SAE Articles Review 2006-2007

I reviewed a host of recent SAE articles. Parentheses are my personal comments:

Study on Maximizing Exergy in Automotive Engines, Endo et al:
The use of waste heat for automobile engines that applied Rankine cycle from the viewpoint of exergy, available energy, was researched. Use of a Rankine (steam) cycle system in a hybrid car increased efficiency from 29 to 33 percent, a 13 percent increase. (Plus or minus 70 percent of automotive fuel energy still goes up in heat. The system is only beneficial at steady states. Response of the system was too slow for stepping on the gas as with city driving.)

Robust Optimization of Engine Lubrication System, Tao et al:
This was a study to optimize design frameworks for new engine lubrication system development. The intent was to prevent parasitic loses from over sized lubrication systems and minimize design time and expenses. The paper revolved around the appropriate amount of oil flow needed at various engine sites. (Hence the importance of oil flow.)

Raman Characterization of Anti-Wear Films Formed from Fresh and Aged Engine OIls, Uy et al:
This article sited research papers from work done in the 1980s. Some showing less tappet wear from used oils as compared to fresh oils. In this recent study (published in 2006) a GF-3 5W-20 grade lubricant with 0.097 % phosphorous was used on a ball-on-flat and cylinder-on-flat test. Fresh and age (artificially) accelerated oils were used. To me the fresh oil seemed to have less wear. They then showed that the chemical composition for the oil film was somewhat different for the test surfaces run on fresh verses aged oil. (The only problem is that this condition never occurs. Fresh oil is only used once on a brand new surface, from then on the surface is coated with additives and a chemical film - after which new fresh oil is added. The condition where used oil is added to brand new engines is just not done. And the fact that the film composition is ever so slightly different does not tell us anything about wear.)

Engine Wear Modeling with Sensitivity to Lubrication Chemistry: A theoretical Framework, Thomas et al:
Evidence was presented to help predict antiwear film evolution and wear performance. As contact severity increases, higher temperatures cause desorption of many physisorbed species, and mechanical shearing also removes the more weakly bound molecules. A key property of friction modifiers is their ability to be easily sheared away, thereby reducing friction. Under mild CONTACT, these highly polar friction modifier molecules will continuously re-adsorb, but under more sever contact regimes, the adsorption of antiwear additives becomes preferential. Similarly, as the contact severity increases further, the antiwear additives become less effective while the extreme pressure additives are activated. Antiwear film relies upon two competing rates: the rate of film formation and the rate of removal. When boundary lubrication conditions are favorable for film formation, the thickness tends to increase to a steady state value of around 100 nm. A number of physio-chemical processes are discussed. (What I see here is that the base oil - viscosity - is not in the equation. The oil is just the vehicle for the chemicals involved in boundary lubrication.)

Effect of Lubricant Properties and Lubricant Degradation on Piston Ring and Cylinder Bore Wear in a Spark-Ignition Engine, Schneider et al:
This contains a lot of useful information and I need to cover this at length and in detail so I will report this later.

aehaas

 

There is some evidence that new oil allows for some more wear than used oil. There are a lot of theories about this. This is one reason that some prefer to change oil less often, or so they say.
One reason for this observation is that new oil loosens up some old crud because the detergents are fresh and strong. This makes new oil initially look bad.

For me the way to go about oil changes is milage and type of driving dependent and also time dependent. I change the oil in all cars in the spring, even though there is never enough miles to justify the change.

aehaas