Plasma-assisted combustion technology using nanosecond pulsed power

A next generation type of ignition system has been developed for gasoline combustion engines called “plasma-assisted combustion technology” which both improves engine performance by increasing lean burn flammability and reduces emissions by applying non-equilibrium plasma to gasoline. However, detailed effects of non-equilibrium plasma on gasoline are poorly understood. This study investigates the reforming mechanism of gasoline by non-equilibrium plasma using gas chromatography. First, a nanosecond pulsed power generator using fast recovery diodes was developed to generate non-equilibrium plasma. This pulse generator supplied 9 ns rise-time, 17 ns FWHM, and 32.5 kV amplitude pulses to a 1 kΩ load. Non-equilibrium plasma can be produced at pressures between 0.1 MPa to 0.5 MPa, limited by the vessel. Pulsed power from this pulsed generator was applied to a spark plug used by conventional ignition systems in gasoline engines. The gasoline was reformed by non-equilibrium plasma at 0.1 MPa; components of the reformed gasoline were then investigated using gas chromatography. Results reveal that lower hydrocarbons such as methane, ethylene, ethane and propylene, were newly produced. Also, increasing pulse shot number was found to increase generated amounts of these lower hydrocarbons. We concluded that the lower hydrocarbons may be produced by the active species generated by the non-equilibrium plasma. It is well known that lower hydrocarbons more easily ignite than higher hydrocarbons. Plasma-assisted combustion technology thus holds potential to improve the engine performance. We are currently investigating the credibility of our hypothesis and effects of non-equilibrium plasma to generate lower hydrocarbons, considering the features of applying pulses.