Acid it real ?

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Dec 12, 2002
From a non engine related area, but it has me shagged. At the power station, we do everything that we possibly can to avoid the exhaust gasses getting to or below "acid dewpoint", at which acids start to condense on steelwork, and eat things up. Keeping the gas temperature high (110C) costs us big time efficiency wise, but allows the ash to flow, and keeps the steelwork where we left it. I've seen the results of an issue where due to air leakage into the gas stream, some rainwater was sucked into the gasses. Created tiny droplets of sulfuric acid. These then started to boil off. Making more and more concentrated acid, which then dropped out in places, and chewed heck out of stuff. So, if during short trip running, acids are being generated, do they really evaporate as temperature gets up ? Or is it simply that high temperature operation simply stops them from forming in the first place ? Higher TBN for around town/short trips/cold weather ?
Not being a chemist, let me give you my OPINION as to what I think. I'd think that it's the heat that create the acid by product as sulfur when burned becomes a form of sulphuric acid so IMO, I don't see it being "burned" off, but actually helps create a carbon residue. When it comes to oil, the reason many oils TBN tend to deplete faster than some others is that the TBN is designed to clean up the acids after formed, where there are others that have a lower TBN that will have higher levels of antioxidants that neutralizes the acids before it can become an acid thus the tbn isn't having to clean up what hasn't begun. The interesting thing is that tbn is not, from what I've seen, a linear depletion. Kinda like a gas gauge. TBN will hold at first normally for a good while but as it gets lower, it will deplete faster, this due in part to the antioxidants becoming depleted thus not there to help the TBN of an oil. So, when I look at an oil, if the tbn is 50% of its original value, and the oil has say 7,000 miles on it, this oil will not go another 7,000 miles and maintain the same rate of tbn depletion. When TBN starts to deplete down to the 50% level, this means that it has lost its ability to neutralize the acids effectively so the oil is already not doing as it was in the beginning.
Shannow, What the sulfur percentage allowed in Australian gasoline? Anyway, it's much less than the sulfur in the powerplant fuel. Most of the acid formers will pass through the exhaust, and you need to keep your exhaust pipe hot enough to stay above the dew point just like the power plant's exhaust--or get a stainless steel exhaust system. You're right about the oil, but you probably want to do rather short oil drain intervals for all the well known reasons with short trips. Ken
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