So, engines run smoothly, thanks to sophisticated, lubricants and oils.
And, that’s why, lubricants and oils, are remarkable fluids.
During winter, the same engine oil, has to operate over temperatures, ranging from -40 °C to above 250 °C.
It also, has to deal with, contaminants, including metal particles, sludge and soot.
Above all, lubricants and oils must deal with these conditions, every day for up to two years. Consequently, the recommended time between oil changes, according to some vehicle manufacturers.
So, What Are They ?
Engine lubricants and oils, play four major roles:
- Control friction and wear in the engine.
- Protect the engine from rusting.
- Cool the pistons.
- Protect the engine oil stored; in the sump from combustion gases.
Also, There Are Four Distinct Types, Of Lubricants And Oils:
- Hydrodynamic lubrication
- Mixed lubrication
- Boundary lubrication
- Elastohydrodynamic lubrication
So, the thickness of the oil determines, its coefficient of friction and defines, four distinct regions of lubrication.
1-Hydrodynamic lubricants and oils
So, engine bearings and the piston mostly operate, in the “hydrodynamic lubrication” region. Where, a thick oil film, separates the moving metal surfaces. As a result, there is no chance of them, coming into contact.
However, when the pistons are momentarily stationary; the layer of oil can be similar in thickness, to the surface roughness. In this “mixed lubrication” region, the metal surfaces, intermittently come into direct contact.
If the thickness of the oil film, is smaller than the surface roughness; then the metal surfaces, rub together repeatedly. Consequently, contact between, the cams and the tappets in the valve train; span the mixed and boundary regions.
4-Elastohydrodynamic, lubricants and oils
“Elastohydrodynamic lubrication” occurs under high loads. Here, the pressure developed in the lubricant; is sufficiently high, to elastically deform the metal surfaces. This happens because, the viscosity of these fluids, increases significantly as the pressure rises. The valves and the piston rings, occasionally operate in this region.
Finally, it’s the additives added to an engine oil; that give it its qualities, to help with its performance.
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