Experimental investigation on spray and ignition characteristics of plasma actuated bluff body flameholder

Abstract

Stable combustion of aero-engines and ramjet combustors is greatly dependent on the quality of atomization. It is quite difficult to achieve wider ignition boundary and good combustion performance under low pressure and low temperature airflow, because the quality of fuel atomization is comparative bad and there is no enough surface area for fuel droplets to mix with surrounding air and evaporate. Internal mechanism of how plasma assisted ignition on spray performance in model aero-engine combustors and ramjet combustors remains not clear. In this study, a novel plasma-actuated bluff-body flameholder is proposed to help improve the quality of fuel atomization and thus enhance the ignition performance and stable combustion of original bluff-body flameholder. Spray and atomization properties of aviation kerosene (RP-3) were investigated under various operating conditions including inlet pressure, inlet temperature and gliding arc plasma actuation. A rotating arc discharge plasma column could be formed during the high-voltage tungsten electrode and the fins of bluff-body flameholder. Macroscopic as well as microscopic spray properties was analysed through simultaneous LIF/MIE technique along with particle/droplet image analysis (PDIA) system. Flame ignition limit at different inlet temperature was conducted under combustor inlet Mach number of 0.2. Results show that mean drop diameters were decreased with increase of inlet temperature and inlet pressure. Gliding arc plasma actuation help fuel injected from bluff-body flameholder breakup into smaller droplets and improve uniformity of fuel spray through heating and transport effect. With actuation of gliding arc plasma, Sauter mean diameter (SMD) was minished by 13%∼20% at inlet pressure of 30 kPa, while droplet uniformity index was increased by around 21.8%. Due to better fuel atomization quality together with more active components generated by gliding arc plasma, flame ignition limit of bluff-body flameholder was obviously extended by about 13%∼30%. The gliding arc plasma was verified to promote fuel droplets atomization and to achieve homogeneous distribution under low temperature and pressure, which is beneficial to wider flame ignition and stabilization boundary.