Investigation of mechanisms in plasma-assisted ignition of dispersed coal particle streams

The plasma-assisted ignition enhancement of pulverized lignite particles is intensively studied in a laminar, upward Hencken flat-flame burner. By applying a pair of pin-to-pin electrodes with a high-voltage DC power supply, the apparent reductions of ignition delay time, about 0.8-3.5 ms, are observed for all three ambient temperatures, 1200 K, 1500 K and 1800 K, across which the ignition mode transits from heterogeneous ignition (HI) to hetero-homogeneous combined one. Concentrated on 1200 K ambience where HI mode prevails, the plasmas-induced reduction of ignition delay time as a function of the applied voltage (0-20 kV) is explored, in which the chemical effect is found to play a key role in cases with voltage less than 3 kV. Then, under the conditions of different oxygen mole fractions, the discharge mechanisms and the reductions of ignition delay time are further examined to distinguish the chemical and thermal effects on the ignition enhancement. Finally, the gas temperature rise, both measured and predicted at a point located 6 mm above the electrodes, verifies the thermal effect. This paper provides a preliminary understanding of plasma-assisted ignition mechanisms on dispersed coal particles that may be applied in practical combustion system.