Abstract The Microwave Assisted Spark Ignition system is a novel and potential ignition method to improve efficiency of spark ignition engines. To better understand the coupling mechanisms/characteristics between microwaves and spark plasma, experiments were conducted to visualize spark discharge and flame development with microwave emitted in a Constant Volume Combustion Chamber. The operation parameters varied included equivalence ratio, ambient pressure, microwave pulse repetition frequency, and peak power. To clearly illuminate the coupling mechanism between microwave and spark plasma, a small-diameter antenna device was specifically designed to minimize heat loss. The microwave assisted spark ignition and flame propagation characteristics of methane-air premixed spherical flames were studied first. Subsequently, non-reactive discharge was experimented to exclude the effects from combustion. Results showed that microwave increased the development speed of an early flame kernel by 60% with 1 kHz microwave pulse repetition frequency and 1000 W peak power under the condition of equivalence ratio 0.6 and ambient pressure 0.1 MPa. The enhancement was believed to be the result of enhanced chemical reaction and the induced flame deformation by collisions between high energy electrons and other particles. As the ambient pressure increased, the enhancement effect of microwaves on flame kernels was found to diminish. In this situation, non-reactive discharge and related MAI experiments showed that a higher pulse repetition frequency or peak power was beneficial to strengthen the effect of microwave as much higher energy absorption efficiency was achieved.

中文翻译：

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微波对甲烷-空气混合物火花点燃球形膨胀火焰的强化作用

摘要 微波辅助火花点火系统是一种提高火花点火发动机效率的新型潜在点火方法。为了更好地理解微波和放电等离子体之间的耦合机制/特性，我们进行了实验，通过在恒定体积燃烧室中发射的微波来可视化火花放电和火焰发展。不同的操作参数包括当量比、环境压力、微波脉冲重复频率和峰值功率。为了清楚地阐明微波和放电等离子体之间的耦合机制，专门设计了一种小直径天线装置，以最大限度地减少热损失。首先研究了甲烷-空气预混球形火焰的微波辅助火花点火和火焰传播特性。随后，试验了非反应性放电以排除燃烧的影响。结果表明，当当量比为0.6、环境压力为0.1 MPa时，微波在微波脉冲重复频率为1 kHz、峰值功率为1000 W的条件下，使早期火焰核的发展速度提高了60%。这种增强被认为是化学反应增强和高能电子与其他粒子碰撞引起的火焰变形的结果。随着环境压力的增加，发现微波对火焰内核的增强作用减弱。在这种情况下，非反应放电和相关的 MAI 实验表明，较高的脉冲重复频率或峰值功率有利于加强微波的作用，因为可以获得更高的能量吸收效率。