Combustion enhancement in a model scramjet by a simple pin-to-pin AC arc plasma

Abstract

A simple pin-to-pin alternative-current (AC) arc plasma located upstream of the cavity was developed to achieve significant combustion enhancement in a Mach 2.52 C2H4-fueled and cavity-based model scramjet. The arc plasma-enhanced combustion process was recorded by high-speed CH⁎ chemiluminescence imaging, optical emission spectroscopy, static pressure measurements, and discharge waveform measurements. In the absence of the arc plasma, the flame heat release intensity was low, and the heat release region was located at the shear layer of the cavity; the flame stayed in a relatively weak combustion state and even appeared in a lower heat release intensity. Once the arc plasma was turned on, the static pressure of the model scramjet at the typical positions was increased by up to 9 %, and the flame area and the flame intensity were significantly enhanced. In the presence of the arc plasma, the position of the flame heat release region moved upstream and even caused the long-scale displacement for the flame with a higher heat release intensity several times. The arc plasma provided a large number of reactive species and Joule heat at the practical influence region of the arc plasma, which contributed to igniting an initial flame upstream of the cavity. The propagation and development of the continuous initial flame generated by the arc plasma can enable the flame to be more frequently transferred into the cavity-assisted jet-wake stabilized combustion mode, leading to significant combustion enhancement.