Yoshiroh Tokunaga

A Study of Direct Injection Diesel Engine Fueled with Hydrogen

In this study, characteristics of the development and auto-ignition/combustion of hydrogen jets were investigated in a constant-volume vessel. The authors focused on the effects of the jet developing process and thermodynamic states of the ambient gas on auto-ignition delays of hydrogen jets. The results show that the ambient gas temperature and nozzle-hole diameter are significantly effective parameters. By contrast, it is clarified that the ambient gas oxygen concentration has a weak effect on the auto-ignition/combustion of hydrogen jets. Consequently, it is supposed that the mixture formation process is capable of improving the autoignition/combustion of hydrogen jets.

Distribution of Gaseous Fuel Concentration in Unsteady Jet Measured by Planar Laser-induced Rayleigh Scattering (Quantitative Measurement for Mixture Concentration in a High-pressure Ambient)

In this study, a planar laser-induced Rayleigh scattering (PLIRS) was applied to unsteady gas jets to understand processes of jet development process and ambient gas entrainment in a relatively high pressure ambient. In the verification of PLIRS, Rayleigh scattered light intensities were in proportion as incident light intensities and molar number densities of scatterer. From the results of this study, it is clarified that dense mixtures occupy in the center part of the jet and large-scale vortices exist around the jet axis as a large-hole nozzle is used, that dense mixtures do not clearly appear as a small-hole nozzle is used, and that in volumetric concentrations in the steady portion of jets distribute according to a law of 3/2.

A Study on Underexpanded Jet Structure under High Pressure Ambient

In this study, underexpanded flows of hydrogen injected into high pressure ambient were focused to clarify the effect of the flow structure on jet developing and mixing processes. Flow behaviors of underexpanded jets injected into atmospheric pressure ambient are well known. However there are few works about the flow under high pressure ambient and about the flow injected through relatively small orifice (<1.0 mm). Therefore, in this study, the jet flows near the nozzle exit were observed by shadowgraph photography with changing conditions of injection, ambient, and nozzle configuration. The objectives are to clarify the effects of those experimental conditions on the jet structures and to suppose the effect of the jet structures on mixing and developing processes. The shadowgraph images were used to measure Mach disc diameter, barrel length, jet radial width, and shock spacing which were related to a pressure ratio of injection to ambient and nozzle diameter. The results show that the pressure ratio has significant effects on underexpanded jet structures and as the increase in the pressure ratio, jet structures near the nozzle exit enlarged, and that the injected mass was conserved at where the Mach disc was generated. From the results, it is supposed that the pressure ratio is significantly related to the scale of the eddy generated just near the shock structure and also related to mixing process.