Ignition of Propane-Air Mixtures by Miniaturized Resonating Microwave Flat-Panel Plasma Igniter

Recent trend in gasoline-powered automobiles focuses heavily on reducing the CO₂ emissions and improving fuel efficiency. Part of the solutions involve changes in combustion chamber geometry to allow for higher turbulence, higher compression ratio which can greatly improve efficiencies. However, the changes are limited by the ignition-source and its location constraint, especially in the case of direct injection SI engines where mixture stratification is important. A new compact microwave plasma igniter based on the principle of microwave resonance was developed and tested for propane combustion inside a constant volume chamber. The igniter was constructed from a thin ceramic panel with metal inlay tuned to the corresponding resonance frequency. Microwaves generated by semiconductor based oscillator were utilized for initiation of discharge. The small and flat form factor of the flat panel igniter allows it to be installed at any locations on the surface of the combustion chamber. Furthermore, the plasma discharged can also be enhanced and sustained using the microwave from the same antenna, which is highly beneficial for combustion performance. High-speed, Schlieren imaging together with pressure measurement were obtained. Successful discharge, ignition and combustion were achieved for a range of equivalence ratios.