Nitration, oxidation, sulfatation

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May 25, 2003
Quebec Canada
3 nice words, but what they mean, I've done a search only to get few and incomplete result. If an oil analysis for gas engine oil shows: Sulfatation 65 Nitration 54 Oxidation 48 What that is telling me ? Are those result are in direct relation with the TBN of a used oil ?
This question should probably go into the oil analysis section, but here is one answer: Oxidation causes an increase in viscosity and promotes acid formation. Oxidation is caused by the absorption of oxygen molecules, and oxygen molecules cause decomposition of base oils and additives. Oxidation is more rapid where you have high oil temperatures and increased moisture. Nitration causes sludge and varnish, and is primarily due to blowby gasses from the combustion process being injected into or mixed with the oil. Poor ignition/combustion and ring sealing may contribute to nitration. Sulfation of the oil is primarily caused by sulfur in fuels, and secondarily by some of the sulfur-containing additives. In any analysis, find out what the scale is. If the analysis number is say Nitration 10% on a scale of 100%, then nitration is relatively low. Trending of UOA's are the most important part of analysis. For example, if you make a mod to the engine and the nitration goes to 70% after the mod, you got a problem. The other important point for analysis is engine and oil global averages for your car's engine and oil(s). This is where the laboratory and the analyst, such as Terry Dyson, can help you, since their experiences and informational databases help to interpret the specific analysis. Ask questions of both the lab and the analyst. This is what you're paying for. [ January 17, 2004, 03:11 PM: Message edited by: MolaKule ]
The TBN is Total Base Number and is an indication of the acid-fighting reserve left in the oil. A TBN around 2 or lower may indicate the oil is becoming too acidic and should be changed. Different oils start out with different TBN's. Some oils start out with TBN's of 8.5 and only degrade to 5.0 or so over the life of the oil, while others start out at 12 and dive to 3.0 or so. Again, in a used oil analysis, you have to examine every aspect of every number in the resulting analysis to gain an appreciation of what is happening, due to the complexity of the oil and the engine. And this is where your full time analyst can help.
Your numbers seem really high. Normal limits for max are about 20% for most engines, but I've also seen numbers given in different sistems. Basic reasons were covered well by Molakule. Within the combustion category you will see that nitration is also seriously affected by the air-fuel ratio. Temperature also affects it. I've seen a single cold cylinder cut oil life by 60%. Check out this article for the most comprehensive information I've seen to date. (with the exception of a presentation I'm putting together on Waukesha and CAT Gas engines for three teams of engineers next week at three locations.
And just to scare everyone with this, i'll looking at data on the Mitsu Evo board with numbers that look like: Oxi:248 Nit:81 Sulf:64 Talk about scary. And this is (supposedly) on M1 10w-30 for 2500 miles!!! I'll post back in the UOA section once we get full info on this. ferb!
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