I am confused by the apparent conflicting conclusions presented by APS. On one hand we have this statement: "For conforming Normally Aspirated Engines, operating on conforming 100LL fuel, there are essentially zero incidents of true detonation." and on the the other hand we are hearing that they are demonstrating knock on atmo engines using this fuel. Which is it? Or are they demonstrating knock using a turbo engine and 91 octane fuel?
Arguably the people racing Sport and Supersport classes at Reno know more about detonation and high power running of traditional aircraft engines than almost anyone (the factory reps there say as much- "we don't know what happens after 70 inches"). I've been involved with several projects over the last several years including the 2010 Super Sport race winner. Even the non ADI equipped engines are making over 600hp on 100LL so factoring out the higher rpm used, BMEP is DOUBLE what a standard 260 hp O-540 is achieving. Detonation is not a factor here even with non-retarded ignition timing. So how is it that APS is measuring detonation at HALF the BMEP on standard engines? Makes no sense.
The causes and factors of knock have been investigated for many decades- primarily they are: spark advance, IAT, AFR, MAP, CR, EBP and chamber temp. The relative effects of these are well documented by many sources, one of my favorites is the 1952 book by Joseph Liston and professor at Purdue. This offers an amalgamation of much of the research done in the '40s and '50s in the US by the aero and auto industries/ NACA as well as references done by Harry Ricardo and Miller before that. There was also some very interesting testing done in Oz in 2000 with a highly instrumented Toyota 3S-FE.
With regards to valve temperatures, what is APS saying is the heating mechanism if not exhaust gases when the exhaust valve is open? Combustion event? If so then it serves to reason that intake and exhaust valve temps would be similar. We certainly know that is not the case since intakes run around 400F cooler than exhaust valves and the reason why different alloys are used. How is APS measuring valve temperatures? What type of knock sensing hardware are they using? How far down the port are the EGT thermocouples?
RV10inOZ- "EGT has no measurable effect on exhaust valve temperature. If one thinks it might, one must explain why as the EGT goes up from 25dF ROP to Peak EGT, that the exhaust valve temperature is going down. That little fact screws up that idea." By the wording here, I'm not quite clear what you are saying about EGT vs. exhaust valve temperature. Are you saying that exhaust valve temp is lower at peak EGT? If so, I think there are a couple factors that could explain that.
On the Conti 550 Reno racer, we data log multiple channels of temps and pressures through the JPI. Near best power AFRs where we operate at, I can assure you that CHT, EGT and ITT all decrease with an increase in FF. We are more concerned with going too rich which results in a power loss but balancing this with a need to limit ITTs. My Turbo Subaru in my RV responds the same way as does every other engine I've ever dynoed over the last 30 years. If APS is seeing something different, I'd be very interested to know why.
Does anyone have any solid data showing an atmo 8 to 1 Lycoming or Continental using standard ignition timing, CHTs within limits etc. can be made to knock on 100LL at say 5000-8000 feet DA, even running at peak EGT? Seems to me if this was true, there would be a lot of broken engines given that 20+ years ago, most aircraft engines were leaned by the "rough and richen a bit" method, without real instrumentation. With mags, "rough" might be 17-18 AFR, richen a bit takes you to 15-16 AFR which corresponds to peak EGT roughly. Chances would be that many were cruising very close to peak EGT for most of their lives and probably most still went to TBO. Highly unlikely they would last detonating all this time.
