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Gas octane rating and Canister exhausts

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Gas octane rating and Canister exhausts

Old 03-11-2004, 07:08 PM
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Kris^
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Default Gas octane rating and Canister exhausts

Last year, when I started tweaking the BME110's I have, using canisters to increase scavenging and also power, I started running into Detonation while using the prescribed 87 octane "regular" gas. For the older BME102's and other motors on the market, this quality of gas should suffice. But, for engines with tuned exhaust setups, canisters, or running bigger props than would be normal, there is a very good chance the engines can run into incipient detonation while running low-octane fuel.

Most times people are told to follow the manufacturers recommendations about fuel quality, but a word to the wise. . IF you are running 87 octane, it is a GOOD idea to up the octane to 89-90 during hot weather, and go as far as 93 (or better) when using tuned canister exhaust systems.

Some things that can happen due to unchecked detonation, especially over a long period of time, say 100 or more flights. You can damage the pistons, actually chipping away the area on the edges of the pistons face or cracking rings, due to the "Hammering" detonation hits your engine with. You can also damage bearings, quickly erode sparkplugs or even destroy the ceramic center insulators, and in some MAJOR cases where the detonation goes on and on and on it's possible to actually fatigue-crack other major structural pieces like rods and cranks (though these pieces are steel, and a lot tougher than aluminum pieces), lead to bearings actually failing, rattle circlips right out of a piston skirt, or break off the skirts of a piston and possibly even blow a hole right through the pistons crown. This hold true for every engine out there, so it's a good idea to keep an eye on it.

If your engine sounds funny in the air, makes a "rattling" sound on a full power pass, or if props or spinners slip when they are tight, you are more than likely running into detonation, and need to address it quickly, before major damage ensues. This is going to become much more prevalent with a lot of people switching to tuned canister exhaust systems, so forewarned is forearmed. My advice. . .FWIW. . .is to automatically go to using PREMIUM gas any time you are running a canister setup, and to also keep a really close eye on your top end fuel mixture. . A lean run will not only run hotter, it will also detonate like crazy.

For anyone interested.
Old 03-11-2004, 07:48 PM
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Default RE: Gas octane rating and Canister exhausts

You Got It! Sounds Right To Me!
Old 03-11-2004, 08:25 PM
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Default RE: Gas octane rating and Canister exhausts

Thank Kris!~) I was wondering why DA recommends running high octane gas when using a tuned system. That make a ton of sense like when I use to run a YS and it would lean a bit too much and detonate before I knew how to tune it. The higher octane is slower burning? letting it hang a bit longer? Anyway, thanks!

joe !~)
Old 03-11-2004, 08:29 PM
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Kris^
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Default RE: Gas octane rating and Canister exhausts

It's more a rating of "stability under pressure/heat" than speed of the burn, Goekeli, but yes, the higher the octane, the slower it burns, and the more stable that burn is. that's what you want. . a burn and expanding flame front. . not a BANG and several flame fronts converging together and hammering the parts. .
Old 03-11-2004, 08:31 PM
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Default RE: Gas octane rating and Canister exhausts

Ahh man! That is an awesome explanation! Thank you

Joe !~)
Old 03-11-2004, 10:33 PM
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Default RE: Gas octane rating and Canister exhausts

It really shouldn't be a surprise to anybody. Running a tuned exhaust system on a 2-stroke has much the same effect as raising the dynamic compression ration, which means higher pressure/temperatures, which as you state Kris, can bring the temperatur very closoe to or above the ignition point of the octane rated fuel used, and a higher octane is needed. Is is just, that there are so many other factors that people consider, when engines don't run right or break, that the fuel octane rating is easily over looked.
DKjens
Old 03-12-2004, 07:20 PM
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Diablo-RCU
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Default RE: Gas octane rating and Canister exhausts

Now wait a minute Kris. What about running 60 octane Coleman fuel in your engine? I read in another thread right here on RCU that octane doesn't matter. Could you run a few gallons of Coleman for us and see if it holes your pistons?......
Old 03-12-2004, 08:34 PM
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Kris^
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Default RE: Gas octane rating and Canister exhausts

I see you have been practicing your "Stand-up Comedy" routine again, Diablo.

It's just amazing, sometimes, the things people actually TRY in this hobby, hoping for a better result than could ever be expected .. .I Especially liked the 40% oil content. . .sounds like he is trying to make it a Diesel. .
Old 03-12-2004, 09:38 PM
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Default RE: Gas octane rating and Canister exhausts

Gentlemen, please, lets keep this civil.
Thank you.
Old 03-12-2004, 11:02 PM
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Default RE: Gas octane rating and Canister exhausts

Kris^'s words below should be followed whether running Glow or gas....

"If your engine sounds funny in the air, makes a "rattling" sound on a full power pass, or if props or spinners slip when they are tight, you are more than likely running into detonation, and need to address it quickly, before major damage ensues. This is going to become much more prevalent with a lot of people switching to tuned canister exhaust systems, so forewarned is forearmed. My advice. . ."

However, there have been many people to have success with Coleman fuel, even with 3W and DA type engines. So learn the above quote from Kris^ and remember it the rest of your flying days.

Another of Kris^'s points is that engines tend to go leaner when they approach a tuned situation.
Old 03-13-2004, 06:53 AM
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Default RE: Gas octane rating and Canister exhausts

agreed
Old 03-13-2004, 08:37 AM
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Default RE: Gas octane rating and Canister exhausts

Coleman fuel has plenty of potential downside with only limited potential upside (no smell). Most of the people in the hobby don't have a "tuner's ear", and can't hear if the engine is lean or detonating. Using 93 octane pump gas is cheaper (and smellier if you spill gas all over the place) with much less risk of destroying engines. Coleman fuel is not intended to be run in an internal combustion engine. It doesn't have any additives for keeping the motor clean.

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