Multichannel gliding arcs actuators were designed to enhance the non-premixed combustion of the kerosene (RP-3) and air mixture in a swirl combustor near lean blow-out limit. The instantaneous voltage and current of the multichannel gliding arcs and the 1kHz high-speed CH* chemiluminescence imaging of the combustion process were simultaneously measured to show the characteristics of the process assisted by the plasma. When reaching near lean blow-out limit in a flow rate of 225 SLPM, at the combustor inlet, the emission intensity and projected flame assisted by the multichannel gliding arcs remain the same with decreased fuel flow rates from 3 to 1 ml/min, which assisted by the single gliding arc decreases nevertheless. The flame structure under the influence of plasma actuators with various channel numbers evolves differently owing to the differences in plasma distributions.
In this paper, aerodynamic actuation characteristics of radio-frequency(RF) discharge plasma are studied and a method is proposed for shock wave control based on RF discharge. Under the static condition, a RF diffuse glow discharge can be observed; under the supersonic inflow, the plasma is blown downstream but remains continuous and stable.Time-resolved schlieren is used for flow field visualization. It is found that RF discharge not only leads to continuous energy deposition on the electrode surface but also induces a compression wave. Under the supersonic inflow condition, a weak oblique shock wave is induced by discharge. Experimental results of the shock wave control indicate that the applied actuation can disperse the bottom structure of the ramp-induced oblique shock wave, which is also observed in the extracted shock wave structure after image processing. More importantly, this control effect can be maintained steadily due to the continuous high-frequency(MHz) discharge. Finally, correlations for schlieren images and numerical simulations are employed to further explore the flow control mechanism. It is observed that the vortex in the boundary layer increases after the application of actuation, meaning that the boundary layer in the downstream of the actuation position is thickened. This is equivalent to covering a layer of low-density smooth wall around the compression corner and on the ramp surface, thereby weakening the compressibility at the compression corner. Our results demonstrate the ability of RF plasma aerodynamic actuation to control the supersonic airflow.
Abstract In the extreme conditions of high altitude, low temperature, low pressure and high speed, the aircraft engine has a strong tendency to extinguish and it is then difficult to start secondary ignition, which means that re-ignition of the aircraft engine faces great challenges. Additionally, the ability of the single-channel gliding arc (1-GA) in assisting the ignition under extreme conditions is weak. In this paper, to solve this problem, a multichannel gliding arcs (MGA) system is proposed, using the principle of multichannel discharge. Experiments on the electrical characteristics and ignition performance of MGA were conducted under atmospheric pressure in a swirl model combustor. The electrical characteristics of MGA were investigated under different air velocities. The ignition process of MGA was recorded by using a high-speed camera with CH * filter. Results show that the three-channel gliding arcs (3-GA) and five-channel gliding arcs (5-GA) generated more averaged power than the 1-GA under a constant air velocity. For example, the 3-GA and 5-GA generated 112.8% and 187.3% more averaged power than that of the 1-GA at 74.6 m s −1 , respectively. The arc shapes of gliding arcs with different channel numbers were different and the duration time of ‘breakdown-stretching-extinguishing’ of MGA shortened. Furthermore, compared with the 1-GA, the percentage of the lean ignition limit widening of the 3-GA and 5-GA can reach 13.5% and 20.9% respectively. The frequency of re-breakdown in the discharge process using different gliding arc channel numbers is different, which can continuously inject energy into the combustor and generate the ‘flame combination’ phenomenon producing a larger flame area. The ignition process of MGA can be divided into three stages: sliding stage, flame combination stage and flame stabilization stage.
In the extreme conditions of high altitude, low temperature, low pressure, and high speed, the aircraft engine is prone to flameout and difficult to start secondary ignition, which makes reliable ignition of combustion chamber at high altitude become a worldwide problem. To solve this problem, a kind of multichannel plasma igniter with round cavity is proposed in this paper, the three-channel and five-channel igniters are compared with the traditional ones. The discharge energy of the three igniters was compared based on the electric energy test and the thermal energy test, and ignition experiments was conducted in the simulated high-altitude environment of the component combustion chamber. The results show that the recessed multichannel plasma igniter has higher discharge energy than the conventional spark igniter, which can increase the conversion efficiency of electric energy from 26% to 43%, and the conversion efficiency of thermal energy from 25% to 73%. The recessed multichannel plasma igniter can achieve greater spark penetration depth and excitation area, which both increase with the increase of height. At the same height, the inlet flow helps to increase the penetration depth of the spark. The recessed multichannel plasma igniter can widen the lean ignition boundary, and the maximum enrichment percentage of lean ignition boundary can reach 31%.
Thermal and induced flow velocity characteristics of radio frequency (RF) surface dielectric barrier discharge (SDBD) plasma actuation are experimentally investigated in this paper. The spatial and temporal distributions of the dielectric surface temperature are measured with the infrared thermography at atmospheric pressure. In the spanwise direction, the highest dielectric surface temperature is acquired at the center of the high voltage electrode, while it reduces gradually along the chordwise direction. The maximum temperature of the dielectric surface raises rapidly once discharge begins. After several seconds (typically 100 s), the temperature reaches equilibrium among the actuator's surface, plasma, and surrounding air. The maximum dielectric surface temperature is higher than that powered by an AC power supply in dozens of kHz. Influences of the duty cycle and the input frequency on the thermal characteristics are analyzed. When the duty cycle increases, the maximum dielectric surface temperature increases linearly. However, the maximum dielectric surface temperature increases nonlinearly when the input frequency varies from 0.47 MHz to 1.61 MHz. The induced flow velocity of the RF SDBD actuator is 0.25 m/s.
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