Lubricity Synergism in Boundary Lubrication

Dimethyl Ether (DME) has been known as a ultra clean smokeless fuel for diesel engines for over a decade now. A significant challenge is to ensure full lifetime for the diesel engine injection equipment when handling the low boiling point DME as this fuel has very low viscosity and lubricity. Pressurised lubricity evaluators show that boundary lubrication additives increase DME lubricity significantly but recent work indicate that adequate performance in quasi-boundary lubrication is necessary for reducing the wear effectively in real pumps. In this regime where the pump surfaces are only separated by a few molecular layers fuel molecular structure and viscosity seem to be important properties. Earlier work showed that addition of low lubricity alkanes raised the high lubricity of a boundary lubricant to an even higher level. In the present work the long linear alkane n-hexadecane was added to DME in different proportions. The lubricities of the blends do not show any minimum but reflect the lubricity of pure n-hexadecane. It is not conclusive whether DME is a boundary or a quasi-boundary lubricant but clarifying tests are currently in progress.