Effect of low initial pressure and oxygen concentration on ignition properties of methane/air mixtures ignited by laser-induced breakdown

The aim of this paper is to study the influence of low initial pressures and varying oxygen concentrations on the ignition characteristics of methane/air mixtures using laser-induced breakdown. Experiments were conducted over a range of equivalence ratios and pressures, with a focus on the determination of ignition energies (E 50 ) and their dependence on these parameters. For a 20% oxygen concentration, a U-shaped dependence of E 50 on equivalence ratio was observed, with minimum energies decreasing significantly with pressure. An empirical model was developed to describe the absorbed energy based on pressure, independent of equivalence ratio. When increasing the oxygen concentration to 30%, a clear reduction in E 50 and an extension of the flammability limits were found. These results underline the potential of laser ignition systems for improved combustion stability in aerospace applications, especially under extreme conditions.