Effect of Pressure and Equivalence Ratio on Minimum Ignition Energy of Methane-Air Mixtures

摘要

In this study experiments were performed to determine the minimum ignition energy of methane-air mixtures at pressures between 1 and 10.3 atmospheres. Laser-induced spark from a 5.5 ns pulse Q-switched Nd-YAG laser at a wavelength of 1064 nm was used to ignite the mixtures. At a given pressure the minimum ignition energy of a methane-air mixture as a function of pressure and equivalence ratio was also investigated. The minimum ignition energy measured in the present investigation for a stoichiometric mixture at 1 atmosphere is 1.3 mJ, which is approximately 3 times larger than that obtained from capacitance-discharge electrical spark ignition. A total laser power of the order of 20 to 40 mJ was found to be sufficient for creating the spark for igniting the mixture with equivalence ratios ranging from 0.6 to 1.2 at all pressures investigated. It is observed that at a given equivalence ratio the minimum ignition energy decreases with increasing pressure. In addition at a given pressure the minimum ignition energy is found to be minimum for a stoichiometric mixture and increases as the mixture deviates from stoichiometric.