Note - I didn't write the article, just copied it out of the Wheels section of my local paper (The Toronto Star Saturday edition March 19, 2005)
Despite the rivers of lubricant poured into engine blocks every day, just how the additives in modern automotive oils work to decrease friction in the heat and pressure of internal combustion is something of a mystery.
A team of chemists and mathematicians at the University of Western Ontario, however, has come up with a theory that appears to explain not only how additives work — but why they sometimes don't.
The most common anti-wear additives are complicated compounds containing zinc and phosphate.
Martin Muser and his colleagues used computer simulations, not laboratory experiments, to deduce what happens at a molecular level when a film of oil containing additives is compressed between two hot, hard surfaces in an engine.
Their conclusion is that as the pressure rises, the molecules of zinc-phosphate dissolved in the oil form cross-links with each other.
More are formed as the pressure increases, until at pressures achieved in engines made of steel alloys, the compounds form a semi-solid molecular mesh.
The mesh is capable of bending and stretching between the steel surfaces, keeping them from wearing each other down.
When the pressure drops, only some of the cross-links undo themselves. Most remain.
This gives the oil a "memory" of its harshest conditions and helps it return more easily to full lubricating capacity.
The findings, reported last week in the journal Science, also explain why zinc-phosphate additives can damage aluminum engines.
The cross-linked mesh can become harder than aluminum and abrade surfaces rather than protect them.
Despite the rivers of lubricant poured into engine blocks every day, just how the additives in modern automotive oils work to decrease friction in the heat and pressure of internal combustion is something of a mystery.
A team of chemists and mathematicians at the University of Western Ontario, however, has come up with a theory that appears to explain not only how additives work — but why they sometimes don't.
The most common anti-wear additives are complicated compounds containing zinc and phosphate.
Martin Muser and his colleagues used computer simulations, not laboratory experiments, to deduce what happens at a molecular level when a film of oil containing additives is compressed between two hot, hard surfaces in an engine.
Their conclusion is that as the pressure rises, the molecules of zinc-phosphate dissolved in the oil form cross-links with each other.
More are formed as the pressure increases, until at pressures achieved in engines made of steel alloys, the compounds form a semi-solid molecular mesh.
The mesh is capable of bending and stretching between the steel surfaces, keeping them from wearing each other down.
When the pressure drops, only some of the cross-links undo themselves. Most remain.
This gives the oil a "memory" of its harshest conditions and helps it return more easily to full lubricating capacity.
The findings, reported last week in the journal Science, also explain why zinc-phosphate additives can damage aluminum engines.
The cross-linked mesh can become harder than aluminum and abrade surfaces rather than protect them.
