into natural gas flame leads to a rise in the soot content of flame. Having the advantage of high absorptivity and emissivity coefficients in the near IR region, the soot particles in turn increase the flame luminosity and, more importantly, its emissivity coefficient. Also, the heat released from the combustion of particles increases the average temperature of flame about 29 C. These raise the radiative heat transfer and thermal efficiency of flame as much as 43% and 21%, respectively. It is noteworthy that the average temperature difference and emissivity coefficient, respectively, account for 17% and 83% of the enhancement of the average radiation flux.

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