Motoichi Murakami

A computational chemistry approach for friction reduction of automotive engines

To improve the fuel efficiency of automobile internal combustion engines, the friction reduction of each engine moving part is important. Recently, carbon films have been attracting much interest as surface-coating materials due to its excellent properties such as low friction and good wear resistance. In this study, the low-friction mechanisms of carbon films were analyzed using molecular dynamics simulations and density functional theory calculations. Molecular dynamics simulation results showed that the termination of OH groups on the surface of the diamond substantially reduced the friction coefficient from 0.07 to 0.01. This reduction was achieved because termination of OH groups weakened the covalent interaction between Fe and C atoms, which was indicated by density functional theory calculations. Additionally, based on the concept of terminating the OH groups on the surface of diamond-like carbon films, we carried out the reciprocating friction experiment between hydrogen-free diamond-like carbon surface and glycerin, which contains large number of OH groups. The friction coefficient of the glycerin was 0.028, much lower than that of the base oil, which was 0.075. The experiments confirmed that OH groups on the surface of hydrogen-free diamond-like carbon films greatly improved the friction properties of its films.

Analysis of Piston Friction in Internal Combustion Engine

Hybrid vehicles (HVs) are becoming more widely used. Since HVs supplement engines drive with motor power, the lubricant oil temperature remains at a lower level than in a conventional gasoline vehicle. This study analyzed the effect of cylinder liner temperature and lubricant oil temperature on engine friction. The results showed that, although the lubricant oil temperature was hardly significant, the liner temperature had an effect on piston friction. It was found that raising the temperature of the middle section of the cylinder liner was the most effective way of reducing piston friction.HV車など低燃費車両の普及でエンジンの低温領域が拡大し、燃費向上のためにその領域の摩擦低減のニーズが高まっている。本研究では、エンジン中最も割合の大きいピストンの摩擦に着目し、ボア壁温分布と油温の寄与率を調査した。その結果、ピストン速度が最大となる摺動位置のボア壁温を上昇させることが有効とわかった。

Development of Piston and Piston Ring Lubrication Analysis

The reduction of CO2 emissions has become an imperative duty in order to cope with environmental compliance. For car manufacturers, CO2 emission has been set by regulation and many consumers prefer a fuel efficient car because of the increasing fuel price. In such a situation, reducing engine friction is an effective way of improving fuel efficiency. Among engine parts, the piston counts for a large percentage of the friction losses. In this study, we established a calculation model for estimating piston and piston ring friction. This paper shows how the accuracy of the calculation model was improved by validating against measurements.