Steveden
Member
Ok, I will check it out, thx
Most of the presentations I have seen appear to give too much concern about red box for normally aspirated engines. IIRC Walt at one time made a comment that it was very hard to induce detonation on 100LL with a normally aspirated engine and CHTs below 400.
I normally cruise at around 65% with EGTs 0-20 degrees lean of peak and haven't found any issues doing that with my RV10. If closer to 75% I might go to 20-30 LOP, but don't see any benefit of going leaner unless running a turbo. My peak EGTs run around 1490-1520.
Would love your thoughts.
Kelly
Thanks David. My IO-540 is about as conforming as it can get, with 8.5 compression and Bendix S-1200 mags. I recall that it was originally certified on 91/96 Avgas, which of course disappeared a few years after Lycoming certified the engine. So I know it has more detonation margin than the big injected Continentals that run the same compression, but were only certified on either 100/130 or 100LL.Kelly, that would make a great talking point indeed. And you are correct, Walter Atkinson would have said, as we teach and demonstrate in class, a normally aspirated "Conforming Engine" running on "Conforming fuel" (avgas) cannot have detonation supported. Different in an engine with advanced timing (mags or EI's set up badly) or high IAT, high oil temp, and high CHT. But that is not conforming of course.
Turbo engines, you can induce it even on a conforming engine.
With all the avgas vs unleaded avgas detonation testing on the GAMI dyno, we have never seen detonation once past peak EGT. It is all concentrated around the 35-40 through 75 or so dF ROP range.
If you want long life and a good engine for overhaul, stick to the APS methods. As you are.
I am sure that Walter right now would have been smiling reading your post. He is missed.
Kelly, that would make a great talking point indeed. And you are correct, Walter Atkinson would have said, as we teach and demonstrate in class, a normally aspirated "Conforming Engine" running on "Conforming fuel" (avgas) cannot have detonation supported. Different in an engine with advanced timing (mags or EI's set up badly) or high IAT, high oil temp, and high CHT. But that is not conforming of course.
Of course. Your engine was never certified on less than 100 octane fuel, either 100/130 that was available when your engine was designed and certified, or 100LL today. 91 octane mogas is at least 10 octane points lower, probably more. Using a really sub-par fuel is going to create issues, probably anything above 65% and leaner than 150 ROP. Not that different from running mogas in a turbocharged engine. The 200 hp angle valve IO-360 is somewhat marginal at its original 25 degree timing on 100 octane, which is why Lycoming changed the timing to 20 degrees.And one more "non-conforming" engine datapoint (and my engine/fuel system is most definitely "non-conforming" in a variety of ways) - on my IO360 with 8.7 compression, I can easily induce detonation in the 25-75 ROP area while running on 91E10 automotive pump gas. My initial climbs are usually done full power and well rich of this area, or pulled back lean of peak for cruise-climb, either will keep the engine happy. The "red-box" is very real when operating on lower quality fuels, not so much on good 100LL.
The biggest threat from mogas is the RVP (Reid Vapour Pressure) which can be quite variable throughout the year.
The amount RVP varies depends a LOT on both temperature and EPA. Here in Phoenix it is 7.0 for the warmest 6 months, and 7.9 for rest of year, but at least 5% and half of the year 10% ethanol. In Alaska, it was 14-15 in the winter, and around 8-9 in the summer.Kelly, yes the octane number for car gas ion the USA is AKI or R+M/2 and in terms of MON it is about 85-86. 100LL is typically 101.5-102 MON, so 15-17 points of MON number.
The biggest threat from mogas is the RVP (Reid Vapour Pressure) which can be quite variable throughout the year.
I assume you have boost pumps at the tank end and not a pump up front sucking fuel all the way to the engine bay? I know you are smarter than the average bear so I guess my assumption is correct.
For anyone reading, this is critical.
The automotive world does not need to handle issues with RVP, because it is adjusted through the refineries and distribution points for the expected temperatures and altitude. The only reason the automotive world went to very high pressure injection (hundreds of psi or more) was to enable direct cylinder injection instead of the older technology port fuel injection. For the timed port fuel injection they use pressures more like you are operating with to get consistent mixture for economy and emissions purposes. Still has little to do with RVP. For cars/trucks RVP is only an issue if you go from low to high altitude or cold to warm temperatures on one tank of gas.Bingo, yes. I run electronic injectors on a common fuel rail at 45 psig, that solves the problem nicely. That's the way the automotive world handles it - because it works.