Contents under Pressure
Modeling motor oil could lead to lighter, more efficient engines
Context: Since the late 1930s, zinc dialkyldithiophosphates – or ZDDPs – have been added to motor oils to prevent wear in steel engines, but no one knows why they works so well. The puzzle is more than academic: the auto industry would like to build engines from aluminum, but aluminum wears quickly, and there is currently no antiwear additive that works for aluminum as well as ZDDPs work for steel. Now a group from the University of Western Ontario has developed a computer model that could lead to new additives that make nonsteel engines feasible.
Methods and Results: Nicholas Mosey and colleagues performed a quantum mechanical simulation of how zinc phosphates – the molecules created when ZDDPs decompose in oil – react to the intense pressures generated when engine components slide against each other. They discovered that zinc phosphate molecules, when squeezed together, form a dense network that withstands friction created by rapidly moving engine parts. Strong materials like steel can stand up to the high pressures needed to create this network, but such pressures are too much for aluminum. Before the zinc phosphates organize into the protective network, they become very hard – harder than aluminum – and would cause abrasive wear.
Why It Matters: Using aluminum in engines could boost fuel economy. With an understanding of how ZDDPs work, additives could be designed for aluminum engines, making them more practical.
Source: Mosey, N. J., et al. 2005. Molecular mechanisms for the functionality of lubricant additives. Science 307:1612-5