Numerical Study and Experimental Validation of Minimum Ignition Energy for Microwave Spark Ignition

Microwave plasma ignition has the potential for energy savings and emission reductions, and the minimum ignition energy (MIE) and the lean limit can be determined by microwave spark plugs (MSPs) under the same microwave power. To predict the relationship among electric field intensity (EFI), equivalence ratio (φ) and MIE, a physical model of microwave spark ignition is established. The calculation results show that the MIE has a U-shaped relationship with φ, and the MIE value of methane-air is minimum at the point of φ = 0.7. Then, a novel MSP with three different electrode structures and EFIs is enabled. Finally, this paper presents a combustion performance analysis focusing on the flame kernel, combustion pressure, and composition of combustion emissions. The results indicate that a larger flame kernel size, peak pressure in the chamber and higher fuel efficiency are all achieved under the condition of φ = 0.7 for the same MSP. On the one hand, the MIE of MSP 1 with a higher EFI is lower than that of MSPs 2 and 3; on the other hand, the experimental relationship between the MIE and φ is qualitatively similar to the theoretical prediction under microwave spark ignition in this paper.