Experimental study on direct ignition of blast furnace gas by plasma igniter in a gas turbine combustor

Abstract

Direct ignition of a gas turbine combustor using blast furnace gas fuel has become a critical issue at present. As an alternative technology of traditional spark plug ignition, plasma-assisted ignition has excellent performance in the gas turbine combustor. In this paper, the ignition system is designed to conduct a direct ignition experiment using the plasma and spark plug igniter. Then, the plasma jet characteristics, ignition limit, and flame propagation of the blast furnace gas combustor are analyzed. The results show that, using blast furnace gas fuel in the gas turbine combustor, the direct ignition of spark plug igniter fails and direct ignition of the plasma igniter succeeds. The jet from the plasma igniter is conical with a length of 30 mm and a diameter of 8 mm, which contains various active species (O、, O*、, O⁺、, O₂⁺、, N₂*, and, N₂⁺). With the increase of air flow rate in the combustor, the equivalence ratio of plasma ignition limit increases from 0.7 to 0.83, and the time required for successful ignition increases from 860 ms to 4300 ms. Meanwhile, the flame propagates from a unidirectional mode to a bidirectional mode in the combustor. The laminar flame characteristics and ignition delay time of BFG/air mixtures were investigated by CHEMKIN package using the Gri-Mech 3.0 model. The active species in the plasma jet can shorten the ignition delay time from 1E-4s to 1E-5s and improve the laminar burning velocities from 7.58 cm/s to 10.90 cm/s. A large-scale initial flame kernel with concentrated energy is formed rapidly so that the flame can successfully propagate to the recirculation zone and burn stably. Finally, the blast furnace gas fuel was successfully ignited directly by the plasma igniter.