Eiji Tomita

Bio: Eiji Tomita is an academic researcher from Okayama University. The author has contributed to research in topics: Combustion & Combustion chamber. The author has an hindex of 26, co-authored 210 publications receiving 2579 citations. Previous affiliations of Eiji Tomita include University of California, Berkeley.

Auto-ignited kernels during knocking combustion in a spark-ignition engine

Abstract: In this study, auto-ignition of end-gas due to flame propagation and intensity oscillations caused by shockwaves that occur during knocking combustion were visualized in a compression–expansion engine using a high-speed video camera. Chemical luminescence emissions of the end-gas were detected to analyze the chemical reactions caused by the auto-ignition. Four main conclusions were drawn from this study. When the end-gas region was compressed due to the propagating flame front, auto-ignited kernels appeared near a negative curvature of the flame front. This negative curvature was related to low-temperature chemistry. The large amount of unburned mixture generated a strong pressure wave caused by the auto-ignited kernels explosion. Visualized images of a regular propagating flame front and auto-ignited kernels confirmed that the knocking intensity had a strong relationship with the mass fraction of the unburned mixture. Oscillations of OH* radicals were synchronized with the in-cylinder pressure oscillations, which were produced due to the resulting shockwave. Before auto-ignition of the end-gas occurred, weak OH* radicals and very weak HCHO* radicals appeared in the end-gas region due to low-temperature chemistry. The OH* radicals played an important role in the low-temperature kinetic reactions. This confirms low-temperature chemical reaction of auto-ignited kernel in the end gas region. OH* radicals are a good indicator of the transition from low-temperature chemistry to high-temperature auto-ignition.

Effects of Gas Density and Vaporization on Penetration and Dispersion of Diesel Sprays

Abstract: Ambient gas density and fuel vaporization effects on the penetration and dispersion of diesel sprays were examined over a gas density range spanning nearly two order of magnitude. This range included gas densities more than a factor of two higher than top-dead-center conditions in current technology heavy-duty diesel engines. The results show that ambient gas density has a significantly larger effect on spray penetration and a smaller effect on spray dispersion than has been previously reported. The increased dependence of penetration on gas density is shown to be the result of gas density effects on dispersion. In addition, the results show that vaporization decreases penetration and dispersion by as much as 20% relative to non-vaporizing sprays; however, the effects of vaporization decrease with increasing gas density. Characteristic penetration time and length scales are presented that include a dispersion term that accounts for the increased dependence of penetration on ambient density. These penetration time and length scales collapse the penetration data obtained over the entire range of conditions examined in the experiment into two distinct non-dimensional penetration curves: one for the non-vaporizing conditions and one for the vaporizing conditions. Comparison of the two nondimensional penetration curves to a theoretical penetration correlation for non-vaporizing sprays helped isolate and explain the effects of droplets and vaporization on penetration. The theoretical penetration correlation was derived using the penetration time and length scales and simple model for a non-vaporizing spray that has been previously presented in the literature. The correlation is in good agreement with the non-vaporizing data from this experiment and other commonly quoted penetration data sets. It also provides a potential explanation for much of scatter in the penetration predicted by various correlations in the literature.

Hydrogen as an energy carrier: Prospects and challenges

Abstract: This paper provides an insight to the feasibility of adopting hydrogen as a key energy carrier and fuel source in the near future. It is shown that hydrogen has several advantages, as well as few drawbacks in using for the above purposes. The research shows that hydrogen will be a key player in storing energy that is wasted at generation stage in large-scale power grids by off-peak diversion to dummy loads. The estimations show that by the year of 2050 there will be a hydrogen demand of over 42 million metric tons or 45 billion gallon gasoline equivalent (GGE) in the United States of America alone which can fuel up 342 million light-duty vehicles for 51 × 1011 miles (82 × 1011 km) travel per year. The production at distributed level has also been discussed. The paper also presents the levels of risk in production, storage and distribution stages and proposes possible techniques to address safety issues. It is shown that the storage in small to medium scale containers is much economical compared to doing the same at large-scale containers. The study concludes that hydrogen has a promising future to be a highly feasible energy carrier and energy source itself at consumer level.