Hajime Fujimoto

Extraction of the suppression effects of oxygenated fuels on soot formation using a detailed chemical kinetic model

Abstract The influence of oxygenated fuels on the soot formation process inside a burning diesel jet plume was examined using a detailed chemical kinetic reaction mechanism. Normal heptane was selected as a representative diesel fuel, and methanol, ethanol and dimethyl ether were used as oxygenated fuels. It was found that the production of soot precursors, such as small unsaturated hydrocarbons and PAHs, are dramatically reduced by the use of oxygenated fuels, leading to “soot-free” diesel jet flame. Furthermore, there are remarkable differences in soot suppression effects between oxygenated fuels, which have the same molecular formula but different structures of atomic bonded oxygen.

Soot Kinetic Modeling and Empirical Validation on Smokeless Diesel Combustion with Oxygenated Fuels

This paper provides new insights on the mechanism of the smokeless diesel combustion with oxygenated fuels, based on a combination of soot kinetic modeling and optical diagnostics. The chemical effects of fuel compositions, including aromatics - paraffins blend, neat oxygenated fuels and oxygenate additives, on sooting equivalence ratio Φ - temperature T dependence were numerically examined using a detailed soot kinetic model. To better understand the physical factors affecting soot formation in oxygenated fuel sprays, the effects of injection pressure and ambient gas temperature on the flame lift-off length and relative soot concentration in oxygenated fuel jets were experimentally investigated.

Two-dimensional imaging of fuel-vapour concentration by use of LIEF technique during mixture formation process in a DI diesel engine

The laser-induced exciplex fluorescence (LIEF) technique, which is based on spectrally resolved two-colour fluorescent emissions, has been applied to an evaporating diesel spray for the simultaneous separation of liquid and vapour phases on the two-dimensional images. The exciplex system is based on the TMPD/naphthalene system proposed by Melton. The temporal and spatial distribution of liquid and vapour phases during the mixture formation process was detected by this technique. In the LIEF technique, the vapour phase is detected by the monomer fluorescence while the liquid phase is tracked by the exciplex fluorescence. It is able to provide quantitative information on the diffusion state for applying the statistical entropy concept. This concept was put into practice in the image sets obtained through LIEF measurement in order to investigate the diffusion process of vapour phase in the evaporating diesel spray. The laser shadowgraph was taken to deduce the effect of turbulent mixing on the ignition. The experiments were conducted in a direct injection diesel engine with optical access required for the two-dimensional laser imaging. From the results, it is found that ignition occurs in the region where turbulent mixing has advanced a nearly homogeneous mixture of fuel vapour and air. Multi-sectional images obtained by LIEF indicate that there is a spatial dependence of ignition on the vapour-phase fuel in the combustion chamber.

Fundamental Study of Single Droplet and Droplets Array Combustion with Premixed Gas

In the actual spray combustion fields, coupled combustion process should be occurred, between the pre-evaporate fuel component and remaining liquid droplets. Therefore it is insufficient to clarify the fundamental spray combustion mechanism with use of only droplet or only premixed mixture analyze method. In this study, the premixed mixture-droplets coupled combustion field was focused, as a model of the actual spray combustion field. In the experiments, the effect of the flame pattern and the burning rate constant by the interference between the droplets were clarified with the variation of droplets fuel. Besides, effect of the premixed gas surrounding the droplets was clarified by the experiment on coupled combustion. The experiments were carried out under the normal gravity field and the microgravity field to estimate the effect of convection in combustion field.