Abstract
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 ( $\varphi$ ) and MIE, a physical model of microwave spark ignition is established. The calculation results show that the MIE has a U-shaped relationship with $\varphi $ , and the MIE value of methane-air is minimum at the point of $\varphi =0.7$ . 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 $\varphi =0.7$ 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 $\varphi $ is qualitatively similar to the theoretical prediction under microwave spark ignition in this paper.
Highlights
The minimum ignition energy is defined as the minimum energy that ignites a combustible gas successfully
FLAME KERNEL FOR DIFFERENT EQUIVALENCE RATIO High-speed camera is used to take photos of initial flame kernels of microwave spark plugs (MSPs) to compare the effect of different φ on the size of the flame kernel by considering the microwave power, initial pressure, temperature and time to remain invariable for the same MSP
The results indicate that complete combustion progresses efficiently as the minimum ignition energy (MIE) needed for ignition decreases
Summary
The minimum ignition energy is defined as the minimum energy that ignites a combustible gas successfully. Numerous alternative ignition systems have emerged to achieve advantages such as low emissions, low energy loss and high thermal efficiency under lean burn conditions. These systems include microwave ignition [10], corona discharge [11], laser. Numerous microwave spark plugs have been designed to study combustion differences between microwave ignition and SI [19]–[21]. These previous works never includes discussions of the relationship among EFI, MIE and equivalence ratio (φ) for microwave ignition. (4) The mixture gas is ideal gas. (5) The DuFour and Sorbet effects and viscous force are ignored
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