Subcritical microwave coupling to femtosecond and picosecond laser ionization for localized, multipoint ignition of methane/air mixtures

Ignition in methane/air mixtures has been achieved using low energy seed laser pulses and an overlapping subcritical microwave pulse. It is shown that the extremely weak ionization of the laser localizes the microwave energy deposition-leading to rapid heating, high temperatures, and ignition. Multiple simultaneous localized regions of ignition are also achieved using the same microwave pulse. Interactions of the seed laser pulse and microwave heating pulse were observed using schlieren and shadowgraph to record the intensity of heating, the scale of the interaction, and for confirmation of ignition. In addition, a coupled one-dimensional gasdynamic-plasma dynamic model has been developed to follow the rapidly evolving plasma properties and the gas properties achieved through this interaction.