Yutaro Wakuri

Bio: Yutaro Wakuri is an academic researcher from Kyushu University. The author has contributed to research in topics: Cylinder (engine) & Lubrication. The author has an hindex of 10, co-authored 47 publications receiving 591 citations. Previous affiliations of Yutaro Wakuri include Oita University & Fukuoka University.

Studies on the Penetration of Fuel Spray in a Diesel Engine

Abstract: Regarding the penetrating distance of fuel spray in a diesel engine, the old theory dealing with the motion of a fuel droplet in still air is recognized not to coincide with the actual phenomenon in a diesel engine because of the extremely small size of atomized fuel droplets and the very high density of gas in cylinder. In this paper, the characteristics of spray penetration are discussed from the viewpoint of momentum theory based on the idea that the air induced into a fuel jet stream makes a kind of mixed gas together with fuel droplets. According to the results of experiment, the authors confirmed that the theory was satisfactory, that there existed the simple relations among several dimensionless numbers which indicate the effect of various factors on the spray penetration, that there is a close relationship between the spray cone angle and penetration, and others.

On the Oil Film Behaviour of Piston Rings : Correction of Effective Pressure Region of Oil Film

Abstract: This paper reports on a theoretical calculating procedure of the oil film behaviour between the piston ring and the cylinder wall. The analysis assumes: (1) that the sliding surface of the ring may be approximated by a parabola; (2) that the oil film viscosity is constant; and (3) that the trailing end of oil film pressure varies according to the Reynolds boundary condition, namely the pressure profile ends at apposition where the pressure becomes a downstream pressure and also the pressure gradient becomes zero. The paper gives also an example of oil film behaviour between the circular-faced piston ring and the cylinder wall which has been calculated under the conditions corresponding to a small sized 4-stroke cycle kerosene engine.

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.

Friction-Reducing Surface-Texturing in Reciprocating Automotive Components

Abstract: A model is presented to study the potential use of micro-surface structure in the form of micro pores to improve tribological properties of reciprocating automotive components. The Reynolds equation and the equation of motion are solved simultaneously for a simplified “piston/cylinder” system with surface texturing. The solution provides the time behavior of both the clearance and the friction force between the “piston ring” and “cylinder liner” surfaces. It is shown that surface texturing can efficiently be used to maintain hydrodynamic effects even with nominally parallel surfaces. It is also shown that optimum surface texturing may substantially reduce the friction losses in reciprocating automotive components. Presented at the 56th Annual Meeting Orlando, Florida May 20–24, 2001