# A Novel Way to Enhance the Spark Plasma-Assisted Ignition for an Aero-Engine Under Low Pressure
###### Abstract  
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 \({}^{\circ}\)C kerosene and 17% from 0.075 to 0.062 at 12 m/s with \(-\)30 \({}^{\circ}\)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. multichannel discharge jet-enhanced spark; plasma-assisted ignition; spark kernel; lean ignition limit +
Footnote †: journal: Applieda secondary ignition ability in an aero-engine ignition system [4]. Not only the ignition energy but also the spatial evolution characteristic of the initial spark kernel limit the improvement of the secondary ignition ability [5]. A sufficient spark penetration depth of the initial spark kernel can not only prolong the service life of the igniter but also help increase the probability of contact with the flammable hydrocarbon mixture of stoichiometric ratio, which contributes to the secondary ignition ability of the igniter. Based on spark discharge, researchers have proposed a variety of multichannel spark ignition methods [6; 7; 8], which can increase ignition energy but result in the increased complexity and reduced reliability of the ignition system. Compared with the surface spark discharge ignition, the plasma jet ignition has a significant advantage in improving the spark penetration depth of the initial spark kernel [9; 10; 11]. However, the plasma jet igniter is based on the external gas source, which increases the complexity of the whole ignition system and becomes an obstacle to its application. Researchers have also proposed other types of ignition methods, such as nanosecond pulse plasma-assisted ignition [12], radio frequency plasma ignition [13], microwave plasma-assisted ignition [14; 15], laser plasma-assisted ignition [16; 17], DC plasma ignition [18], and so on. However, there is still much work to be done due to the severe electromagnetic interference of the nanosecond pulse discharge, the complex power supply, and the fairly large size and weight of radio-frequency (RF) discharge and microwave discharge. At this time, a more practical ignition system with an excellent secondary ignition performance for relight of aero-engines at high altitude is urgently needed [19]. Following the development of plasma synthetic jet actuators, the gas inside the cavity is rapidly heated and pressurized by the strong pulsed spark between the internal electrode couple.