Lubrication effect in a DI engine when using Vegetable Oils

Vegetable oils consist of triglycerides, which are esters derived from glycerol and three fatty acids. These types of oils are often unsaturated. This means that some of the carbons form double bonds with other carbons instead of bonding with hydrogen. The double bond region is chemically active and can react with other molecules in the oil or with oxygen from the surrounding air.

There are two negative aspects of these reactions:

- Acidic substances that may form can cause corrosion of the surfaces in contact, and

- Οxidized molecules are deposited in engines.

Vegetable oils do have an advantage compared to mineral oils:

- A vegetable oil molecule has a polar part, which can add to metal surfaces. These molecules form a protective layer that resembles a shag carpet and they are well suited for use in boundary lubrication applications.