Laser-initiated, microwave driven ignition in methane/air mixtures

We have recently demonstrated the use of a pre-ionization laser pulse and a second microwave heating pulse to achieve ignition in near-stoichiometric methane/air mixtures. An ultrashort, 800nm non-resonant laser pulse (200 fs, 200 μJ) for seed ionization in combination with a 3GHz microwave pulse (2 μs, 50 mJ) achieved ignition in a premixed methane/air mixture with an equivalence ratio of 0.8. Microwave energy deposition- limited to only the region of laser interaction-was observed by shadowgraph in both air and methane/air mixtures. In addition, ignition of volumetric regions and multiple ignition points has been demonstrated using single laser and microwave pulses. We also present a numerical simulation of initial microwave heating corresponding to experimental conditions. The goal of moving towards a real combustor implementation is promoted through the design of a novel open microwave resonator configuration allowing a large access area for diagnostics and combustor access not limited to a specific geometry.