Research and Development of Microwave Plasma Combustion Engine (Part I: Concept of Plasma Combustion and Plasma Generation Technique)

This study aims to develop innovative plasma combustion system to improve fuel economy and achieve higher efficiency without any modification of current engine configuration. A new plasma generation technique, that used a combination of spark discharge and microwave, was proposed. This technique was applied to gasoline engine as an ignition source, which was intensive and stable even in lean condition. In this technique, firstly, small plasma source was generated by spark discharge. Secondly, microwave was radiated to the plasma source to expand the plasma. The microwave power was absorbed by the plasma source and large non-thermal plasma was formed. In non-thermal plasma, the electron temperature was high and the gas temperature was low. Then many OH radicals were generated in the plasma. The frequency of the microwave was 2.45 GHz because we used a magnetron for microwave oven. Magnetrons for microwave oven were high efficiency and reasonable. So, plasma generation systems, which were compact and economical, could be easily constructed. By using the standard spark plug, it was easy to generate plasma in high pressure condition. We successfully performed to generate plasma in high pressure air of 2.0 MPa. As the microwave plasma was generated, emission intensity of OH radical was increased to 300 times larger than spark discharge. In order to apply this technique to gasoline engine, a spark plug having a microwave antenna inside was developed. The spark plug could form plasma in high pressure condition of 1.0 MPa.