Somewhere in the past I heard about adding a couple % acetone to glowfuel. What is it supposed to do??  I will post my observations of adding 3% after I see some response from the engine gurus or those who have actually tried it. I am holding off my findings as I don't want to skew anyone else's opinions or actual results.
Don

With zero nitro fuel 3% acetone gives about the same starting and idling qualities as 5% nitro. I've used it on a few occasions but seeing I get one flick starts with zero nitro anyway it's of no real benefit. Idling of course is only for the dark side crowd . However it always puzzled me (and others) why Shell A Racing fuel contained 3% acetone which could only be bought in their own 20 litre drums until I discovered that the acetone reduces the hygroscopic ability of methanol.

Acetone is added in small quantities to methanol in motorcycle racing engines as an igniter. 

With zero nitro fuel 3% acetone gives about the same starting and idling qualities as 5% nitro. I've used it on a few occasions but seeing I get one flick starts with zero nitro anyway it's of no real benefit.........I discovered that the acetone reduces the hygroscopic ability of methanol.

Brian,
What engines are you running with zero nitro? 
The reduction in hygroscopic action seems useful.

Kim,
All glow engines but to limit the list to stunt then Merco 35, Enya 45 model 6001, ST G51, OS 40 and 46VF, Irvine 40RLS, Stalker 61RE and currently Enya 61CXLRS.

Brian,
Impressive list!  Are you running stock compression?

.....I will post my observations of adding 3% after I see some response from the engine gurus or those who have actually tried it. I am holding off my findings as I don't want to skew anyone else's opinions or actual results.
Don

Don,
Looking forward to seeing your findings.  Thanks.

I was hoping for more info before responding but in any case, here are my findings. I flew two different airplanes, a '59 "T" Bird with a Magnum 36XL engine and the SBD Dauntless profile with an LA 46 engine. I got the same results in both cases. First flights setting the engine as my notes stated, both airplane went way too fast. I found I had to drop the launch RPM by about 400 to 500 RPM and I had to put about 1/4 ounce less fuel in the tank. I also thought the Magnum ran better than ever. The LA 46 only had a few flights so I need to get more experience with it. Approximately a 5% change in RPM and fuel. Now could someone explain the RPM change to me??

Don,
Is this with 3% acetone and no nitro, or acetone + nitro?

The fuel I spiked was Omega 10% nitro 11% each castor and synthetic by volume. I would expect other 11/11 fuels would act the same way.

Well that's interesting, I replied about 12 hours ago but it seems to have disappeared.

However, I've run all my engines mentioned earlier with standard compression except after about 40 flights on the Enya 61RE I decided to raise the compression from the standard 8.8:1 because it uses a button head so is quite easy to change. I was aiming for 13.5 but overshot some machining and ended up with 12.4:1 and decided that was close enough. Results were very good with a much broader range of 4 stroking with a hint of 2 stroking but power at max revs with a 13.5x5 Bolly prop increased by 26% which was surprising. So far I've had around 60 flights with the HC head.

Brian,
8.8 to 12.4 is a substantial increase.  Your good results go along with what I've heard before about higher compression engines liking no-nitro fuel.  The button head certainly comes in handy.  Have you noticed any tendency for small changes in needle setting to make relatively large changes in runtime, either at low or high compression?  A flying partner of mine says he experienced that effect with a Rustler-Merco .61 on no-nitro (an engine which interestingly would not tolerate any nitro content).

Your countryman Geoff Goodworth emailed me and said that he has used no-nitro fuel successfully with other engines we commonly use here, including FP 20 and 25, Thunder Tiger GP 25, LA 46 and Brodak 40.  Something of a surprise to me.  It might be interesting to run compression increase tests on some of these engines, though the convenience of button heads isn't available, so machine work on spare heads might be required.

Don,
It's interesting that even though nitro and acetone both function as ignitors, nitro reduces runtime, while acetone increases it.  Possibly this is partly because nitro is also a secondary oxygen source.  In any case, it sounds like acetone could be useful when a bit more runtime is needed to get through the pattern and available tank space is limited. 

Have you noticed any tendency for small changes in needle setting to make relatively large changes in runtime, either at low or high compression?

