Abstract Microwave Assisted Spark Ignition (MAI) is a potential technology to improve lean combustion characteristics in spark ignition engines. This paper investigates the MAI performance with C2H2-Air spherical expanding flames in a Constant Volume Combustion Chamber (CVCC) system under ambient pressures from 0.1 to 0.6 MPa and equivalence ratios (φ) from 0.5 to 1.9. Results show that MAI greatly increases early flame kernel radius compared with SI mode particularly in the cases close to lean or rich limit under 0.1 MPa. The enhancement decreases obviously as equivalence ratio approaches stoichiometric ratio. With ambient pressure increasing, the MAI enhancement gets weakened. Normalized Reduced Electric Field (REF) is found to correlate well with the decreasing trend of normalized flame radius enhancement with increasing ambient pressure, indicating that REF is probably one of the key factors affecting MAI performance. The influence of microwave Pulse Repetition Frequency (PRF) on MAI under PRF from 1 to 80 kHz are studied and discussed for both non-combustion discharge and ignition tests. Increasing PRF, the enhancement of MAI is strengthened as more microwave energy is injected in high-absorption-efficiency period which is dominated by electron density. At last, the formation mechanism for “fluorescence spot” and its dependence on pressure are offered to explain the observed increasing light intensity in the flame kernel with ambient pressure.

中文翻译：

---

微波辅助火花点火对膨胀C2H2-Air球形火焰的实验研究

摘要 微波辅助火花点火（MAI）是一种改善火花点火发动机稀薄燃烧特性的潜在技术。本文研究了在 0.1 到 0.6 MPa 的环境压力和 0.5 到 1.9 的当量比 (φ) 下，在恒容燃烧室 (CVCC) 系统中使用 C2H2-Air 球形膨胀火焰的 MAI 性能。结果表明，与 SI 模式相比，MAI 大大增加了早期火焰核半径，特别是在 0.1 MPa 以下接近贫或富极限的情况下。当当量比接近化学计量比时，增强作用明显降低。随着环境压力的增加，MAI 增强减弱。发现归一化减小电场 (REF) 与归一化火焰半径随环境压力增加的减小趋势密切相关，表明REF可能是影响MAI性能的关键因素之一。针对非燃烧放电和点火测试，研究和讨论了微波脉冲重复频率 (PRF) 在 1 至 80 kHz 的 PRF 下对 MAI 的影响。随着 PRF 的增加，MAI 的增强会随着更多的微波能量注入高吸收效率期而增强，该高吸收效率期以电子密度为主。最后，提出了“荧光点”的形成机制及其对压力的依赖性，以解释观察到的火焰内核中随环境压力增加的光强。针对非燃烧放电和点火测试，研究和讨论了微波脉冲重复频率 (PRF) 在 1 至 80 kHz 的 PRF 下对 MAI 的影响。随着 PRF 的增加，MAI 的增强会随着更多的微波能量注入高吸收效率期而增强，该高吸收效率期以电子密度为主。最后，提出了“荧光点”的形成机制及其对压力的依赖性，以解释观察到的火焰内核中随环境压力增加的光强。针对非燃烧放电和点火测试，研究和讨论了微波脉冲重复频率 (PRF) 在 1 至 80 kHz 的 PRF 下对 MAI 的影响。随着 PRF 的增加，MAI 的增强会随着更多的微波能量注入高吸收效率期而增强，该高吸收效率期以电子密度为主。最后，提出了“荧光点”的形成机制及其对压力的依赖性，以解释观察到的火焰内核中随环境压力增加的光强。