Two enhancements in microwave-assisted spark ignition and their causes

As a prospective ignition technique, microwave-assisted spark ignition (MAI) efficiently enhances ignition with plasma absorbing microwave energy. This paper achieves MAI through radiating a single 0.2 ms microwave pulse after the initial spark ignition , investigates the ignition performance , the pre-cise absorbed energy of MAI in different absorption patterns. The absorption pattern is tailored by the microwave pulse power. The results show that the enhancement of MAI can be divided into two cat-egories based on ignition performance and absorbed energy: the glow enhancement and the incandes-cence enhancement. Compared to the glow enhancement, the incandescence enhancement has a greater energy absorption efficiency and thus induces more significant ignition enhancement. Additionally, the effect of gas parameters, including gas pressure and components, on these two enhancement categories is studied. Increasing pressure or decreasing methane concentration facilitates the generation of incan-descence enhancement. Ultimately, the causes of both enhancements are discussed. The incandescence enhancement may be originated from the ionization of metal particles in the microwave field, whereas the glow enhancement is attributed to gas ionization. This work highlights the potential application of metal-microwave discharge on MAI, which can play a crucial role in suiting different conditions and fur-ther understanding the mechanisms of MAI.(c) 2023 The Combustion Institute. Published by Elsevier Inc. All rights reserved.