It's difficult for me to answer that because, never having used nitro, I don't have any reference for it. What I can say though, based on how various fuels work, is that tuning is more critical with zero nitro than when nitro is mixed in.

It's interesting that even though nitro and acetone both function as ignitors, nitro reduces runtime, while acetone increases it.

This is kind of a follow on from what I said above. Nitro reduces run time (higher fuel consumption) because, compared to methanol, its fuel/air ratio is extraordinarily rich and also has an extraordinarily wide range of acceptable mixture. That's what makes needle settings easier than with just methanol. Acetone though has a much leaner air/fuel ratio being about halfway between methanol and petrol so adding petrol would increase flight times more than acetone. The air/fuel ratios giving maximum power for the various fuels are; methanol 4.5-6.5:1, nitro 0.5-2.5:1, acetone 9.5-10.5:1 and petrol 12.5-13.5:1.

Interesting responses but none address the question of why I had to drop my takeoff rpm ~500 rpm. Run time is not a concern in my case, the rpm change is the big mystery to me.

Interesting responses but none address the question of why I had to drop my takeoff rpm ~500 rpm. Run time is not a concern in my case, the rpm change is the big mystery to me.

Don,
My guess is it may be that no one has run the tests on acetone as a fuel additive that could answer your question--at least no one on Stunthangar.  Fuel formula changes often require needle setting changes.  An answer to the question why might venture into the realm of organic chemistry.

Since acetone is a powerful solvent, how does one prevent damaging a dope finish just in case some raw fuel gets on the plane?  (it ALWAYS happens!)

Floyd

Yessirree.  Poor old dope takes quite a beating.  Come to think of it, straight methanol without either nitro or acetone might be the easiest on dope finishes. 

This from the Fall Fallies topic on the main forum:

"This year, it was foggy and high 30's. Mark Scarborough expected short engine runs with his SSW Magnum .53 powered Avenger, and got all of that, with his engine quitting during the OH8. Dave Royer-Cotton stepped up and drove to the nearby K-Mart and got a liter bottle of Coleman Lantern/Stove fuel. Mark had about 3/4 gallon of 10-20 SIG fuel and on Dave's instructions, added 2.5 oz of the stuff. BINGO! Rule of thumb: DO NOT put more than 4 oz into a gallon of glow fuel. Dave says it lights off easily, and is one of the major reasons he gets 1 flip starts with his Merco .61 powered Humongus." .......

Steve,
Cool.  Another readily available ignition/mileage additive.  Did Mark mention how much longer his Magnum ran after adding the Coleman fuel?  (I checked the Fall Follies topic to see if this was already answered).  Thanks.

I dont have an exact time,, but on my second flight,, I tached it in the pits,, ( with care for other airplanes,, ) then went to the line and started-flew without retaching it,, I ended up with aas I recall 17 laps past the completion of the pattern. so given I did not tach it which generally leads to maybe thirty seconds,, I would say I gained about 40 seconds.
but that is not conclusive,, because typically I was running out in the first loop of the clover which acts as a cut off loop to the airplane,, regardless, it allowed me to complete the flight,,

the instances of running out in the overheads was rather early when it was still below 50 degrees air temp, so its hard to really use that as a good measuring stick

I have found the answer to the acetone/RPM change!! Just prior to heading out to baton Rouge, I thought it would be a good idea to check out my equipment. One of the items was to check the battery in my TNC tach. It was down to about 7 volts! A new battery and Voila!!, now I am back to 9900/10k takeoff rpm. Appears that the tach was missing a small percentage of the blade counts at low voltage.

Good work Detective Hutchinson!  It goes to show how cause and effect are sometimes not so easily identified, especially when there is a likely suspect that turns out to be coincidental.  Sounds like either a design flaw in the TNC or something wrong with yours, since it's a situation designers would want to avoid.   

Thanks Steve and Mark.     

A bit more info. Even with the low battery voltage, the tach read 3600 when near a fluorescent lamp so one cannot trust this diagnostic. Check the battery voltage! In my opinion now, the acetone had almost no effect on how the engine ran.

Coleman fuel is white gas, or no lead. nitro will not mix with gas. May act like adding water to you fuel, this will make you engine run longer because you will have to lean it out.

Steve