Control of Microwave Plasma for Ignition Enhancement Using Microwave Discharge Igniter

The Microwave Discharge Igniter (MDI) was developed to create microwave plasma for ignition improvement inside combustion engines. The MDI plasma discharge is generated using the principle of microwave resonance with microwave (MW) originating from a 2.45 GHz semiconductor oscillator; it is then further enhanced and sustained using MW from the same source. The flexibility in the control of semiconductors allows multiple variations of MW signal which in turn, affects the resonating plasma characteristics and subsequently the combustion performance. In this study, a wide range of different MW signal parameters that were used for the control of MDI were selected for a parametric study of the generated Microwave Plasma. Schlieren imaging of the MDI-ignited propane flame were carried out to assess the impact on combustion quality of different MW parameters combinations. Optical emission spectroscopy of the plasmas generated from the same parameter set was also performed to help determine its characteristics. Based on the results, the ignition enhancement mechanism when using MDI-generated plasma was characterized and the most effective parameters for achieving such plasma conditions were determined. Power and duty cycle of the plasma-sustainment MW pulse appears to be the most critical parameters in improving combustion quality. The ignition enhancement is most likely the effect of additional radicals produced from the MW plasma of MDI.