This discussion on additives and lubricity has caused me to do more reading on the subject than a good novel. Here is another good reference for others interested in tribology (wear & friction).
http://www.infineum.com/Documents/Fuels Technical Papers/SAE/2009-01-0848.pdf
From all my reading, the European and US test standards for wear (HFRR) are very similar. There are two minor differences that I can see, test temperature, and humidity control. I suspect we can compare the data and as Scrod pointed out, the European standard requires a lower wear rate than the US does.
Also I learned that the term 'biodiesel' is not simply the waste fats and oils, but rather it is further treated to produce simple esters from the triglycerides that make up the fats and oils. These esters turn out to be amongst the best lubricity additives, i.e. wear reducing agents in the wear tests. Hence the really great performance of 'biodiesel' when added to untreated fuel feed stock.
The best of the nitrogen containing additives seems to be 8-hydroxyquinoline.
Also, as I found in my studies with plastics all those years ago, the biggest bang for the buck comes with the lowest additive concentrations. The additional improvements decrease with increasing concentrations and actually level off. This is shown in several publications including in the link above.
Bottom line, some extra additives may be helpful, but there are several published cautions about mixing additive types (what the fuel distributor added and your own mix). Adding esters (biodiesel) is likely the safest way to go if you are going to add more but this is just my interpretation of less than what I would call detailed studies.
So now it is time to study the MSDS for the various additives.
Bobk
