Experimental study of the ignition chamber with accelerating cavity applying to methanol lean combustion

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Owing to the high laminar flame velocity and broad flammability limit of methanol (CH3OH), it is ideal for lean burning. How to obtain high energy and reliable ignition is one of the biggest challenges with lean or ultra-low combustion. To gain good ultra-lean burn performance, one solution is utilizing an turbulent jet ignition (TJI)system. Moreover, the methanol can be directly used in the jet ignition chamber for its low vaporization temperature and volatile characteristics. To enhance the methanol jet ignition performance, the two-stage accelerating cavity was applied to accelerate the combustion and extend the lean-burn limit in this research. In a optical experimental apparatus, jet ignition and combustion process of premixed methanol in the main combustion chamber (MCC) were investigated using the shadowgraph and transient pressure data acquisition methods. The experiment results showed that the pressure of the MCC emerged an obvious two-stage rising process to use the two-stage accelerating cavity (SAC). In addition, when the SAC was applied in the ignition chamber (IC), the proportion and peak value of the first stage heat release in the MCC were clearly higher than those of the single straight hole (SSH). Moreover, the ignition chamber compounded with SAC exhibited a short ignition delay and long jet ignition duration. Compared to SSH, the methanol combustion duration in the MCC by using SAC shortened by approximately 28% under both stoichiometric and lean conditions. In other words, The SAC accelerated the combustion process of methanol. More significantly, it was found that the proper secondary acceleration hole diameter (SAHD) play an crucial role in the jet ignition and combustion process, especially under ultra-lean conditions. In addition, by utilizing SAC-3-4.5, the combustion duration of was shortened by 41.9% than that of using SAC-3-3 at the equivalence ratio of 0.6. Finally, the ultra-lean burn limit could be extended to 0.35 by using SAC-3-4.5, which greatly expanded the methanol lean combustion limit.