Excitation characteristics of pulverized coal flow under different depth of focus position

The laser-induced breakdown spectroscopy was applied to the measurement of pulverized coal flow. The interaction between laser and sample stream, as well as the effects of different focal depth on the plasma excitation characteristics was analyzed. On the self-built two-phase flow experimental bench, the coal particles flow was ablated with laser in the atmospheric environment, under 1, 0.5, 0, -0.5 and -1 mm depth of focus, and the spectrometer was used to collect the plasma signal. Under certain conditions of laser energy and angle of received light, the changes of the plasma temperature, the electron density and the spectra of C, Si and Al with laser focal depth were studied. The results show that the laser focal depth has obvious impacts on the plasma temperature, electron density and elemental spectral intensity. The overall variation of the three parameters are consistency, and the most optimum point is at 0 mm, followed by 1.0, 0.5, -0.5 mm and the worst point is at -1 mm.