A Novel Way to Enhance the Spark Plasma-Assisted Ignition for an Aero-Engine Under Low Pressure

Finding a new ignition strategy for ignition enhancement in a lean-burn combustor has always been the biggest challenge for high-altitude, long-endurance unmanned aerial vehicles (UAVs). It is of great importance for the development of high-altitude, long-endurance aircraft to improve the secondary ignition ability of the aero-engine at high altitude where the ignition capability of the aero-engine igniter rapidly declines. An innovative ignition mode is therefore urgently needed. A novel plasma-assisted ignition method based on a multichannel discharge jet-enhanced spark (MDJS) was proposed in this study. Compared to the conventional spark igniter (SI), the arc discharge energy of the MDJS was increased by 13.6% at 0.12 bar and by 14.7% at 0.26 bar. Furthermore, the spark plasma penetration depth of the MDJS was increased by 49% and 103% at 0.12 bar and 0.26 bar, respectively. The CH* radicals showed that the MDJS obtained a larger initial spark kernel and reached a higher spark plasma penetration depth, which helped accelerate the burning velocity. Ignition tests in a model swirl combustor showed that the lean ignition limit was extended 24% from 0.034 to 0.026 at 25 m/s with 20 °C kerosene and 17% from 0.075 to 0.062 at 12 m/s with −30 °C kerosene maximally. The MDJS was a unique plasma-assisted ignition method, activated by the custom ignition power supply instead of a special power supply with an extra gas source. The objective of this study was to provide a novel multichannel discharge jet-enhanced spark ignition strategy which would help to increase the arc discharge energy, the spark plasma penetration depth and the activated area without changing the power supply system and to improve the safety and performance of aero-engines.

Analytic Model and the Influence of Actuator Number on the Performance of Plasma Synthetic Jet Actuator Array

Coupled with the multichannel discharge model and plasma synthetic jet actuator (PSJA) aerodynamic model, an analytical model to predict the performance of the PSJA array is put forward. The multichannel discharge model takes these factors into consideration, the delay time in the breakdown process, the electrical transformation of the discharge channel from a capacitor to a resistor induced by the air breakdown, and the varying plasma resistance in the discharge process. The PSJA aerodynamic model is developed based on the conservation equations of mass, momentum, energy, and the lumped capacitance method. The multichannel discharge model can simulate the multichannel discharge process and give the discharge energy in the plasma channel. With a constant heating efficiency, the time-independent heating energy deposition power in a discharge channel is obtained. Importing the heating energy, the PSJA aerodynamic model presents the evolution process of the jet. Simulation results show that the jet strength induced by a single actuator decreases with the number of actuators in the PSJA array. When the actuator number increases from 1 to 20, the weakening extent of mass ejected, peak jet velocity, and jet duration time is 62%, 54%, and 33%, respectively. The discharge efficiency increases with the actuator number, while the thermodynamic efficiency decreases with the actuator number. As a result, the total energy efficiency doesn’t always increase with an increase in the number of actuators. When the discharge efficiency of a conventional one channel discharge has been a relatively large value, the total energy efficiency actually decreases with the growth of actuator number.