Ignition of Coals by Laser Pulses in the Free-Running Mode

Abstract—The ignition thresholds and kinetic characteristics of the glow of flames under the action of nanosecond laser pulses (τ_i = 14 ns) of a YAG:Nd³⁺ laser (λ = 1064 nm) on coals of DG (long-flame gas), G (gas), Zh (fat), and K (coking) grades from the Kuznetsk Basin were measured. The stages associated with the evaporation of microprotrusions on the surface of particles and the development of an electron avalanche were distinguished. The threshold $H_{{{\text{cr}}}}^{{(1)}}$ did not depend on the coal grade. The glow amplitude was a nonlinear function of H, and the kinetics of glowing contained two components with τ₁ ~ 20 ns and τ₂ ~ 1 μs. When the energy density $H_{{{\text{cr}}}}^{{(2)}}$ was reached, glow in a microsecond time interval was observed due to the ignition of the coke residue. The ignition threshold $H_{{{\text{cr}}}}^{{(2)}}$ decreased with an increase in the degree of coalification and a decrease in the volatile matter content.