Hirokazu Kojima

Breakdown plasma and vortex flow control for laser ignition using a combination of nano- and femto-second lasers

The breakdown plasma and successive flow leading to combustion are controlled by the combination of a nano-second Nd:YAG laser and a femto-second Ti:Sapphire (TiS) laser. The behaviors are captured by an intensified charged coupled device (ICCD) camera and a high-speed schlieren optical system. The TiS laser determines the initial position of the breakdown by supplying the initial electrons in the optical axis of focusing YAG laser pulses. We show that the initial position of the breakdown can be controlled by the incident position of the TiS laser. In addition, the ignition lean limit of the flammable mixture changes depending on the TiS laser incident position, which is influenced by hot gas distribution and the flow in the flame kernel.

Control of pressure increase rate in compression ignition by pulsed plasma irradiation

Homogeneous charge compression ignition (HCCI) engines are potentially high-efficiency, low-polluting alternatives to conventional internal combustion engines. However, the usable operation range of these engines is limited by too rapid combustion for high-load operation. The combustion is brought by the simultaneous ignition over the cylinder volume. An attempt to suppress it has been tried by realizing stratified temperature or fuel distribution in the cylinder. In this paper, the possibility of pulsed dielectric-barrier discharge (DBD) irradiating the air/fuel mixture is discussed as the new stratified ignition method. A rapid compression and expansion machine (RCEM), which can simulate a single engine cycle, was used to investigate it. DBD was generated in the intake tube of the RCEM. The stratified distribution of the irradiated premixture was obtained by the discharge formation at the end of the induction period. By the pulsed DBD method, the rate of pressure increase was decreased and the characteristic oscillation at the top of the pressure waveform was suppressed. These behaviors were confirmed by observation using a high-speed camera.

Development of dynamic simulator of alkaline water electrolyzer for optimizing renewable energy systems

In order to analyse dynamic behaviours of hydrogen production by alkaline water electrolysis against fluctuating electric power, we developed a large-scale electrolyzer simulator. The measurement d...

Laser-Induced Breakdown Spectroscopy in a High-temperature and High-pressure Spray

Mixture composition in a spray formed by injecting n-heptane into high-temperature and high-pressure gas was measured by laser-induced breakdown spectroscopy (LIBS). The results show that LIBS has a potential for the measurement in a diesel spray.

Laser Ignition Study in AIST

The results of the studies conducted at the National Institute of Advanced Industrial Science and Technology (AIST) in Japan on laser spark ignition are discussed.