Experimental Study On Laser-induced Spark Ignition Of CH₄/O₂/N₂Mixture

In this era of non-renewable energy facing exhausted, increasing air pollutionas well as a higher demand on the performance of engines in more high-tech areas,how to enhance the combustion efficiency and ignition probability of a burner hasbeen a hot topic in combustion research. Compared with conventional ignitionmechanisms, laser induced spark ignition technique has been attracting lots ofinterest, due to its superior advantages, such as non-invasive ignition, precisioncontrollable ignition location and ignition time, multi-time ignition and multipointignition enabled.This work performed a fundamental study on the hotspots, such as theminimum ignition energy, ignition delay time and how to reduce the laser energyrequired for laser-induced spark ignition. First，we conducted experimental studyon the characterization of laser-induced spark ignition in CH₄/O₂/N₂non premixedgas. A coaxial double quartz tube burner is utilized to simulate the real performanceof an engine, thus the characterizations of minimum ignition energy and ignitiondelay time of laser-induced spark ignition were obtained. Due to the fact that thenon-premixed gas flow is closer to the combustion chamber on application, the flowfield of mixed gas is very complex, thus the results had a low regularity, andhowever, initial explorations likewise is of great significance for further study.Secondly, in this paper, we employed laser-induced metal target spark ignitionmethod to reduce the laser energy required for laser-induced spark ignition. Theminimum laser energy required for laser-induced metal target spark ignition hasbeen reduced to3-5mJ and by over70%compared with the laser-induced sparkignition directly on CH₄/O₂/N₂premixed gas. In addition, the ignition delay time isin the range of500¹100μm, which is approximately equal to that of laserbreakdown method. This work confirmed the feasibility of reducing minimum laserenergy by the method of laser-induced metal target spark ignition, and it providedreliable references and experimental study for further study.