LAUSR

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.