Can a piston-powered plane use isooctane directly?

[donkeyking]

Can a piston-powered plane replace 100UL or 100LL with isooctane as it's fuel?

If yes, how much are the three kind of fuels?

Thanks

Donkeyking

 

[mikewint]

donkeyking, i'm no expert but the hydrocarbon n-octane is what the "octane rating" is based on. the iso- is the shifting of a CH3 group to one of the other 7 carbon atoms and should make no difference in combustion. but gasoline fuels contain lots of other additive compounds to do various things for the engine. i'd not want to use pure octane in any engine i wanted to keep using for a long period of time

 

[robwkamm]

If im not mistaken they used heptain? ( not sure of spelling) during the testing of the acessory sections on radial engines during the war. it would boost a 2000hp rating to around 4000. it was used to see what would give out. they used it in airracing in the late 40s when it was surplus and the planes/engines were relatively inexpensive. i think the F2G corsair racer used it. i think thats were i read it. can anyone confirm this?

 

[mikewint]

robwkamm, you almost got it, it's heptane, one carbon and 2 hydrogens less than octane which has 8 carbon atoms
the only thing i've ever heard of to boost performance that high is Nitro (nitro methane)

 

[PWR4360-59B]

For knock testing in engines heptane is the zero octane rating fuel. Iso-octane is the 100% octane rating fuel. So it was not heptane that was used for a huge boost, it would have been iso-octane. And yes for a high boost or compression ratio, iso-octane would be the way to go.
It wouldn't be needed in 100% quantity, it could be mixed with a lower octane fuel.
Reference Fuels

 

[mikewint]

engguy, when the octane rating system came into effect to prevent station owners from adulterating fuels 100 octane insured that you were getting just that 100% pure octane. as fuel tech increased fuels that burned better (rathar than exploded) in the newer high compression engines were developed. 100 octane no longer means 100% octane, just that it burns like 100% octane.
fuel tech also produced fuels that burned better than octane thus the advent of 110 or 120 octane fuels.
low octane fuels exploded in the cylinders before the spark thus knocking. higher octane fuels are less explosive and do not ignite under high compression and heat, they wait for the spark and less prone to knocking
ethanols low energy content insures slow burning characteristics and gives it an octane rating of 129

 

[robwkamm]

here is a link that mensions the fuel im talking about. 200 octane rating. it was used for testing. i cannot find anymore about it. i have a book at home with the info i think. how do you post a link? cut and paste not working.

 

[robwkamm]

Motorsports Hall of Fame of America and Museum look up article on cook cleland and his F2G corsair experimental fuel. i want some.

 

[mikewint]

Guys, i think that you are confusing octane rating and energy content. 200 octane would be a VERY slow burning VERY non-explosive fuel. you could certainly use it in your car but would get no extra energy from it. remember pure alcohol (grain) is 129 octane. filling your tank with pure ethanol is not going to make it take off like a jet.
and jet fuel is very similar to diesel fuel. any diesel will run on jet fuel but putting jet fuel into a spark engine will stop it dead

 

[cherry blossom]

I think that the heptane isomer suggested was 2,2,3-trimethylbutane also called triptane. I have read that while triptane is similar to iso-octane alone, when tetraethyl lead is added the mixture has very good anti knock properties. There have been posts elsewhere on this http://warbirdsforum.com/showthread.php?t=1635

 

[tail end charlie]

putting jet fuel into a spark engine will stop it dead

Ive done it twice with petrol into a diesel It didnt stop dead but ran like a bag of hammers making a huge amount of smoke, luckily I hadnt filled the tank so I went straight back both times and filled up with diesel. The cars still running now. It was just on the radio today a garage put the fuels in the wrong storage tank cars broken down all over the town

 

[Airframes]

Good job it wasn't the other way around ! Petrol would at least clean the (Diesel) injectors, if nothing else, but Diesel in a petrol engine = a lot of potential expense !

 

[robwkamm]

i own a gas station so i understand that. higher the octane the slower the burn. they had a "military experimantal ". it was made by Shell. called Triptane. it was super slow burn. they cranked as much timing into the motors. it says when the air was cool it suffered from backfires that blew off the intake scoops of the race 4360s. if they could have puta higher compression piston in there with ADI its would have made crazy HP. the book also said they used hydrogen peroxide mix instead of water in the ADI. must have been some good times back then when it was no biggie to blow up a 4360.

 

[mikewint]

TEC - adding some gasoline to diesel is a time honored method to clean out the engine. all that black smoke you were belching out was the carbon accumulation in your engine. it's rough on the engine and don't do it too often, but it does work
robwkamm- triptane is indeed 2,2,3,-trimethylbutane, a total of 7-carbon atoms so an isomer of heptane. it slows burning and reduces a fuels tendency to explode before the spark, thus triptane, like tetra ethyl lead is a anti-knock compound. any high compression engine requires high octane fuel to keep from knocking but high octane ratings to not equate to high energy content fuel. if your car is designed for 82 octane fuel it will not run better, faster, or more powerfully on 92 octane. on the other hand an engine designed for 92 octane will knock and will run poorly on 82 octane
hydrogen peroxide decomposes to produce oxygen gas thus the engine is receiving extra oxygen which will cause anything to burn faster releasing more energy per unit of time

 

[Aaron Brooks Wolters]

Very informative gentlemen. Thank you.

 

[PWR4360-59B]

I understand the difference between octane, and cetane real well.

It is debateable whether high octane means slow burning or not, I do know from experience high octane burned cooler. And actually rapid burning at initial spark maybe a good thing, I have seen many disscusions on this else where. I'm sure something like nitromethane doesn't delay much when its fired off.
Back to isooctane, I read something about how it would be a better alternative than mtbe.

 

[mikewint]

engguy, cetane number is a measure of ignition delay in diesel engines. a high cetane number indicates a short delay period which is required for high speed diesels. US diesels follow ASTM D975 with a minimum cetane of 40 with most between 42-45. bio-diesels from vegetable oils produce cetane from 46 - 52 and animal fat bio-diesels from 56 -60. since there is no advantage past 55 bio-diesels all tend to be veg derived.
MTBE or Methyl Tertiary Butyl Ether is an oxygenator added to gasoline (10-15%) to raise octane numbers and provide more oxygen for more complete combustion since it is considered to be a carcinogen and in several instances has leaked from underground storage tanks into the ground water US production has practically ceased. It has been replaced by ethanol though there is a strong movement toward ETBE or Ethyl Tertiary Butyl Ether which is derived from methanol. ETBE has many advantages over ethanol. It has an equal or better effect on octane, does not raise the vapor pressure of the fuel as does ethanol causing higher evaporation rates and increasing pollution levels, and has a lower solubility in water so leaks will not enter ground water.
SLOW burning was probably a bad term to use, i meant slow as opposed to explosive. Spark engine fuels must not ignite (explode) until they are sparked. octane rating measures this resistance to pre-ignition. once sparked the reaction is very rapid (explosive)