Formation of Carbon-Based Tribofilm Under Palm Methyl Ester

The popularity of biodiesel is continuously increasing nowadays because of fossil fuel’s shortage and environment concerns. Biodiesel is renewable, carbon neutral, and, most importantly, usable in diesel engines without modification. Particularly, the biodiesel from palm oil, palm methyl ester (PME), has become the main source of the world’s biodiesel due to its availability. One of the main concerns in biodiesel fuel usage is its ability to lubricate the mechanical components of the fuel system such as injection pump and nozzle sprayer since those parts are mainly lubricated by the fuel. In this research, an investigation has been conducted to analyze the characteristic of a tribofilm (boundary film) produced by friction of self-mated stainless steel at boundary lubrication condition using palm methyl ester as the lubricant. The friction tests were conducted using a ball on disk tribometer. The results show that excessive wear of the material was prevented; thanks to the tribofilm formed on the contact interface. The analysis shows that the tribofilm has a unique characteristic indicated by the presence of D-band’s peak but the absence of G-band’s peak in its Raman spectra. It seems that the carbon-based tribofilm was formed on the solid surface as a result of carbon decomposition from the palm methyl ester assisted by the tribo-chemical reaction. Although its real structure is still not clear, the tribofilm has an excellent ability to protect the material from severe friction and wear.