Spectral-kinetic characteristics of laser ignition of pulverized brown coal

In this study, we measured the spectral-kinetic characteristics of ignition of dustlike (pulverized) coal particles with a particle size of $\le$ 100 $\mu$m using an yttrium-aluminum garnet laser with an admixture of neodymium operating in the free-running mode (120 $\mu$s). We discovered three stages of the process, each of which has a threshold character. During the laser pulse in the energy density range of 0.3–1.5 J/cm$^2$, a rapid heating of the sample surface to 3000 K occurs due to the absorption of laser energy and initiation of a chemical reaction in the coal particles. In the energy density range of 1.6–2.1 J/cm$^2$, the yield and ignition of volatile matter above the sample surface are observed in the time interval of 0.5–2 ms. In the emission spectra of the flame, we are able to distinguish bands associated with the combustion of volatile matter including the CO flame and the emission of excited H$_2$O and H$_2$ molecules. At $H>$ 2 J/cm$^2$, ignition and burning of the coke residue takes place in a time interval of 10–100 ms. Its emission spectrum corresponds to the emission spectrum of a black body at 1800 K.