No. 14

April 16, 2021

DECOMPOSITION OF OILS BY ACTION OF DISCHARGE PLASMA(1)-ORIGINAL DISCHARGE PLASMA GENERATOR-70n-Hexadecane

605040302010010203040506070

80

Electrodes distance, μm

Fig.2 Dependence of hydrogen production on electrodes distanceAmount of hydrogen, ppm

Figure 1 (a) and (b) shows the principle of the needle-plateelectrodes type plasma generator that we invented and thechromatograph to analyze the gases evolved by decompositionof oils due to discharge plasma action, respectively. Discharge
was geneared between the needle and plate electrodes in oil,where a voltage was applied between the electrodes using an
external high voltage power supply (HV). Prior to theexperiments, the chamber was filled with dry air by passing dry
air into the chamber for 30 seconds to eliminate the effect ofmoisture. The discharging was generated for 10 seconds,
during which current and voltage were monitored using anoscilloscope. After discharging, leaving it for 20 seconds, thegases produced in the chamber were sampled using a
microsyringe and then they were inserted into thechromatographic column to measure the amount of H2.

Amount of hydrogen, ppm

One of the main problems in alternators is the extremely short fatigue life of the rolling bearings. As a possible cause of the shortlife, it has been assumed that hydrogen is produced inside the bearing and then it penetrates into the bearing material to causehydrogen embrittlement, which results in the short life. However, it is unknown from where the hydrogen comes. On the other hand, it
is reported that plasma is generated in oil lubrication. In this study, we invented a new apparatus that generates discharge plasmas inoil. Using it, we have investigated whether hydrogen is produced or not through oil decomposition by discharge plasma action.

120n-Hexadecane

10080604020001020304050

Discharge time, sFig.3 Dependence of hydrogen production on discharge time

distance of 50µm and the discharge time of 30 s for the experimental condition, in which we could successfully acquire reproducible data.
Fig.1 Schematic view of discharge plasma generator.

Figure 2 shows the relation between the amount of hydrogenproduced in n-hexadecane for 10 seconds discharging and theelectrodes distance. It is shown that the amount of hydrogendecreases with increasing electrodes distance, having thesmallest data variation at 50µm. Figure 3 shows the amount ofhydrogen versus discharge time at the electrodes distance of
50µm in n-hexadecane. The amount of hydrogen rapidly increases with increasing discharge time and then saturates at
30 to 40 s. Based on these data, we adopted the electrodes

Kyodo Yushi Co., Ltd.

The needle-plate electrodes discharge plasma generator invented in this study enabled discharge plasma generation, notonly in air but also in oil. Using the plasma generator, we haveverified that the straight-chain hydrocarbon oil is decomposedby discharging in oil to produce hydrogen. Reaction mechanisms of oil decomposition due to plasma action will be further
examined from various perspectives for both in base oils andadditives to develop new applied plasma technologies.
IIJIMA, M., NAKAYAMA, K.: JAST Tribology Conference, 2017 Tokyo, C13
NOYAMA, S., NAKAYAMA, K. et al.: JAST Tribology Conference, 2017 Takamatsu, A20

2-2-30 Tsujido Kandai, Fujisawa, 251-8588 Japan

http://www.kyodoyushi.co.jp