Investigation of tall oil fatty acid as antiwear agent to improve the lubricity of ultra-low sulfur diesels

The tall oil fatty acid (TOFA) used as antiwear agent was applied respectively to the ultra-low sulfur non-additive diesel and ultra-low sulfur additive diesel. The effect of TOFA on the lubricity of the two kinds of ultra-low sulfur diesel was evaluated using the wear scar diameters (WSD) and coefficient of friction (COF). The results showed that the antiwear agent could improve the lubricity of ultra-low sulfur non-additive 0# diesel effectively; both the WSD and COF were reduced significantly. When the content of TOFA antiwear agent increased from 0 to 500 µg/g, the WSD of the non-additive 0# diesel decreased from initial 630 µm to 250 µm, reducing by 60.3%; the COF reduced by 95.7%, from initial 0.47 to 0.02. The wear scar on discs and the wear reflected by Fe element were reduced obviously. The TOFA antiwear agent also showed a trend to reduce the metal content in the diesel friction solution, and there was no influence on other physical and chemical properties of the non-additive diesel. Similarly, the TOFA could also enhance the lubricity of commercial ultra-low sulfur additive 0# diesels. The polar organic substances of TOFA antiwear agent have strong polarity, easy to adsorb on friction surface to form the lubricant protective film, to effectively reduce the friction and wear, thus improve the lubricity of the diesel.