I’ve just read on a US site that the inventor of Camguard did a presentation out there, and said that one of the most corrosive things in the engine is partially combusted fuel that gets past the piston rings and into the oil.
That would suggest that your oil will be cleaner if you run peak-EGT or LOP, than if you run ROP.
However, it’s not clear to me whether this will show up in a standard oil analysis because that looks for metals.
Blackstone’s check for Fuel in the Properties section. In the last report they even mentioned it in the comments section:
NORMAN: It’s another good report for your Vans. We mentioned before how the copper is from the use of
A/S 15W/50 and therefore isn’t a problem. As long as it stays steady, we’ll probably unhighlight it next time.
The other wear metals are low and steady, which is what you expect to see from an engine that’s running
normally. No fuel or moisture was present and the air and oil filters kept silicon and insolubles under control.
Even the viscosity is perfect for 15W/50. Don’t change a thing. This engine is ready for the winter months
It does not look only for metals but for other elements too. It has been valid a long time, i think, that LPP engines run cooler and cleaner. I only fly LOP (with injected engines) … and it’s even possible with carbureted engines like the O-470, to a point and if the fuel distribution is ot completely off
Blackstone seems to be the only lab reporting this, and they report only very simply e.g. < 0.5%.
My analysis shows exactly the same as above
That’s lots of lead. The average being 5890 ppm which is 0.6 % A 540 has about 10 q or 5 l, roughly 4 kg of oil. This means 24 grams of lead, or 6g/l. 100LL has a lead content 0.3-0.56 g/l. If this is after 50 h, then for each hour the engine is run, it is picking up 0.6 g of lead (on average), or the equivalent of 1-2 l of AVGAS, let’s say 1.5 l. But oil is consumed also, varying greatly, but maybe as much as 0.5 l/h. For each our, the engine looses 10% of the oil. So roughly speaking, after 10 h the oil is replaced with new oil at a rate where you cannot get more lead into it. The engine is really picking up closer to 3 g/h of lead, it uses only 10 hours to reach a steady 6 g/l, a point where the added lead from the fuel equals the lost lead due to oil consumption. The exact number is of course impossible to know without knowing the exact oil consumption, so somewhere around 0.6 g and 3 g per hour.
Further, if the engine (O540) uses 50 l/h (to pick an easy number), then it has consumed 15 – 28 g lead. This correspond to a blow-by of at least 2 % and no more than 20 %.
I really don’t see the use in an oil analysis. The single most important factor affecting it, is oil consumption. On a Lycoming the oil system is an open system, not a closed system, and oil consumption is also a factor of how much you top it up, maybe mostly so. If you constantly top it up, the oil consumption is not oil consumption at all, just oil being lost overboard through the breather.
A good calculation, though I would say that an engine burning that much oil would be, ahem, needing to be “looked at”. Mine burns about 0.1 to 0.2 litre per hour. The Lyco airworthiness limit is IIRC 1 litre (1 quart actually – close enough) per hour.
Yes the oil consumption increases greatly if one fills too high. What that means is engine dependent but I suspect is a lot lower than most people think.
Mine (the IO-550N for which the above analysis was made) burned 0.2 quarts in the last 2.5 hours.
The only thing i find interesting is the metals … aluminum, copper …
Since the oil report is from a SR22, which runs LOP, the conclusion would be that LOP ops does not reduce blow-by products. However, it seems not logical.
However, it seems not logical.
One can only speculate. The burning of the fuel/air mixture has to start from the spark, furthest possible point from the piston/cylinder. When pressure builds up and the piston move down, there will be plenty of time for blow by before the flame front reaches the piston. Besides, LOP is not the same as running with excessive air, as is done in a diesel, far from it. When running LOP, you also run with excessive fuel, only to a slightly lesser extend than when not running LOP.
