Taisuke Shiraishi

Nanosecond Plasma Ignition for Improved Performance of an Internal Combustion Engine

Transient plasma, or plasma during a formative true nonequilibrated phase, is studied as an ignition methodology in comparison with traditional spark ignition (2.5-3 ms and 80 mJ) in a single-cylinder gasoline internal combustion engine. Transient plasmas were generated by applying high-voltage pulses that had comparable energy but that were applied for times that were three to four orders of magnitude shorter-85-ns 60-mJ and 20-ns 57-mJ pulses. These created volume-distributed arrays of streamers, which produced electronically excited species during nanosecond time scales. Reductions in ignition delay, higher peak pressure, and increased net heat release ratio relative to conventional spark ignition were observed in these studies. Transient plasma ignition is demonstrated to initiate combustion rapidly, approaching an ideal constant volume cycle; has potential for improving lean combustion operation; is energy efficient; and is potentially useful for gasoline engine emissions reduction.

A trial of ignition innovation of gasoline engine by nanosecond pulsed low temperature plasma ignition

Application of nanosecond pulsed low temperature plasma as an ignition technique for automotive gasoline engines, which require a discharge under conditions of high back pressure, has been studied experimentally using a single-cylinder engine. The nanosecond pulsed plasma refers to the transient (non-equilibrated) phase of a plasma before the formation of an arc discharge; it was obtained by applying a high voltage with a nanosecond pulse (FWHM of approximately 80 or 25 ns) between coaxial cylindrical electrodes. It was confirmed that nanosecond pulsed plasma can form a volumetric multi-channel streamer discharge at an energy consumption of 60 mJ cycle−1 under a high back pressure of 1400 kPa. It was found that the initial combustion period was shortened compared with the conventional spark ignition. The initial flame visualization suggested that the nanosecond pulsed plasma ignition results in the formation of a spatially dispersed initial flame kernel at a position of high electric field strength around the central electrode. It was observed that the electric field strength in the air gap between the coaxial cylindrical electrodes was increased further by applying a shorter pulse. It was also clarified that the shorter pulse improved ignitability even further.

Non-equilibrium plasma ignition for internal combustion engines

High-voltage nanosecond gas discharge has been shown to be an efficient way to ignite ultra-lean fuel air mixtures in a bulk volume, thanks to its ability to produce both high temperature and radical concentration in a large discharge zone. Recently, a feasibility study has been carried out to study plasma-assisted ignition under high-pressure high-temperature conditions similar to those inside an internal combustion engine. Ignition delay times were measured during the tests, and were shown to be decreasing under high-voltage plasma excitation. The discharge allowed instant control of ignition, and specific electrode geometry designs enabled volumetric ignition even at high-pressure conditions.

Fundamental Mechanism Analysis on the Underlying Processes of LSPI Using Experimental and Modeling Approaches

In view of growing global mobility requirements, energy security and climate change remain prominent issues. Consequently, there are strong drivers for further improved efficiency of vehicle powertrains, especially for internal combustion engines, which represent today’s mainstream technology.