Effect of Microwave Pulses on the Morphology and Development of Spark-Ignited Flame Kernel

Xiaobei Cheng, Xinhua Zhang, Zhaowen Wang, Huimin Wu, Zhaowu Wang and Jyh-Yuan Chen
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Xiaobei Cheng: State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan 430074, China
Xinhua Zhang: State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan 430074, China
Zhaowen Wang: State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan 430074, China
Huimin Wu: State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan 430074, China
Zhaowu Wang: Henan Key Laboratory of Photoelectric Energy Storage Materials and Applications, School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471023, China
Jyh-Yuan Chen: Department of Mechanical Engineering, University of California—Berkeley, Berkeley, CA 94720, USA

Energies, 2021, vol. 14, issue 19, 1-19

Abstract: Microwave-assisted spark ignition (MAI) is a promising way to enhance the ignition performance of engines under lean conditions. To understand the effect of microwave-induced flow during MAI, the development and morphology of spark-ignited methane-air flame kernel under various microwave pulse parameters are experimentally studied. Experiments are conducted in a constant volume combustion chamber, and flame development is recorded through a high-speed shadowgraph method. Flame area and deformation index are adopted to evaluate the flame characteristic. Results show that increasing the microwave pulse energy from 0 to 150 mJ exhibits a threshold process for expanding the flame kernel area under 0.2 MPa ambient pressure. When the pulse energy is below the threshold of 90 mJ, the microwave enhancing efficiency is much lower than that beyond the threshold. Increasing microwave pulse repetition frequency (PRF) changes the flow on flame surface and raises the absorption efficiency for microwave energy, and thus helps to improve the MAI performance under higher pressures. Hence, 1 kHz pulses cause more obvious flame deformation than those with higher PRF pulses under 0.2 MPa, while this tendency is reversed as the ambient pressure increases to 0.6 MPa. Besides, microwave pulses of different repetition frequencies lead to different flame kernel morphology, implying the various regimes behind the interaction between a microwave and spark kernel.

Keywords: microwave pulses; spark ignition; flame kernel morphology; energy absorption; interaction regime (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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